The philosophy of Reid as contained in the "Inquiry into the human mind on the principles of common sense"

Series of flDooern pbilosopbers.

Edited by E. Hershey Sneatb, Ph.D.

DESCARTES by PROF. H. A. P. TORREY of the

University of Vermont.*
SPINOZA by PROF. GEO. S. FULLERTON of the

University of Pennsylvania.*

LOCKE by PROF. JOHN E. RUSSELL of Williams

College.*
BERKELEY by EX-PRESIDENT NOAH PORTER

of Yale University.

HUME by PROF. H. AUSTIN A1KINS of Trinity
College, N. C.

REID by E. HERSHEY SNEATH of Yale Uni-
versity.*

KANT by PROF. JOHN WATSON of Queen's

University, Canada.*
HEGEL by PROF. JOSIAH ROYCE of Harvard

University.

* Those marked with an asterisk are ready

HENRY HOLT & CO., PUBLISHERS,

NEW YORK.

Series of flfoofcern

Edited by E. Hershey Sneath, Ph.D.

AS CONTAINED IN THE

"INQUIRY INTO THE HUMAN MIND

ON THE PRINCIPLES OF

COMMON SENSE"

WITH INTRODUCTION AND SELECTED NOTES
BY

E. HERSHEY SNEATH, PH.D.

Instructor in Philosophy in Yale University

NEW YORK
HENRY HOLT AND COMPANY

1892

\ TORONTO 5, CANADA,

171932

^-570

COPYRIGHT, 1892,

BY
HENRY HOLT & CO.

PREFACE.

AFTER careful consideration, it seemed better to me,
and, at the same time, to be consistent with the idea
of the " Series" of which this book is a member, to
present Reid's Philosophy in an edition of the " In-
quiry," rather than in a book of extracts taken from
the " Inquiry" and the " Intellectual Powers." The
substance of Reid's Philosophy is contained in his
theory of perception and his doctrine of common
sense. Herein, too, lies his historical significance.
The " Inquiry" contains all that is essential for an
understanding of Reid's views on these subjects, and
presents it in a comparatively brief form. By omit-
ting Sees. IX-XIX (pp. 199-287), which can be easily
spared, the subject-matter will be brought within the
limits prescribed by the " Series. " The sections re-
ferred to above will be found interesting, especially
when studied in connection with Berkeley's famous
" Theory of Vision," — hence their retention. The
text of this edition is taken from Sir Wm. Hamilton's
seventh edition of Reid's Works (Edinburgh, 1872).
The most important notes of Hamilton, as well as his
Index, abridged, have been retained. The " Inquiry"
affords an inviting field for criticism, but the limits of
the Introduction forbade my entering upon it.

E. H. S.

CONTENTS.

PAGE

BIOGRAPHICAL SKETCH. i

BIBLIOGRAPHY 7

RELATION OF REID'S PHILOSOPHY TO ITS PHILOSOPHICAL

ANTECEDENTS n

THE INFLUENCE OF REID'S PHILOSOPHY UPON SUBSEQUENT

PHILOSOPHIC THOUGHT 47

AN INQUIRY INTO THE HUMAN MIND.
DEDICATION 65

CHAPTER I. INTRODUCTION.

Section I. The Importance of the subject, and the Means

of prosecuting it 70

II. The Impediments to our knowledge of the mind.. 72

III. The Present State of this part of philosophy. Of

Descartes, Malebranche, and Locke 76

IV. Apology for those philosophers 80

V. Of Bishop Berkeley ; the " Treatise of Human

Nature" ; and of Scepticism , 81

VI. Of the ' ' Treatise of Human Nature" 84

VII. The system of all these authors is the same, and

leads to Scepticism ~ 86

VIII. We ought not to despair of a better 87

CHAPTER II. OF SMELLING.

Section I. The Order of proceeding. Of the medium and

organ of Smell 89

II. The Sensation considered abstractly 90

III. Sensation and Remembrance, natural principles

of Belief 92

6

VI CONTENTS.

PACK

Section IV. Judgment and Belief in some cases precede Sim-
ple Apprehension 95

V. Two Theories of the Nature of Belief refuted.

Conclusions from what hath been said 96

VI. Apology for metaphysical absurdities. Sensa-
tion without a sentient, a consequence of the
theory of Ideas. Consequences of this strange

opinion 99

VII. The conception and belief of a sentient being, or
Mind, is suggested by our constitution. The
notion of Relations not always got by Com-

iparing the related ideas 105

VIII. There is a quality or virtue in bodies, which we
call their Smell. How this is connected in the

imagination with the sensation. . . 109

IX. That there is a principle in human nature, from
which the notion of this, as well as all other

natural virtues or causes, is derived in

X. Whether in Sensation the mind is Active or

Passive 116

CHAPTER III. OF TASTING 118

CHAPTER IV. OF HEARING.

Section I. Variety of Sounds. Their place and distance

learned by Custom, without reasoning 122

II. Of Natural Language 124

CHAPTER V. OF TOUCH

Section I. Of Heat and Cold 129

II. Of Hardness and Softness 131

III. Of Natural Signs 135

IV. Of Hardness, and other Primary Qualities 139

V. Of Extension 141

VI. Of Extension 144

VII. Of the existence of a Material World 148

VIII. Of the Systems of Philosophers concerning the

Senses 156

CONTENTS. Vll

CHAPTER VI. OF SEEING.

Section I. The excellence and dignity of this faculty 162

II. Sight discovers almost nothing which the Blind

may not comprehend. The reason of this. . . . 164

III. Of the Visible Appearances of objects 169

IV. That Colour is a quality of bodies, not a sensation

of the mind 173

V. An inference from the preceding 177

VI. That none of our sensations are Resemblances of

any of the qualities of bodies 181

VII. Of visible Figure and Extension 187

VIII. Some Queries concerning Visible Figure an-
swered 192

IX. Of the Geometry of Visibles 199

X. Of the Parallel Motion of the eyes 211

XI. Of our seeing objects Erect by inverted images. . 215

XII. The same subject continued. . 222

XIII. Of seeing objects Single with two eyes 238

XIV. Of the laws of vision in Brute animals 246

XV. Squinting considered hypothetically 249

XVI. Facts relating to Squinting 261

XVII. Of the effect of Custom in seeing objects Single. . 265
XVIII. Of Dr. Porterfield's account of single and double

vision 272

XIX. Of Dr. Brigg's theory, and Sir Isaac Newton's

conjecture on this subject 276

XX. Of Perception in general 287

XXI. Of the Process of Nature in perception 297

XXII. Of the Signs by which we learn to perceive Dis-
tance from the eye 303

XXIII. Of the Signs used in other acquired perceptions. . . 316
XXIV Of the Analogy between Perception, and the

credit we give to Human Testimony 320

•

CHAPTER VII. CONCLUSION.

Containing Reflections upon the opinions of Philosophers

on this subject 338

INDEX 363

BIOGRAPHICAL SKETCH.

DUGALD STEWART truly says, that the life of Thomas
Reid "was uncommonly barren of those incidents
which furnish materials for biography." His life was
spent in comparative quiet and retirement, and was,
therefore, not replete with varied incident He was
born April 26th, 1710, at Strachan, Kincardineshire,
Scotland. His father was the Rev. Lewis Reid, a
highly respected clergyman, who was descended from a
succession of ministers of the Church of Scotland. His
mother, Margaret Gregory, belonged to a family some-
what distinguished in Scotland for their scientific attain-
ments. Early in life Reid was sent to the parish school
of Kincardine where he spent two years. From the
parish school he went to Aberdeen, where he received
instruction in the classics. When about twelve or thir-
teen years of age he entered Marischal College. Here he
was instructed in Philosophy by Dr. George Turnbull,
who undoubtedly exerted a great influence upon his philo-
sophical thinking.* He graduated from college in 1726.
Receiving ah appointment of librarian to the University,
he continued his connection with it until 1736. During

* Dr. McCosh says that Turnbull exercised a greater influence
upon Reid's thinking " than all other masters and writers " com-
bined. "The Scottish Philosophy," pp. 95-106.

2 BIOGRAPHICAL SKETCH.

this period he devoted much of his time to the study of
Mathematics. Resigning his office in 1736, he visited
England in company with his friend, John Stewart, who
afterward held the chair of Mathematics in Marischal
College. They visited London, Oxford and Cambridge,
where they were introduced to many noted literary men.
In 1737, having been presented " to the living of New-
Machar, " by King's College, Aberdeen, he entered upon
his clerical work. The early part of his ministerial life in
this parish was signalized by an intense hostility to him on
the part of his parishioners. This was occasioned specially
by the aversion which his people had to the law of
patronage. Furthermore, he was accustomed, because
of his modesty, to preach the sermons of Drs. Tillotson
and Evans instead of his own. This practice was very
offensive to the people. However, despite his unpopu-
larity, through his fidelity to the interests of his parish,
and his amiability of disposition, he soon ingratiated
himself into the good will and affections of the people.
In 1740, he was married to his cousin, Elizabeth Reid,
daughter of Dr. George Reid, a London physician. His
wife proved a great help to him in his work at New-
Machar. While living here, "the greater part of his
time, " says Dugald Stewart, ' ' was spent in the most
intense study; more particularly in a careful examina-
tion of the laws of external perception, and of the other
principles which form the groundwork of human
knowledge."* In 1748, his first publication appeared.
It was in the form of an Essay, published in the
"Transactions" of the Royal Society of London, and

" Collected Works," vol. x, p. 251.

BIOGRAPHICAL SKETCH. - 3

was entitled, "An Essay on Quantity, occasioned by
reading a Treatise in which Simple and Compound
Ratios are applied to Virtue and Merit. " The ' ' Trea-
tise" to which Reid alludes was Hutcheson's "Inquiry
into the Origin of our Ideas of Beauty and Virtue." In
this "Treatise," Hutcheson made use of mathematical
forms in illustrating moral subjects. Whether he meant
to apply mathematical reasoning to such subjects may be
doubted. Reid, however, was aware of the fact that
Pitcairn and Cheyne had applied this form of reasoning
to medicine, and he felt constrained to write an essay
showing what rendered a subject capable of mathemati-
cal treatment.

In 1752, he was elected Professor of Philosophy, in
King's College, Aberdeen. Shortly after his removal to
Aberdeen, the ' ' Aberdeen Philosophical Society " was
founded, principally through his endeavors. It included
among its members such men as Campbell, Gerard,
Beattie and John Gregory.* While connected with this
society, he read papers which contained the essential
principles of the "Inquiry." In 1764, he published
the " Inquiry into the Human Mind on the Principles
of Common Sense." Reid's speculations on the subjects
treated in the " Inquiry" were really begun in 1739, on
the appearance of Hume's "Treatise of Human Nature."
In the "Inquiry" Reid attempts to refute the scepti-
cism of Hume by attacking the "theory of ideas" on
which he thought this scepticism to be founded. Being
thus directed against the sceptical philosophy of Hume,

* Cf. McCosh, "The Scottish Philosophy," pp. 227-9, f°r an
account of this society.

4 BIOGRAPHICAL SKETCH.

he was desirous of subjecting his manuscript to Hume's
perusal, so as not to misrepresent his philosophy in any
particular. He was enabled to do this through the
kind services of Dr. Blair, a mutual friend. After
perusing it carefully, Hume wrote to Reid the following
complimentary words : "By Dr. Blair's means I have
been favored with the perusal of your performance,
which I have read with great pleasure and attention.
It is certainly very rare that a piece so deeply philo-
sophical is wrote with so much spirit, and affords so
much entertainment to the reader."* In 1763, Reid
was called to the Professorship of Moral Philosophy, in the
University of Glasgow, to succeed Adam Smith, who had
resigned. He accepted the call, removing to Glasgow
the following year. In the University he lectured on
the intellectual and active powers of man, and on natu-
ral jurisprudence and politics. Many of his colleagues
were able men and they proved to be a great inspiration
to him. During his connection with the University, he
published "An Account of the Logic of Aristotle," as
an appendix to Lord Kame's "Sketches of the History
of Man." In 1781, he retired from the professorship,
for the purpose of devoting his attention to the comple-
tion of his philosophical works. In 1785, he published
the "Essays on the Intellectual Powers of Man," — a
more elaborate treatment of the powers of the mind
than is contained in the " Inquiry." In 1788, he pub-
lished the "Essays on the Active Powers of the Human
Mind," advocating one form of Intuitional Ethics. This
was the last work of his published during his lifetime.

* Stewart's " Collected Works," vol. x., p. 256.

BIOGRAPHICAL SKETCH. 5

Reid remained an active student almost till death.
Among the most important efforts of the closing years
of his life, were several papers written probably for
a literary society in Glasgow. These were entitled,
" Some Observations on the Modern System of Ma-
terialism," and "A Free Discussion of the Doctrines
of Materialism and Philosophical Necessity." One
thing marred the serenity of these closing years. It
was the death of his wife, with whom he had lived
fifty-two years. Only one daughter, Mrs. Carmichael,
of a large family of children, was still living. She was
a great solace to him in his old age. On the 7th of
October, 1 796, after a brief illness, he died.

As a man, Reid was modest, sober, sincere, and de-
vout. He was modest almost to diffidence. Indeed,
Dugald Stewart expresses doubt as to whether Reid's
modesty would have permitted him to publish the
"Inquiry," had he not been encouraged to do so by
his friends. His soberness and earnestness are manifest
both in his life and writings. Something of his devout
character may be learned from a confession and re-ded-
ication of himself to the service of God, during his
wife's illness, in the sixth year of their marriage. It is
a most penitent and pathetic confession of dereliction of
duty, and a most solemn pledge of a more devoted ser-
vice to God.*

As a philosophical thinker, Reid, if not profound,
was, at least, deeply earnest and original. Cousin
thought him to be a man of genius. He says: "Yes,
Reid is a man of genius, and of a true and powerful

* Cf. McCosh, " The Scottish Philosophy," pp. 199-200,

6 BIOGRAPHICAL SKETCH.

originality; so we said in 1819, and so we say in 1857,
after having held long converse with mighty systems,
discovered their secret, and taken their measure."*
McCosh says: " He has not the mathematical consecu-
tiveness of Descartes, the speculative genius of Leibnitz,
the sagacity of Locke, the spirituel of Berkeley, or the de-
tective skill of Hume; but he has a quality quite as valua-
ble as any of these, even in philosophy; he has in per-
fection that common sense which he so commends, "f
Sober earnestness and originality seem to be his merits
as a philosophical thinker. His earnestness is manifest
in his anxious endeavor to establish the reality of know-
ledge, and thus to s'ave philosophy from nihilistic
scepticism. His originality is manifest in his breaking
away from the " theory of ideas" which he had accepted
on authority, and establishing philosophy upon a new
basis.

* Quoted by McCosh, " The Scottish Philosophy," p. 193.
f Ibid., pp. 192-3.

BIBLIOGRAPHY.
/. On. the Life of Reid.

Dugald Stewart, "Account of the Life and Writings of
Thomas Reid, D.D.," "Collected Works," ed. by Hamilton,
Edinburgh, 1854-60, vol. x, ch. v. Published also in
"The Works of Thomas Reid, D.D.," ed. by Hamilton,
Edinburgh, 1872, vol. i, pp. 1-35. Cf. Notes A, B, C, D,
E, F, of Hamilton, appended to this account.

James McCosh, "The Scottish Philosophy," New York,
1874, Art. xxvi.

II. The Works of Reid.

Complete Works in English: " The Works of Thomas
Reid, D.D., now fully collected, with Selections from his
Unpublished Letters. Preface, Notes, and Supplementary
Dissertations, by Sir William Hamilton, Bart.," etc., 7th
ed., Edinburgh, 1872, 2 vols. In French: " CEuvres Com-
pletes de Thomas Reid, par M. Th. Jouffroy, avec des
Fragments de M. Royer Collard," Paris, 1828-9, 6 tomes.

For information concerning various editions of individ-
ual works of Reid, cf. N. Porter, " Ueberweg's History
of Philosophy," translated by Geo. S. Morris, New York,
1871-3, vol. ii, Appendix I, pp. 396-7.

///. Books of Reference.

In English: J. Priestley, "Examination of Dr. Reid's
Inquiry," etc., London, 1774.

Dugald Stewart, " Collected Works," ed. by Hamilton,
Edinburgh, 1854-60, vols. i, pp. 108-13; v, pp. 101-13.

7

8 BIBLIOGRAPHY.

Th. Brown, " Inquiry into the Relation of Cause and
Effect," 3d ed., Edinburgh, 1818. "Lectures on the Phi-
losophy of the Human Mind," Hallowell, 1829, especially
lectures xxvi, xxvii.

Sir Wm. Hamilton, "Lectures on Metaphysics," ed. by
Mansel and Veitch, Edinburgh and London, 1870, vol. i,
Appendix I (B), vol. ii, lectures xxi-xxiii. Also, "Preface,
Notes and Supplementary Dissertations," in his edition of
Reid's "Works," referred to above.

J. F. Ferrier, " Reid and the Philosophy of Common
Sense," " Blackwood's Magazine," 1847; the same in Lec-
tures, ed. by Grant and Lushington, London, 1866, vol. ii,

pp. 4°7-59-

J. Walker, Notes in his abridged edition of Reid's " In-
tellectual Powers of Man," Philadelphia, 1850.

A. C. Fraser, "Essays in Philosophy," Edinburgh, 1856,
Essays II and III.

J. McCosh, "The Scottish Philosophy," New York, 1874,
pp. 192-227, " Realistic Philosophy," New York, 1887, vol.
ii, pp. 173-81.

Thomas E. Webb, " The Veil of Isis," Dublin and Lon-
don, 1885, pp. 123-62.

A. Seth, " Scottish Philosophy," Edinburgh and London,
1885. Article on Reid, " Encyclopaedia Britannica," gth
ed., vol. xx.

In French: Royer Collard, "Fragments de Royer Col-
lard," Jouffroy's translation of Reid's Works.

V. Cousin, " Philosophic Ecossaise," Paris, 1846, pp.
185-281.

Thomas Jouffroy, Preface to his "(Euvres Completes de
Thomas Reid," Paris, 1828-9.

A. Gamier, ''Critique de la Philosophic de Thomas Reid,"
Paris, 1840.

J. P. A. Remusat, "Melanges," Paris, 1842.

L. Peisse, Preface to " Fragments de Philosophic," 1840.

In German : M. Kappes, " Der Common Sense bei
Thomas Reid," Munich, 1890.

E. Koenig, " Die Entwickelung des Causalproblems von
Cartesius bis Kant," Leipzig, 1888.

BIBLIOGRAPHY. 9

IV.

Consult also the following writers on the History of
Philosophy: J. D. Morrel, " History of Modern Philos-
ophy," 2d ed., London, 1847, vol. i, pp. 281-94.

N. Porter, " Ueberweg's History of Philosophy," trans-
lated by Geo. S. Morris, New York, 1871-3, vol. ii, Appen-
dix I, pp. 394-403-

F. D. Maurice, "Moral and Metaphysical Philosophy,"
London, 1873, vo^ "• PP- 580-6.

G. H. Lewes, " Biographical History of Philosophy,"
New York, 1883, vol. ii, pp. 618-629.

Falckenberg's " Geschichte der Neueren Philosophic,"
Leipzig, 1886, pp. 180-82.

J. E. Erdmann, "History of Philosophy," ed. by W. S.
Hough, London and New York, 1890, pp. 271-4.

RELATION OF REID'S PHILOSOPHY TO
ITS PHILOSOPHICAL ANTECEDENTS.

REID'S philosophy, like every other system of philos-
ophy, cannot be thoroughly understood without taking
into consideration its relation to preceding philosophic
thought. It was one of two movements in the world of
philosophy awakened by the scepticism of Hume — the
Philosophy of Common Sense, and the Critical Philos-
ophy of Kant. Reid had been a disciple of Berkeley,
virtually accepting the Idealism of that acute thinker.
But when he saw what he thought to be the logical out-
come of Berkeley's philosophy, as manifested in the
scepticism of Hume, he was somewhat alarmed, and be-
gan to suspect the validity of "the principles commonly
received with regard to the human understanding."*
After careful examination, he came to the conclusion
that Hume's scepticism was the legitimate outcome of
the " theory of ideas," i. e., the theory of perception,
upon which it was founded. In his letter, dedicating
the " Inquiry" to James, Earl of Findlater and Seafield,
he says: "For my own satisfaction, I entered into a
serious examination of the principles upon which this
sceptical system is built; and was not a little surprised to
find that it leans with its whole weight upon a hypothesis
which is ancient indeed, and hath been very generally
* "Works," vol. i, I. P., p. 283.

12 RELATION OF REID'S PHILOSOPHY

received by philosophers, but of which I could find no
solid proof. The hypothesis I mean is, that nothing is
perceived but what is in the mind which perceives it.
That we do not really perceive things that are external,
but only certain images and pictures of them imprinted
upon the mind, which are called impressions and ideas" *
This theory he ascribed to all preceding philosophy —
both ancient and modern. In regard to Descartes,
Malebranche, Locke, Berkeley, and Hume, he says:
" The system of all these authors is the same, and leads
to scepticism. " ' ' Descartes no sooner began to dig in
this mine, than scepticism was ready to break in upon
him. He did what he could to shut it out. Malebranche
and Locke, who dug deeper, found the difficulty of
keeping out this enemy still to increase: but they labored
honestly in the design. Then Berkeley, who carried on
the work, despairing of securing all, bethought himself
of an expedient: — By giving up the material world, which
he thought might be spared without loss, and even with
advantage, he hoped, by an impregnable partition, to
secure the world of spirits. But, alas ! the ' Treatise of
Human Nature ' wantonly sapped the foundation of this
partition, and drowned all in one universal del uge."f It
was the sceptical outcome of this "theory of ideas " which
awakened Reid from his serene repose in authority, just
as later it awakened Kant from his dogmatic slumber,
and he resolved to make a new inquiry into " this sub-
ject," independent of authority; for, said he: "I thought
it unreasonable, upon the authority of philosophers, to
admit a hypothesis which, in my opinion, overturns all
* " Works," Inq., p. 96. f Ibid., p. 103.

TO ITS PHILOSOPHICAL ANTECEDENTS. 1$

philosophy, all religion and virtue, and all common
sense — and, finding that all systems concerning the human
understanding which I was acquainted with, were built
upon this hypothesis, I resolved to inquire into this sub-
ject anew, without regard to any hypothesis. " * Since,
then, the special task of Reid was an examination of the
"theory of ideas," it may be well for a thorough ap-
preciation of his task, to briefly survey the development
of modern philosophy from Descartes to Reid, with spe-
cial reference to the ' ' theory of ideas. "

The scepticism into which modern philosophy had
issued, prior to Reid, seems to have been the result of
its peculiar subjective tendency. This tendency char-
acterized it from the beginning. Descartes' sceptical
method forced him back upon the authority of conscious-
ness. His starting-point in philosophy was universal
doubt, f But this very fact of doubt led him to the rec-
ognition of a fact that had to be accepted — his own
existence. Because, he reasoned, though I doubt every-
thing, doubt, at least, remains. Doubt, however, is a
form of thought. Hence the formula: — cogito, ergo
sum. | Now, it is possible to think myself devoid of
everything but thought; hence I must conclude that I
am a being, the very essence of which is thought. §
Thus we arrive at a knowledge of mind. But what of
our knowledge of an external world ? He inferred from
the existence of clear and distinct ideas of things in the

*" Works," Inq., p. 96.
f " First Meditation,"
J "Second Meditation."
§ Ibid.

14 RELATION OF REID'S PHILOSOPHY

mind, the objective reality of things which occasioned
them — that these ideas were images or copies of things
existing without the mind.* In short, his theory of
perception is representative perception. However, this
vicarious or representative character of ideas is only in-
ferential with Descartes. He falls back upon the vera-
city of God, (whose existence and veracity are known to
us through our innate idea of God f ) for the trustworthiness
of our knowledge of the external world. \ We see, then,
in both the sceptical method of Descartes, and also in his
theory of representative perception the subjective tend-
ency referred to above.

Turning to Malebranche we find in his teaching, also, this
subjective trend manifested. He says, material things
are known to us only under the forms of ideas. § As to
the origin of these ideas, we are informed that they are
not originated by the mind from itself — because of its
inability. || Neither are they given to us by things them-
selves. \ How, then, do we come into possession of
them ? Malebranche answers : through the mind's union
with God, who possesses within Himself ideas repre-
senting all things created by Him. God, by His pres-
ence, is united to the finite mind — He being the " place
of spirits " just as " space is the place of bodies." This
union makes it possible for the mind to see in God that

* "Sixth Meditation."

| " Third and Fourth Meditations.'

J "Sixth Meditation."

§ " De la Recherche de la Verite," Ivr. iii, pt. ii, ch. I.

|| Ibid., ch. 3.

If Ibid., ch. 2.

TO ITS PHILOSOPHICAL ANTECEDENTS. 1$

which represents things, viz., ideas.* It is thus that
" we see all things in God."

In the philosophy of Locke we find the same element
of subjectivity. He wrote his famous '' Essay on Human
Understanding " with the purpose of explaining the or-
igin, certainty and extent of knowledge. After explain-
ing away all innate ideas, f Locke endeavored to show
how we come into possession of ideas. He assumes
that the mind in its original condition is like a blank
sheet of paper, or a tabula rasa. \ Whence, then, come
its ideas ? The source of ideas is experience — sensation and
reflection. § Having thus given the source of our ideas,
he divides them into two kinds, simple and complex.
A simple idea contains in it nothing but a uniform ap-
pearance or conception in the mind, and is not distin-
guishable into different ideas. These constitute the ma-
terial of all knowledge. Complex ideas are formed by
the mind by combining and uniting simple ideas. ||
Locke then proceeds to make another distinction be-
tween our ideas, by pointing out the objective character
of some, and the subjective character of others. He,
of course, assumes the existence of an external world of
corporeal bodies. Now, that which in a body occasions
an idea in the mind, he calls a quality. There are
some qualities in bodies which cause ideas in the mind
which are exact likenesses or resemblances of these
qualities. The idea in the mind is a copy of the quali-
ty in the body. These qualities are called primary

* " De la Recherche de la Verite," Ivr. iii. pt. ii, ch. 3.
f " Essay," bk. i, chs. 2, 3, 4. \ " Essay," bk. ii, ch. I.
§ Ibid., bk. ii., ch. I. || Ibid., ch. 2.

15

l6 RELATION OF REID'S PHILOSOPHY

or original qualities of matter, viz., extension, solid-
ity, figure, motion, number, etc. But there are other
ideas in the mind which have no resemblance to the
qualities in the bodies which cause them. To this class
belong most of the ideas of sensation, viz., colors,
sounds, tastes, smells, etc. These do not resemble their
causes. The qualities which cause such ideas in us are
the secondary qualities of bodies.*

Locke then proceeds to the explanation of the idea of
substance, and it is important to note his remarks on
this point, because of the positions taken by Berkeley
and Hume afterward. This idea, according to Locke,
is not derived from sensation and reflection, as simple
ideas are derived. Its origin is as follows: We frequent-
ly recognize a certain combination of simple ideas, and
we cannot conceive them as self-subsisting, so we are
wont to provide a substratum for them as a ground of
subsistence, and as a cause of their existence, which we
call substance. However, although substance is an
abstract idea, he believed in its objective reality, f

After this consideration of the sources and kinds of
ideas the mind has, we are prepared to hear Locke's
conception of knowledge. Knowledge is simply ' ' con-
versant about our ideas." It is, "nothing but the
perception of the connection and agreement or dis-
agreement and repugnancy of any of our ideas."
Things are not known immediately by the mind, but
through the intervention of ideas. How far, then, is
knowledge real ? Only " so far as there is a conformity
between our ideas and the reality of things. " But what

* " Essay," bk. ii, ch. 8. t.Ibid-» bk« "» ch- 23-

TO ITS PHILOSOPHICAL ANTECEDENTS. VJ

shall be our criterion in determining this conformity ?
As Locke himself asks: " How shall the mind, when it
perceives nothing but its own ideas, know, that they
agree with things themselves ? " He answers this ques-
tion by telling us that there are two kinds of ideas of
which we may have assurance of their agreement with
things. First, we have simple ideas, which are affections
of the mind produced by external things, " operating on
the mind in a natural way." Hence these ideas cannot
be fictions, but, being produced in this way, they "carry
with them all the conformity which is intended or
which our state requires." The second kind of ideas to
which he refers in this connection, is complex ideas.
These being formed by the mind itself, and not, with
the exception of the ideas of substances, being intended
to represent anything external, cannot mislead us.*

We see, then, in what Locke says in regard to know-
ledge, a recognition of its subjectivity. He admits that
the mind does not have an immediate knowledge of
things. It only knows them " by the intervention of
ideas." He gives no other than a practical reason for
the correspondence of ideas and things. In this recogni-
tion of the subjective character of our knowledge he cer-
tainly anticipated Berkeley, as Reid suggests. He even
anticipated Hume, and his taking refuge in a practical
reason was doubtless more for the purpose of avoiding
scepticism than idealism. Even for the assumption of
the existence of an external world of corporeal substances,
involved in his theory of perception, he really gives us no
warrant of a speculative character. This, too, he ulti-

* " Essay," bk. iv, chs. i, 4.

1 8 RELATION OF REID'S PHILOSOPHY

mately rests on practical grounds; apparently, also, for
the purpose of escaping scepticism.

It was this subjectivity of knowledge as involved in
Locke's " theory of ideas," and the idealism and scepti-
cism which were ultimately developed from it, which at-
tracted Reid's attention, and impelled him to examine
this theory, hoping to be instrumental in its overthrow,
and to establish knowledge on a firm foundation. We
must, then, trace this subjective tendency as manifested
in the philosophy of Berkeley, and then in the scepti-
cism of Hume, which awakened the reactionary philos-
ophy of Reid.

Berkeley's problem, as Prof. Fraser suggests, was an
inquiry into the real meaning of substance and cause as
external. In answering the first part of the question,
the real meaning of material substance, he endeavored
to show that the doctrine of substance as advocated by
the philosophers, involved a contradiction. He claimed
that the objects of knowledge are ideas, which ideas, of
course, exist in the mind. Knowledge is concerned
only with ideas. Now, when we ask what is meant by
the existence of sensible things, it is evident "that their
esse is percipi." All that really is meant by the exist-
ence of a thing is that it is seen, touched, etc., — in short,
that it is perceived. To speak of something existing
independent of a mind perceiving it is unintelligible and
impossible. So-called things are objects perceived by
sense, " and what do we perceive besides our own ideas
or sensations ? and is it not plainly repugnant that any
one of these, or any combination of them, should exist
unperceived ? " The being of things, then, consists in
their being perceived. Ideas cannot be images of sub-

TO ITS PHILOSOPHICAL ANTECEDENTS. 19

stantial things, because an idea can only be like an idea,
and things to be perceived must be ideas, and, if not,
there is no sense in saying an idea is like something of
which we can know nothing.*

Berkeley then discusses the subject of primary and
secondary qualities, in which discussion he apparently
had Locke in mind. He objects to the distinction
made by Locke, affirming our knowledge of primary
qualities to be just as subjective as our knowledge of
secondary qualities; extension, solidity, figure, etc., are
ideas in the mind just as colors, odors, etc., are ideas;
and, as ideas can only resemble ideas, and, as they exist
only in the mind, extension, figure, etc. , cannot exist in
an unthinking external substance. The very ' ' notion "
of matter, then, involves a contradiction, f

But if there be no external material substance — if
there be no world of corporeal substances — how are we
to account for the existence of our ideas ? They must
have a cause. This brings us to the consideration of the
second part of Berkeley's question, the nature of the
originating cause. This cause, he says, cannot be an
idea, for all ideas are "visibly inactive.-" "There is
nothing of power or agency in them," and hence an
idea cannot be a cause. In the second place, the cause
cannot be a material substance, for we have seen there is
no such thing. What, then, is the cause ? The cause
of the ideas must be an "incorporeal active substance
or spirit. " But it is not my spirit which originates them,
because the ideas of sense are not originated by me—

* " Principles," §§ 4, 6, 8, 10. f Ibid., § 15.

20 RELATION OF REID'S PHILOSOPHY.

they are not produced by my will. The Will or Spirit
which does originate them Berkeley infers to be God.*

In our knowledge of spirit we seem to be conversant
with something more than ideas. He tells us we have
no idea of a spirit and can have none. However, he
says, we have a "notion" of spirit. We have also a
"notion" of other spirits and of relations. "We com-
prehend our own existence by inward feeling or Reflection,
and that of other spirits by Reason (inference). We may
be said to have some knowledge or notion of our own
minds, of spirits and active beings, whereof in a strict
sense we have not ideas. In like manner we know
and have a notion of relations between things or ideas,
which relations are distinct from the ideas or things re-
lated, inasmuch as the latter may be perceived by us
without our perceiving the former, "f The preceding
quotation is important as showing Berkeley's deviation
from the position taken in the beginning of the ' ' Princi-
ples," where he affirmed ideas to constitute the objects
of our knowledge (see § i). Here he recognizes another
object of knowledge in ' ' notions. " Reid suggests that
Berkeley took refuge in the ' ' notion " because of an aver-
sion to scepticism. J

Thus we see that Berkeley, beginning with Locke's
doctrine of ideas as the only objects of knowledge,
carried it so far as to reject his arbitrary assumption
as to the objective character of certain ideas, existing
as qualities of a substratum called substance, which
substratum is also an unwarrantable assumption, thus

* " Principles," §§ 25, 26, 29. f Ibid., § 89, cf. also § 27.
\ "Works," Inq., p. 207.

TO ITS PHILOSOPHICAL ANTECEDENTS. 21

resolving the world of material things into a world of
ideas. In all of this the subjectivity heretofore referred
to is still more manifest than in the preceding systems
considered. In the philosophy of Hume, which we are
now to consider, we shall see the culmination of this
subjective tendency in scepticism.

In the "Treatise on Human Nature " Hume argues as
follows : —

"All perceptions of the human mind resolve them-
selves into two distinct kinds, which I shall call impres-
sions and ideas." By impressions, he means, " sen-
sations, passions, and emotions." By ideas, he means,
' ' the faint images of these in thinking and reasoning. "
Ideas, then, are images of impressions.* Every simple
impression has its corresponding idea, and every simple
idea has its corresponding impression, and he holds to
the general proposition, ' ' That all our simple ideas, in
their first appearance, are derwd from simple impressions,
which are correspondent to them, and which they exactly
represent, "f

As to the division of impressions and ideas Hume said,
that they could be divided into two classes — simple and
complex. Simple impressions and ideas admit of no
distinction and are inseparable. Complex ideas are
distinguishable into parts. Complex ideas include ideas
of substances, modes and relations. "The idea of a
substance as well as that of a mode, is nothing but a
collection of simple ideas that are united by the imagi-
nation, and have a particular name assigned them, by

* " Treatise on Human Nature," ed. by Green and Grose, Lon.
don, 1886, vol. I, p. 311. | Ibid,, p. 314.

22 RELATION OF REID'S PHILOSOPHY

which we are able to recall, either to ourselves or others,
that collection."* Since we have no simple idea of sub-
stance, derived from an impression of sense, Hume
joined with Berkeley in refusing to affirm the objective
existence of material substance.

He then takes up the question of knowledge. Here
he makes quite an effort to provide for that synthesis
which knowledge implies. He finds this synthetic
power in imagination, with its principles of association.
In knowledge the imagination deals with seven different
kinds of relations: "Resemblance, identity, relations
of time and place, proportion in quantity or number,
degrees in any quality, contrariety, and causation. " f
These relations may be divided into two classes, the
one depending upon the ideas compared : the other
relations are "such as may be changed without any
change in the ideas." Resemblance, contrariety, degree,
proportion belong to the first class. They arise out of
the very nature of the ideas, and certainty can only arise
with these as objects of knowledge, but the knowledge is
purely subjective. It can never transcend perceptions.
Hume says that in the other class of relations it seems as
though we are carried beyond our perceptions, but in
this we are deceived. Neither identity, nor time, nor
space carries us beyond perceptions.! But how is it
with causation ? Here we seem to have assurance of
conclusions which extend beyond the impressions of
sense. § Hence this relation must be carefully examined,
and this examination on the part of Hume constitutes

* " Treatise," pp. 312, 313, 321, 324. f Ibid., p. 372.
I Ibid., pp. 375, sq. § Ibid., pp-376-7-

TO ITS PHILOSOPHICAL ANTECEDENTS. 23

the principal merit of his philosophy. When we believe
in the existence of an object we have simply an idea of
the object — and no additional idea, and belief is distin-
guished from incredulity simply in its superior liveliness
and vigor. The vividness of an idea and belief are one
and the same. Now, when an impression is vivid it gives
its vividness to the ideas associated with it by resemblance,
contiguity or causation. * Now, how are we to explain
our belief in causation ? This idea we gain from ex-
perience. Experience presents us with objects in con-
stant conjunction, and thus produces in us "a habit
of surveying them in that relation, that we cannot
without a sensible violence survey them in any oth-
er, "f But whence the belief of necessary connection
implied in the relation of cause and effect ? This
may be accounted for by a propensity, born of cus-
tom, to pass from the impression or idea of an object to
the idea of the object which usually attends it. "When
any object is presented to it, it immediately conveys to
the mind a lively idea of that object which is usually
found to attend it, and this determination forms the ne-
cessary connection of these objects. "| In brief, we
mean by causation simply this : that when two objects
have been constantly conjoined (in experience), the pres-
ence of one determines the mind to form the idea of the
other, and this determination is the result of habit or cus-
tom. Hence this relation of cause and effect, which at first
seemed to carry us beyond impressions, does not really
do so, but resolves itself into a propensity, begotten of

* "Treatise," pp. 394-400, sq. f Ibid., p. 424.

\ Ibid., pp. 450-68.

24 RELATION OF REID'S PHILOSOPHY

custom, to pass from the impression or idea of an object
to the idea of that object which usually attends it. The
causal relation between things and ideas involved in
the theory of Locke, Hume regarded as a mere assump-
tion which experience did not justify. " The mind," he
says, " has never anything present to it but the percep-
tions, and cannot possibly reach the experience of their
connection with objects. The supposition of such a
connection is, therefore, without any foundation in rea-
soning." The ultimate realities, then, with which the
mind has to deal are individual, unreferable impressions,
and from such impressions we cannot infer the existence
of external material objects. Here we see idealism pure
and simple.

But he did not rest content with a denial of the reality of
an external world; he also denied the reality of the soul.
" Since all our perceptions are different from each other,
and from everything else in the universe, they are also dis-
tinct and separable, and may be considered as separately
existent, and may exist separately, and have no need of
anything else to support their existence." * Hence there
is no necessity of a self as a substratum or subject of our
perceptions. Proceeding upon his original thesis, that
the perceptions of the mind are resolvable into impres-
sions and ideas — ideas being mere images of impressions
— he says : "If any impression gives rise to the idea of
self, that impression must continue invariably the same,
through the whole course of our lives ; since self is sup-
posed to exist after that manner. But there is no impres-

* "Treatise," p. 5f8.

TO ITS PHILOSOPHICAL ANTECEDENTS. 35

sion constant and invariable. Pain and pleasure, grief
and joy, passions and sensations succeed each other,
and never all exist at the same time. It cannot, there-
fore, be from any of these impressions, or from any
other, that the idea of self is derived, and consequently
there is no such idea." * Hume thinks we have no more
an idea of a thinking substance as the support of per-
ceptions than we have of an external substance as the
support of qualities, and Berkeley in rejecting the one
ought to have rejected the other, f

To make his scepticism complete, Hume impeaches
the veracity of reason : (i) Because it leads to con-
clusions different from those of the senses ; (2) Because
it is so frequently found to be fallible. (3) Because each
judgment must be tested by other judgments "contain-
ing uncertainty," and these in turn by other judgments
containing uncertainty, and so on ad infinitum. Nihilistic
scepticism is the fruit of Hume's endeavors. J

Thus, in our brief historical survey of modern philos-
ophy down to Hume, we find it culminating in scepti-
cism. The subjectivity which characterizes it from the
beginning peculiarly paves the way toward the conclu-
sion. It was against this scepticism that Reid recoiled.
Repugnant as it was to him, and, as before stated, be-
lieving it to be "inlaid" in all modern philosophy, and
traceable to the theory of perception which he believed
to be common to these systems, § he determined to
make a new inquiry into the subject, with the pur-

* "Treatise," p. 533. f Ibid., pp. 517-18.

\ Ibid., p. 472, sq. § "Works," Inq., pp. 96, 103, 106.

26 RELATION OF REID'S PHILOSOPHY

pose of refuting this theory of perception, and plac-
ing philosophy upon a new basis, by substituting a
new theory of perception, and a new philosophical
organon in the principle of common sense.

In inquiring anew into this subject, Reid adopted a
particular method. The " Inquiry" especially bears the
marks of its age. Like other systems of philosophy,
it is affected by the ' ' Zeit-Geist. " It is not often, if ever,
that we have a purely closet philosophy — a philosophy
produced absolutely independent of the spirit of the
age. Consciously or unconsciously speculation is af-
fected by the subtle influences of the intellectual and
moral atmosphere in which it is brought forth. This
influence of the spirit of the age upon Reid's philosophy
may be seen in the method which he adopts — the exper-
imental or inductive method. The results of an appli-
cation of this method in the study of physical phenom-
ena, by such men as Newton, were wonderful. Reid,
who was an earnest student of physics, was greatly im-
pressed by the validity and fruitfulness of this method,
and he came to the conclusion that it was the only
method which should be employed in the investigation of
the phenomena of the mind, and determined to apply
it. All through the "Inquiry" the steadfastness of his
purpose is manifest. Dugald Stewart truly remarks,
that "the influence of the general view opened in the
' Novum Organon' may be traced in almost every page
of his writings: and, indeed, the circumstance by which
these are so strongly and characteristically distinguished,
is that they exhibit the first systematical attempt to ex-
emplify in the study of human nature the same plan of

TO ITS PHILOSOPHICAL ANTECEDENTS. 27

investigation which conducted Newton to the properties
of light and to the law of gravitation. " *

Having thus stated the aim and method of Reid's
philosophy, let us proceed to an exposition of the same.
And, first, let us consider the theory of perception, which
he urged in opposition to the ' ' theory of ideas. "

His theory of perception has both negative and positive
aspects. In its negative aspect, it is a denial of (i) the
particular form of perception which Reid ascribed to
all preceding philosophy. This particular form Reid
conceived to be, as Hamilton suggests, that the object
before the mind in perception is " always a tertium quid
numerically different both from the object existing and
from the subject knowing. " f This is the theory which
Reid felt called upon to deny — the calling into question
of which he deemed to be the special merit of his own
philosophy. | (2) In its negative aspect, Reid's theory
of perception is a denial that we attain our knowledge
of external objects by an act of reasoning.

In denying the theory of ideas his argument runs as
follows: §

i. The theory is in direct opposition to the universal
sense of men uninstructed in philosophy. When a plain
man sees the sun and moon he does not doubt that there
are objects far distant from himself, and not merely ideas
in his mind. If he asks whether there are no substantial
beings called sun and moon, the answer which he will

* " Collected Works," vol. x, p. 259.

t Works, Inq., Note, p. 106.

J Ibid., p. 88.

§ Cf. " Works," Inq., pp. 201-1 1 and especially I. P., pp. 298-309.

28 RELATION OF REID'S PHILOSOPHY

get from the philosophers will differ. Locke and his
predecessors will answer, that there are such beings, but
they never appear to us in person, but only by ideas —
which are their representatives in our minds, and all we
know of them must be gained from these ideas. Berke-
ley and Hume would say, that there are no such sub-
stantial beings. That is simply a prejudice of the
vulgar. Berkeley would say that nothing exists but ideas
and minds, and these things are simply ideas in our
minds. Hume would say, only ideas exist, and the
mind is simply a series of ideas bound together by a few
relations. To the plain man this must, of course, be op-
posed to ." the dictates of common understanding."

2. Those who advocate the ' ' theory of ideas " have,
as a rule, assumed the existence of the ideas, and have
regarded their existence as unquestionable. The few
arguments which they have incidentally offered in their
behalf have been " too weak to support the conclusion."
Locke, for example, says we are conscious of such ideas.
But, says Reid, we are not conscious of them. All we
are conscious of, are the operations of the mind, such as
perceiving, remembering, etc., and not of the objects of
such operations. And thus he quotes others, endeavoring
to show the assumptive character of their positions, and
the weakness of their "incidental arguments."

3. Although there is a unanimous agreement among
philosophers on the subject of the existence of ideas,
there seems to be a pronounced disagreement among
them with respect to everything else concerning the ideas.
This ought not to be, if they are a reality, for of all things
they ought to be most easily accessible to knowledge.
Some hold that they are self-existent; others, that they

TO ITS PHILOSOPHICAL ANTECEDENTS. 29

exist in the Divine mind. Some hold that they exist in
our minds; others, that they exist in the brain or
sensorium. Some hold that they are innate, or, at least,
a part of them; others, that they are all adventitious.
Some, that they are gained through the senses; others,
that they are derived from sensation and reflection. As
to how they arise, some think the mind originates them;
others, that they are occasioned by external causes: still
others, that they are produced by God acting upon the
mind. And so on, in regard to other features of the
ideas there is this wide disagreement. This, as has been
suggested, ought not to be, if ideas really exist, for they
ought to be very accessible to knowledge.

4. Ideas do not improve our knowledge of the various
operations of the mind. They were, doubtless, brought
forward for this purpose. ' ' This power of perceiving ideas
is just as inexplicable as any of the powers explained
by it."

5. The consequences of this theory are such as to pre-
judice every man against it who has a due regard for the
common sense of mankind. Aside from the peculiarities
and absurdities which flow from the theory as seen in
ancient philosophy, we see in modern philosophy con-
sequences which are enough to prejudice mankind
against it. It has led to the attempts of trying to prove
the existence of material things. And who does not see
that philosophy must make a very ridiculous figure in
the eyes of sensible men while it is employed in muster-
ing up metaphysical arguments to prove that there is a
sun and a moon, an earth and a sea ? It has led to
such paradoxes as, "that the secondary qualities of body
are not qualities of body at all, but sensations of the

JO RELATION OF REID'S PHILOSOPHY

mind: That the primary qualities of body are resem-
blances of our sensations: That we have no notion of
duration, but from the succession of ideas in our minds:
That personal identity consists in consciousness; so that
the same individual thinking being may make two or
three different persons, and several different thinking be-
ings make one person: That judgment is nothing but a
perception of the agreement or disagreement of our ideas."
But these consequences are tolerable when brought into
comparison with those which we find in Berkeley and
Hume. Here we have the negation of the world of mat-
ter and the world of mind, and nothing is left us but
ideas. A general scepticism is the result. These are the
"noble fruits" which this "theory of ideas " has brought
forth. Such consequences, so startling to common
sense, must cause a reaction against the theory.

In the second place, Reid denies that we attain to a
knowledge of external objects by an act of reasoning.
He depends mainly upon the strength of his own theory
of perception for an overthrowal of this doctrine.

Having thus considered the negative aspects of Reid's
theory of perception let us proceed to a consideration of
its positive aspects.

The following are the main features of his theory:

/ Sensation.

1. A sensation is a simple, inexplicable affection of
the mind. "It appears to be a simple and original af-
fection or feeling of the mind, altogether inexplicable
and unaccountable." *

2. Sensations exist only in the mind. They do not

* "Works," Inq., p. 105.

TO ITS PHILOSOPHICAL ANTECEDENTS. 31

exist in material things — not even in our own bodies.
"The sensations of touch, of seeing, and hearing, are all
in the mind, and can have no existence but when they
are perceived. " *

3. Sensations are antecedent to perceptions. The
"sensation is followed by the perception of the ob-
ject, "f

// Perception.

i. Perception defined. Sensation naturally suggests
a ' ' notion " or " conception " of, together with a be-
lief in the existence of, an object. This is perception.
' ' But I think it appears, from what hath been said, that
there are natural suggestions: particularly that sensation
suggests the notion of present existence and the belief
that what we perceive or feel does now exist, . . . and
that our sensations and thoughts do also suggest the
notion of a mind, and the belief of its existence, and of
its relation to our thoughts. . . . And in like manner
. . . certain sensations of touch, by the constitution of
our nature, suggest to us extension, solidity and mo-
tion. "| In the "Intellectual Powers," we find Reid
essentially agreeing with his definition of perception
given in the "Inquiry." He says: "If, therefore, we
attend to that act of our mind which we call the perception
of an external object of sense, we shall find in it these
three things: — First, Some conception or notion of the
object perceived ; Secondly, a strong and irresistible
conviction and a belief of its present existence; and

* " Works," Inq., pp. 159, 105, 187; I. P., pp. 229, 310.
f Ibid., pp. 186, 187; I. P., p. 320.
J Ibid., Inq., p. in.

32 RELATION OF REID'S PHILOSOPHY

Thirdly, that this conviction and belief are immediate,
and not the effect of reasoning." In other words:
Sensations are attended by certain original "sugges-
tions " and beliefs, and this constitutes perception.

2. Perception illustrated. This theory of perception
will be more intelligible to us if we examine Reid's
doctrine of "suggestion " as we find it illustrated in his
treatment of the so-called secondary and primary quali-
ties of body. Reid agreed with Locke in regard to the
essential distinction between the secondary and primary
qualities, which Berkeley and Hume had endeavored to
remove.* The two points of distinction to which he
directs attention, are: (i) The ease with which we
distinguish between the sensation and its external corre-
late in the case of secondary qualities as compared with
primary qualities. (2) The sensations in the case of
secondary qualities only suggest a power or quality of
the object as a cause; whereas, in the case of the pri-
mary qualities, the sensation also suggests the nature of
the cause. Now, in the treatment of the secondary and
primary qualities, as above stated, we may see Reid's
theory of perception, as sensation attended by original
suggestions and beliefs, fully illustrated.

(a. ) In the case of secondary qualities, take, for ex-
ample, the secondary quality — smell. On this point
Reid makes the following remarks: "The smell of a
rose signifies two things: First, a sensation, which can
have no existence but when it is perceived, and can only
be in a sentient being or mind. Secondly, it signifies
some power, quality, or virtue, in the rose, or in efHu-

* " Works," Inq., p. 123; I. P., p. 314.

TO ITS PHILOSOPHICAL ANTECEDENTS. 33

via proceeding from it, which hath a permanent exist-
ence, independent of the mind, and which, by the con-
stitution of nature, produces the sensation in us. By
the original constitution of our nature we are both led to
believe that there is a permanent cause of the sensation,
and prompted to seek after it: and experience determines
us to place it in the rose." * That is, sensations of smell
and, as he elsewhere suggests, those of taste, sound, etc.,
suggest to us qualities in objects as the causes of these
sensations. Thus sensations attended by suggestions are
perception so far as the secondary qualities are con-
cerned. As Hamilton interprets Reid on this point:
"In a sensation (proper) of the secondary qualities, as
affections in us, we have a perception (proper) of them
as properties in objects and causes of the affections in us. " f
(b. ) In the case of primary qualities his theory of per-
ception as sensations attended by original " suggestions"
and beliefs is still more marked. Take, for example,
the sense of touch. Here we are liable to confound the
sensation and the quality of body from which it arises.
The sensation is only a ' ' sign "of a quality in the ex-
ternal body: but we are wont to pass quickly from the
" sign" to the thing signified without making a distinc-
tion. There is, nevertheless, a distinction. The sensa-
tion has no similitude to the quality known as hardness
in the external object. How, then, do we come to have
the "conception" and "belief" (perception) of the ob-
jective reality of what we call hardness in body ? For cer-
tainly we have such a perception. This " conception

* "Works," Inq., p. 114.
f Ibid., Note D, p. 884.

34 RELATION OF REID'S PHILOSOPHY

and belief," Reid answers, comes to us in the following
manner: "By an original principle of our constitution
a certain sensation of touch both suggests to the mind
the conception of hardness, and creates the belief of it:
or, in other words, that this sensation is a natural sign
of hardness."* Now what is true of hardness is also true
of softness, roughness, smoothness, figure and motion.
" All these," say s^ Reid, "by means of corresponding
sensations of touch, are presented to the mind as real
external qualities; the conception and belief of them
are invariably connected with the corresponding sensa-
tions, by an original principle of human nature, "f The
same thing is true in regard to extension and figure.
Our perception of extension and figure is a natural sug-
gestion attending sensations of touch. "Extension,
therefore, seems to be a quality suggested to us, by the
very same sensations which suggest the other quali-
ties above mentioned (i. e., other primary qualities).
When I grasp a ball in my hand, I perceive it at once
hard, figured and extended. The feeling is very simple,
and hath not the resemblance to any quality of body.
Yet it suggests to us three primary qualities perfectly
distinct from one another, as well as from the sensation
which indicates them. When I move my hand along
the table, the feeling is so simple that I find it difficult
to distinguish it into things of different natures: yet, it
immediately suggests hardness, smoothness, extension
and motion — things of very different natures, and all of
them as distinctly understood as the feeling which sug-

* "Works," Inq., p. 121. f Ibid., Inq., p. 123.

TO ITS PHILOSOPHICAL ANTECEDENTS. 35

gests them. " * It is apparent from the above quotations
concerning both the secondary and primary qualities
that what Reid means by perception is sensations at-
tended by original " suggestions " in the form of "no-
tions" or " conceptions" and beliefs. When he uses the
terms "sign " and "signify," he means simply that the
sensation is a "sign" of a quality in the external thing ;
and what he means by this, is that the sensation suggests a
" notion" or " conception" of, and belief in the existence
of, that quality. The "notion" and "conception" are
"suggestions " attending sensations, immediately inspired
by the constitution of our nature. The ' ' belief " in the
existence of the quality or object attending sensations is
also immediately inspired by our constitution. Percep-
tion, then, according to Reid, is, as was suggested in
the beginning, sensations attended by certain original
suggestions and beliefs. Or, to put the definition more
nearly in his own language: perception is the " notion "
or "conception" of an object, together with a belief in
its existence; which " notion " and belief are originally
"suggested" or " inspired " by the constitution of our
nature, on the occasion of a sensation arising in the
mind.

The foregoing is the substance of Reid's theory of per-
ception as we find it developed in both the "Inquiry"
and the ' ' Intellectual Powers. " Two questions very nat-
urally suggest themselves here: i. Was Reid right in
attributing the "theory of ideas" to preceding philoso-
phy? In regard to this question there is a differ-
ence of opinion. Such critics of Reid as Priestley, f

""Works," Inq., pp. 124-5.

f " Remarks on Reid, Beattie, and Oswald," 2d ed., § 3, p. 30.

36 RELATION OF REID'S PHILOSOPHY

Brown,* and Webb f think that Reid seriously erred
in his interpretation of the large majority of previ-
ous systems of philosophy. On the other hand,
Hamilton J comes to Reid's defense, and, while admit-
ting him to be mistaken in several instances, regards
him, especially in respect to modern philosophy, to
have good grounds for ascribing this theory to
his predecessors. To discuss this question would
require a survey of the entire history of philosophy,
which, of course, cannot be done here. If, however,
the reader desires to determine the correctness of Reid's
interpretation, I will be pardoned in once more call-
ing attention to the fact that Reid's conception of the
"theory of ideas "was not what is ordinarily under-
stood by representative perception. The theory which
he ascribes to his predecessors is, that in perception
there is an image or " idea " existing between the mind
perceiving and the existing object — numerically different
from both. 2. From all that is said upon the sub-
ject, what are we to understand Reid's theory of per-
ception really to be ? Is it the theory of immediate or intui-
tive perception — a direct gaze upon extra-mental, substan-
tial objects; or, is it some form of representative percep-
tion, only one form of which, viz., the tertium quid form,
it is claimed by some, he really combated ? Concerning
this question, it must be admitted that it is an exceed-
ingly difficult task to determine precisely what Reid's
theory of perception is. This difficulty is the result not
only of the looseness of his presentation of the subject,

* " Philosophy of the Human Mind," lees, xxvi, xxvii.
t " The Veil of Isis," pp. 125-162.
\ "Metaphysics," lees, xxi, xxii.

TO ITS PHILOSOPHICAL ANTECEDENTS. 37

but also of his failure to fully think the subject through.
By some, and doubtless by the majority of scholars who
have given Reid's philosophy thoughtful consideration,
he is supposed to advocate the theory of immediate per-
ception. So emphatically do they affirm this to be his
theory, that they regard it, in connection with his doc-
trine of common sense, to determine his historical posi-
tion or significance. By others, and for very good rea-
sons, he is supposed to teach some form of representative
perception. This form, to use the terminology of Ham-
ilton, may be called egoistical representationism, i. e.,
the object before the mind in perception is a subjective
representative object, which subjective object is a modi-
fication of the mind. And, as there are two forms of
egoistical representationism, the form which is ascribed
to Reid is: that the subjective object is really identical with
the perceptive act, but logically distinguished from it, ' ' being
simply the perceptive act itself, considered in one of its
relations, to wit, to the immediate object, the reality rep-
resented, and which, in and through that representation
alone, is objectified to consciousness and perceived."*
As has been suggested, those who ascribe some form of
representative perception to Reid, have good grounds
for doing so. His use of "notion," "conception,"
"suggestion," etc., certainly is favorable to an interpre-
tation of his teachings in favor of some form of mediate,
rather than immediate, perception. On the other hand,
there are good reasons for believing that he meant to teach
the doctrine of immediate or intuitive perception. SirWm.
Hamilton has, with characteristic thoroughness, careful -

• " Works," Note C, p. 818.

38 RELATION OF REID'S PHILOSOPHY

ly selected and arranged the evidence to be found
in both the "Inquiry" and the "Intellectual Powers"
bearing on each view of Reid's theory of perception. An
examination of this evidence will put us in a better posi-
tion to come to some conclusion on this disputed point*
Following the order of Hamilton, the following is the
substance of the leading arguments in favor of egoistical
representationism in the form stated above, f

I. Reid's doctrine of primary qualities implies it. He
teaches that the primary qualities of body are sug-
gested through certain sensations. They are suggestions,
or conceptions, immediately arising in the mind, we
know not how — by a natural magic as it were — on oc-
casion of certain sensations. If the primary qualities are
nothing more than suggestions, or conceptions ' ' inspired
by a means unknown, " then they are only representations of
it knows not what, blindly determined by the mind. Per-
ception is simply the consciousness of these concep-
tions or suggestions, hence our knowledge of the exter-
nal world would certainly not be immediate. The im-
mediate object before the mind would be a conception
or suggestion and not an extra-mental object. Hence
Reid must be considered an advocate of representative
perception. (Inq., pp. 122, 123, 128, 183, 188 ; I. P.,
pp. 258, 318, 320.) This argument, somewhat over-
drawn by Hamilton, seems to me to be one of the
strongest arguments in favor of Reid's theory being that
of egoistical representationism: because in his teach-
ing, concerning the primary qualities, the mind has
naught but sensations accompanied by "suggestions"

* «« Works," Note C, pp. 819-24. f n»d-» Note C, p. 820 2.

TO ITS PHILOSOPHICAL ANTECEDENTS. 39

or " conceptions" to deal with. Hamilton, who be-
lieves Reid to hold the theory of immediate perception,
makes a plea for his view in regard to this point by say-
ing, we must not hold Reid too rigidly to what he says
in the "Inquiry" on the subject of "suggestion," as he
does not mention it in the "Intellectual Powers," which
would seem that he was doubtful of its tendency. But
this plea, to my mind, has little force, because, in the
first place, Reid did not retract the doctrine of "sug-
gestion "in the "Intellectual Powers ;" and, in the second
place, although he does not use the word "suggestion"
in the " Intellectual Powers," his theory of perception in
both the "Inquiry" and "Intellectual Powers" is
essentially the same.

2. Intuitive perception implies that a knowledge and
belief of the existence of an external world is given in
perception, and there is no need of resorting to " natural
magic," "inspiration," etc., to explain that knowledge
and belief, as Reid really does. In the case of cos-
mothetic idealism, whose theory of perception is repre-
sentative perception, in which " the mind is determined
to represent to itself the external world, which, ex hypo-
thesi, it does not know, the fact of such representation
can only be conceived possible through some hyper-
physical agency." Now, the rationale of Reid's theory
of perception — "natural magic," "inspiration," "in-
fused faith," etc., — rather makes a representationist than
a presentationist out of him. (Inq., 122, 188; I. P.,

257.)

There is certainly some force in the above argument,
and in the "Intellectual Powers," Reid, in a measure,
approaches the Cartesian doctrine of a Deus ex machina

40 RELATION OF REID'S PHILOSOPHY

in his remarks on perception. (Seel. P., p. 257.) Even
Hamilton admits this. (See note, p. 257, of Reid's
"Works," also Note C, p. 821.)

3. Reid equalizes perception and imagination. He
speaks of imagination as a faculty of immediate know-
ledge. Now all will admit that in an act of the imagina-
tion the external object is known only mediately, in a
representative way. Hence Reid must have meant by
ascribing to the faculty of imagination immediate know-
ledge, that its knowledge is not representative in the
tertium quid sense, as advocated by the "theory of
ideas, " but that it is really mediate in the sense in which
we ordinarily speak of the images of the imagination be-
ing representative. If this be so, in the case of the im-
agination, then when Reid equalizes perception and
imagination by attributing to both of them immediate
knowledge, he must use the word immediate in the case
of perception, just as he uses it in the case of imagination,
viz., immediate in opposition to mediate as advocated
by the tertium quid theory, but nevertheless mediate in
the true sense. Or, as Hamilton states the argument:
"In calling imagination of the past, the distant, etc., an
immediate knowledge, Reid, it may be said, could only
mean by immediate, a knowledge effected not through
the supposed intermediation of a vicarious object, nu-
merically different from the object existing and the mind
knowing, but through a representation of the past, or
real, object in and by the mind itself ; in other words,
that by mediate knowledge he denoted a non-egoistical,
by immediate knowledge an egoistical, representation.
This being established, it may be further argued — that in
calling perception an immediate knowledge, he, on the

TO ITS PHILOSOPHICAL ANTECEDENTS. 4!

same analogy, must be supposed to deny, in reference to
this faculty, only the doctrine of non-egoistical represen-
tation. This is confirmed by his not taking the distinc-
tion between perception as a presentative, and memory,
for instance (/'. e., recollective imagination), as a repre-
sentative cognition : which he ought to have done, had
he contemplated, in the former, more than a faculty,
through which the ego represents to itself the non-ego,
of which it has no consciousness — no true objective and
immediate apprehension." * (Inq., p. 106; I. P., pp.
226, 233, 292, 293, etc.)

Hamilton tries to lessen the force of this argument
by saying that it merely " proves that Reid's perception
may be representative, not that it actually is so."f How-
ever, when taken in connection with the preceding argu-
ments, it at least shows that the logical implication of
Reid's presentation of his theory of perception is repre-
sentationism.

4. Reid, in some instances, seems to make perception
the result of inference, so that the remote cause is the
object perceived, and, hence, not the immediate object
of perception. Hence perception cannot be immediate.
(Inq., p. 125; I. P., 259, 260, 309, 326, 328.)

This argument has weight. Reid seems to teach that
perception is the result of inference, thus making it
mediate instead of immediate. However, it must be
taken into consideration, that there are other passages in
which he expressly denies that perception is the result
of inference. (I. P., 259, 260, 309, 326, 328.)

There are several minor arguments favoring this inter-

* " Works," Note C, pp. 821-822. f Ibid., p. 822.

42 RELATION OF REID's PHILOSOPHY

pretation of Reid, but they are hardly of sufficient im-
portance to be noticed here.* On the other hand, let us
state the evidence favoring the interpretation of Reid's
theory of perception as immediate perception, f

1. " Knowledge and existence only infer each other
when a reality is known itself or as existing." That is,
knowledge and existence are only convertible when there
is a knowledge of reality in itself. It is only under such
conditions that we can say that the reality ' ' is known
because it exists, and exists since it is known. " This is
what constitutes an immediate perception. Now Reid's
teaching is in harmony with the above position. He
says: "It seems admitted as a first principle, by the
learned and unlearned, that what is really perceived
must exist, and that to perceive what does not really exist
is impossible." (I. P., p. 274.)

2. All philosophers agree that the idea or representa-
tive object is immediately apprehended, and that as thus
apprehended it exists necessarily. Now if Reid affirms
that external objects are perceived not less immediately
he must be regarded as holding the theory of immediate
perception. This he affirms. (I. P., 263, 272, 274,
289, 446.)

3. All admit that mankind at large believe that the
external reality is the immediate object of perception.
Mankind, in general, take the "common- sense" view
of the world — t. e., they believe in the existence of a world
of substantial "things," which " things " are immediate-
ly perceived. Only philosophers affirm the contrary.

• Reid's " Works," Note C, pp. 821-2.
f Ibid., pp. 822-3.

TO ITS PHILOSOPHICAL ANTECEDENTS. 43

Now Reid affirms himself to be on the side of mankind
in general — or, as he suggests, on the side of the vulgar,
in this respect. (I. P., 275, 284, 298, 299, 302.)

This argument certainly has great force. Reid refers
frequently to the view of the " vulgar," which is the be-
lief that in perception we gaze immediately upon an ex-
ternal world of "things," and then places himselt on the
side of the "vulgar." (See above references.)

4. Reid affirms, that in self-consciousness we have an
immediate knowledge of the modifications of self: and
adds, that in perception we have knowledge just as
immediate of the qualities of the "not-self." (I. P.,
263, 269, 373.)

Thus runs the evidence in favor of both interpreta-
tions. It is apparent at once that there are good
grounds for holding either view. Sir Wm. Hamilton
and most interpreters, for the reasons above mentioned,
think that Reid really held the theory of immediate per-
ception. Brown, Webb, and Ferrier think his theory
was a theory of representative perception — egoistical
representationism. When the doctors disagree, who shall
decide? It is quite evident, from a consideration of
the above evidence, that it is not well to dogmatically
affirm either view. My own opinion is, that Reid meant
to teach natural realism, with its theory of immediate
perception; but his presentation of the subject is so
loose, owing to a looseness of language and a failure to
fully think the subject through, as to afford good
grounds for supposing him to teach cosmothetic ideal-
ism, with its theory of egoistical representationism.
This is the only way that Reid can be saved from self-
contradiction.

44 RELATION OF REID*S PHILOSOPHY

Let us now proceed to the second .feature of Reid's
philosophy — his doctrine of common sense. Not only
did Reid oppose to scepticism his theory of immediate
perception, to subvert the "theory of ideas," on which
he supposed this scepticism to be based; but he also es-
tablished his organon of common sense as authority, for
the acceptance of certain fundamental principles which
this scepticism denied. Reid used this term in a rather am-
biguous way, and often in such a way as to mislead the
reader as to his real meaning. Especially careless is he
in the use of the term in the "Inquiry," * where he lays
himself open to an interpretation which is really opposed
to his real meaning — particularly as indicated in the
"Intellectual Powers. "f Reid is sometimes supposed
to mean by common sense, the undeveloped belief of
the masses, which he would oppose to the reasonings of
philosophers. Again, he is supposed to mean by the
term ' ' good sense, " — sound understanding. Even Kant
was misled in thus interpreting Reid. J Sometimes he is
thought to mean the voice of the majority, or uni-
versal assent. But, while his carelessness lays some of
his remarks open to such interpretations, a critical study
of his works reveals the fact, that what he really means
by the principles of common sense is, the self-evident prin-
ciples of reason; &t\& what he means by common sense is
the faculty of such principles ; or, reason judging self-ev-
ident truth. This is quite evident from the following
statements, taken both from the "Inquiry" and the
"Intellectual Powers": —

* P- 101. f P- 425-

t " Prolegomena," pp. 4-6.

TO ITS PHILOSOPHICAL ANTECEDENTS. 45

"If there be certain principles, as I think there are,
which the constitution of our nature leads us to believe,
and which we are under a necessity to take for granted
in the common concerns of life, without being able to
give a reason for them; these are what we call the
principles of common sense ; and what is manifestly con-
trary to them is what we call absurd. " * " It is absurd to
conceive that there can be any opposition between reason
and common sense. It is indeed the firstborn of reason:
and, as they are commonly joined together in speech and
in writing, they are inseparable in their nature We
ascribe to reason two offices, or two degrees. The first
is to judge of things self-evident; the second to draw con-
clusions that are not self-evident from those that are.
The first of these is the province, and the sole province,
of common sense: and, therefore, it coincides with reason
in its whole extent, and is only another name for one
branch or one degree of reason, "f The self-evident
principles of reason, then, are what Reid means by com-
mon-sense principles; and by common sense he means
reason declaring self-evident truth. It will appear, also,
from the above citations, that the criteria of common-
sense principles, with Reid, are, necessity and self-evi-
dence.

Reid, however, was very unfortunate in his classification
of these principles. He places on the list of common-
sense principles, truths which are nothing more than
mere generalizations of experience. His loose classifica-
tion has had considerable to do in bringing condemnation
upon his philosophy. \

* "Works," Inq,, p. 108. f "Ibid., I. P., p. 425.

J Ibid., I. P., pp. 434-468.

46 RELATION OF REID'S PHILOSOPHY.

The historical significance of Reid's philosophy, then,
lies in calling into question the " theory of ideas" on
which the scepticism of Hume is founded, and in op-
posing to it the theory of immediate perception, and the
organon of common sense.

* •• Works," I. P., pp. 441-461.

THE INFLUENCE OF REID'S PHILOSO-
PHY UPON SUBSEQUENT PHILO-
SOPHIC THOUGHT.

CONTEMPORANEOUS with Reid, and influenced by him,
were James Oswald * and James Beattie,f also exponents
of the doctrine of common sense. Both adhered more
slavishly to the doctrine than Reid. Oswald, in his
" Appeal, " virtually uses the same argument which is
used by Reid, so far as the validity of so-called funda-
mental truths is concerned. Common sense discerns and
vouches for all fundamental truths. It is reason de-
claring self-evident truth. Now just as common sense
declares self-evident truth in other departments of
thought, so it declares primary truths in the domain of
morals and religion. In endeavoring to strengthen the
argument from common sense he makes use of the
reductio ad absurdum. Beattie's ' ' Essay " was called
forth specially by the scepticism of Hume. In it, with
Reid, he opposes the affirmations of common sense to
scepticism. He holds to the validity of so-called
primary truths. Our ground for accepting them is their

* " An Appeal to Common Sense in behalf of Religion," London,
1766-72.

t " Essay on the Nature and Immutability of Truth in Opposition
to Sophistry and Scepticism," 4th ed., London, 1773.

47

48 THE INFLUENCE OF REID'S PHILOSOPHY

own self-evidence. So that his doctrine is essentially
the same as Reid's.

The real successor of Reid was Dugald Stewart.* He,
too, is in substantial harmony with the views of Reid.

1. He agrees with him in regard to the method which
ought to be adopted in studying the phenomena of the
human mind — the inductive method, f

2. In his theory of perception he is in substantial
agreement with Reid. He regards perception as the
"notion " of an object, which notion and belief are in-
stinctively suggested or inspired on the occasion of sen-
sation. J Like Reid, he doubtless meant to teach imme-
diate perception, but, unfortunately, did not succeed
much better than Reid in clearing his doctrine of those
inconsistencies and ambiguities which render the theory
capable of a two-fold interpretation. That is, although
he doubtless meant to teach the theory of immediate
perception common to natural realism, his presenta-
tion of the subject involves egoistical representationism.

3. With respect to his doctrine of common sense,
we find him also in substantial agreement with Reid.
However, Stewart did not like the term — " the principles
of common sense," thinking it open to serious objections,
because of its associations and ambiguity. For this term
he substituted the expression: " the fundamental laws
of human belief." These laws he considered "the
constituent elements of reason." This doctrine he
emphasized just as much as Reid did, and he saw in it

* " Collected Works," ed. by Hamilton, Edinburgh, 1854-60.
t Ibid., vol. ii, Int., §§ i and 2.
\ Ibid., vol. ii, ch. i.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 49

the only true organon for philosophy, and the antidote
for scepticism. *

Dr. Thomas Brown, f was also, to a certain extent, a
disciple of Reid. Influenced, however, by the teach-
ings of Hartley, and the sensationalism of the French
Ideologists, he, in a measure, deviated from some of the
positions of the Scottish School. This is especially
manifest in his analysis and classification of the pheno-
mena of the mind. Reid and Stewart being emphati-
cally opposed to sensationalism, did not carry their psy-
chological analysis as far as they doubtless would have
done, had not sensationalism been such a bugbear to
them. Brown, however, was not to be so easily fright-
ened, and he carried his analysis to a greater simplifica-
tion. He tried to unite some of the positions of the
Sensational School with certain positions of the Scot-
tish School.

1. His method was that of the Scottish School, viz.,
the inductive method. He insisted upon applying the
method adopted by physical science. J

2. The result of an application of this method was a
reduction of the number of original faculties to which
Reid and Stewart held, and the resolving of all mental
phenomena into modifications of the mind itself. §

3. His theory of perception differs from the theory of
Reid and Stewart. It is egoistical representationism, i. e. ,

* "Collected Works," vol. iii, ch. I.

f " Lectures on the Philosophy of the Human Mind," Hallo well.,
1829.

{ Ibid., lees, ix, x, xi.
§ Ibid., lees, xvi, xvii.

5O THE INFLUENCE OF REID'S PHILOSOPHY

the object before the mind in perception is not an extra-
mental, material object, but a mental object, which ob-
ject is merely a modification of the mind itself."*

4. On what authority, then, do we believe in an ex-
ternal world? Brown answers: through the intuitive
principle of causation, we are led to infer the existence
of an external world. On occasion of certain sensations
arising in the mind, we infer an extra-mental reality as
their cause, which external cause he affirmed to be an
extended, material object f

Brown, then, retreats from natural realism with its
doctrine of immediate perception, and goes over to
cosmothetic idealism, with its doctrine of mediate
perception — affirming, however, the existence of an
external, material world on the strength of the causal
principle.

In Sir William Hamilton^ we have the ablest expo-
nent and special defender of the Scottish realism. To
fully appreciate his philosophy, as Dr. McCosh suggests,
we must bear in mind the influence of four men upon
his thinking: Aristotle, Reid, Kant, and Jacobi. Our
interest here extends only to the influence exerted upon
his philosophical thinking by Reid. This is manifest in
his theory of perception and his doctrine of common
sense.

i. His theory of perception is intuitive or immediate

* " Lectures on the Philosophy of the Human Mind," Hallowell,
1820, lees, xxv-xxvii.

f Ibid.

| "Lectures on Metaphysics," Edinburgh and London, 1870; Cf.
also Reid's " Works," Notes and Dissertations.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 51

perception.* The mind gazes immediately upon extra-
mental reality. He differs from Reid, however, in ex-
cluding from the objects immediately known, objects
which are not in correlation to the bodily organism.
According to Hamilton, the objects which the mind
immediately perceives in sense-perception are the organ-
ism, and the extra-bodily objects in correlation to the
organism, i. e., extra-bodily objects in their resistance
to our locomotive or muscular energy, f The grounds
on which he bases the theory of immediate perception
are, positively, the testimony of consciousness,! and,
negatively, the sceptical consequences which he regards
to be the inevitable result of a denial of this theory. §

2. Reid's influence upon Hamilton is very marked
indeed in his doctrine of common sense. Hamilton
made an elaborate attempt not only to establish the
legitimacy of the argument from common sense, and to
point out the criteria of common-sense principles, but
also to vindicate the use of the term "common sense.'
The propriety of using the term" common sense " he tries
to establish by an appeal to the history of philosophy.
He traces the use of the word ' ' from the dawn of specu-
lation to the present day," finding it in use by nearly
every philosopher. This historical survey evinces a
patience and erudition which are simply remarkable.

* " Metaphysics," vol ii, lees, xxiv-xxviii, also Reid's " Works,"
Note D.

f Ibid. See in Note D other differences of a minor character,
pp. 882-6.

J Ibid.

§ Reid's "Works," Note A.

52 THE INFLUENCE OF REID'S PHILOSOPHY

In the works of one hundred and six writers, he finds
witnesses to the legitimacy of the term " common sense."
Among these writers are numbered the greatest names
in philosophy. As to the meaning and authority of
common sense he says:

Demonstration, if proof be possible at all, must
ultimately rest upon certain fundamental propositions
which must be accepted. These propositions are more
on the order of facts, feelings, beliefs, than cognitions,
because of their inexplicable character. Nevertheless,
Hamilton calls them cognitions. Now, if they must be
accepted, the question arises as to the authority for
accepting them. The answer to this is: they must be
accepted because they are the conditions sine qud non of
knowledge, and to impeach them is to impeach the data
of consciousness. To show that a denial of a certain
proposition would impeach the integrity of an original
datum of consciousness, is to argue from common
sense. "Limiting, therefore, our consideration to the
question of authority: how, it is asked, do these pri-
mary propositions — these cognitions at first hand — these
fundamental facts, feelings, beliefs, certify us of their
own veracity ? To this the only possible answer is —
that as elements of our mental constitution — as the
essential conditions of our knowledge — they must by us
be accepted as true. To suppose their falsehood, is to
suppose that we are created capable of intelligence, in
order to be made the victims of delusion: that God is a
deceiver, and the root of our nature a lie. But such a
supposition, if gratuitous, is manifestly illegitimate.
For, on the contrary, the data of our original conscious-
ness must, it is evident, in the first instant! be presumed

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 53

true. It is only if proved false, that their authority can,
in consequence of that proof, be, in the second instance,
disallowed. Speaking, therefore, generally, to argue
from common sense is simply to show, that the denial
of a given proposition would involve the denial of some
original datum of consciousness: but as every original
datum of consciousness is to be presumed true, that the
proposition in question, as dependent on such a prin-
ciple, must be admitted."*

But still it may be urged: Why trust the deliverances
of consciousness ? To this question Hamilton replies:
"If, therefore, it can be shown on the one hand, that
the deliverances of consciousness must philosophically
be accepted, until their certain or probable falsehood
has been positively evinced: and if, on the other hand,
it cannot be shown that any attempt to discredit the
veracity of consciousness has ever yet succeeded: it
follows that, as philosophy now stands, the testimony of
consciousness must be viewed as high above suspicion,
and its declarations entitled to demand prompt and un-
conditional assent, "f

In regard to the first point it must be acknowledged
that, at least, in the first instance, the veracity of con-
sciousness must be accepted. We may not gratuitously
assume that Nature works " in counteraction of her-
self." Unless there are reasons to the contrary, it is not
to be supposed that our faculty of knowledge is "an
instrument of illusion."

But, secondly, even though in the outset the veracity
of the deliverances of consciousness must be admitted,

* « Works," Note A, p. 743. t Ibid., p. 745.

54 THE INFLUENCE OF REID'S PHILOSOPHY

"it still remains competent to lead a proof that they are
undeserving of credit." The question, however, arises
as to how this is to be accomplished. This can only
be done (i) by showing, inasmuch as there are quite a
number of these primary data, that they immediately
contradict each other, or (2) that they are indirectly con-
tradictory, inasmuch as conclusions derived from them,
and for which they are responsible, are mutually con-
tradictory. This would prove the inconsistency of con-
sciousness with itself, and, of course, as a consequence,
its inconsistency with the unity of truth. But such con-
tradiction or inconsistency, says Hamilton, has never
yet been established. ' ' No attempt to show that the
data of consciousness are (either in themselves, or in
their necessary consequences) mutually contradictory,
has yet succeeded: and the presumption in favor of the
truth of consciousness and the possibility of philosophy
has therefore, never been redargued. In other words,
an original, universal, dogmatic subversion of knowledge
has hitherto been found impossible." * We must, then,
accept the primary deliverances of consciousness as true,
and the argument from common sense which shows that
a denial of a certain proposition discredits an original
datum of consciousness must be regarded as legitimate.
The essential marks which distinguish these original
or fundamental cognitions or convictions from those
which are derived, are four, viz., incomprehensibility,
simplicity, necessity and absolute universality, and com-
parative evidence and certainty. A conviction is in-
comprehensible when it is merely given in consciousness

* " Works," Note A, p. 746.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 55

that its object is, and not why or how it is. A cognition
or belief is simple when it is not compounded of other
cognitions or beliefs. A cognition or belief is necessary
or universal (these are coincident) when it is impossible
to think it false. By comparative evidence and cer-
tainty is meant, quoting from Aristotle, "If we know
and believe through certain original principles, we
must know and believe these with paramount certainty,
for the very reason that we know and believe all else
through them." These four marks, then, incompre-
hensibility, simplicity, necessity and absolute universality,
and comparative evidence and certainty, constitute the
essential characters by which original cognition or beliefs
are known.* Common -sense principles, then, are in-
comprehensible, simple, necessary, and absolutely uni-
versal principles, which if an attempt be made to prove
or disprove them would involve a resort to principles
"neither more evident nor more certain."

Hamilton made no such attempt as that of Reid's to
classify, or to make a list of, these principles. However,
he emphatically pronounces the immediate perceptions
of self and of an extra-mental world of extended objects
to be common-sense principles, for they are primary data
of consciousness.

Our interest here in Hamilton's philosophy, as before
suggested, does not extend beyond his theory of per-
ception and his doctrine of common sense. These are
the features which ally him to Reid and the Scottish
School. These we have found to be immediate or
intuitive perception and the veracity of consciousness in

* " Works," Note A, p. 754; " Metaphysics," lee. xxxviii.

56 THE INFLUENCE OF REID'S PHILOSOPHY

its original deliverances in the form of ' ' cognitions " or
" beliefs."

In France, the philosophy of Reid exerted considera-
ble influence. It was first used by M. Royer-Collard *
as a weapon against sensationalism and materialism.
The philosophy of Condillac and the French Ideolo-
gists was strongly established there. Collard saw that
the sensationalism of Condillac rested upon the same
foundation as that which underlay the scepticism of
Hume; and, with Reid, he felt that if the premises be
accepted the conclusion legitimately followed. The prem-
ises of scepticism and sensationalism are the same, the
"theory of ideas." The same means which Reid used
for the overthrowal of these premises were used by Col-
lard — the theory of immediate perception and the prin-
ciple of common sense — meaning by common sense a
sort of mental instinct.

Another French philosopher on whose thinking Reid's
philosophy exerted considerable influence was M. Victor
Cousin, f the real father of eclecticism in France. He bor-
rows largely from the Scottish and German schools of
philosophy, but acknowledges the principal factor of this
eclecticism to be taken from the Scottish philosophy.
In the adoption of the inductive method, in basing phi-
losophy upon psychology, in the use of the doctrine of
common sense in a modified form, we see the in-
fluence of Reid's philosophy upon the thinking of
Cousin.

* " Fragmens de Royer-Collard," Jouffroy's trans, of the works
of Reid.

t " Philosophic Ecossaise," Paris, 1846.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 57

Th. Jouffroy,* the pupil of Cousin, was also greatly
influenced by Reid's philosophy. He translated the
works of Reid into French, and it was through his
teaching, together with the teaching of Collard and
Cousin, that the Scottish philosophy became for a
while the prevailing philosophy in France. He, too,
is an eclectic, but some of the positions of the Scottish
School are prominent factors in his eclecticism. The
application of the inductive method to the study of the
phenomena of consciousness, and the common-sense at-
titude toward the problem of substance, indicate the in-
fluence of Reid and Stewart upon his thinking, f

In Germany, Reid's influence upon philosophy
amounts to very little indeed. Kant regarded his phi-
losophy with more or less contempt. There are some
evidences of its influence in the philosophy of Benecke. |

In America, directly and indirectly (through his dis-
ciples) Reid's philosophy has exerted great influence.
Dr. Porter says: "The Scottish philosophy has had a
wide-spread influence in this country. The works of
Reid were not so generally circulated on account of the
pre-occupations of the American War for Independence
and the organization of the new political union, 1770-
1800, but when the attention of thinking men was
aroused to the practical consequences of the theological
and political philosophy of England and France, the
works of Reid were studied for a better system. As
soon as Dugald Stewart appeared upon the arena, his

* " Preface a la Traduction des CEuvres de Reid," 1835.
f Cf. McCosh, " The Scottish Philosophy," pp. 302-3.
J " Die Neue Psychologic," Berlin, 1845.

58 THE INFLUENCE OF REID'S PHILOSOPHY

lectures were resorted to by a few favored American
pupils, and his works were reprinted as fast as they ap-
peared, and some of them became the favored text-
books in our leading colleges."* Later, through the
works of Hamilton, widely circulated in this country,
and the works of prominent American thinkers identi-
fied with the Scottish School, the essential principles of
Reid's philosophy became widely known, being taught
in many colleges. Among the American writers on
philosophy, just referred to, Dr. James McCosh and Dr.
Noah Porter may be mentioned. McCosh, | though differ-
ing from Reid in points of minor importance, accepts with
slight alterations the cardinal features of his philosophy.

i. His theory of perception is intuitive or immediate
perception. In sense-perception we have an immediate
knowledge of extra-mental material objects. J These
objects are the bodily organism, the various parts of
which " as affected " are immediately perceived through
the different senses; and extra-bodily material objects in
correlation to the body, perceived specially through the
muscular sense.

" We may notice here that sense-perception gives us
(i) Externality. We perceive all material objects as
out of, and independent of, the perceiving mind. This
is associated with (2) Extension. We perceive things
as extended by all the senses, not only as Locke thought
by sight and touch, but by smell, taste and hearing ; by

* " Ueberweg's History of Philosophy," Appendix i, vol. ii,
pp. 451-2.

f "Psychology," New York, 1886; "Realistic Philosophy," New
York, 1887, 2 vols., etc. } "Psychology," pp. 20-69.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 59

all these we know our affected organism as in a certain
direction and so in space ; by taste and smell we know
the palate and nostrils as affected, and by hearing, our
ear as affected. (3) We perceive body exercising en-
ergy. We do so especially by the muscular sense ; we
find body resisting locomotive energy. Perhaps we have
some vague sense of energy by all the senses : the ob-
jects perceived seem to affect us. But the sense of power
is specially given by our energy and the resistance to our
energy."* These three cognitions Dr. McCosh calls
primitive or intuitive cognitions.

2. His doctrine of " First and Fundamental Truths "
evinces the influence of Reid. Demonstration, he says,
cannot go on forever. We cannot prove all things by
mediate evidence. We can show, however, that we
are justified in making certain fundamental assumptions.
Of these assumptions, which he calls fundamental truths,
the tests are : self-evidence, necessity, and universality, f

Dr. Porter's writingsj evince the influence of German
speculative thought, as well as that of Reid and his
School. However, the influence of the Scottish thinkers
is predominant. As in Dr. McCosh's philosophy, this
may be seen in his theory of perception and primary
truths.

i . His theory of perception is intuitive perception. The
object is known immediately. The object thus known

* " Psychology," p. 68.

f "Realistic Philosophy," vol. i, pp. 33-43. Cf. also "Intui-
tions of the Mind."

t " The Human Intellect," New York, 1875; " The Elements of
Intellectual Science," New York, 1884.

60 THE INFLUENCE OF REID'S PHILOSOPHY

is "the sensorium in some form of excited action."
The eye, ear, nostril, hand, etc., "with the nerves at-
tached as capable of the sentient function when acting
in a living organism, are known by the collective term,
the sensorium, or sensory." This sensorium is known
immediately not only as a non-ego, but also as extended.*
Extra-organic bodies are not known immediately. Our
knowledge of them is "indirect or acquired."! On this
latter point he differs from Reid who holds to an im-
mediate perception of extra-organic objects.

2. We have an intuitive knowledge of first principles.
The criteria of such principles are: universality, necessity
and logical independence and originality. J

However, notwithstanding the wide influence exerted
by the philosophy of Reid in Great Britain, France and
America, his historical significance is not great. Cousin
regarded him as the modern Socrates. This estimate of
his historical position is true in one sense. Being the
first philosopher to attempt to save philosophy from the
scepticism of Hume, he occupies the same position in
modern philosophy which Socrates holds in Greek phi-
losophy in his opposition to the scepticism of the Sophists.
But in his influence upon the subsequent development
of philosophic thought, Reid cannot be compared with
Socrates. To Kant must be awarded the honor of such
a comparison. It was his great work which determined
the main course of philosophy subsequent to Hume,
just as the philosophizing of Socrates determined the

* " Elements of Intellectual Science," p. 106.
f Ibid., p. 155.
J Ibid., pp. 416-45.

UPON SUBSEQUENT PHILOSOPHIC THOUGHT. 6l

course of Greek philosophy, subsequent to the Sophists.
Indeed, as in the philosophy of Socrates we find the best
standpoint from which to survey the development of
ancient philosophy from Thales to the Christian era, so
in the philosophy of Kant we find the best standpoint
from which to view the development of modern philoso-
phy from Des Cartes to Von Hartmann.

E. HERSHEY SNEATH.

AN INQUIRY INTO THE HUMAN MIND ON

THE PRINCIPLES OF COMMON SENSE,

BY THOMAS REID, D. D.

DEDICATION.

TO THE RIGHT HONOURABLE JAMES, EARL OF

FINDLATER AND SE AFIELD, CHANCELLOR

OF THE UNIVERSITY OF OLD

ABERDEEN.

MY LORD, — Though I apprehend that there are things,
new and of some importance, in the following Inquiry,
it is not without timidity that I have consented to the
publication of it. The subject has been canvassed by
men of very great penetration and genius: for who
does not acknowledge Des Cartes, Malebranche, Locke,
Berkeley, and Hume, to be such ? A view of the human
understanding, so different from that which they have ex-
hibited, will, no doubt, be condemned by many, without
examination, as proceeding from temerity and vanity.

But I hope the candid and discerning Few, who are
capable of attending to the operations of their own minds,
will weigh deliberately what is here advanced, before
they pass sentence upon it. To such I appeal, as the
only competent judges. If they disapprove, I am prob-
ably in the wrong, and shall be ready to change my
opinion upon conviction. If they approve, the Many
will at last yield to their authority, as they always do.

However contrary my notions are to those of the wri-
ters I have mentioned, their speculations have been of
great use to me, and seem even to point out the road
which I have taken: and your Lordship knows, that the
merit of useful discoveries is sometimes not more justly

65

66 THE PHILOSOPHY OF REID.

due to those that have hit upon them, than to others that
have ripened them, and brought them to the birth.

I acknowledge, my Lord, that I never thought of call-
ing in question the principles commonly received with
regard to the human understanding, until the "Treatise
of Human Nature " was published in the year 1739. The
ingenious author of that treatise upon the principles of
Locke — who was no sceptic — hath built a system of scep-
ticism, which leaves no ground to believe any one thing
rather than its contrary. His reasoning appeared to me
to be just ; there was, therefore, a necessity to call in
question the principles upon which it was founded, or to
admit the conclusion.*

But can any ingenuous mind admit this sceptical sys-
tem without reluctance ? I truly could not, my Lord ;
for I am persuaded, that absolute scepticism is not
more destructive of the faith of a Christian than of the
science of a philosopher, and of the prudence of a
man of common understanding. I am persuaded,
that the unjust live by faith as well as the just ; that,
if all belief could be laid aside, piety, patriotism, friend-
ship, parental affection, and private virtue, would appear
as ridiculous as knight-errantry ; and that the pursuits
of pleasure, of ambition, and of avarice, must be
grounded upon belief as well as those that are honour-
able or virtuous.

* "This doctrine of ideas" (says Dr. Reid, in a subsequent work)
" I once believed so firmly, as to embrace the whole of Berkeley's
system in consequence of it ; till, finding other consequences to follow
from it, which gave me more uneasiness than the want of a material
world, it came into my mind, more than forty years ago, to put the
question, What evidence have I for this doctrine, that all the objects
of my knowledge are ideas in my own mind?" — Essays on the
Intellectual Powers, Ess. II. ch. x. p. 162.

In like manner, Kant informs us, that it was by Hume's sceptical
inferences, in regard to the causal nexus, that he also " was first
roused from his dogmatic slumber." See the " Prolegomena," p. 13.
— H.

THE PHILOSOPHY OF REID. 67

The day-labourer toils at his work, in the belief that he
shall receive his wages at night ; and, if he had not this
belief, he would not toil. We may venture to say, that
even the author of this sceptical system wrote it in the
belief that it should be read and regarded. I hope he
wrote it in the belief also that it would be useful to man-
kind; and, perhaps, it may prove so at last. For I con-
ceive the sceptical writers to be a set of men whose busi-
ness it is to pick holes in the fabric of knowledge wher-
ever it is weak and faulty ; and, when these places are
properly repaired, the whole building becomes more firm
and solid than it was formerly.

For my own satisfaction, I entered into a serious ex-
amination of the principles upon which this sceptical sys-
tem is built ; and was not a little surprised to find, that
it leans with its whole weight upon a hypothesis, which
is ancient indeed, and hath been very generally received
by philosophers, but of which I could find no solid proof.
The hypothesis I mean is, That nothing is perceived but
what is in the mind which perceives it : That we do not
really perceive things that are external, but only certain
images and pictures of them imprinted upon the mind,
which are called impressions and ideas.

If this be true, supposing certain impressions and ideas
to exist in my mind, I cannot, from their existence, in-
fer the existence of anything else : my impressions and
ideas are the only existences of which I can have any
knowledge or conception; and they are such fleeting and
transitory beings, that they can have no existence at all,
any longer than I am conscious of them. So that, upon
this hypothesis, the whole universe about me, bodies and
spirits, sun, moon, stars, and earth, friends and relations,
all things without exception, which I imagined to have
a permanent existence, whether I thought of them or not,
vanish at once ;

" And, like the baseless fabric of a vision,
Leave not a track behind."

68 THE PHILOSOPHY OF REID.

I thought it unreasonable, my Lord, upon the author-
ity of philosophers, to admit a hypothesis which, in my
opinion, overturns all philosophy, all religion and virtue,
and all common sense — and, finding that all the sys-
tems concerning the human understanding which I was
acquainted with, were built upon this hypothesis/ I re-
solved to inquire into this subject anew, without regard
to any hypothesis.

What I now humbly present to your Lordship, is the
fruit of this inquiry, so far only as it regards the five
senses: in which I claim no other merit than that of
having given great attention to the operations of my own
mind, and of having expressed, with all the perspicuity I
was able, what I conceive every man, who gives the same
attention, will feel and perceive. The productions of im-
agination require a genius which soars above the com-
mon rank ; but the treasures of knowledge are commonly
buried deep, and may be reached by those drudges who
can dig with labour and patience, though they have not
wings to fly. The experiments that were to be made in
this investigation suited me, as they required no other
expense but that of time and attention, which I could
bestow. The leisure of an academical life, disengaged
from the pursuits of interest and ambition ; the duty of my
profession, which obliged me to give prelections on these
subjects to the youth ; and an early inclination to specu-
lations of this kind, have enabled me, as I flatter myself,
to give a more minute attention to the subject of this in-
quiry, than has been given before.

My thoughts upon this subject were, a good many years
ago, put together in another form, for the use of my pu-
pils, and afterwards were submitted to the judgment of a
private philosophical society,* of which I have the honour
to be a member, A great part of this Inquiry was hon-
oured even by your Lordship's perusal. And the en-

* Aberdeen Philosophical Society founded by Reid and Dr. John
Gregory. — S.

THE PHILOSOPHY OF REID. 69

couragement which you, my. Lord, and others, whose
friendship is my boast, and whose judgment I reverence,
were pleased to give me, counterbalanced my timidity and
diffidence, and determined me to offer it to the public.

If it appears to your Lordship to justify the common
sense and reason of mankind, against the sceptical sub-
tilties which, in this age, have endeavoured to put them
out of countenance — if it appears to throw any new
light upon one of the noblest parts of the divine work-
manship— your Lordship's respect for the arts and sci-
ences, and your attention to everything which tends
to the improvement of them, as well as to everything else
that contributes to the felicity of your country, leave me
no room to doubt of your favourable acceptance of this
essay, as the fruit of my industry in a profession where-
in I was accountable to your Lordship ; and as a testi-
mony of the great esteem and respect wherewith I have
the honour to be,

My Lord, your Lordship's most obliged and most de-
voted Servant,

THO. REID.

AN

INQUIRY INTO THE HUMAN MIND.

CHAPTER I.

INTRODUCTION.

Section I.

THE IMPORTANCE OF THE SUBJECT, AND THE MEANS OF
PROSECUTING IT.

THE fabric of the human mind is curious and won-
derful, as well as that of the human body. The facul-
ties of the one are with no less wisdom adapted to their
several ends than the organs of the other. Nay, it is
reasonable to think, that, as the mind is a nobler work
and of a higher order than the body, even more of the
wisdom and skill of the divine Architect hath been em-
ployed in its structure. It is, therefore, a subject highly
worthy of inquiry on its own account, but still more
worthy on account of the extensive influence which the
knowledge of it hath over every other branch of science.

In the arts and sciences which have least connection
with the mind, its faculties are the engines which we
must employ; and the better we understand their nature
and use, their defects and disorders, the more skilfully
we shall apply them, and with the greater success. But
in the noblest arts," the mind is also the subject upon
which we operate. The painter, the poet, the actor, the
orator, the moralist, and the statesman, attempt to oper-

70

SEC. I.] THE PHILOSOPHY OF REID. 71

ate upon the mind in different ways, and for different
ends; and they succeed according as they touch properly
the strings of the human frame. Nor can their several
arts ever stand on a solid foundation, or rise to the
dignity of science, until they are built on the principles
of the human constitution.

Wise men now agree, or ought to agree, in this, that
there is but one way to the knowledge of nature's works
— the way of observation and experiment. By our con-
stitution, we have a strong propensity to trace particular
facts and observations to general rules, and to apply
such general rules to account for other effects, or to di-
rect us in the production of them. This procedure of
the understanding is familiar to every human creature in
the common affairs of life, and it is the only one by
which any real discovery in philosophy can be made.

The man who first discovered that cold freezes water,
and that heat turns it into vapour, proceeded on the
same general principles, and in the same method by
which Newton discovered the law of gravitation and the
properties of light. His regulce philosophandi are maxims
of common sense, and are practised every day in com-
mon life; and he who philosophizes by other rules,
either concerning the material system or concerning the
mind, mistakes his aim.

Conjectures and theories are the creatures of men, and
will always be found very unlike the creatures of God.
If we would know the works of God, we must consult
themselves with attention and humility, without daring
to add anything of ours to what they declare. A just
interpretation of nature is the only sound and orthodox
philosophy: whatever we add of our own, is apocryphal,
and of no authority.

All our curious theories of the formation of the earth,
of the generation of animals, of the origin of natural and
moral evil, so far as they go beyond a just induction
from facts, are vanity and folly, no less than the Vortices

72 THE PHILOSOPHY OF REID. iCH. I.

of Des Cartes, or the Archseus of Paracelsus. Perhaps
the philosophy of the mind hath been no less adulterated
by theories, than that of the material system. The
theory of Ideas is indeed very ancient, and hath been
very universally received; but, as neither of these titles
can give it authenticity, they ought not to screen it from
a free and candid examination; especially in this age,
when it hath produced a system of scepticism that seems
to triumph over all science, and even over the dictates of
common sense.

All that we know of the body, is owing to anatomical
dissection and observation, and it must be by an anat-
omy of the mind that we can discover its powers and
principles.

Section //.

THE IMPEDIMENTS TO OUR KNOWLEDGE OF THE MIND.

But it must be acknowledged, that this kind of anat-
omy is much more difficult chan the other; and, there-
fore, it needs not seem strange that mankind have made
less progress in it. To attend accurately to the opera-
tions of our minds, and make them an object of thought,
is no easy matter even to the contemplative, and to the
bulk of mankind is next to impossible.

An anatomist who hath happy opportunities, may have
access to examine with his own eyes, and with equal ac-
curacy, bodies of all different ages, sexes, and conditions;
so that what is defective, obscure or preternatural in one,
may be discerned clearly and in its most perfect state in
another. But the anatomist of the mind cannot have
the same advantage. It is his own mind only that he
can examine with any degree of accuracy and distinct-
ness. This is the only subject he can look into. He
may, from outward signs, collect the operations of other
minds; but these signs are for the most part ambiguous,
and must be interpreted by what he perceives within
himself.

SEC. II.] THE PHILOSOPHY OF REID. 73

So that, if a philosopher could delineate to us, dis-
tinctly and methodically, all the operations of the think-
ing principle within him, which no man was ever able
to do, this would be only the anatomy of one particular
subject; which would be both deficient and erroneous,
if applied to human nature in general. For a little re-
flection may satisfy us, that the difference of minds is
greater than that of any other beings which we consider
as of the same species.

Of the various powers and faculties we possess, there
are some which nature seems both to have planted and
reared, so as to have left nothing to human industry.
Such are the powers which we have in common with the
brutes, and which are necessary to the preservation of
the individual, or the continuance of the kind. There
are other powers, of which nature hath only planted the
seeds in our minds, but hath left the rearing of them to
human culture. It is by the proper culture of these
that we are capable of all those improvements in
intellectuals, in taste, and in morals, which exalt and
dignify human nature; while, on the other hand, the
neglect or perversion of them makes its degeneracy and
corruption.

The two-legged animal that eats of nature's dainties,
what his taste or appetite craves, and satisfies his thirst at
the crystal fountain, who propagates his kind as occasion
and lust prompt, repels injuries, and takes alternate
labour and repose, is, like a tree in the forest, purely of
nature's growth. But this same savage hath within him
the seeds of the logician, the man of taste and breeding,
the orator, the statesman, the man of virtue, and the
saint; which seeds, though planted in his mind by na-
ture, yet, through want of culture and exercise, must lie
for ever buried, and be hardly perceivable by himself or
by others.

The lowest degree of social life will bring to light
some of those principles which lay hid in the savage state;

74 THE PHILOSOPHY OF REID. [Cn. I.

and, according to his training, and company, and man-
ner of life, some of them, either by their native vigor, or
by the force of culture, will thrive and grow up to great
perfection, others will be strangely perverted from their
natural form, and others checked, or perhaps quite
eradicated.

This makes human nature so various and multiform
in the individuals that partake of it, that, in point of
morals and intellectual endowments, it fills up all that
gap which we conceive to be between brutes and devils
below, and the celestial orders above; and such a pro-
digious diversity of minds must make it extremely dim-
cult to discover the common principles of the species.

The language of philosophers, with regard to the
original faculties of the mind, is so adapted to the pre-
vailing system, that it cannot fit any other; like a coat
that fits the man for whom it was made, and shews him
to advantage, which yet will sit very awkward upon one
of a different make, although perhaps as handsome and
as well proportioned. It is hardly possible to make any
innovation in our philosophy concerning the mind and
its operations, without using new words and phrases, or
giving a different meaning to those that are received— a
liberty which, even when necessary, creates prejudice
and misconstruction, and which must wait the sanction
of time to authorize it; for innovations in language, like
those in religion and government, are always suspected
and disliked by the many, till use hath made them famil-
iar, and prescription hath given them a title.

If the original perceptions and notions of the mind
were to make their appearance single and unmixed, as
we first received them from the hand of nature, one ac-
customed to reflection would have less difficulty in tracing
them; but before we are capable of reflection, they are so
mixed, compounded, and decompounded, by habits, as-
sociations, and abstractions, that it is hard to know what
they were originally. The mind may, in this respect,

SEC. II.] THE PHILOSOPHY OF REID, 75

be compared to an apothecary or a chemist, whose
materials indeed are furnished by nature; but, for the
purposes of his art, he mixes, compounds, dissolves,
evaporates, and sublimes them, till they put on a quite
different appearance; so that it is very difficult to know
what they were at first, and much more to bring them
back to their original and natural form. And this work
of the mind is not carried on by deliberate acts of mature
reason, which we might recollect, but by means of in-
stincts, habits, associations, and other principles, which
operate before we come to the use of reason; so that it is
extremely difficult for the mind to return upon its own
footsteps, and trace back those operations which have
employed it since it first began to think and to act.

Could we obtain a distinct and full history of all that
hath past in the mind of a child, from the beginning of
life and sensation, till it grows up to the use of reason —
how its infant faculties began to work, and how they
brought forth and ripened all the various notions,
opinions and sentiments which we find in ourselves
when we come to be capable of reflection — this would be
a treasure of natural history, which would probably give
more light into the human faculties, than all the systems
of philosophers about them since the beginning of the
world. But it is in vain to wish for what nature has not
put within the reach of our power. Reflection, the only
instrument by which we can discern the powers of the
mind, comes too late to observe the progress of nature,
in raising them from their infancy to perfection.

It must therefore require great caution, and great
application of mind, for a man that is grown up in all
the prejudices of education, fashion, and philosophy, to
unravel his notions and opinions, till he find out the
simple and original principles of his constitution, of
which no account can be given but the will of our
Maker. This may be truly called an analysis of the
human faculties; and, till this is performed, it is in vain

76 THE PHILOSOPHY OF REID. [CH. I.

we expect any just system of the mind — that is, an
enumeration of the original powers and laws of our con-
stitution, and an explication from them of the various
phaenomena of human nature.

Success in an inquiry of this kind, it is not in human
power to command ; but, perhaps, it is possible, by
caution and humility, to avoid error and delusion. The
labyrinth may be too intricate, and the thread too fine,
to be traced through all its windings; but, if we stop
where we can trace it no farther, and secure the ground
we have gained, there is no harm done; a quicker eye may
in time trace it farther.

It is genius, and not the want of it, that adulterates
philosophy, and fills it with error and false theory. A
creative imagination disdains the mean offices of dig-
ging for a foundation, of removing rubbish, and carry-
ing materials; leaving these servile employments to the
drudges in science, it plans a design, and raises a fabric.
Invention supplies materials where they are wanting, and
fancy adds colouring and every befitting ornament. The
work pleases the eye, and wants nothing but solidity and
a good foundation. It seems even to vie with the works
of nature, till some succeeding architect blows it into
rubbish, and builds as goodly a fabric of his own in its
place. Happily for the present age, the castle-builders
employ themselves more in romance than in philosophy.
That is undoubtedly their province, and in those regions
the offspring of fancy is legitimate, but in philosophy it
is all spurious.

Section III.

THE PRESENT STATE OF THIS PART OF PHILOSOPHY OF DBS

CARTES, MALEBRANCHE, AND LOCKE.

That our philosophy concerning the mind and its
faculties is but in a very low state, may be reasonably
conjectured even by those who never have narrowly ex-

SEC. III.] THE PHILOSOPHY OF REID. 77

amined it. Are there any principles, with regard to the
mind, settled with that perspicuity and evidence which
attends the principles of mechanics, astronomy and
optics ? These are really sciences built upon laws of
nature which universally obtain. What is discovered in
them is no longer matter of dispute: future ages may
add to it ; but, till the course of nature be changed,
what is already established can never be overturned. But
when we turn our attention inward, and consider the
phaenomena of human thoughts, opinions, and percep-
tions, and endeavour to trace them to the general laws
and the first principles of our constitution, we are im-
mediately involved in darkness and perplexity; and,
if common sense, or the principles of education, hap-
pen not to be stubborn, it is odds but we end in absolute
scepticism.

Des Cartes, finding nothing established in this part of
philosophy, in order to lay the foundation of it deep,
resolved not to believe his own existence till he should
be able to give a good reason for it. He was, perhaps,
the first that took up such a resolution; but, if he could
indeed have effected his purpose, and really become
diffident of his existence, his case would have been de-
plorable, and without any remedy from reason or philos-
ophy. A man that disbelieves his own existence, is
surely as unfit to be reasoned with as a man that believes
he is made of glass. There may be disorders in the
human frame that may produce such extravagancies, but
they will never be cured by reasoning. Des Cartes, in-
deed, would make us believe that he got out of this
delirium by this logical argument, Cogito, ergo sum; but
it is evident he was in his senses all the time, and never
seriously doubted of his existence; for he takes it for
granted in this argument, and proves nothing at all. I
am thinking, says he — therefore, I am. And is it not
as good reasoning to say, I am sleeping — therefore, I
am ? or, I am doing nothing — therefore, I am ? If a

78 THE PHILOSOPHY OF REID. [CH. I.

body moves, it must exist, no doubt; but, if it is at rest
it must exist likewise.*

Perhaps Des Cartes meant not to assume his own ex-
istence in this enthymeme, but the existence of thought;
and to infer from that the existence of a mind, or subject
of thought. But why did he not prove the existence of
his thought ? Consciousness, it may be said, vouches
that. But who is voucher for consciousness ? Can any
man prove that his consciousness may not deceive him ?
No man can; nor can we give a better reason for trusting
to it, than that every man, while his mind is sound, is
determined, by the constitution of his nature, to give
implicit belief to it, and to laugh at or pity the man who
doubts its testimony. And is not every man, in his wits,
as much determined to take his existence upon trust as
his consciousness?

The other proposition assumed in this argument,
That thought cannot be without a mind or subject, is
liable to the same objection: not that it wants evidence
but that its evidence is no clearer, nor more immediate,
than that of the proposition to be proved by it. And,
taking all these propositions together — I think; I am
conscious; Everything that thinks, exists; I exist — would
not every sober man form the same opinion of the man
who seriously doubted any one of them ? And if he was
his friend, would he not hope for his cure from physic
and good regimen, rather than from metaphysic and
logic ?

But supposing it proved, that my thought and my
consciousness must have a subject, and consequently that
I exist, how do I know that all that train and succession
of thoughts which I remember belong to one subject,
and that the I of this moment is the very individual I of
yesterday and of times past ?

* The nature ot the Cartesian Doubt and its solution is here mis-
apprehended.— H. See note, I. P., T'.ssay ii., ch. 8.

SEC. III.] THE PHILOSOPHY OF REID. 79

Des Cartes did not think proper to start this doubt ;
but Locke has done it ; and, in order to resolve it,
gravely determines that personal identity consists in
consciousness — that is, if you are conscious that you did
such a thing a twelvemonth ago, this consciousness makes
you to be the very person that did it. Now conscious-
ness of what is past can signify nothing else but the re-
membrance that I did it ; so that Locke's principle must
be, That identity consists in remembrance ; and, conse-
quently, a man must lose his personal identity with re-
gard to everything he forgets.

Nor are these the only instances whereby our philos-
ophy concerning the mind appears to be very fruitful in
creating doubts, but very unhappy in resolving them.

Des Cartes, Malebranche, and Locke, have all em-
ployed their genius and skill to prove the existence of
a material world : and with very bad success. Poor
untaught mortals believe undoubtedly that there is a
sun, moon, and stars ; an earth, which we inhabit ;
country, friends, and relations, which we enjoy ; land,
houses, and movables, which we possess. But philos-
ophers, pitying the credulity of the vulgar, resolve to
have no faith but what is founded upon reason.* They
apply to philosophy to furnish them with reasons for the
belief of those things which all mankind have believed,
without being able to give any reason for it. And surely
one would expect, that, in matters of such importance,
the proof would not be difficult : but it is the most dif-
ficult thing in the world. For these three great men,
with the best good will, have not been able, from all the
treasures of philosophy, to draw one argument that is fit
to convince a man that can reason, of the existence of
any one thing without him. Admired Philosophy !

* Reason is here employed, by Reid, not as a synonyme for Com-
mon Sense, (you?, locus principiorum) and as he himself more cor-
rectly employs it in his later works, but as equivalent to Reasoning,
(Sidvoia, discursus mentalis.) See Note A. — H.

8o THE PHILOSOPHY OF REID. [CH. I.

daughter of light ! parent of wisdom and knowledge !
if thou art she, surely thou hast not yet arisen upon the
human mind, nor blessed us with more of thy rays than
are sufficient to shed a darkness visible upon the human
faculties, and to disturb that repose and security which
happier mortals enjoy, who never approached thine
altar, nor felt thine influence ! But if, indeed, thou hast
not power to dispel those clouds and phantoms which
thou hast discovered or created, withdraw this penurious
and malignant ray; I despise Philosophy, and renounce
its guidance — let my soul dwell with Common Sense. *

Section IV.

APOLOGY FOR THOSE PHILOSOPHERS.

But, instead of despising the dawn of light, we ought
rather to hope for its increase : instead of blaming the
philosophers I have mentioned for the defects and blem-
ishes of their system we ought rather to honour their mem-
ories, as the first discoverers of a region in philosophy
formerly unknown ; and however lame and imperfect the
system may be, they have opened the way to future dis-
coveries, and are justly entitled to a great share in the
merit of them. They have removed an infinite deal of
dust and rubbish, collected in the ages of scholastic soph-
istry, which had obstructed the way. They have put
us in the right road — that of experience and accurate re-
flection. They have taught us to avoid the snares of am-
biguous and ill-defined words, and have spoken and
thought upon this subject with a distinctness and perspi-
cuity formerly unknown. They have made many open-
ings that may lead to the discovery of truths which they
did not reach, or to the detection of errors in which they
were involuntarily entangled.

* Mr. Stewart very justly censures the vagueness and ambiguity
of this passage. Elem. vol ii., ch. i., § 3, p. 92, 8vo editions. — H-

SEC. V.] THE PHILOSOPHY OF REID. 8l

It may be observed, that the defects and blemishes in
the received philosophy concerning the mind, which have
most exposed it to the contempt and ridicule of sensible
men, have chiefly been owing to this — that the votaries
of this Philosophy, from a natural prejudice in her fa-
vour, have endeavoured to extend her jurisdiction beyond
its just limits, and to call to her bar the dictates of Com-
mon Sense. But these decline this jurisdiction ; they dis-
dain the trial of reasoning, and disown its authority; they
neither claim its aid, nor dread its attacks.

In this unequal contest betwixt Common Sense and
Philosophy, the latter will always come off both with
dishonour and loss; nor can she ever thrive till this rival-
ship is dropt, these encroachments given up, and a
cordial friendship restored: for, in reality, Common
Sense holds nothing of Philosophy, nor needs her aid.
But, on the other hand, Philosophy (if I may be per-
mitted to change the metaphor) has no other root but
the principles of Common Sense ; it grows out of them,
and draws its nourishment from them. Severed from this
root, its honours wither, its sap is dried up, it dies and rots.

The philosophers of the last age, whom I have men-
tioned, did not attend to the preserving this union and
subordination so carefully as the honour and interest of
philosophy required: but those of the present have waged
open war with Common Sense, and hope to make a
complete conquest of it by the subtilties of Philosophy —
an attempt no less audacious and vain than that of the
giants to dethrone almighty Jove.

Section V.

OF BISHOP BERKELEY THE "TREATISE OF HUMAN NA-
TURE '' AND OF SCEPTICISM.

The present age, I apprehend, has not produced two
more acute or more practised in this part of philosophy,

82 THE PHILOSOPHY OF REID. [Cii. I.

than the Bishop of Cloyne, and the author of the
" Treatise of Human Nature." The first was no friend
to scepticism, but had that warm concern for religious
and moral principles which became his order : yet the
result of his inquiry was a serious conviction that there
is no such thing as a material world — nothing in nature
but spirits and ideas; and that the belief of material sub-
stances, and of abstract ideas, are the chief causes of all
our errors in philosophy, and of all infidelity and heresy
in religion. His arguments are founded upon the
principles which were formerly laid down by Des Cartes,
Malebranche, and Locke, and Which have been very
generally received.

And the opinion of the ablest judges seems to be, that
they neither have been, nor can be confuted; and that he
hath proved by unanswerable arguments what no man
in his senses can believe.

The second proceeds upon the same principles, but
carries them to their full length; and, as the Bishop un-
did the whole material world, this author, upon the same
grounds, undoes the world of spirits, and leaves nothing
in nature but ideas and impressions, without any sub-
ject on which they may be impressed.

It seems to be a peculiar strain of humour in this
author, to set out in his introduction by promising, with
a grave face, no less than a complete system of the
sciences, upon a foundation entirely new — to wit, that
of human nature — when the intention of the whole work
is to shew, that there is neither human nature nor science
in the world. It may perhaps be unreasonable to com-
plain of this conduct in an author who neither believes his
own existence nor that of his reader; and therefore could
not mean to disappoint him, or to laugh at his credulity.
Vet I cannot imagine that the author of the "Treatise
of Human Nature" is so sceptical as to plead this
apology. He believed, against his principles, that he
should be read, and that he should retain his personal

SEC. V.] THE PHILOSOPHY OF REID. 83

identity, till he reaped the honour and reputation justly
due to his metaphysical acumen. Indeed, he ingeniously
acknowledges, that it was only in solitude and retirement
that he could yield any assent to his own philosophy;
society, like daylight, dispelled the darkness and fogs
of scepticism, and made him yield to the dominion of
common sense. Nor did I ever hear him charged with
doing anything, even in solitude, that argued such a de-
gree of scepticism as his principles maintain. Surely if
his friends apprehended this, they would have the charity
never to leave him alone.

Pyrrho the Elean, the father of this philosophy,
seems to have carried it to greater perfection than any of
his successors : for, if we may believe Antigonus the
Carystian, quoted by Diogenes Laertius, his life cor-
responded to his doctrine. And, therefore, if a cart run
against him, or a dog attacked him, or if he came upon
a precipice, he would not stir a foot to avoid the danger,
giving no credit to his senses. But his attendants, who,
happily for him, were not so great sceptics, took care
to keep him out of harm's way; so that he lived till he
was ninety years of age. Nor is it to be doubted but
this author's friends would have been equally careful to
keep him from harm, if ever his principles had taken too
strong a hold of him.

It is probable the "Treatise of Human Nature" was
not written in company; yet it contains manifest indica-
tions that the author every now and then relapsed into
the faith of the vulgar, and could hardly, for half a dozen
pages, keep up the sceptical character.

In like manner, the great Pyrrho himself forgot his
principles on some occasions; and is said once to have
been in such a passion with his cook, who probably had
not roasted his dinner to his mind, that with the spit in
his hand, and the meat upon it, he pursued him even
into the market-place.

It is a bold philosophy that rejects, without ceremony,

84 THE PHILOSOPHY OF REID. [Cn. I.

principles which irresistibly govern the belief and the
conduct of all mankind in the common concerns of life;
and to which the philosopher himself must yield, after
he imagines he hath confuted them. Such principles are
older, and of more authority, than Philosophy: she rests
upon them as her basis, not they upon her. If she could
overturn them, she must be buried in their ruins; but all
the engines of philosophical subtil ty are too weak for
this purpose; and the attempt is no less ridiculous than
if a mechanic should contrive an axis in peritrochio to
remove the earth out of its place; or if a mathematician
should pretend to demonstrate that things equal to the
same thing are not equal to one another.

Zeno endeavoured to demonstrate the impossibility of
motion; Hobbes, that there was no difference between
right and wrong; and this author, that no credit is to be
given to our senses, to our memory, or even to demon-
stration. Such philosophy is justly ridiculous, even to
those' who cannot detect the fallacy of it. It can have
no other tendency, than to shew the acuteness of the so-
phist, at the expense of disgracing reason and human
nature, and making mankind Yahoos.

Section VI.
OF THE "TREATISE OF HUMAN NATURE."

There are other prejudices against this system of hu-
man nature, which, even upon a general view, may
make one diffident of it.

Des Cartes, Hobbes, and this author, have each of
them given us a system of human nature; an undertak-
ing too vast for any one man, how great soever his ge-
nius and abilities may be. There must surely be reason
to apprehend, that many parts of human nature never
came under their observation; and that others have been
stretched and distorted, to fill up blanks, and complete

SEC. VI.] THE PHILOSOPHY OF REID. 85

the system. Christopher Columbus, or Sebastian Cabot,
might almost as reasonably have undertaken to give us a
complete map of America.

There is a certain character and style in Nature's
works, which is never attained in the most perfect imi-
tation of them. This seems to be wanting in the systems
of human nature I have mentioned, and particularly in
the last. One may see a puppet make variety of motions
and gesticulations, which strike much at first view ; but
when it is accurately observed, and taken to pieces, our
admiration ceases: we comprehend the whole art of the
maker. How unlike i-s it to that which it represents !
What a poor piece of work compared with the body of a
man, whose structure the more we know, the more won-
ders we discover in it, and the more sensible we are of
our ignorance ! Is the mechanism of the mind so easily
comprehended, when that of the body is so difficult ?
Yet, by this system, three laws of association, joined to
a few original feelings, explain the whole mechanism of
sense, imagination, memory, belief, and of all the actions,
and passions of the mind. Is this the man that Na-
ture made ? I suspect it is not so easy to look behind
the scenes in Nature's work. This is a puppet, surely,
contrived by too bold an apprentice of Nature, to mimic
her work. It shews tolerably by candle-light ; but,
brought into clear day, and taken to pieces, it will ap-
pear to be a man made with mortar and a trowel. The
more we know of other parts of nature, the more we
like and approve them. The little I know of the planet-
ary system, of the earth, which we inhabit ; of minerals,
vegetables, and animals ; of my. own body ; and of the
laws which obtain in these parts of nature — opens to my
mind grand and beautiful scenes, and contributes equally
to my happiness and power. But, when I look within,
and consider the mind itself, which makes me capable
of all these prospects and enjoyments — if it is, indeed,
what the "Treatise of Human Nature" makes it — I find

86 THE PHILOSOPHY OF REID. [CH. I.

I have been only in an enchanted castle, imposed upon
by spectres and apparitions. I blush inwardly to think
how I have been deluded ; I am ashamed of my frame,
and can hardly forbear expostulating with my destiny.
Is this thy pastime, O Nature, to put such tricks upon a
silly creature, and then to take off the mask, and shew
him how he hath been befooled ? If this is the philo-
sophy of human nature, my soul, enter thou not int'o her
secrets ! It is surely the forbidden tree of knowledge ;
I no sooner taste of it, than I perceive myself naked,
and stript of all things — yea, even of my very self. I see
myself, and the whole frame of nature, shrink into fleet-
ing ideas, which, like Epicurus's atoms, dance about in
emptiness.

Section VII.

THE SYSTEM OF ALL THESE AUTHORS IS THE SAME, AND
LEADS TO SCEPTICISM.

But what if these profound disquisitions into the first
principles of human nature, do naturally and necessarily
plunge a man into this abyss of scepticism ? May we not
reasonably judge so from what hath happened ? Des
Cartes no sooner began to dig in this mine, than scepti-
cism was ready to break in upon him. He did what he
could to shut it out. Malebranche and Locke, who dug
deeper, found the difficulty of keeping out this enemy
still to increase; but they laboured honestly in the design.
Then Berkeley, who carried on the work, despairing of
securing all, bethought himself of an expedient: — By
giving up the material world, which he thought might
be spared without loss, and even with advantage, he
hoped, by an impregnable partition, to secure the world
of spirits. But alas ! the "Treatise of Human Nature"
wantonly sapped the foundation of this partition, and
drowned all in one universal deluge.

These facts, which are undeniable, do, indeed, give

SEC. VIII.] THE PHILOSOPHY OF REID. 87

reason to apprehend that Des Cartes' system of the hu-
man understanding, which I shall beg leave to call the ideal
system, and which, with some improvements made by la-
ter writers, is now generally received, hath some original
defect; that this scepticism is inlaid in it, and reared
along with it : and, therefore, that we must lay it open
to the foundation, and examine the materials, before we
can expect to raise any solid and useful fabric of know-
ledge on this subject.

Section VIII.

WE OUGHT NOT TO DESPAIR OF A BETTER.

But is this to be despaired of, because Des Cartes and
his followers have failed ? By no means. This pusilla-
nimity would be injurious to ourselves and injurious to
truth. Useful discoveries are sometimes indeed the effect
of superior genius, but more frequently they are the birth of
time and of accidents. A traveller of good judgment
may mistake his way, and be unawares led into a wrong
track; and while the road is fair before him, he may go
on without suspicion and be followed by others; but,
when it ends in a coal-pit, it requires no great judgment
to know that he hath gone wrong, nor perhaps to find
out what misled him.

In the meantime, the unprosperous state of this part
of philosophy hath produced an effect, somewhat dis-
couraging indeed to any attempt of this nature, but an
effect which might be expected, and which time only
and better success can remedy. Sensible men, who
never will be sceptics in matters of common life, are apt
to treat with sovereign contempt everything that hath
been said, or is to be said, upon this subject. It is meta-
physic, say they : who minds it ? Let scholastic sophis-
ters entangle themselves in their own cobwebs ; I am re-

88 THE PHILOSOPHY OF KEID. [CH. I., SEC. VIII.

solved to take my own existence, and the existence of
other things, upon trust ; and to believe that snow is cold,
and honey sweet, whatever they may say to the contrary.
He must either be a fool, or want to make a fool of me,
that would reason me out of my reason and senses.

I confess I know not what a sceptic can answer to this,
nor by what good argument he can plead even for a hear-
ing ; for either his reasoning is sophistry, and so deserves
contempt ; or there is no truth in human faculties — and
then why should we reason ?

If, therefore, a man find himself intangled in these meta-
physical toils, and can find no other way to escape, let
him bravely cut the knot which he cannot loose, curse
metaphysic, and dissuade every man from meddling with
it ; for, if I have been led into bogs and quagmires by
following an ignis fatuus, what can I do better than to
warn others to beware of it? If philosophy contradicts
herself, befools her votaries, and deprives them of every
object worthy to be pursued or enjoyed, let her be sent
back to the infernal regions from which she must have
had her original.

But is it absolutely certain that this fair lady is of the
party ? Is it not possible she may have been misrepre-
sented? Have not men of genius in former ages often
made their own dreams to pass for her oracles? Ought
she then to be condemned without any further hearing ?
This would be unreasonable. I have found her in all
other matters an agreeable companion, a faithful coun-
sellor, a friend to common sense, and to the happiness
of mankind. This justly entitles her to my correspond-
ence and confidence, till I find infallible proofs of her
infidelity.

CH. II., SEC. I. THE PHILOSOPHY OF REID. 89

CHAPTER II.

OF SMELLING.

Section I.

THE ORDER OF PROCEEDING OF THE MEDIUM AND ORGAN

OF SMELL.

IT is so difficult to unravel the operations of the hu-
man understanding, and to reduce them to their first
principles, that we cannot expect to succeed in the at-
tempt, but by beginning with the simplest, and proceed-
ing by very cautious steps to the more complex. The
five external senses may, for this reason, claim to be first
considered in an analysis of the human faculties. And
the same reason ought to determine us to make a choice
even among the senses, and to give the precedence,
not to the noblest or most useful, but to the simplest,
and that whose objects are least in danger of being mis-
taken for other things.

In this view, an analysis of our sensations may be
carried on, perhaps with most ease and distinctness, by
taking them in this order: Smelling, Tasting, Hearing,
Touch, and, last of all, Seeing.

Natural philosophy informs us, that all animal and
vegetable bodies, and probably all or most other bodies,
while exposed to the air, are continually sending forth
effluvia of vast subtilty, not only in their state of life
and growth, but in the states of fermentation and putre-
faction. These volatile particles do probably repel each
other, and so scatter themselves in the air, until they
meet with other bodies to which they have some chemi-
cal affinity, and with which they unite, and form new
concretes. All the smell of plants, and of other bodies,

90 THE PHILOSOPHY OF REID. |CH. 11.

is caused by these volatile parts, and is smelled wherever
they are scattered in the air : and the acuteness of smell
in some animals, shews us, that these effluvia spread far,
and must be inconceivably subtile.

Whether, as some chemists conceive, every species of
bodies hath a spiritus rector, a kind of soul, which causes
the smell and all the specific virtues of that body, and
which, being extremely volatile, flies about in the air
in quest of a proper receptacle, I do not inquire. This,
like most other theories, is perhaps rather the product
of imagination than of just induction. But that all
bodies are smelled by means of effluvia which they emit,
and which are drawn into the nostrils along with the
air, there is no reason to doubt. So that there is mani-
fest appearance of design in placing the organ of smell
in the inside of that canal, through which the air is con-
tinually passing in inspiration and expiration.

Anatomy informs us, that the membrana pituitaria, and
the olfactory nerves, which are distributed to the villous
parts of this membrane, are the organs destined by the
wisdom of nature to this sense; so that when a body emits
no effluvia, or when they do not enter into the nose, or
when the pituitary membrane or olfactory nerves are
rendered unfit to perform their office, it cannot be smelled.

Yet, notwithstanding this, it is evident that neither the
organ of smell, nor the medium, nor any motions we
can conceive excited in the membrane above mentioned,
or in the nerve or animal spirits, do in the least resem-
ble the sensation of smelling; nor could that sensation of
itself ever have led us to think of nerves, animal spirits,
or effluvia.

Section II.

THE SENSATION CONSIDERED ABSTRACTLY.

Having premised these things with regard to the me-
dium and organ of this sense, let us now attend careful-

SEC. II.] THE PHILOSOPHY OF REID. 91

ly to what the mind is conscious of when we smell a rose
or a lily; and, since our language affords no other name
for this sensation, we shall call it a smell or odour, care-
fully excluding from the meaning of those names every-
thing but the sensation itself, at least till we have ex-
amined it.

Suppose a person who never had this sense before, to
receive it all at once, and to smell a rose — can he per-
ceive any similitude or agreement between the smell and
the rose? or indeed between it and any other object what-
soever? Certainly he cannot. He finds himself affected
in a new way, he knows not why or from what cause.
Like a man that feels some pain or pleasure, formerly un-
known to him, he is conscious that he is not the cause
of it himself; but cannot, from the nature of the thing,
determine whether it is caused by body or spirit, by
something near, or by something at a distance. It has
no similitude to anything else, so as to admit of a com-
parison; and, therefore, he can conclude nothing from it,
unless, perhaps, that there must be some unknown
cause of it.

It is evidently ridiculous to ascribe to it figure, colour,
extension, or any other quality of bodies. He cannot
give it a place, any more than he can give a place to
melancholy or joy; nor can he conceive it to have any
existence, but when it is smelled. So that it appears to
be a simple and original affection or feeling of the mind,
altogether inexplicable and unaccountable. It is, in-
deed, impossible that it can be in any body: it is a sen-
sation, and a sensation can only be in a sentient thing.

The various odours have each their different degrees of
strength or weakness. Most of them are agreeable or
disagreeable; and frequently those that are agreeable
when weak, are disagreeable when stronger. When we
compare different smells together, we can perceive very
few resemblances or contrarieties, or, indeed, relations
of any kind between them. They are all so simple in

92 THE PHILOSOPHY OF REID. |CH. II.

themselves, and so different from each other, that it is
hardly possible to divide them into genera and species.
Most of the names we give them are particular; as the
smell of a rose, of a jessamine, and the like. Yet there
are some general names — as sweet, stinking, musty, putrid,
cadaverous, aromatic. Some of them seem to refresh and
animate the mind, others to deaden and depress it.

Section III.

SENSATION AND REMEMBRANCE, NATURAL PRINCIPLES OF
BELIEF.

So far we have considered this sensation abstractly.
Let us next compare it with other things to which it
bears some relation. And first I shall compare this sen-
sation with the remembrance, and the imagination of it.

I can think of the smell of a rose when I do not smell it;
and it is possible that when I think of it, there is neither
rose nor smell anywhere existing. But when I smell
it, I am necessarily determined to believe that the sen-
sation really exists. This is common to all sensations,
that, as they cannot exist but in being perceived, so they
cannot be perceived but they must exist. I could as
easily doubt of my own existence, as of the existence of
my sensations. Even those profound philosophers who
have endeavoured to disprove their own existence, have
yet left their sensations to stand upon their own bottom,
stript of a subject, rather than call in question the reali-
ty of their existence.

Here, then, a sensation, a smell, for instance, may be
presented to the mind three different ways: it may be
smelled, it may be remembered, it may be imagined or
thought of. In the first case, it is necessarily accom-
panied with a belief of its present existence; in the sec-
ond, it is necessarily accompanied with a belief of its past
existence; and in the last, it is not accompanied with be-

SEC. HI.] THE PHILOSOPHY OF REID. 93

lief at all,* but is what the logicians call a simple appre-
hension.

Why sensation should compel our belief of the pres-
ent existence of the thing, memory a belief of its past ex-
istence, and imagination no belief at all, I believe no
philosopher can give a shadow of reason, but that such
is the nature of these operations: they are all simple and
original, and therefore inexplicable acts of the mind.

Suppose that once, and only once, I smelled a tube-
rose in a certain room, where it grew in a pot, and gave
a very grateful perfume. Next day I relate what I saw
and smelled. When I attend as carefully as I can to
what passes in my mind in this case, it appears evident
that the very thing I saw yesterday, and the fragrance I
smelled, are now the immediate objects of my mind,
when I remember it. Further, I can imagine this pot
and flower transported to the room where I now sit, and
yielding the same perfume. Here likewise it appears,
that the individual thing which I saw and smelled, is
the object of my imagination.

Philosophers indeed tell me, that the immediate ob-
ject of my memory and imagination in this case, is not
the past sensation, but an idea of it, an image, phan-
tasm, or species, f of the odour I smelled: that this idea
now exists in my mind, or in my sensorium; and the
mind, contemplating this present idea, finds it a repre-
sentation of what is past, or of what may exist; and ac-
cordingly calls it memory, or imagination. This is the
doctrine of the ideal philosophy; which we shall not

* This is not strictly correct. The imagination of an object is
necessarily accompanied with a belief of the existence of the mental
representation. Reid uses the term existence for objective existence
only, and takes no account of the possibility of a subjective exist-
ence.— H .

f It will be observed, that Reid understands by Idea, Image,
Phantasm, Species, &C., always a tertinm ^«/</ numerically different
both from the Object existing and from the Subject knowing. He
had formed no conception of a doctrine in which a representative ob-

94 THE PHILOSOPHY OF REID. [CH. n.

now examine, that we may not interrupt the thread of
the present investigation. Upon the strictest attention,
memory appears to me to have things that are past, and
not present ideas, for its object. We shall afterwards
examine this system of ideas, and endeavour to make it
appear, that no solid proof has ever been advanced of
the existence of ideas; that they are a mere fiction and
hypothesis, contrived to solve the phenomena of the
human understanding; that they do not at all answer
this end; and that this hypothesis of ideas or images of
things in the mind, or in the sensorium, is the parent of
those many paradoxes so shocking to common sense,
and of that scepticism which disgrace our philosophy of
the mind, and have brought upon it the ridicule and
contempt of sensible men.

In the meantime, I beg leave to think, with the vul-
gar, that, when I remember the smell of the tuberose,
that very sensation which I had yesterday, and which
has now no more any existence, is the immediate object
of my memory; and when I imagine it present, the sen-
sation itself, and not any idea of it, is the object of my
imagination. But, though the object of my sensation,
memory, and imagination, be in this case the same, yet
these acts or operations of the mind are as different, and
as easily distinguishable, as smell, taste, and sound. I
am conscious of a difference in kind between sensation
and memory, and between both and imagination. I
find this also, that the sensation compels my belief of the
present existence of the smell, and memory my belief of
its past existence. There is a smell, is the immediate
testimony of sense; there was a smell, is the immediate
testimony of memory. If you ask me, why I believe
that the smell exists, I can give no other reason, nor

ject is allowed, but only as a modification of the mind itself. On
the evil consequences of this error, both on his own philosophy and
on his criticism of other opinions, — [I.

SEC. IV.] THE PHILOSOPHY OF REID. 95

shall ever be able to give any other, than that I smell it.
If you ask, why I believe that it existed yesterday, I can
give no other reason but that I remember it.

Sensation and memory, therefore, are simple, original,
and perfectly distinct operations of the mind, and both
of them are original principles of belief. Imagination is
distinct from both, but is no principle of belief. Sen-
sation implies the present existence of its object, mem-
ory its past existence, but imagination views its object
naked, and without any belief of its existence or non-
existence, and is therefore what the schools call Simple
Apprehension. *

Section IV.

JUDGMENT AND BELIEF IN SOME CASES PRECEDE SIMPLE AP-
PREHENSION.

But here, again, the ideal system comes in our way: it
teaches us that the first operation of the mind about its
ideas, is simple apprehension — that is, the bare concep-
tion of a thing without any belief about it: and that,
after we have got simple apprehensions, by comparing
them together, we perceive agreements or disagreements
between them; and that this perception of the agreement
or disagreement of ideas, is all that we call belief, judg-
ment, or knowledge. Now, this appears to me to be
all fiction, without any foundation in nature; for it is
acknowledged by all, that sensation must go before
memory and imagination; and hence it necessarily fol-
lows, that apprehension, accompanied with belief and
knowledge, must go before simple apprehension, at least
in the matters we are now speaking of. So that here, in-

* Simple Apprehension, in the language of the Schools, has no
reference to any exclusion of belief. It was merely given to the con-
ception of simple, in contrast to the cognition of complex, terms.
— H.

96 THE PHILOSOPHY OF 'REID. [CH. II.

stead of saying that the belief or knowledge is got by put-
ting together and comparing the simple apprehensions,
we ought rather to say that the simple apprehension is per-
formed by resolving and analysing a natural and origi-
nal judgment. And it is with the operations of the
mind, in this case, as with natural bodies, which are,
indeed, compounded of simple principles or elements.
Nature does not exhibit these elements separate, to
be compounded by us; she exhibits them mixed and
compounded in concrete bodies, and it is only by art
and chemical analysis that they can be separated.

Sec/ion V.

TWO THEORIES OF THE NATURE OF BELIEF REFUTED — CON-
CLUSIONS FROM WHAT HATH BEEN SAID.

But what is this belief or knowledge which accompa-
nies sensation and memory ? Every man knows what it
is, but no man can define it. Does any man pretend to
define sensation, or to define consciousness ? It is hap-
py, indeed, that no man does. And if no philosopher
had endeavoured to define and explain belief, some par-
adoxes in philosophy, more incredible than ever were
brought forth by the most abject superstition or the most
frantic enthusiasm, had never seen the light. Of this
kind surely is that modern discovery of the ideal philos-
ophy, that sensation, memory, belief, and imagination,
when they have the same object, are only different de-
grees of strength and vivacity in the idea. * Suppose the
idea to be that of a future state after death: one man be-
lieves it firmly — this means no more than that he hath a
strong and lively idea of it; another neither believes nor
disbelieves — that is, he has a weak and faint idea. Sup-
pose, now, a third person believes firmly that there is no

* He refers to Hume. — H.

SEC. V.] THE PHILOSOPHY OF REID. 97

such thing, I am at a loss to know whether his idea be
faint or lively: if it is faint, then there may be a firm belief
where the idea is faint; if the idea is lively, then the be-
lief of a future state and the belief of no future state
must be one and the same. The same arguments that
are used to prove that belief implies only a stronger
idea of the object than simple apprehension, might as
well be used to prove that love implies only a stronger
idea of the object than indifference. And then what
shall we say of hatred, which must upon this hypothe-
sis be a degree of love, or a degree of indifference ? If
it should be said, that in love there is something more
than an idea — to wit, an affection of the mind — may it
not be said with equal reason, that in belief there is
something more than an idea — to wit, an assent or per-
suasion of the mind ?

But perhaps it may be thought as ridiculous to argue
against this strange opinion, as to maintain it. Indeed,
if a man should maintain that a circle, a square, and a
triangle differ only in magnitude, and not in figure, I
believe he would find nobody disposed either to believe
him or to argue against him; and yet I do not think it
less shocking to common sense, to maintain that sensa-
tion, memory, and imagination differ only in degree,
and not in kind. I know it is said, that, in a delirium,
or in dreaming, men are apt to mistake one for the
other. But does it follow from this, that men who are
neither dreaming nor in a delirium cannot distinguish
them ? But how does a man know that he is not in a
delirium ? I cannot tell: neither can I tell how a man
knows that he exists. But, if any man seriously doubts
whether he is in a delirium, I think it highly probable
that he is, and that it is time to seek for a cure, which I
am persuaded he will not find in the whole system of
logic.

I mentioned before Locke's notion of belief or know-
ledge ; he holds that it consists in a perception of the

98 THE PHILOSOPHY OF REID. [CH. II.

agreement or disagreement of ideas ; and this he values
himself upon as a very important discovery.

We shall have occasion afterwards to examine more
particularly this grand principle of Locke's philosophy,
and to shew that it is one of the main pillars of modern
scepticism, although he had no intention to make that
use of it. At present let us only consider how it agrees
with the instances of belief now under consideration ;
and whether it gives any light to them. I believe that
the sensation I have exists ; and that the sensation I
remember does not now exist, but did exist yesterday.
Here, according to Locke's system, I compare the idea
of a sensation with the ideas of past and present exist-
ence : at one time I perceive that this idea agrees with
that of present existence, but disagrees with that of past
existence ; but, at another time, it agrees with the idea
of past existence, and disagrees with that of present ex-
istence. Truly these ideas seem to be very capricious
in their agreements and disagreements. Besides, I can-
not, for my heart, conceive what is meant by either. I
say a sensation exists, and I think I understand clearly
what I mean. But you want to make the thing clearer,
and for that end tell me, that there is an agreement be-
tween the idea of that sensation and the idea of existence.
To speak freely, this conveys to me no light, but
darkness ; I can conceive no otherwise of it, than as an
odd and obscure circumlocution. I conclude, then,
that the belief which accompanies sensation and mem-
ory, is a simple act of the mind, which cannot be de-
fined. It is, in this respect, like seeing and hearing,
which can never be so defined as to be understood by
those who have not these faculties ; and to such as
have them, no definition can make these operations
more clear than they are already. In like manner,
every man that has any belief — and he must be a curi-
osity that has none — knows perfectly what belief is, but
can never define or explain it. I conclude, also, that

SEC. VI.] THE PHILOSOPHY OF REID. 99

sensation, memory, and imagination, even where they
have the same object, are operations of a quite differ-
ent nature, and perfectly distinguishable by those who
are sound and sober. A man that is in danger of con-
founding them, is indeed to be pitied ; but whatever
relief he may find from another art, he can find none
from logic or metaphysic. I conclude further, that it is
no less a part of the human constitution, to believe the
present existence of our sensations, and to believe the
past existence of what we remember, than it is to believe
that twice two make four. The evidence of sense, the
evidence of memory, and the evidence of the necessary
relations of things, are all distinct and original kinds of
evidence, equally grounded on our constitution : none
of them depends upon, or can be resolved into another.
To reason against any of these kinds of evidence, is
absurd; nay, to reason for them is absurd. They are
first principles ; and such fall not within the province
of reason,* but of common sense.

Section VI.

APOLOGY FOR METAPHYSICAL ABSURDITIES SENSATION WITH-
OUT A SENTIENT, A CONSEQUENCE OF THE THEORY OF
IDEAS CONSEQUENCES OF THIS STRANGE OPINION.

Having considered the relation which the sensation of
smelling bears to the remembrance and imagination of
it, I proceed to consider what relation it bears to a
mind or sentient principle. It is certain, no man can
conceive or believe smelling to exist of itself, without a
mind, or something that has the power of smelling, of
which it is called a sensation, an operation, or feeling.
Yet, if any man should demand a proof, that sensation
cannot be without a mind or sentient being, I confess

* See note, p. 79- — H.

100 THE PHILOSOPHY OF REID. [Cn. II.

that I can give none ; and that to pretend to prove it,
seems to me almost as absurd as to deny it.

This might have been said without any apology before
the "Treatise of Human Nature" appeared in the
world. For till that time, no man, as far as I know,
ever thought either of calling in question that principle,
or of giving a reason for his belief of it. Whether
thinking beings were of an ethereal or igneous nature,
whether material or immaterial, was variously disputed;
but that thinking is an operation of some kind of being
or other, was always taken for granted, as a principle
that could not possibly admit of doubt.

However, since the author above mentioned, who is
undoubtedly one of the most acute metaphysicians that
this or any age hath produced, hath treated it as a vulgar
prejudice, and maintained that the mind is only a suc-
cession of ideas and impressions without any subject;
his opinion, however contrary to the common appre-
hensions of mankind, deserves respect. I beg there-
fore, once for all, that no offence may be taken at charg-
ing this or other metaphysical notions with absurdity,
or with being contrary to the common sense of mankind.
No disparagement is meant to the understandings of the
authors or maintainers of such opinions. Indeed, they
commonly proceed, not from defect of understanding,
but from an excess of refinement the reasoning that
leads to them often gives new light to the subject, and
shews real genius and deep penetration in the author ;
and the premises do more than atone for the conclu-
sion.

If there are certain principles, as I think there are,
which the constitution of our nature leads us to believe,
and which we are under a necessity to take for granted
in the common concerns of life, without being able to
give a reason for them — these are what we call the prin-
ciples of common sense ; and what is manifestly con-
trary to them, is what we call absurd.

SEC. VI.] THE PHILOSOPHY OF REID. IOI

Indeed, if it is true, and to be received as a principle
of philosophy, that sensation and thought may be with-
out a thinking being, it must be acknowledged to be the
most wonderful discovery that this or any other age hath
produced. The received doctrine of ideas is the princi-
ple from which it is deduced, and of which indeed it
seems to be a just and natural consequence. And it is
probable, that it would not have been so late a discov-
ery, but that it is so shocking and repugnant to the com-
mon apprehensions of mankind, that it required an un-
common degree of philosophical intrepidity to usher it
into the world. It is a fundamental principle of the ideal
system, that every object of thought must be an impres-
sion or an idea — that is, a faint copy of some preceding
impression. This is a principle so commonly received,
that the author above mentioned, although his whole sys-
tem is built upon it, never offers the least proof of it. It
is upon this principle, as a fixed point, that he erects his
metaphysical engines, to overturn heaven and earth, body
and spirit. And, indeed, in my apprehension, it is alto-
gether sufficient for the purpose. For, if impressions
and ideas are the only objects of thought, then heaven
and earth, and body and spirit, and everything you
please, must signify only impressions and ideas, or they
must be words without any meaning. It seems, there-
fore, that this notion, however strange, is closely con-
nected with the received doctrine of ideas, and we must
either admit the conclusion, or call in question the
premises.

Ideas seem to have something in their nature un-
friendly to other existences. They were first introduced
into philosophy, in the humble character of images or
representatives of things : and in this character they
seemed not only to be inoffensive, but to serve admir-
ably well for explaining the operations of the human un-
derstanding. But, since men began to reason clearly
and distinctly about them, they have by degrees sup-

IO2 THE PHILOSOPHY OF REID. [CH. II.

planted their constituents, and undermined the existence of
everything but themselves. First, they discarded all sec-
ondary qualities of bodies ; and it was found out by
their means, that fire is not hot, nor snow cold, nor
honey sweet ; and, in a word, that heat and cold, sound,
colour, taste, and smell, are nothing but ideas or impres-
sions. Bishop Berkeley advanced them a step higher,
and found out, by just reasoning from the same princi-
ples, that extension, solidity, space, figure, and body,
are ideas, and that there is nothing in nature but ideas
and spirits. But the triumph of ideas was completed by
the "Treatise of Human Nature," which discards spirits
also, and leaves ideas and impressions as the sole exist-
ences in the universe. What if, at last, having nothing
else to contend with, they should fall foul of one another,
and leave no existence in nature at all ? This would
surely bring philosophy into danger ; for what should
we have left to talk or to dispute about ?

However, hitherto these philosophers acknowledge
the existence of impressions and ideas ; they acknow-
ledge certain laws of attraction, or rules of precedence,
according to which, ideas and impressions range them-
selves in various forms, and succeed one another : but
that they should belong to a mind, as its proper goods
and chattels, this they have found to be a vulgar error.
These ideas are as free and independent as the birds of
the air, or as Epicurus's atoms when they pursued their
journey in the vast inane. Shall we conceive them like
the films of things in the Epicurean system ?

Principio hoc dice, rerum simulacra vagari,
Multa modis multis, in cunctas undique parteis
Tenuia, quoe facile inter se junguntur in auris,
Obvia cum veniunt.— LUCR.

Or do they rather resemble Aristotle's intelligible species,
after they are shot forth from the object, and before they
have yet struck upon the passive intellect ? But why

SEC. VI.] THE PHILOSOPHY OF REID. 103

should we seek to compare them with anything, since
there is nothing in nature but themselves ? They make
the whole furniture of the universe ; starting into exist-
ence, or out of it, without any cause ; combining into
parcels, which the vulgar call minds ; and succeeding
one another by fixed laws, without time, place, or author
of those laws.

Yet, after all, these self-existent and independent ideas
look pitifully naked and destitute, when left thus alone
in the universe, and seem, upon the whole, to be in a
worse condition than they were before. Des Cartes,
Malebranche, and Locke, as they made much use of
ideas, treated them handsomely, and provided them in
decent accommodation ; lodging them either in the pineal
gland, or in the pure intellect, or even in the divine
mind. They moreover clothed them with a commission,
and made them representatives of things, which gave them
some dignity and character. But the " Treatise of Hu-
man Nature, " though no less indebted to them, seems
to have made but a bad return, by bestowing upon them
this independent existence : since thereby they are
turned out of house and home, and set adrift in the
world, without friend or connection, without a rag to
cover their nakedness ; and who knows but the whole
system of ideas may perish by the indiscreet zeal of their
friends to exalt them ?

However this may be, it is certainly a most amazing
discovery that thought and ideas may be without any
thinking being — a discovery big with consequences
which cannot easily be traced by those deluded mortals
who think and reason in the common track. We were
always apt to imagine, that thought supposed a thinker,
and love a lover, and treason a traitor : but this, it seems,
was all a mistake ; and it is found out, that there may
be treason without a traitor, and love without a lover,
laws without a legislator, and punishment without a suf-
ferer, succession without time, and motion without any-

104 THE PHILOSOPHY OF REID, [CH. II.

thing moved, or space in which it may move : or if, in
these cases, ideas are the lover, the sufferer, the traitor,
it were to be wished that the author of this discovery
had farther condescended to acquaint us whether ideas
can converse together, and be under obligations of duty
or gratitude to each other ; whether they can make
promises and enter into leagues and covenants, and ful-
fil or break them, and be punished for the breach. If
one set of ideas makes a covenant, another breaks it,
and a third is punished for it, there is reason to think
that justice is no natural virtue in this system.

It seemed very natural to think, that the ' ' Treatise of
Human Nature" required an au.thor, and a very
ingenious one too; but now we learn that it is only a
set of ideas which came together and arranged them-
selves by certain associations and attractions.

After all, this curious system appears not to be fitted
to the present state of human nature. How far it may
suit some choice spirits, who are refined from the dregs
of common sense, I cannot say. It is acknowledged, I
think, that even these can enter into this system only in
their most speculative hours, when they soar so high in
pursuit of those self-existent ideas as to lose sight of all
other things. But when they condescend to mingle
again with the human race, and to converse with a
friend, a companion, or a fellow-citizen, the ideal sys-
tem vanishes; common sense, like an irresistible torrent,
carries them along; and, in spite of all their reasoning
and philosophy, they believe their own existence, and
the existence of other things.

Indeed, it is happy they do so; for, if they should
carry their closet belief into the world, the rest of man-
kind would consider them as diseased, and send them to
an infirmary. Therefore, as Plato required certain pre-
vious qualifications of those who entered his school, I
think it would be prudent for the doctors of this ideal
philosophy to do the same, and to refuse admittance to

SEC. VIIJ THE PHILOSOPHY OF REID. 105

every man who is so weak as to imagine that he ought
to have the same belief in solitude and in company,
or that his principles ought to have any influence upon
his practice ; for this philosophy is like a hobby-horse,
which a man in bad health may ride in his closet, with-
out hurting his reputation; but, if he should take him
abroad with him to church, or to the exchange, or to the
play-house, his heir would immediately call a jury, and
seize his estate.

Section VII.

THE CONCEPTION AND BELIEF OF A SENTIENT BEING OR MIND
IS SUGGESTED BY OUR CONSTITUTION THE NOTION OF RE-
LATIONS NOT ALWAYS GOT BY COMPARING THE RELATED
IDEAS.

Leaving this philosophy, therefore, to those who have
occasion for it, and can use it discreetly as a chamber
exercise, we may still inquire how the rest of mankind,
and even the adepts themselves, except in some solitary
moments, have got so strong and irresistible a belief,
that thought must have a subject, and be the act of some
thinking being; how every man believes himself to be
something distinct from his ideas and impressions — some-
thing which continues the same identical self when all
his ideas and impressions are changed. It is impossible
to trace the origin of this opinion in history; for all lan-
guages have it interwoven in their original construction.
All nations have always believed it. The constitution
of all laws and governments, as well as the common
transactions of life, suppose it.

It is no less impossible for any man to recollect when
he himself came by this notion; for, as far back as we
can remember, we were already in possession of it, and
as fully persuaded of our own existence, and the exist-
ence of other things, as that one and one make two. It
seems, therefore, that this opinion preceded all reasoning,

106 THE PHILOSOPHY OF REID. [CH. II.

and experience, and instruction; and this is the more
probable, because we could not get it by any of these
means. It appears, then, to be an undeniable fact, that,
from thought or sensation, all mankind, constantly and
invariably, from the first dawning of reflection, do infer
a power or faculty of thinking and a permanent being
or mind to which that faculty belongs; and that we as
invariably ascribe all the various kinds of sensation and
thought we are conscious of, to one individual mind or
self.

But by what rules of logic we make these inferences,
it is impossible to shew; nay, it is impossible to shew
how our sensations and thoughts can give us the very
notion and conception either of a mind or of a faculty.
The faculty of smelling is something very different from
the actual sensation of smelling; for the faculty may re-
main when we have no sensation. And the mind is no
less different from the faculty; for it continues the same
individual being when that faculty is lost. Yet this sen-
sation suggests to us both a faculty and a mind; and not
only suggests the notion of them, but creates a belief of
their existence; although it is impossible to discover, by
reason, any tie or connection between one and the
other.

What shall we say, then ? Either those inferences
which we draw from our sensations — namely, the exist-
ence of a mind, and of powers or faculties belonging to
it — :are prejudices of philosophy or education, mere fic-
tions of the mind, which a wise man should throw off
as he does the belief of fairies; or they are judgments of
nature — judgments not got by comparing ideas, and per-
ceiving agreements and disagreements, but immediately
inspired by our constitution.

If this last is the case, as I apprehend it is, it will be
impossible to shake off those opinions, and we must
yield to them at last, though we struggle hard to get rid
of them. And if we could, by a determined obstinacy,

SEC. VII.] THE PHILOSOPHY OF REID. 107

shake off the principles of our nature, this is not to act
the philosopher, but the fool or the madman. It is in*
cumbent upon those who think that these are not
natural principles, to shew, in the first place, how we
can otherwise get the notion of a mind and its faculties;
and then to shew how we come to deceive ourselves into
the opinion that sensation cannot be without a sentient
being.

It is the received doctrine of philosophers, that our
notions of relations can only be got by comparing the
related ideas: but, in the present case, there seems to be
an instance to the contrary. It is not by having first
the notions of mind and sensation, and then comparing
them together, that we perceive the one to have the rela-
tion of a subject or substratum, and the other that of an
act or operation: on the contrary, one of the related
things — to wit, sensation — suggests to us both the cor-
relate and the relation.

I beg leave to make use of the word suggestion, be-
cause I know not one more proper, to express a power
of the mind, which seems entirely to have escaped the
notice of philosophers, and to which we owe many of
our simple notions which are neither impressions nor
ideas, as well as many original principles of belief.
I shall endeavor to illustrate, by an example, what I
understand by this word. We all know, that a certain
kind of sound suggests immediately to the mind, a
coach passing in the street; and not only produces the
imagination, but the belief, that a coach is passing. Yet
there is here no comparing of ideas, no perception of
agreements or disagreements, to produce this belief: nor
is there the least similitude between the sound we hear
and the coach we imagine and believe to be passing.*

* "The word suggest " (says Mr. Stewart, in reference to the pre-
ceding passage) "is much used by Berkeley, in this appropriate and
technical sense, not only in his ' Theory of Vision,' but in his ' Prin-

108 THE PHILOSOPHY OF REID. |Cn. II.

It is true that this suggestion is not natural and original;
it is the result of experience and habit. But I think it
appears, from what hath been said, that there are natural
suggestions: particularly, that sensation suggests the no-
tion of present existence, and the belief that what we
perceive or feel does now exist; that memory suggests the
notion of past existence, and the belief that what we
remember did exist in time past; and that our sensations
and thoughts do also suggest the notion of a mind, and
the belief of its existence, and of its relation to our

ciples of Human Knowledge,' and in his ' Minute Philosopher.' It
expresses, indeed, the cardinal principle on which his • Theory of
Vision ' hinges, and is now so incorporated with some of our best
metaphysical speculations, that one cannot easily conceive how
the use of it was so long dispensed with. Locke uses the word excite
for the same purpose; but it seems to imply an hypothesis concerning
the mechanism of the mind, and by no means expresses the fact in
question with the same force and precision.

"It is remarkable, that Dr. Reid should have thought it incum-
bent on him to apologise for introducing into philosophy a word so
familiar to every person conversant with Berkeley's works. ' I beg
leave to make use of the word suggestion, because, ' &c

" So far Dr. Reid's use of the word coincides exactly with that of
Berkeley; but the former will be found to annex to it a meaning
more extensive than the latter, by employing it to comprehend, not
only those intimations which are the result of experience and habit;
but another class of intimations, (quite overlooked by Berkeley,)
those which result from the original frame of the human mind." —
Dissertation on the History of Metaphysical and Ethical Science.
P. 167. Second edition.

Mr. Stewart might have adduced, perhaps, a higher and, certainly,
a more proximate authority, in favour, not merely of the term in
general, but of Reid's restricted employment of it, as an intimation
of what he and others have designated the Common Sense of man-
kind. The following sentence of Tertullian contains a singular an-
ticipation, both of the philosophy and of the philosophical phrase-
ology of our author. Speaking of the universal belief of the soul's
immortality: — " Natura pleraque suggerttntur, quasi de publico sensu
quo animam Deus ditare dignatus est." — DE ANIMA, c. 2.

Some strictures on Reid's employment of the term suggestion may
be seen in the " Versuche " of Tetens, I., p. 508, sqq. — H.

SEC. VIII.] THE PHILOSOPHY OF REID. 109

thoughts. By a like natural principle it is, that a be-
ginning of existence, or any change in nature, suggests
to us the notion of a cause, and compels our belief of its
existence. And, in like manner, as shall be shewn when
we come to the sense of touch, certain sensations of
touch, by the constitution of our nature, suggest to us
extension, solidity, and motion, which are nowise like
to sensations, although they have been hitherto con-
founded with them.

Section VIII.

THERE IS A QUALITY OR VIRTUE IN BODIES, WHICH WE CALL
THEIR SMELL HOW THIS IS CONNECTED IN THE IMAGINA-
TION WITH THE SENSATION.

We have considered smell as signifying a sensation,
feeling, or impression upon the mind; and in this sense,
it can only be in a mind, or sentient being: but it is evi-
dent that mankind gives the name of smell much more
frequently to something which they conceive to be ex-
ternal, and to be a quality of body: they understand
something by it which does not at all infer a mind; and
have not the least difficulty in conceiving the air per-
fumed with aromatic odours in the deserts of Arabia, or
in some uninhabited island, where the human foot
never trod. Every sensible day-labourer hath as clear a
notion of this, and as full a conviction of the possibility
of it, as he hath of his own existence; and can no more
doubt of the one than of the other.

Suppose that such a man meets with a modern phi-
losopher, and wants to be informed what smell in plants
is. The philosopher tells him, that there is no smell
in plants, nor in anything but in the mind; that it is
impossible there can be smell but in a mind; and that all
this hath been demonstrated by modern philosophy.
The plain man will, no doubt, be apt to think him
merry: but, if he finds that he is serious, his next conclu-

110 THE PHILOSOPHY OF REID. [Cn. It.

sion will be that he is mad; or that philosophy, like
magic, puts men into a new world, and gives them
different faculties from common men. And thus philoso-
phy and common sense are set at variance. But who is
to blame for it ? In my opinion the philosopher is to
blame. For if he means by smell, what the rest of man-
kind most commonly mean, he is certainly mad. But if
he puts a different meaning upon the word, without ob-
serving it himself, or giving warning to others, he abuses
language and disgraces philosophy, without doing any
service to truth: as if a man should exchange the mean-
ing of the words daughter and cow, and then endeavour to
prove to his plain neighbour, that his cow is his daughter,
and his daughter his cow.

I believe there is not much more wisdom in many of
those paradoxes of the ideal philosophy, which to plain
sensible men appear to be palpable absurdities, but with
the adepts pass for profound discoveries. I resolve, for
my own part, always to pay a great regard to the dictates
of common sense, and not to depart from them without
absolute necessity: and, therefore, I am apt to think that
there is really something in the rose or lily, which is by
the vulgar called smell, and which continues to exist
when it is not smelled: and shall proceed to inquire what
this is; how we come by the notion of it; and what rela-
tion this quality or virtue of smell hath to the sensation
which we have been obliged to call by the same name,
for want of another.

Let us therefore suppose, as before, a person begin-
ning to exercise the sense of smelling; a little experience
will discover to him that the nose is the organ of this
sense, and that the air, or something in the air, is a
medium of it. And finding, by farther experience, that,
when a rose is near, he has a certain sensation, when it
is removed, the sensation is gone, he finds a connection
in nature betwixt the rose and this sensation. The rose
is considered as a cause, occasion, or antecedent of the

SEC. IX.] THE PHILOSOPHY OF REID. Ill

sensation; the sensation as an effect or consequence of
the presence of the rose; they are associated in the mind,
and constantly found conjoined in the imagination.

But here it deserves our notice, that, although the sen-
sation may seem more closely related to the mind its
subject, or to the nose its organ, yet neither of these con-
nections operate so powerfully upon the imagination as
its connection with the rose its concomitant. The reason
of this seems to be, that its connection with the mind is
more general, and noway distinguisheth it from other
smells, or even from tastes, sounds, and other kinds of
sensations. The relation it hath to the organ is likewise
general, and doth not distinguish it from other smells;
but the connection it hath with the rose is special and
constant; by which means they become almost insepa-
rable in the imagination, in like manner as thunder and
lightning, freezing and cold.

Section IX.

THAT THERE IS A PRINCIPLE IN HUMAN NATURE, FROM WHICH
THE NOTION OF THIS, AS WELL AS ALL OTHER NATURAL
VIRTUES OR CAUSES, IS DERIVED.

In order to illustrate further how we come to conceive
a quality or virtue in the rose which we call smell, and
what this smell is, it is proper to observe, that the mind
begins very early to thirst after principles which may
direct it in the exertion of its powers. The smell of a
rose is a certain affection or feeling of the mind; and, as
it is not constant, but comes and goes, we want to know
when and where we may expect it; and are uneasy till
we find something which, being present, brings this
feeling along with it, and, being removed, removes
it. This, when found, we call the cause of it; not in
a strict and philosophical sense, as if the feeling were
really effected or produced by that cause, but in a popu-

112 THE PHILOSOPHY OF REID. [Cu. II.

lar sense; for the mind is satisfied if there is a constant
conjunction between them; and such causes are in reality
nothing else but laws of nature. Having found the smell
thus constantly conjoined with the rose, the mind is at
rest, without inquiring whether this conjunction is owing
to a real efficiency or not; that being a philosophical
inquiry, which does not concern human life. But every
discovery of such a constant conjunction is of real im-
portance in life, and makes a strong impression upon
the mind.

So ardently do we desire to find everything that hap-
pens within our observation thus connected with some-
thing else as its cause or occasion, that we are apt to
fancy connections upon the slightest grounds; and this
weakness is most remarkable in the ignorant, who know
least of the real connections established in nature. A
man meets with an unlucky accident on a certain day of the
year, and, knowing no other cause of his misfortune, he
is apt to conceive something unlucky in that day of the
calendar; and, if he finds the same connection hold a
second time, is strongly confirmed in his superstition. I
remember, many years ago, a white ox was brought into
this country, of so enormous a size that people came
many miles to see him. There happened, some months
after, an uncommon fatality among women in child-bear-
ing. Two such uncommon events, following one an-
other, gave a suspicion of their connection, and oc-
casioned a common opinion among the country-people
that the white ox was the cause of this fatality.

However silly and ridiculous this opinion was, it
sprung from the same root in human nature on which
all natural philosophy grows — namely, an eager desire to
find out connections in things, and a natural, original,
and unaccountable propensity to believe that the con-
nections which we have observed in time past will
continue in time to come. Omens, portents, good and
bad luck, palmistry, astrology, all the numerous arts of

SEC. IX.] THE PHILOSOPHY OF REID. 113

divination and of interpreting dreams, false hypotheses
and systems, and true principles in the philosophy of
nature, are all built upon the same foundation in the
human constitution, and are distinguished only accord-
ing as we conclude rashly from too few instances, or
cautiously from a sufficient induction.

As it is experience only that discovers these connec-
tions between natural causes and their effects; without
inquiring further, we attribute to the cause some vague
and indistinct notion of power or virtue to produce the
effect. And, in many cases, the purposes of life do not
make it necessary to give distinct names to the cause
and the effect. Whence it happens, that, being closely
connected in the imagination, although very unlike to
each other, one name serves for both; and, in common
discourse, is most frequently applied to that which, of
the two, is most the object of our attention. This occa-
sions an ambiguity in many words, which, having the
same causes in all languages, is common to all, and is
apt to be overlooked even by philosophers. Some
instances will serve both to illustrate and confirm what
we have said.

Magnetism signifies both the tendency of the iron to-
wards the magnet, and the power of the magnet to pro-
duce that tendency; and, if it was asked, whether it is a
quality of the iron or of the magnet, one would perhaps
be puzzled at first; but a little attention would discover,
that we conceive a power or virtue in the magnet as the
cause, and a motion in the iron as the effect; and,
although these are things quite unlike, they are so united
in the imagination, that we give the common name of
magnetism to both. The same thing may be said of
gravitation, which sometimes signifies the tendency of
bodies towards the earth, sometimes the attractive power
of the earth, which we conceive as the cause of that ten-
dency. We may observe the same ambiguity in some
of Sir Isaac Newton's definitions; and that even in words

114 THE PHILOSOPHY OF REID. [CH. II.

of his own making. In three of his definitions, he ex-
plains very distinctly what he understands by the absolute
quantity, what by the accelerative quantity, and what by
the motive quantity, of a centripetal force. In the first
of these three definitions, centripetal force is put for the
cause, which we conceive to be some power or virtue in
the centre or central body; in the two last, the same
word is put for the effect of this cause, in producing
velocity, or in producing motion towards that centre.

Heat signifies a sensation, and cold a contrary one;
but heat likewise signifies a quality or state of bodies,
which hath no contrary, but different degrees. When a
man feels the same water hot to one hand and cold to
the other, this gives him occasion to distinguish between
the feeling and the heat of the body; and, although he
knows that the sensations are contrary, he does not
imagine that the body can have contrary qualities at the
same time. And when he finds a different taste in the
same body in sickness and in health, he is easily con-
vinced, that the quality in the body called taste is the
same as before, although the sensations he has from it
are perhaps opposite.

The vulgar are commonly charged by philosophers,
with the absurdity of imagining the smell in the rose to
be something like to the sensation of smelling; but I
think unjustly; for they neither give the same epithets
to both, nor do they reason in the same manner from
them. What is smell in the rose ? It is a quality or vir-
tue of the rose, or of something proceeding from it,
which we perceive by the sense of smelling; and this is
all we know of the matter. But what is smelling? It
is an act of the mind, but is never imagined to be a qual-
ity of the mind. Again, the sensation of smelling is con-
ceived to infer necessarily a mind or sentient being; but
smell in the rose infers no such thing. We say, this
body smells sweet, that stinks; but we do not say, this
mind smells sweet and that stinks. Therefore, smell in

SEC. IX] THE PHILOSOPHY OF REID. 115

the rose, and the sensation which it causes, are not con-
ceived, even by the vulgar, to be things of the same
kind, although they have the same name.

From what hath been said, we may learn that the
smell of a rose signifies two things: First, a sensation,
which can have no existence but when it is perceived,
and can only be in a sentient being or mind; Secondly,
it signifies some power, quality, or virtue, in the rose, or
in effluvia proceeding from it, which hath a permanent
existence, independent of the mind, and which, by the
constitution of nature, produces the sensation in us. By
the original constitution of our nature, we are both led
to believe that there is a permanent cause of the sensa-
tion, and prompted to seek after it; and experience de-
termines us to place it in the rose. The names of all
smells, tastes, sounds, as well as heat and cold, have a
like ambiguity in all languages; but it deserves our at-
tention, that these names are but rarely, in common lan-
guage, used to signify the sensations; for the most part,
they signify the external qualities which are indicated by
the sensations — the cause of which phenomenon I take
to be this. Our sensations have very different degrees of
strength. Some of them are so quick and lively as to
give us a great deal either of pleasure or of uneasiness.
When this is the case, we are compelled to attend to the
sensation itself, and to make it an object of thought and
discourse; we give it a name, which signifies nothing but
the sensation; and in this case we readily acknowledge,
that the thing meant by that name is in the mind only,
and not in anything external. Such are the various kinds
of pain, sickness, and the sensations of hunger and other
appetites. But, where the sensation is not so interesting
as to require to be made an object of thought, our con-
stitution leads us to consider it as a sign of something
external, which hath a constant conjunction with it; and,
having found what it indicates, we give a name to that:
the sensation, having no proper name, falls in as an ac-

Il6 THE PHILOSOPHY OF REID. |CH. II.

cessory to the thing signified by it, and is confounded
under the same name. So that the name may, indeed,
be applied to the sensation, but most properly and com-
monly is applied to the thing indicated by that sensation.
The sensations of smell, taste, sound, and colour, are of
infinitely more importance as signs or indications, than
they are upon their own account; like the words of a
language, wherein we do not attend to the sound but to
the sense.

Section X.

WHETHER IN SENSATION THE MIND IS ACTIVE OR PASSIVE ?

There is one inquiry remains, Whether, in smelling,
and in other sensations, the mind is active or passive ?
This possibly may seem to be a question about words,
or, at least, of very small importance; however, if it leads
us to attend more accurately to the operations of our
minds than we are accustomed to do, it is, upon that
very account, not altogether unprofitable. I think the
opinion of modern philosophers is, that in sensation the
mind is altogether passive.* And this undoubtedly is
so far true, that we cannot raise any sensation in our
minds by willing it; and, on the other hand, it seems
hardly possible to avoid having the sensation when the
object is presented. Yet it seems likewise to be true,
that, in proportion as the attention is more or less turned
to a sensation or diverted from it, that sensation is more
or less perceived and remembered. Every one knows
that very intense pain may be diverted by a surprise, or by
anything that entirely occupies the mind. When we
are engaged in earnest conversation, the clock may
strike by us without being heard; at least, we remember
not, the next moment, that we did hear it. The noise
and tumult of a great trading city is not heard by them
who have lived in it all their days; but it stuns those
strangers who have lived in the peaceful retirement of the

* This is far too absolutely stated. — H.

SEC. X.] THE PHILOSOPHY OF REID. 117

country. Whether, therefore, there can be any sensation
where the mind is purely passive, I will not say; but I think
we are conscious of having given some attention to every
sensation which we remember, though ever so recent.

No doubt, where the impulse is strong and uncom-
mon, it is as difficult to withhold attention as it is to
forbear crying out in racking pain, or starting in a sud-
den fright. But how far both might be attained by
strong resolution and practice, is not easy to determine.
So that, although the Peripatetics had no good reason to
suppose an active and a passive intellect, since attention
may be well enough accounted an act of the will, yet I
think they came nearer to the truth, in holding the mind
to be in sensation partly passive and partly active, than
the moderns in affirming it to be purely passive. Sensa-
tion, imagination, memory and judgment, have, by the
vulgar in all ages, been considered as acts of the mind.
The manner in which they are expressed in all languages,
shews this. When the mind is much employed in them,
we say it is very active; whereas, if they were impressions
only, as the ideal philosophy would lead us to conceive,
we ought, in such a case, rather to say, that the mind is
very passive; for, I suppose, no man would attribute
great activity to the paper I write upon, because it re-
ceives variety of characters.

The relation which the sensation of smell bears to the
memory and imagination of it, and to a mind or subject,
is common to all our sensations, and, indeed, to all the
operations of the mind: the relation it bears to the will
is common to it with all the powers of understanding:
and the relation it bears to that quality or virtue of
bodies which it indicates, is common to it with the sen-
sations of taste, hearing, colour, heat, and cold — so that
what hath been said of this sense, may easily be applied
to several of our senses, and to other operations of the
mind; and this, I hope, will apologize for our insisting
so long upon it.

118 THE PHILOSOPHY OF REID. [Cn. III.

CHAPTER III.
OF TASTING.

A GREAT part of what hath been said of the sense of
smelling, is so easily applied to those of tasting and
hearing, that we shall leave the application entirely to
the reader's judgment, and save ourselves the trouble
of a tedious repetition.

It is probable that everything that affects the taste is,
in some degree, soluble in the saliva. It is not con-
ceivable how any thing should enter readily, and of its
own accord, as it were, into the pores of the tongue,
palate, and fauces, unless it had some chemical affinity
to that liquor with which these pores are always replete.
It is, therefore, an admirable contrivance of nature, that
the organs of taste should always be moist with a liquor
which is so universal a menstruum, and which deserves
to be examined more than it hath been hitherto, both in
that capacity, and as a medical unguent. Nature
teaches dogs, and other animals, to use it in this last
way; and its subserviency both to taste and digestion
shews its efficacy in the former.

It is with manifest design and propriety, that the or-
gan of this sense guards the entrance of the alimentary
canal, as that of smell the entrance of the canal for
respiration. And from these organs being placed in such
manner that everything that enters into the stomach
must undergo the scrutiny of both senses, it is plain that
they were intended by nature to distinguish wholesome
food from that which is noxious. The brutes have no
other means of choosing their food; nor would mankind,
in the savage state. And it is very probable that the
smell and taste, noway vitiated by luxury or bad habits,

CH. III.] THE PHILOSOPHY OF REID. 119

would rarely, if ever, lead us to a wrong choice of food
among the productions of nature; although the artificial
compositions of a refined and luxurious cookery, or of
chemistry and pharmacy, may often impose upon both,
and produce things agreeable to the taste and smell,
which are noxious to health. And it is probable that
both smell and taste are vitiated, and rendered less fit to
perform their natural offices, by the unnatural kind of
life men commonly lead in society.

These senses are likewise of great use to distinguish
bodies that cannot be distinguished by our other senses,
and to discern the changes which the same body under-
goes, which, in many "cases, are sooner perceived by
taste and smell than by any other means. How many
things are there in the market, the eating-house, and the
tavern, as well as in the apothecary and chemist's shops,
which are known to be what they are given out to be,
and are perceived to be good or bad in their kind, only
by taste or smell ? And how far our judgment of things,
by means of our senses, might be improved by accurate
attention to the small differences of taste and smell, and
other sensible qualities, is not easy to determine. Sir
Isaac Newton, by a noble effort of his great genius, at-
tempted, from the colour of opaque bodies, to discover
the magnitude of the minute pellucid parts of which they
are compounded: and who knows what new lights nat-
ural philosophy may yet receive from other secondary
qualities duly examined ?

Some tastes and smells stimulate the nerves and raise
the spirits: but such an artificial elevation of the spirits
is, by the laws of nature, followed by a depression,
which can only be relieved by time, or by the repeated
use of the like stimulus. By the use of such things we
create an appetite for them, which very much resembles,
and hath all the force of a natural one. It is in this
manner that men acquire an appetite for snuff, tobacco,
strong liquors, laudanum, and the like.

I2O THE PHILOSOPHY OF REID. [Cn. III.

Nature, indeed, seems studiously to have set bounds
to the pleasures and pains we have by these two senses,
and to have confined them within very narrow limits,
that we might not place any part of our happiness in
them; there being hardly any smell or taste so disagree-
able that use will not make it tolerable, and at last per-
haps agreeable, nor any so agreeable as not to lose its
relish by constant use. Neither is there any pleasure or
pain of these senses which is not introduced or followed
by some degree of its contrary, which nearly balances it;
so that we may here apply the beautiful allegory of the
divine Socrates — that, although pleasure and pain are
contrary in their nature, and th"eir faces look different
ways, yet Jupiter hath tied them so together that he that
lays hold of the one draws the other along with it.

As there is a great variety of smells, seemingly simple
and uncompounded, not only altogether unlike, but
some of them contrary to others, and as the same thing
may be said of tastes, it would seem that one taste is not
less different from another than it is from a smell : and
therefore it may be a question, how all smells come
to be considered as one genus, and all tastes as
another ? What is the generical distinction ? Is it
only that the nose is the organ of the one and the pal-
ate of the other ? or, abstracting from the organ, is there
not in the sensations themselves something common to
smells, and something else common to tastes, whereby
the one is distinguished from the other? It seems most
probable that the latter is the case; and that, under the
appearance of the greatest simplicity, there is still in
these sensations something of composition.

If one considers the matter abstractly, it would seem
that a number of sensations, or, indeed, of any other
individual things, which are perfectly simple and uncom-
pounded, are incapable of being reduced into genera and
species; because individuals which belong to a species
must have something peculiar to each, by which they

CH. III.] THE PHILOSOPHY OF REID. 121

are distinguished, and something common to the whole
species. And the same may be said of species which be-
long to one genus. And, whether this does not imply
some kind of' composition, we shall leave to' metaphy-
sicians to determine.

The sensations both of smell and taste do undoubtedly
admit of an immense variety of modifications, which no
language can express. If a man was to examine five
hundred different wines, he would hardly find two of
them that had precisely the same taste. The same thing
holds in cheese, and in many other things. Yet, of five
hundred different tastes in cheese or wine, we can hardly
describe twenty, so as to give a distinct notion of them
to one who had not tasted them.

Dr. Nehemiah Grew, a most judicious and laborious
naturalist, in a discourse read before the Royal Society,
anno 1675, hath endeavoured to shew that there are at
least sixteen different simple tastes, which he enumerates.
How many compounded ones may be made out of all
the various combinations of two, three, four, or more
of these simple ones, they who are acquainted with the
theory of combinations will easily perceive. All these
have various degrees of intenseness and weakness.
Many of them have other varieties; in some the taste is
more quickly perceived upon the application of the sapid
body, in others more slowly — in some the sensation is
more permanent, in others more transient — in some it
seems to undulate or return after certain intervals, in
others it is constant: the various parts of the organ — as
the lips, the tip of the tongue, the root of the tongue,
the/auces, the uvula, and the throat — are some of them
chiefly affected by one sapid body, and others by an-
other. All these, and other varieties of tastes, that ac-
curate writer illustrates by a number of examples.
Nor is it to be doubted, but smells, if examined with
the same accuracy, would appear to have as great variety.

122 THE PHILOSOPHY OF REID. [Cn. IV.

CHAPTER IV.

OF HEARING.

Section I.

VARIETY OF SOUNDS — THEIR PLACE AND DISTANCE LEARNED
BY CUSTOM, WITHOUT REASONING.

SOUNDS have probably no less variety of modifications,
than either tastes or odours. For, first, sounds differ in
tone. The ear is capable of perceiving four or five hun-
dred variations of tone in sound, and probably as many
different degrees of strength; by combining these, we
have above twenty thousand simple sounds that differ
either in tone or strength, supposing every tone to be
perfect. But it is to be observed, that to make a perfect
tone, a great many undulations of elastic air are required,
which must all be of equal duration and extent, and fol-
low one another with perfect regularity; and each undu-
lation must be made up of the advance and recoil of in-
numerable particles of elastic air, whose motions are all
uniform in direction, force, and time. Hence we may
easily conceive a prodigious variety in the same tone,
arising from irregularities of it, occasioned by the con-
stitution, figure, situation, or manner of striking the sono-
rous body; from the constitution of the elastic medium,
or its being disturbed by other motions; and from the
constitution of the ear itself, upon which the impres-
sion is made.

A flute, a violin, a hautboy, and a French horn, may
all sound the same tone and be easily distinguishable.
Nay, if twenty human voices sound the same note, and
with equal strength, there will still be some difference.

SEC. I.] THE PHILOSOPHY OF REID. 123

The same voice, while it retains its proper distinctions,
may yet be varied many ways, by sickness or health,
youth or age, leanness or fatness, good or bad humour.
The same words spoken by foreigners and natives — nay,
by persons of different provinces of the same nation-
may be distinguished.

Such an immense variety of sensations of smell, taste,
and sound, surely was not given us in vain. They are
signs by which we know and distinguish things without
us; and it was fit that the variety of the signs should, in
some degree, correspond with the variety of the things
signified by them.

It seems to be by custom that we learn to distinguish
both the place of things, and their nature, by means of
their sound. That such a noise is in the street, such
another in the room above me; that this is a knock at
my door, that a person walking up stairs — is probably
learnt by experience. I remember, that once lying abed,
and having been put into a fright, I heard my own heart
beat; but I took it to be one knocking at the door, and
arose and opened the door oftener than once, before I
discovered that the sound was in my own breast. It is
probable, that, previous to all experience, we should as
little know whether a sound came from the right or left,
from above or below, from a great or a small distance,
as we should know whether it was the sound of a drum,
or a bell, or a cart. Nature is frugal in her operations,
and will not be at the expense of a particular instinct, to
give us that knowledge which experience will soon
produce, by means of a general principle of human
nature.

For a little experience, by the constitution of human
nature, ties together, not only in our imagination, but in
our belief, those things which were in their nature un-
connected. When I hear a certain sound, I conclude
immediately, without reasoning, that a coach passes by.
There are no premises from which this conclusion is in-

124 THE PHILOSOPHY OF REID. [CH. IV.

ferred by any rules of logic. It is the effect of a princi-
ple of our nature, common to us with the brutes.

Although it is by hearing that we are capable of the
perceptions of harmony and melody, and of all the charms
of music, yet it would seem that these require a higher
faculty, which we call a musical ear. This seems to be
in very different degrees, in those who have the bare fac-
ulty of hearing equally perfect; and, therefore, ought not
to be classed with the external senses, but in a higher
order.

Seclion II.

OF NATURAL LANGUAGE.

One of the noblest purposes of sound undoubtedly is
language, without which mankind would hardly be able
to attain any degree of improvement above the brutes.
Language is commonly considered as purely an inven-
tion of men, who by nature are no less mute than the
brutes; but, having a superior degree of invention and
reason, have been able to contrive artificial signs of their
thoughts and purposes, and to establish them by com-
mon consent. But the origin of language deserves to be
more carefully inquired into, not only as this inquiry
may be of importance for the improvement of language,
but as it is related to the present subject, and tends to
lay open some of the first principles of human nature.
I shall, therefore, offer some thoughts upon this sub-
ject.

By language I understand all those signs which man-
kind use in order to communicate to others their
thoughts and intentions, their purposes and desires.
And such signs may be conceived to be of two kinds:
First, such as have no meaning but what is affixed to
them by compact or agreement among those who use
them — these are artificial signs; Secondly, such as, previ-
ous to all compact or agreement, have a meaning which

SEC. II.] THE PHILOSOPHY OF REID. 125

every man understands by the principles of his nature.
Language, so far as it consists of artificial signs, may be
called artificial; so far as it consists of natural signs, I
call it natural.

Having premised these definitions, I think it is de-
monstrable, that, if mankind had not a natural lan-
guage they could never have invented an artificial one by
their reason and ingenuity. For all artificial language
supposes some compact or agreement to affix a certain
meaning to certain signs; therefore, there must be com-
pacts or agreements before the use of artificial signs; but
there can be no compact or agreement without signs, nor
without language; and, therefore, there must be a natu-
ral language before any artificial language can be in-
vented: which was to be demonstrated.

Had language in general been a human invention, as
much as writing or printing, we should find whole na-
tions as mute as the brutes. Indeed, even the brutes
have some natural signs by which they express their own
thoughts, affections, and desires, and understand those
of others. A chick, as soon as hatched, understands the
different sounds whereby its dam calls it to food, or
gives the alarm of danger. A dog or a horse under-
stands, by nature, when the human voice caresses, and
when it threatens him. But brutes, as far as we know,
have no notion of contracts or covenants, or of moral
obligation to perform them. If nature had given them
these notions, she would probably have given them nat-
ural signs to express them. And where nature has de-
nied these notions, it is as impossible to acquire them by
art, as it is for a blind man to acquire the notion of col-
ours. Some brutes are sensible of honour or disgrace; they
have resentment and gratitude; but none of them, as far
as we know, can make a promise or plight their faith,
having no such notions from their constitution. And
if mankind had not these notions by nature, and
natural signs to express them by, with all their wit

126 THE PHILOSOPHY OF REID. [CH. IV.

and ingenuity they could never have invented lan-
guage.

The elements of this natural language of mankind, or
the signs that are naturally expressive of our thoughts,
may, I think, be reduced to these three kinds: modula-
tions of the voice, gestures, and features. By means of
these, two savages who have no common artificial lan-
guage, can converse together, can communicate their
thoughts in some tolerable manner; can ask and refuse,
affirm and deny, threaten and supplicate; can traffic,
enter into covenants, and plight their faith. This might
be confirmed by historical facts of undoubted credit, if
it were necessary.

Mankind having thus a common language by nature,
though a scanty one, adapted only to the necessities of
nature, there is no great ingenuity required in improving
it by the addition of artificial signs, to supply the deficiency
of the natural. These artificial signs must multiply with
the arts of life, and the improvements of knowledge. The
articulations of the voice seem to be, of all signs, the
most proper for artificial language; and as mankind have
universally used them for that purpose, we may reason-
ably judge that nature intended them for it. But nature
probably does not intend that we should lay aside the
use of the natural signs; it is enough that we supply their
defects by artificial ones. A man that rides always in a
chariot, by degrees loses the use of his legs; and one who
uses artificial signs only, loses both the knowledge and
use of the natural. Dumb people retain much more
of the natural language than others, because necessity
obliges them to use it. And for the same reason, sav-
ages have much more of it than civilized nations. It is
by natural signs chiefly that we give force and energy to
language; and the less language has of them, it is the
less expressive and persuasive. Thus, writing is less ex-
pressive than reading, and reading less expressive
than speaking without book; speaking without the

SEC. II.) THE PHILOSOPHY OF REID. 127

proper and natural modulations, force, and variations of
the voice, is a frigid and dead language, compared with
that which is attended with them; it is still more express-
ive when we add the language of the eyes and features;
and is then only in its perfect and natural state, and at-
tended with its proper energy, when to all these we
superadd the force of action.

Where speech is natural, it will be an exercise, not of
the voice and lungs only, but of all the muscles of the
body; like that of dumb people and savages, whose lan-
guage, as it has more of nature, is more expressive, and
is more easily learned.

Is it not pity that the refinements of a civilized life, in-
stead of supplying the defects of natural language, should
root it out and plant in its stead dull and lifeless articu-
lations of unmeaning sounds, or the scrawling of insig-
nificant characters ? The perfection of language is com-
monly thought to be, to express human thoughts and
sentiments distinctly by these dull signs; but if this is
the perfection of artificial language, it is surely the cor-
ruption of the natural.

Artificial signs signify, but they do not express; they
speak to the understanding, as algebraical characters
may do, but the passions, the affections, and the will,
hear them not; these continue dormant and inactive,
till we speak to them in the language of nature, to which
they are all attention and obedience.

It were easy to show, that the fine arts of the musician,
the painter, the actor, and the orator, so far as they are
expressive — although the knowledge of them requires in
us a delicate taste, a nice judgment, and much study
and practice — yet they are nothing else but the language
of nature, which we brought into the world with us, but
have unlearned by disuse, and so find the greatest diffi-
culty in recovering it.

Abolish the use of articulate sounds and writing
among mankind for a century, and every man would be a

128 THE PHILOSOPHY OF REID. [Cn. IV., SEC. 11.

painter, an actor, and an orator. We mean not to
affirm that such an expedient is practicable; or, if it were,
that the advantage would counterbalance the loss; but
that, as men are led by nature and necessity to converse
together, they will use every mean in their power to
make themselves understood; and where they cannot do
this by artificial signs, they will do it, as far as possible,
by natural ones: and he that understands perfectly the
use of natural signs, must be the best judge in all the
expressive arts.

CH. V., SEC. I.] THE PHILOSOPHY OF REID. 129

CHAPTER V.

OF TOUCH.

Section I.

OF HEAT AND COLD.

THE senses which we have hitherto considered, are
very simple and uniform, each of them exhibiting only
one kind of sensation, and thereby indicating only one
quality of bodies. By the ear we perceive sounds, and
nothing else; by the palate, tastes; and by the nose.,
odours. These qualities are all likewise of one order,
being all secondary qualities; whereas, by touch we
perceive not one quality only, but many, and those
of very different kinds. The chief of them are heat and
cold, hardness and softness, roughness and smoothness,
figure, solidity, motion, and extension. We shall con-
sider these in order.

As to heat and cold, it will easily be allowed that they
are secondary qualities, of the same order with smell,
taste, and sound. And, therefore, what hath been
already said of smell, is easily applicable to them; that
is, that the words heat and cold have each of them two
significations; they sometimes signify certain sensations
of the mind, which can have no existence when they are
not felt, nor can exist anywhere but in a mind or sen-
tient being; but more frequently they signify a quality in
bodies, which, by the laws of nature, occasions the sen-
sations of heat and cold in us — a quality which, though
connected by custom so closely with the sensation, that
we cannot, without difficulty, separate them, yet hath not

130 THE PHILOSOPHY OF REID. TCH. V.

the least resemblance to it, and may continue to exist
when there is no sensation at all.

The sensations of heat and cold are perfectly known;
for they neither are, nor can be, anything else than what
we feel them to be; but the qualities in bodies which we
call heat and cold are unknown. They are only con-
ceived by us, as unknown causes or occasions of the sen-
sations to which we give the same names. But, though
common sense says nothing of the nature of these quali-
ties, it plainly dictates the existence of them; and to deny
that there can be heat and cold when they are not felt,
is an absurdity too gross to merit confutation. For
what could be more absurd, than to say, that the ther-
mometer cannot rise or fall, unless some person be pre-
sent, or that the coast of Guinea would be as cold as
Nova Zembla, if it had no inhabitants ?

It is the business of philosophers to investigate, by
proper experiments and induction, what heat and cold
are in bodies. And whether they make heat a particu-
lar element diffused through nature, and accumulated in
the heated body, or whether they make it a certain vi-
bration of the parts of the heated body; whether they
determine that heat and cold are contrary qualities, as
the sensations undoubtedly are contrary, or that heat
only is a quality, and cold its privation: these questions
are within the province of philosophy; for common sense
says nothing on the one side or the other.

But, whatever be the nature of that quality in bodies
which we call heat, we certainly know this, that it can-
not in the least resemble the sensation of heat. It is no
less absurd to suppose a likeness between the sensation
and the quality, than it would be to suppose that the
pain of the gout resembles a square or a triangle. The
simplest man that hath common sense, does not imagine
the sensation of heat, or anything that resembles that
sensation, to be in the fire. He only imagines that there
is something in the fire which makes him and other

SEC. II.] THE PHILOSOPHY OF REID. 131

sentient beings feel heat. Yet, as the name of heat, in
common language, more frequently and more properly
signifies this unknown something in the fire, than the
sensation occasioned by it, he justly laughs at the phi-
losopher who denies that there is any heat in the fire,
and thinks that he speaks contrary to common sense.

Section II.

OF HARDNESS AND SOFTNESS.

Let us next consider hardness and softness ; by which
words we always understand real properties or qualities
of bodies of which we have a distinct conception.

When the parts of a body adhere so firmly that it
cannot easily be made to change its figure, we call it
hard ; when its parts are easily displaced, we call it soft.
This is the notion which all mankind have of hardness
and softness ; they are neither sensations, nor like any
sensation ; they were real qualities before they were per-
ceived by touch, and continue to be so when they are
not perceived ; for if any man will affirm that diamonds
were not hard till they were handled, who would reason
with him ?

There is, no doubt, a sensation by which we perceive
a body to be hard or soft. This sensation of hardness
may easily be had, by pressing one's hand against the
table, and attending to the feeling that ensues, setting
aside, as much as possible, all thought of the table and
its qualities, or of any external thing. But it is one
thing to have the sensation, and another to attend to it,
and make it a distinct object of reflection. The first
is very easy; the last, in most cases, extremely difficult.

We are so accustomed to use the sensation as a sign, and
to pass immediately to the hardness signified, that, as
far as appears, it was never made an object of thought,
either by the vulgar or by philosophers ; nor has it a

132 THE PHILOSOPHY OF REID. [CH. V.

name in any language. There is no sensation more dis-
tinct, or more frequent ; yet it is never attended to, but
passes through the mind instantaneously, and serves
only to introduce that quality in bodies, which, by a
law of our constitution, it suggests.

There are, indeed, some cases, wherein it is no difficult
matter to attend to the sensation occasioned by the hard-
ness of a body ; for instance, when it is so violent as to
occasion considerable pain : then nature calls upon us
to attend to it, and then we acknowledge that it is a mere
sensation, and can only be in a sentient being. If a man
runs his head with violence against a pillar, I appeal to
him whether the pain he feels resembles the hardness of
the stone, or if he can conceive anything like what he
feels to be in an inanimate piece of matter.

The attention of the mind is here entirely turned
towards the painful feeling; and, to speak in the common
language of mankind, he feels nothing in the stone, but
feels a violent pain in his head. It is quite otherwise
when he leans his head gently against the pillar ; for
then he will tell you that he feels nothing in his head,
but feels hardness in the stone. Hath he not a sensation
in this case as well as in the other ? Undoubtedly he hath ;
but it is a sensation which nature intended only as a
sign of something in the stone ; and, accordingly, he
instantly fixes his attention upon the thing signified ; and
cannot, without great difficulty, attend so much to the
sensation as to be persuaded that there is any such thing
distinct from the hardness it signifies.

But, however difficult it may be to attend to this
fugitive sensation, to stop its rapid progress, and to dis-
join it from the external quality of hardness, in whose
shadow it is apt immediately to hide itself; this is what
a philosopher by pains and practice must attain, other-
wise it will be impossible for him to reason justly upon
this subject, or even to understand what is here advanced.
For the last appeal, in subjects of this nature, must

SEC. II.] THE PHILOSOPHY OF REID. 133

be to what a man feels and perceives in his own
mind.

It is indeed strange that a sensation which we have
every time we feel a body hard, and which, conse-
quently, we can command as often and continue as long
as we please, a sensation as distinct and determinate as
any other, should yet be so much unknown as never to
have been made an object of thought and reflection, nor
to have been honoured with a name in any language :
that philosophers, as well as the vulgar, should have
entirely overlooked it, or confounded it with that quality
of bodies which we call hardness, to which it hath not
the least similitude. May we not hence conclude, that
the knowledge of the human faculties is but in its in-
fancy ? — that we have not yet learned to attend to those
operations of the mind, of which we are conscious every
hour of our lives ? — that there are habits of inattention
acquired very early, which are as hard to be overcome
as other habits ? For I think it is probable, that the
novelty of this sensation will procure some attention
to it in children at first ; but, being in nowise interesting
in itself, as soon as it becomes familiar, it is overlooked,
and the attention turned solely to that which it signifies.
Thus, when one is learning a language, he attends to the
sounds ; but when he is master of it, he attends only to
the sense of what he would express. If this is the case,
we must become as little children again, if we will be
philosophers ; we must overcome this habit of inattention
which has been gathering strength ever since we began
to think — a habit, the usefulness of which, in common
life, atones for the difficulty it creates to the philosopher
in discovering the first principles of the human mind.

The firm cohesion of the parts of a body, is no more
like that sensation by which I perceive it to be hard, than
the vibration of a sonorous body is like the sound I hear :
nor can I possibly perceive, by my reason, any connec-
tion between the one and the other. No man can give

134 THE PHILOSOPHY OF REID. [Cn. V.

a reason, why the vibration of a body might not have
given the sensation of smelling, and the effluvia of bodies
affected our hearing, if it had so pleased our Maker. In
like manner, no man can give a reason why the sen-
sations of smell, or taste, or sound, might not have
indicated hardness, as well as that sensation which,
by our constitution, does indicate it. Indeed, no man
can conceive any sensation to resemble any known
quality of bodies. Nor can any man show, by any good
argument, that all our sensations might not have been as
they are, though no body, nor quality of body, had ever
existed.

Here, then, is a phaenomenon of human nature, which
comes to be resolved. Hardness of bodies is a thing
that we conceive as distinctly, and believe as firmly, as
anything in nature. We have no way of coming at this
conception and belief, but by means of a certain sensa-
tion of touch, to which hardness hath not the least simil-
itude; nor can we, by any rules of reasoning, infer the
one from the other. The question is, How we come by
this conception and belief?

First, as to the conception: Shall we call it an idea of
sensation, or of reflection ? The last will not be affirmed;
and as little can the first, unless we will call that an idea
of sensation which hath no resemblance to any sensation.
So that the origin of this idea of hardness, one of the
most common and most distinct we have, is not to be
found in all our systems of the mind: not even in those
which have so copiously endeavoured to deduce all our
notions from sensation and reflection.

But, secondly, supposing we have got the conception
of hardness, how come we by the belief of it ? Is it self-
evident, from comparing the ideas, that such a sensation
could not be felt, unless such a quality of bodies existed ?
No. Can it be proved by probable or certain arguments ?
No; it cannot. Have we got this belief, then, by tradi-
tion, by education, or by experience ? No; it is not got

SEC. III.] THE PHILOSOPHY OF REID. 135

in any of these ways. Shall we then throw off this be-
lief as having no foundation in reason ? Alas ! it is not
in our power; it triumphs over reason, and laughs at all
the arguments of a philosopher. Even the author of the
"Treatise of Human Nature," though he saw no reason
for this belief, but many against it, could hardly conquer
it in his speculative and solitary moments; at other
times, he fairly yielded to it, and confesses that he found
himself under a necessity to do so.

What shall we say, then, of this conception, and this
belief, which are so unaccountable and untractable ? I
see nothing left, but to conclude, that, by an original
principle of our constitution, a certain sensation of touch
both suggests to the mind the conception of hardness,
and creates the belief of it: or, in other words, that this
sensation is a natural sign of hardness. And this I
shall endeavour more fully to explain.

Section III.

OF NATURAL SIGNS.

As in artificial signs there is often neither similitude
between the sign and thing signified, nor any connec-
tion that arises necessarily from the nature of the things,
so it is also in natural signs. The word gold has no
similitude to the substance signified by it; nor is it in
its own nature more fit to signify this than any other sub-
stance; yet, by habit and custom, it suggests this and no
other. In like manner, a sensation of touch suggests
hardness, although it hath neither similitude to hardness,
nor, as far as we can perceive, any necessary connection
with it. The difference betwixt these two signs lies only
in this — that, in the first, the suggestion is the effect of
habit and custom; in the second, it is not the effect of
habit, but of the original constitution of our minds.

It appears evident from what hath been said on the

136 THE PHILOSOPHY OF REID. [Cn. V.

subject of language, that there are natural signs as well
as artificial; and particularly, that the thoughts, pur-
poses, and dispositions of the mind, have their natural
signs in the features of the face, the modulation of the
voice, and the motion and attitude of the body: that,
without a natural knowledge of the connection between
these signs and the things signified by them, language
could never have been invented and established among
men: and, that the fine arts are all founded upon this
connection, which we may call the natural language of
mankind. It is now proper to observe, that there are
different orders of natural signs, and to point out the
different classes into which they may be distinguished,
that we may more distinctly conceive the relation
between our sensations and the things they suggest, and
what we mean by calling sensations signs of external
things.

The first class of natural signs comprehends those
whose connection with the thing signified is established
by nature, but discovered only by experience. The
whole of genuine philosophy consists in discovering such
connections, and reducing them to general rules. The
great Lord Verulam had a perfect comprehension of
this, when he called it an interpretation of nature. No
man ever more distinctly understood or happily ex-
pressed the nature and foundation of the philosophic
art. What is all we know of mechanics, astronomy, and
optics, but connections established by nature, and dis-
covered by experience or observation, and consequences
deduced from them ? All the knowledge we have in agri-
culture, gardening, chemistry, and medicine, is built
upon the same foundation. And if ever our philosophy
concerning the human mind is carried so far as to de-
serve the name of science, which ought never to be de-
spaired of, it must be by observing facts, reducing them
to general rules, and drawing just conclusions from them.
What we commonly call natural causes might, with more

SEC. Hi:] THE PHILOSOPHY OF REID. 137

propriety, be called natural signs, and what we call
effects, the things signified. The causes have no proper
efficiency or causality, as far as we know: and all we can
certainly affirm is, that nature hath established a con-
stant conjunction between them and the things called
their effects; and hath given to mankind a disposition
to observe those connections, to confide in their contin-
uance, and to make use of them for the improvement of
our knowledge, and increase of our power.

A second class is that wherein the connection between
the sign and thing signified, is not only established by
nature, but discovered to us by a natural principle, with-
out reasoning or experience. Of this kind are the nat-
ural signs of human thoughts, purposes, and desires,
which have been already mentioned as the natural lan-
guage of mankind. An infant may be put into a fright
by an angry countenance, and soothed again by smiles
and blandishments. A child that has a goo.d musical
ear, may be put to sleep or to dance, may be made mer-
ry or sorrowful, by the modulation of musical sounds.
The principles of all the fine arts, and of what we call
a fine taste, may be resolved into connections of this
kind. A fine taste may be improved by reasoning and
experience; but if the first principles of it were not
planted in our minds by nature, it could never be ac-
quired. Nay, we have already made it appear, that a
great part of this knowledge which we have by nature,
is lost by the disuse of natural signs, and the substitution
of artificial in their place.

A third class of natural signs comprehends those
which, though we never before had any notion or con-
ception of the thing signified, do suggest it, or conjure
it up, as it were, by a natural kind of magic, and at
once give us a conception and create a belief of it. I
shewed formerly, that our sensations suggest to us a
sentient being or mind to which they belong — a being
which hath a permanent existence, although the sensa-

138 THE PHILOSOPHY OP REID. [Cn. V.

tions are transient and of short duration — a being which
is still the same, while its sensations and other operations
are varied ten thousand ways — a being which hath the
same relation to all that infinite variety of thoughts, pur-
poses, actions, affections, enjoyments, and sufferings,
which we are conscious of, or can remember. The
conception of a mind is neither an idea of sensation nor
of reflection; for it is neither like any of our sensations,
nor like anything we are conscious of. The first con-
ception of it, as well as the belief of it, and of the com-
mon relation it bears to all that we are conscious of, or
remember, is suggested to every thinking being, we do
not know how.

The notion of hardness in bodies, as well as the belief
of it, are got in a similar manner; being, by an original
principle of our nature, annexed to that sensation which
we have when we feel a hard body. And so naturally
and necessarily does the sensation convey the notion and
belief of hardness, that hitherto they have been con-
founded by the most acute inquirers into the principles
of human nature, although they appear, upon accurate
reflection, not only to be different things, but as unlike as
pain is to the point of a sword.

It may be observed, that, as the first class of natural
signs I have mentioned is the foundation of true philoso-
phy, and the second the foundation of the fine arts, or
of taste — so the last is the foundation of common sense
— a part of human nature which hath never been ex-
plained.

I take it for granted, that the notion of hardness, and
the belief of it, is first got by means of that particular
sensation which, as far back as we can remember, does
invariably suggest it ; and that, if we had never had such
a feeling, we should never have had any notion of hard-
ness. I think it is evident, that we cannot, by reasoning
from our sensations, collect the existence of bodies at
all, far less any of their qualities. This hath been proved

SEC. IV.] THE PHILOSOPHY OF REID. 139

by unanswerable arguments by the Bishop of Cloyne, and
by the author of the "Treatise of Human Nature." It
appears as evident that this connection between our sen-
sations and the conception and belief of external exist-
ences cannot be produced by habit, experience, educa-
tion, or any principle of human nature that hath been
admitted by philosophers. At the same time, it is a
fact that such sensations are invariably connected with
the conception and belief of external existences. Hence,
by all rules of just reasoning, we must conclude that this
connection is the effect of our constitution, and ought
to be considered as an original principle of human
nature, till we find some more general principle into
which it may be resolved.*

Section IV.

OF HARDNESS, AND OTHER PRIMARY QUALITIES.

Further, I observe that hardness is a quality, of which
we have as clear and distinct a conception as of anything
whatsoever. The cohesion of the parts of a body with
more or less force, is perfectly understood, though its
cause is not ; we know what it is, as well as how it
affects the touch. It is, therefore, a quality of a quite
different order from those secondary qualities we have
already taken notice of, whereof we know no more nat-
urally than that they are adapted to raise certain sensa-
tions in us. If hardness were a quality of the same
kind, it would be a proper inquiry for philosophers, what
hardness in bodies is ? and we should have had various
hypotheses about it, as well as about colour and heat.

* This whole doctrine of natural signs, on which his philosophy
is in a great measure established, was borrowed by Reid, in principle,
and even in expression, from Berkeley. Compare "Minute Philoso-
pher," Dial. IV., §§ 7, n, 12; " New Theory of Vision," §§ 144,
147; "Theory of Vision Vindicated," §§ 38-43- — H.

140 THE PHILOSOPHY OF REID. [Cn. V.

But it is evident that any such hypothesis would be
ridiculous. If any man should say, that hardness in
bodies is a certain vibration of their parts, or that it is
certain effluvia emitted by them which affect our touch
in the manner we feel — such hypotheses would shock
common sense ; because we all know that, if the parts
of a body adhere strongly, it is hard, although it should
neither emit effluvia nor vibrate. Yet, at the same time,
no man can say, but that effluvia or the vibration of the
parts of- a body, might have affected our touch, in the
same manner that hardness now does, if it had so pleased
the Author of our nature ; and, if either of these hypoth-
eses is applied to explain a secondary quality — such as
smell, or taste, or sound, or colour, or heat — there ap-
pears no manifest absurdity in the supposition.

The distinction betwixt primary and secondary quali-
ties hath had several revolutions. Democritus and Epi-
curus, and their followers, maintained it. Aristotle and
the Peripatetics abolished it. Des Cartes, Malebranche,
and Locke, revived it, and were thought to have put it
in a very clear light. But Bishop Berkeley again discard-
ed this distinction, by such proofs as must be con-
vincing to those that hold the received doctrine of ideas. *
Yet, after all, there appears to be a real foundation for
it in the principles of our nature.

What hath been said of hardness, is so easily appli-
cable not only to its opposite, softness, but likewise to
roughness and smoothness, to figure and motion, that we
may be excused from making the application, which
would only be a repetition of what hath been said. All
these, by means of certain corresponding sensations of
touch, are presented to the mind as real external quali-
ties ; the conception and the belief of them are invariably

* On this distinction of Primary and Secondary Qualities, see
"Essays on the Intellectual Powers," Essay II., chap. 17, and
Note D, at the end of the volume. — H.

SEC. V.] THE PHILOSOPHY OF REID. 14!

connected with the corresponding sensations, by an
original principle of human nature. Their sensations
have no name in any language ; they have not only been
overlooked by the vulgar, but by philosophers ; or, if
they have been at all taken notice of, they have been
confounded with the external qualities which they sug-
gest.

Section V.

OF EXTENSION.

It is further to be observed, that hardness and softness,
roughness and smoothness, figure and motion, do all
suppose extension, and cannot be conceived without it ;
yet, I think it must, on the other hand, be allowed that,
if we had never felt any thing hard or soft, rough or
smooth, figured or moved, we should never have had a
conception of extension ;* so that, as there is good
ground to believe that the notion of extension could not
be prior to that of other primary qualities, so it is cer-
tain that it could not be posterior to the notion of any
of them, being necessarily implied in them all.f

Extension, therefore, seems to be a quality suggested
to us, by the very same sensations which suggest the
other qualities above mentioned. When I grasp a ball
in my hand, I perceive it at once hard, figured, and ex-

* According to Reid, Extension (Space) is a notion a posteriori,
the result of experience. According to Kant, it is a priori ; experi-
ence only affording the occasions required by the mind to exert the
acts, of which the intuition of space is a condition. To the former
it is thus a contingent : to the latter, a necessary mental possession. — H.

f In this paragraph, to say nothing of others in the " Inquiry,"
Reid evidently excludes sight as a sense, through which the notion
of extension or space, enters into the mind. In his later work, the
" Essays on the Intellectual Powers," he, however, expressly allows
that function to sight and touch, and to those senses alone. See
Essay II., chap. 19, p. 262, quarto edition. — H.

142 THE PHILOSOPHY OF REID. [Cn. V.

tended. The feeling is very simple, and hath not the
least resemblance to any quality of body. Yet it sug-
gests to us three primary qualities perfectly distinct from
one another, as well as from the sensation which indi-
cates them. When I move my hand along the table,
the feeling is so simple that I find it difficult to distin-
guish it into things of different natures ; yet, it immedi-
ately suggests hardness, smoothness, extension, and mo-
tion— things of very different natures, and all of them as
distinctly understood as the feeling which suggests
them.

We are commonly told by philosophers, that we get
the idea of extension by feeling along the extremities of
a body, as if there was no manner of difficulty in the
matter. I have sought, with great pains, I confess, to
find out how this idea can be got by feeling ; but I have
sought in vain. Yet it is one of the clearest and most
distinct notions we have ; nor is there anything whatso-
ever about which the human understanding can carry on
so many long and demonstrative trains of reasoning.

The notion of extension is so familiar to us from in-
fancy, and so constantly obtruded by everything we see
and feel, that we are apt to think it obvious how it comes
into the mind ; but upon a narrower examination we
shall find it utterly inexplicable. It is true we have
feelings of touch, which every moment present extension
to the mind ; but how they come to do so, is the ques-
tion ; for those feelings do no more resemble extension,
than they resemble justice or courage — nor can the ex-
istence of extended things be inferred from those feelings
by any rules of reasoning ; so that the feelings we have
by touch, can neither explain how we get the notion,
nor how we come by the belief of extended things.

What hath imposed upon philosophers in this matter
is, that the feelings of touch, which suggest primary
qualities, have no names, nor are they ever reflected
upon. They pass through the mind instantaneously,

SEC. V.] THE PHILOSOPHY OP REID. 143

and serve only to introduce the notion and belief of ex-
ternal things, which, by our constitution, are connected
with them. They are natural signs, and the mind im-
mediately passes to the thing signified, without making
the least reflection upon the sign, or observing that there
was any such thing. Hence it hath always been taken
for granted, that the ideas of extension, figure, and mo-
tion, are ideas of sensation, which enter into the mind
by the sense of touch, in the same manner as the sensa-
tions of sound and smell do by the ear and nose. The
sensations of touch are so connected, by our constitution,
with the notions of extension, figure, and motion, that
philosophers have mistaken the one for the other, and
never have been able to discern that they were not only
distinct things, but altogether unlike. However, if we
will reason distinctly upon this subject, we ought to give
names to those feelings of touch ; we must accustom
ourselves to attend to them, and to reflect upon them,
that we may be able to disjoin them from, and to compare
them with, the qualities signified or suggested by them.

The habit of doing this is not to be attained without
pains and practice ; and till a man hath acquired this
habit, it will be impossible for him to think distinctly,
or to judge right, upon this subject.

Let a man press his hand against the table — he feels
it hard. But what is the meaning of this ? — The mean-
ing undoubtedly is, that he hath a certain feeling of
touch, from which he concludes, without any reasoning,
or comparing ideas, that there is something external
really existing, whose parts stick so firmly together,
that they cannot be displaced without considerable force.

There is here a feeling, and a conclusion drawn from
it, or some way suggested by it. In order to compare
these, we must view them separately, and then consider
by what tie they are connected, and wherein they resem-
ble one another. The hardness of the table is the con-
clusion, the feeling is the medium by which we are led

144 THE PHILOSOPHY OF REID. [Cn. V,

to that conclusion. Let a man attend distinctly to this
medium, and to the conclusion, and he will perceive
them to be as unlike as any two things in nature. The
one is a sensation of the mind, which can have no ex-
istence but in a sentient being ; nor can it exist one
moment longer than it is felt ; the other is in the table,
and we conclude, without any difficulty, that it was in
the table before it was felt, and continues after the feel-
ing is over. The one implies no kind of extension, nor
parts, nor cohesion ; the other implies all these. Both,
indeed, admit of degrees, and .the feeling, beyond a cer-
tain degree, is a species of pain ; but adamantine hard-
ness does not imply the least pain.

And as the feeling hath no similitude to hardness, so
neither can our reason perceive the least tie or connec-
tion between them ; nor will the logician ever be able to
shew a reason why we should conclude hardness from
this feeling, rather than softness, or any other quality
whatsoever. But, in reality, all mankind are led by
their constitution to conclude hardness from this feeling.

The sensation of heat, and the sensation we have by
pressing a hard body, are equally feelings ; nor can we,
by reasoning, draw any conclusion from the one but
what may be drawn from the other ; but, by our consti-
tution, we conclude from the first an obscure or occult
quality, of which we have only this relative conception,
that it is something adapted to raise in us the sensation
of heat ; from the second, we conclude a quality of
which we have a clear and distinct conception — to wit,
the hardness of the body.

Section VI.

OF EXTENSION.

To put this matter in another light, it may be proper
to try, whether from sensation alone we can collect any

SEC VI.] THE PHILOSOPHY OF REID. 145

notion of extension, figure, motion, and space. I take
it for granted, that a blind man hath the s'ame notions
of extension, figure, and motion, as a man that sees ;
that Dr. Saunderson had the same notion of a cone, a
cylinder, and a sphere, and of the motions and distances
of the heavenly bodies, as Sir Isaac Newton.

As sight, therefore, is not necessary for our acquiring
those notions, we shall leave it out altogether in our
inquiry into the first origin of them ; and shall suppose
a blind man, by some strange distemper, to have lost all
the experience, and habits, and notions he had got by
touch ; not to have the least conception of the existence,
figure, dimensions, or extension, either of his own body,
or of any other ; but to have all his knowledge of exter-
nal things to acquire anew, by means of sensation, and
the power of reason, which we suppose to remain entire.

We shall, first, suppose his body fixed immovably in
one place, and that he can only have the feelings of
touch, by the application of other bodies to it. Suppose
him first to be pricked wrth a pin — this will, no doubt,
give a smart sensation: he feels pain ; but what can he
infer from it ? Nothing, surely, with regard to the ex-
istence or figure of a pin. He can infer nothing from
this species of pain, which he may not as well infer from
the gout or sciatica. Common sense may lead him to
think that this pain has a cause ; but whether this cause
is body or spirit, extended or unextended, figured or not
figured, he cannot possibly, from any principles he is
supposed to have, form the least conjecture. Having
had formerly no notion of body or of extension, the
prick of a pin can give him none.

Suppose, next, a body not pointed, but blunt, is ap-
plied to his body with a force gradually increased until
it bruises him. What has he got by this, but another
sensation or train of sensations, from which he is able to
conclude as little as from the former? A scirrhous
tumour in any inward part of the body, by pressing upon

146 THE PHILOSOPHY OF REID. [Cn. V.

the adjacent parts, may give the same kind of sensation
as the pressure of an external body, without conveying
any notion but that of pain, which, surely, hath no re-
semblance to extension.

Suppose, thirdly, that the body applied to him touches
a larger or a lesser part of his body. Can this give him
any notion of its extension or dimensions ? To me it
seems impossible that it should, unless he had some
previous notion of the dimensions and figure of his own
body, to serve him as a measure. When my two hands
touch the extremities of a body, if I know them to be a
foot asunder, I easily collect that the body is a foot
long ; and, if I know them to be five feet asunder, that
it is five feet long ; but, if I know not what the distance
of my hands is, I cannot know the length of the object
they grasp ; and, if I have no previous notion of hands
at all, or of distance between them, I can never get that
notion by their being touched.

Suppose, again, that a body is drawn along his hands
or face, while they are at rest. Can this give him any
notion of space or motion? It no doubt gives a new
feeling ; but how it should convey a notion of space or
motion to one who had none before, I cannot conceive.
The blood moves along the arteries and veins, and this
motion, when violent, is felt : but I imagine no man,
by this feeling, could get the conception of space or
motion, if he had it not before. Such a motion may
give a certain succession of feelings, as the colic may do ;
but no feelings, nor any combination of feelings, can
ever resemble space or motion

Let us next suppose, that he makes some instinctive
effort to move his head or his hand ; but that no motion
follows, either on account of external resistance, or of
palsy. Can this effort convey the notion of space and
motion to one who never had it before? Surely it
cannot.

Last of all, let us suppose that he moves a limb by

SEC. VI.] THE PHILOSOPHY OF REID. 147

instinct, without having had any previous notion of space
or motion. He has here a new sensation, which accom-
panies the flexure of joints, and the swelling of muscles.
But how this sensation can convey into his mind the idea
of space and motion, is still altogether mysterious and
unintelligible. The motions of the heart and lungs are
all performed by the contraction of muscles, yet give no
conception of space or motion. An embryo in the womb
has many such motions, and probably the feelings that
accompany them, without any idea of space or motion.
Upon the whole, it appears that our philosophers
have imposed upon themselves and upon us, in pre-
tending to deduce from sensation the first origin of our
notions of external existences, of space, motion, and ex-
tension,* and all the primary qualities of body — that is,
the qualities whereof we have the most clear and distinct
conception. These qualities do not at all tally with any
system of the human faculties that hath been advanced.
They have no resemblance to any sensation, or to any
operation of our minds ; and, therefore, they cannot be
ideas either of sensation or of reflection. The very con-
ception of them is irreconcilable to the principles of all
our philosophic systems of the understanding. The be-
lief of them is no less so.

* That the notion of Space is a necessary condition of thought,
and that, as such, it is impossible to derive it from experience, has
been cogently demonstrated by Kant. But that we may not,
through sense, have empirically an immediate perception of some-
thing extended, I have yet seen no valid reason to doubt. The
a priori Conception does not exclude the a posteriori Perception ;
and this latter cannot be rejected without belying the evidence of
consciousness, which assures us that we are immediately cognizant,
not only of a Self but of a Not Self, not only of mind but of matter:
and matter cannot be immediately known — that is known as existing
— except as something extended. In this, however, I venture a
step beyond Reid and Stewart, no less than beyond Kant; though I am
convinced that the philosophy of the two former tended to this con-
clusion, which is, in fact, that of the common sense of mankind, — H,

148 THE PHILOSOPHY OF REID. iCu. V.

Section VIL

OF THE EXISTENCE OF A MATERIAL WORLD.

It is beyond our power to say when, or in what order,
we came by our notions of these qualities. When we
trace the operations of our minds as far back as memory
and reflection can carry us, we find them already in pos-
session of our imagination and belief, and quite familiar
to the mind : but how they came first into its acquaint-
ance, or what has given them so strong a hold of our be-
lief, and what regard they deserve, are, no doubt, very
important questions in the philosophy of human nature.

Shall we, with the Bishop of Cloyne, serve them with
a quo warranio, and have them tried at the bar of philos-
ophy, upon the statute of the ideal system ? Indeed, in
this trial they seem to have come off very pitifully ; for,
although they had very able counsel, learned in the law
— viz., Des Cartes, Malebranche, and Locke, who said
everything they could for their clients — the Bishop of
Cloyne, believing them to be aiders and abetters of
heresy and schism, prosecuted them with great vigour,
fully answered all that had been pleaded in their defence,
and silenced their ablest advocates, who seem, for half a
century past, to decline the argument, and to trust to
the favour of the jury rather than to the strength of their
pleadings.

Thus, the wisdom of philosophy is set in opposition to
the common sense of mankind. The first pretends to de-
monstrate, a priori, that there can be no such thing as a
material world; that sun, moon, stars, and earth, vegeta-
ble and animal bodies, are, and can be nothing else, but
sensations in the mind, or images of those sensations in
the memory and imagination; that, like pain and joy,
they can have no existence when they are not thought
of. The last can conceive no otherwise of this opinion,
than as a kind of metaphysical lunacy, and concludes

SEC. VII.] THE PHILOSOPHY OF REID. 149

that too much learning is apt to make men mad; and
that the man who seriously entertains this belief, though
in other respects he may be a very good man, as a man
may be who believes that he is made of glass; yet, surely
he hath a soft place in his understanding, and hath been
hurt by much thinking.

This opposition betwixt philosophy and common
sense, is apt to have a very unhappy influence upon the
philosopher himself. He sees human nature in an odd,
unamiable, and mortifying light He considers himself,
and the rest of his species, as born under a necessity of
believing ten thousand absurdities and contradictions,
and endowed with such a pittance of reason as is just
sufficient to make this unhappy discovery: and this is all
the fruit of his profound speculations. Such notions of
human nature tend to slacken every nerve of the soul, to
put every noble purpose and sentiment out of counte-
nance, and spread a melancholy gloom over the whole
face of things.

If this is wisdom, let me be deluded with the vulgar.
I find something within me that recoils against it, and
inspires more reverent sentiments of the human kind,
and of the universal administration. Common Sense
and Reason * have both one author; that Almighty Au-
thor in all whose other works we observe a consistency,
uniformity, and beauty which charm and delight the un-
derstanding: there must, therefore, be some order and
consistency in the human faculties, as well as in other
parts of his workmanship. A man that thinks reverent-
ly of his own kind, and esteems true wisdom and philos-
ophy, will not be fond, nay, will be very suspicious, of
such strange and paradoxical opinions. If they are
false, they disgrace philosophy; and, if they are true,

* The reader will again notice this and the other instances which
follow, of the inaccuracy of Reid's language in his earlier work, con-
stituting, as different, Reason and Common Sense. — H.

150 THE PHILOSOPHY OF REID. [CH. V.

they degrade the human species, and make us justly
ashamed of our frame.

To what purpose is it for philosophy to decide against
common sense in this or any other matter ? The belief
of a material world is older, and of more authority, than
any principles of philosophy. It declines the tribunal
of reason,* and laughs at all the artillery of the logician.
It retains its sovereign authority in spite of all the edicts
of philosophy, and reason itself must stoop to its orders.
Even those philosophers who have disowned the author-
ity of our notions of an external material world, confess
that they find themselves under a necessity of submitting
to their power.

Methinks, therefore, it were better to make a virtue of
necessity; and, since we cannot get rid of the vulgar
notion and belief of an external world, to reconcile our
reason to it as well as we can; for, if Reason* should
stomach and fret ever so much at this yoke, she cannot
throw it off; if she will not be the servant of Common
Sense, she must be her slave.

In order, therefore, to reconcile Reason to Common
Sense* in this matter, I beg leave to offer to the consid-
eration of philosophers these two observations. First,
That, in all this debate about the existence of a material
world, it hath been taken for granted on both sides, that
this same material world, if any such there be, must be
the express image of our sensations ; that we can have
no conception of any material thing which is not like
some sensation in our minds; and particularly that the sen-
sations of touch are images of extension, hardness, figure,
and motion. Every argument brought against the exist-
ence of a material world, either by the Bishop of Cloyne, or
by the author of the ft Treatise of Human Nature," sup-
poseth this. If this is true, their arguments are conclu-
sive and unanswerable; but, on the other hand, if it is

* See last note.— H.

SEC. VII.] THE PHILOSOPHY OF REID 15!

not true, there is no shadow of argument left. Have
those philosophers, then, given any solid proof of this
hypothesis, upon which the whole weight of so strange
a system rests. No. They have not so much as at-
tempted to do it. But, because ancient and modern
philosophers have agreed in this opinion, they have taken
it for granted. But let us, as becomes philosophers, lay
aside authority; we need not, surely, consult Aristotle or
Locke, to know whether pain be like the point of a
sword. I have as clear a conception of extension, hard-
ness, and motion, as I have of the point of a sword; and,
with some pains and practice, I can form as clear a no-
tion of the other sensations of touch as I have of pain.
When I do so, and compare them together, it appears to
me clear as daylight, that the former are not of kin to
the latter, nor resemble them in any one feature. They
are as unlike, yea as certainly and manifestly unlike, as
pain is to the point of a sword. It may be true, that
those sensations first introduced the material world to
our acquaintance; it may be true, that it seldom or never
appears without their company; but, for all that, they
are as unlike as the passion of anger is to those features
of the countenance which attend it.

So that, in the sentence those philosophers have passed
against the material world, there is an error persona.
Their proof touches not matter, or any of its qualities;
but strikes directly against an idol of their own imagina-
tion, a material world made of ideas and sensations,
which never had nor can have an existence.

Secondly, The very existence of our conceptions of
extension, figure and motion, since they are neither ideas
of sensation nor reflection, overturns the whole ideal
system, by which the material world hath been tried
and condemned;* so that there hath been likewise in
this sentence an error juris.

* It only overturns that Idealism founded on the clumsy hypothe-
sis of ideas being something different, both from the reality they

152 THE PHILOSOPHY OF REID, [CH. V.

Itis a very fine and a just observation of Locke, that, as
no human art can create a single particle of matter, and
the whole extent of our power over the material world
consists in compounding, combining, and disjoining
the matter made to our hands; so, in the world of
thought, the materials are all made by nature, and can
only be variously combined and disjoined by us. So
that it is impossible for reason or prejudice, true or false
philosophy, to produce one simple notion or conception,
which is not the work of nature, and the result of our
constitution. The conception of extension, motion, and
the other attributes of matter, cannot be the effect of
error or prejudice; it must be the work of nature. And
the power or faculty by which we acquire those concep-
tions, must be something different from any power of the
human mind that hath been explained, since it is neither
sensation nor reflection.

This I would, therefore, humbly propose, as an exper-
imentum cruets, by which the ideal system must stand or
fall; and it brings the matter to a short issue: Extension,
figure, motion, may, any one or all of them, be taken
for the subject of this experiment. Either they are ideas
of sensation, or they are not. If any one of them can
be shewn to be an idea of sensation, or to have the least
resemblance to any sensation, I lay my hand upon my
mouth, and give up all pretense to reconcile reason
to common sense in this matter, and must suffer the
ideal scepticism to triumph. But if, on the other hand,
they are not ideas of sensation, nor like to any sen-
sation, then the ideal system is a rope of sand, and
all the laboured arguments of the sceptical philosophy
against a material world, and against the existence of

represent, and from the mind contemplating their representation, and
which, also, derives all such ideas from without. This doctrine
may subvert the Idealism of Berkeley, but it even supplies a basis
for an Idealism like that of Fichte.— H.

SEC. VII.] THE PHILOSOPHY OF REID. 153

everything but impressions and ideas, proceed upon a
false hypothesis.

If our philosophy concerning the mind be so lame
with regard to the origin of our notions of the clearest,
most simple, and most familiar objects of thought, and
the powers from which they are derived, can we expect
that it should be more perfect in the account it gives of
the origin of our opinions and belief? We have seen
already some instances of its imperfection in this respect:
and, perhaps, that same nature which hath given us the
power to conceive things altogether unlike to any of our
sensations, or to any operation of our minds, hath like-
wise provided for our belief of them, by some part of our
constitution hitherto not explained.

Bishop Berkeley hath proved, beyond the possibility
of reply, that we cannot by reasoning infer the existence
of matter from our sensations ; and the author of the
"Treatise of Human Nature" hath proved no less clearly,
that we cannot by reasoning infer the existence of our
own or other minds from our sensations. But are we to
admit nothing but what can be proved by reasoning?
Then we must be sceptics indeed, and believe nothing
at all. The author of the "Treatise of Human Nature"
appears to me to be but a half-sceptic. He hath not
followed his principles so far as they lead him; but, after
having, with unparalleled intrepidity and success, com-
bated vulgar prejudices, when he had but one blow to
strike, his courage fails him, he fairly lays down his arms,
and yields himself a captive to the most common of all
vulgar prejudices — I mean the belief of the existence of
his own impressions and ideas.

I beg, therefore, to have the honour of making an ad-
dition to the sceptical system, without which I conceive
it cannot hang together. I affirm, that the belief of the
existence of impressions and ideas, is as little supported
by reason, as that of the existence of minds and bodies.
No man ever did or could offer any reason for this belief.

1$4 THE PHILOSOPHY OF REID. (Cn. V.

Des Cartes took it for granted, that he thought, and had
sensations and ideas; so have all his followers done.
Even the hero of scepticism hath yielded this point, I
crave leave to say, weakly and imprudently. I say so,
because I am persuaded that there is no principle of his
philosophy that obliged him to make this concession.
And what is there in impressions and ideas so formida-
ble, that this all-conquering philosophy, after triumph-
ing over every other existence, should pay homage to
them? Besides, the concession is dangerous: for belief
is of such a nature, that, if you leave any root, it will
spread; and you may more easily pull it up altogether,
than say, Hitherto shalt thou go and no further: the ex-
istence of impressions and ideas I give up to thee; but
see thou pretend to nothing more. A thorough and con-
sistent sceptic will never, therefore, yield this point; and
while he holds it, you can never oblige him to yield any-
thing else.

To such a sceptic I have nothing to say; but of the
semi-sceptics, I should beg to know, why they believe
the existence of their impressions and ideas. The true
reason I take to be, because they cannot help it ; and
the same reason will lead them to believe many other
things.

All reasoning must be from first principles ; and for
first principles no other reason can be given but this,
that, by the constitution of our nature, we are under
a necessity of assenting to them. Such principles are
parts of our constitution, no less than the power of think-
ing: reason can neither make nor destroy them; nor can
it do anything without them: it is like a telescope, which
may help a man to see farther, who hath eyes; but, with-
out eyes, a telescope shews nothing at all. A mathema-
tician cannot prove the truth of his axioms, nor can he
prove anything, unless he takes them for granted. We
cannot prove the existence of our minds, nor even of our
thoughts and sensations. A historian, or a witness, can

SEC. VII.] THE PHILOSOPHY OF REID. 15$

prove nothing, unless it is taken for granted that the
memory and senses may be trusted. A natural philoso-
pher can prove nothing, unless it is taken for granted
that the course of nature is steady and uniform.

How or when I got such first principles, upon which I
build all my reasoning, I know not; for I had them be-
fore I can remember : but I am sure they are parts of
my constitution, and that I cannot throw them off. That
our thoughts and sensations must have a subject, which
we call ourself, is not therefore an opinion got by reason-
ing, but a natural principle. That our sensations of
touch indicate something external, extended, figured,
hard or soft, is not a deduction of reason, but a natural
principle. The belief of it, and the very conception of
it, are equally parts of our constitution. If we are de-
ceived in it, we are deceived by Him that made us, and
there is no remedy. *

I do not mean to affirm, that the sensations of touch
do, from the very first, suggest the same notions of body
and its qualities which they do when we are grown up.
Perhaps Nature is frugal in this, as in her other opera-
tions. The passion of love, with all its concomitant

* The philosophers who have most loudly appealed to the veraci-
ty of God, and the natural conviction of mankind, in refutation of
certain obnoxious conclusions, have too often silently contradicted
that veracity and those convictions, when opposed to certain favour-
ite opinions. But it is evident that such authority is either good for
all, or good for nothing. Our natural consciousness assures us (and
the_/brfof that assurance is admitted by philosophers of all opin-
ions) that we have an immediate knowledge of the very things them-
selves of an external and extended world; and, on the ground of this
knowledge alone, is the belief of mankind founded, that such a
world really exists. Reid ought, therefore, either to have given up
his doctrine of the mere suggestion of extension, &c., as subjective
notions, on the occasion of sensation, or not to appeal to the Divine
veracity, and the common sense of mankind, in favour of conclu-
sions of which that doctrine subverts the foundation. In this incon-
sistency, Reid has, however, besides Des Cartes, many distinguished
copartners. — H.

156 THE PHILOSOPHY OF REID. |CH. V.

sentiments and desires, is naturally suggested by the
perception of beauty in the other sex; yet the same per-
ception does not suggest the tender passion till a certain
period of life. A blow given to an infant, raises grief
and lamentation; but when he grows up, it as naturally
stirs resentment, and prompts him to resistance. Per-
haps a child in the womb, or for some short period of
its existence, is merely a sentient being; the faculties by
which it perceives an external world, by which it reflects
on its own thoughts, and existence, and relation to other
things, as well as its reasoning and moral faculties, un-
fold themselves by degrees; so that it is inspired with the
various principles of common sense, as with the passions
of love and resentment, when it has occasion for them.

Section VIII.

OF THE SYSTEMS OF PHILOSOPHERS CONCERNING THE SENSES.

All the systems of philosophers about our senses and
their objects have split upon this rock, of not distin-
guishing properly sensations which can have no existence
but when they are felt, from the things suggested by
them. Aristotle — with as distinguishing a head as ever
applied to philosophical disquisitions — confounds these
two; and makes every sensation to be the form, without
the matter, of the thing perceived by it. As the impres-
sion of a seal upon wax has the form of the seal but
nothing of the matter of it, so he conceived our sensa-
tions to be impressions upon the mind, which bear the
image, likeness, or form of the external thing perceived,
without the matter of it. • Colour, sound, and smell, as
well as extension, figure, and hardness, are, according to
him, various forms of matter: our sensations are the same
forms imprinted on the mind, and perceived in its own
intellect. It is evident from this, that Aristotle made no
distinction between primary and secondary qualities of

SEC. VlII.j THE PHILOSOPHY OF REID. 157

bodies, although that distinction was made by Democri-
tus, Epicurus, and others of the ancients.

Des Cartes, Malebranche, and Locke, revived the dis-
tinction between primary and secondary qualities ; but
they made the secondary qualities mere sensations, and
the primary ones resemblances of our sensations. They
maintained that colour, sound, and heat, are not any-
thing in bodies, but sensations of the mind ; at the same
time, they acknowledged some particular texture or
modification of the body to be the cause or occasion of
those sensations ; but to this modification they gave no
name. Whereas, by the vulgar, the names of colour,
heat, and sound, are but rarely applied to the sensations,
and most commonly to those unknown causes of them,
as hath been already explained. The constitution of our
nature leads us rather to attend to the things signified by
the sensation than to the sensation itself, and to give a
name to the former rather than to the latter. Thus
we see, that, with regard to secondary qualities, these
philosophers thought with the vulgar, and with common
sense. Their paradoxes were only an abuse of words ;
for when they maintain, as an important modern dis-
covery, that there is no heat in the fire, they mean no
more, than that the fire does not feel heat, which every
one knew before.

With regard to primary qualities, these philosophers
erred more grossly. They indeed believed the existence
of those qualities ; but they did not at all attend to the
sensations that suggest them, which, having no names,
have been as little considered as if they had no existence.
They were aware that figure, extension, and hardness, are
perceived by means of sensations of touch ; whence they
rashly concluded, that these sensations must be images
and resemblances of figure, extension, and hardness.

The received hypothesis of ideas naturally led them to
this conclusion: and indeed cannot consist with any
other ; for, according to that hypothesis, external things

158 THE PHILOSOPHY OF REID. [Cn. V.

must be perceived by means of images of them in the
mind ; and what can those images of external things in
the mind be, but the sensations by which we perceive
them ?

This, however, was to draw a conclusion from a hy-
pothesis against fact. We need not have recourse to any
hypothesis to know what our sensations are, or what
they are like. By a proper degree of reflection and at-
tention we may understand them perfectly, and be as
certain that they are not like any quality of body, as we
can be, that the toothache is not like a triangle. How
a sensation should instantly make us conceive and be-
lieve the existence of an external thing altogether un-
like to it, I do not pretend to know; and when I say that
the one suggests the other, I mean not to explain the
manner of their connection, but to express a fact, which
every one may be conscious of — namely, that, by a law
of our nature, such a conception and belief constantly
and immediately follow the sensation.

Bishop Berkeley gave new light to this subject, by
shewing, that the qualities of an inanimate thing, such
as matter is conceived to be, cannot resemble any sen-
sation; that it is impossible to conceive anything like
the sensations of our minds, but the sensations of other
minds. Every one that attends properly to his sensa-
tions must assent to this : yet it had escaped all the philos-
ophers that came before Berkeley; it had escaped even
the ingenious Locke, who had so much practised reflec-
tion on the operations of his own mind. So difficult it
is to attend properly even to our own feelings. They
are so accustomed to pass through the mind unobserved
and instantly to make way for that which nature intended
them to signify, that it is extremely difficult to stop, and
survey them ; and when we think we have acquired this
power, perhaps the mind still fluctuates between the
sensation and its associated quality, so that they mix to-
gether, and present something to the imagination that is

Sue. VIII.] THE PHILOSOPHY OF REID. 159

compounded of both. Thus, in a globe or cylinder,
whose opposite sides are quite unlike in colour, if you
turn it slowly, the colours are perfectly distinguishable
and their dissimilitude is manifest; but if it is turned
fast, they lose their distinction, and seem to be of one
and the same colour.

No succession can be more quick than that of tangi-
ble qualities to the sensations with which nature has as-
sociated them ; but when one has once acquired the art
of making them separate and distinct objects of thought,
he will then clearly perceive that the maxim of Bishop
Berkeley, above-mentioned, is self-evident ; and that the
features of the face are not more unlike to a passion of
the mind which they indicate, than the sensations of touch
are to the primary qualities of body.

But let us observe what use the Bishop makes of this
important discovery. Why, he concludes, that we can
have no conception of an inanimate substance, such as
matter is conceived to be, or of any of its qualities ;
and that there is the strongest ground to believe that
there is no existence in nature but minds, sensations, and
ideas ; if there is any other kind of existence, it must be
what we neither have nor can have any conception of.
But how does this follow? Why, thus: We can have
no conception of anything but what resembles some sen-
sation or idea in our minds ; but the sensations and ideas
in our minds can resemble nothing but the sensations
and ideas in other minds ; therefore, the conclusion is
evident. This argument, we see, leans upon two propo-
sitions. The last of them the ingenious author hath,
indeed, made evident to all that understand his reason-
ing, and can attend to their own sensations: but the first
proposition he never attempts to prove ; it is taken from
the doctrine of ideas, which hath been so universally re-
ceived by philosophers, that it was thought to need no
proof.

We may here again observe, that this acute writer ar-

160 THE PHILOSOPHY OF REID. [Cn. V.

gues from a hypothesis against fact, and against the com-
mon sense of mankind. That we can have no concep-
tion of anything, unless there is some impression, sensa-
tion, or idea, in our minds which resembles it, is indeed
an opinion which hath been very generally received among
philosophers ; but it is neither self-evident, nor hath it
been clearly proved ; and therefore it hath been more
reasonable to call in question this doctrine of philoso-
phers, than to discard the material world, and by that
means expose philosophy to the ridicule of all men who
will not offer up common sense as a sacrifice to meta-
physics.

We ought, however, to do this justice both to the
Bishop of Cloyne and to the author of the " Treatise of
Human Nature," to acknowledge, that their conclusions
are justly drawn from the doctrine of ideas, which has
been so universally received. On the other hand, from
the character of Bishop Berkeley, and of his predecessors,
Des Cartes, Locke, and Malebranche, we may venture to
say, that, if they had seen all the consequences of this
doctrine, as clearly as the author before mentioned did,
they would have suspected it vehemently, and examined
it more carefully than they appear to have done.

The theory of ideas, like the Trojan horse, had a
specious appearance both of innocence and beauty ; but
if those philosophers had known that it carried in its
belly death and destruction to all science and common
sense, they would not have broken down their walls to
give it admittance.

That we have clear and distinct conceptions of exten-
sion, figure, motion, and other attributes of body, which
are neither sensations, nor like any sensation, is a fact of
which we may be as certain as that we have sensations.
And that all mankind have a fixed belief of an external
material world — a belief which is neither got by reason-
ing nor education, and a belief which we cannot shake
off, even when we seem to have strong arguments against

SEC. VIII.] THE PHILOSOPHY OF REID. l6l

it and no shadow of argument for it — is likewise a fact,
for which we have all the evidence that the nature of the
thing admits. These facts are phsenomena of human
nature, from which we may justly argue against any
hypothesis, however generally received. But to argue
from a hypothesis against facts, is contrary to the rules
of true philosophy.

162 THE PHILOSOPHY OF REID. [Ca. VI.

CHAPTER VI.

OF SEEING.

Section I.

THE EXCELLENCE AND DIGNITY OF THIS FACULTY.

THE advances made in the knowledge of optics in the
last age and in the present, and chiefly the discoveries of
Sir Isaac Newton, do honour, not to philosophy only,
but to human nature. Such discoveries ought for ever to
put to shame the ignoble attempts of our modern sceptics
to depreciate the human understanding, and to dispirit
men in the search of truth, by representing the human
faculties as fit for nothing but to lead us into absurdities
and contradictions.

Of the faculties called the five senses, sight is without
doubt the noblest. The rays of light, which minister to
this sense, and of which, without it, we could never have
had the least conception, are the most wonderful and
astonishing part of the inanimate creation. We must be
satisfied of this, if we consider their extreme minuteness;
their inconceivable velocity; the regular variety of colours
which they exhibit; the invariable laws according to which
they are acted upon by other bodies, in their reflections,
inflections, and refractions, without the least change of
their original properties ; and the facility with which
they pervade bodies of great density and of the closest
texture, without resistance, without crowding or disturb-
ing one another, without giving the least sensible impulse
to the lightest bodies.

The structure of the eye, and of all its appurtenances,
the admirable contrivances of nature for performing all

SEC. I.] THE PHILOSOPHY OF REID. 163

its various external and internal motions, and the variety
in the eyes of different animals, suited to their several
natures and ways of life, clearly demonstrate this organ
to be a masterpiece of Nature's work. And he must be
very ignorant of what hath been discovered about it, or
have a very strange cast of understanding, who can seri-
ously doubt whether or not the rays of light and the eye
were made for one another, with consummate wisdom,
and perfect skill in optics.

If we shall suppose an order of beings, endued with
every human faculty but that of sight, how incredible
would it appear to such beings, accustomed only to the
slow informations of touch, that, by the addition of an
organ consisting of a ball and socket of an inch diam-
eter, they might be enabled, in an instant of time,
without changing their place to perceive the dis-
position of a whole army or the order of a battle, the
figure of a magnificent palace or all the variety of a
landscape ! If a man were by feeling to find out the fig-
ure of the peak of Teneriffe, or even of St. Peter's Church
at Rome, it would be the work of a lifetime.

It would appear still more incredible to such beings
as we have supposed, if they were informed of the dis-
coveries which may be made by this little organ in
things far beyond the reach of any other sense : that by
means of it we can find our way in the pathless ocean ;
that we can traverse the globe of the earth, determine
its figure and dimensions, and delineate every region of
it; — yea, that we can measure the planetary orbs, and
make discoveries in the sphere of the fixed stars.

Would it not appear still more astonishing to such
beings, if they should be farther informed, that, by means
of this same organ, we can perceive the tempers and dis-
positions, the passions and affections, of our fellow-
creatures, even when they want most to conceal them ?
that, when the tongue is taught most artfully to lie and
dissemble, the hypocrisy should appear in the counte-

164 THE PHILOSOPHY OF REID. [CH. VI.

nance to a discerning eye ? — and that, by this organ, we
can often perceive what is straight and what is crooked
in the mind as well as in the body ? How many myste-
rious things must a blind man believe, if he will give
credit to the relations of those that see ? Surely he
needs as strong a faith as is required of a good Christian.
It is not therefore without reason that the faculty of
seeing is looked upon, not only as more noble than
the other senses, but as having something in it of a na-
ture superior to sensation. The evidence of reason is
called seeing, not feeling, smelling, or tasting. Yea, we
are wont to express the manner of the Divine knowledge
by seeing, as that kind of knowledge which is most per-
fect in us.

Section II.

SIGHT DISCOVERS ALMOST NOTHING WHICH THE BLIND MAY
NOT COMPREHEND THE REASON OF THIS.

Notwithstanding what hath been said of the dignity
and superior nature of this faculty, it is worthy of our
observation, that there is very little of the knowledge
acquired by sight, that may not be communicated to a
man born blind. One who never saw the light, may be
learned and knowing in every science, even in optics ;
and may make discoveries in every branch of philosophy.
He may understand as much as another man, not only
of the order, distances, and motions of the heavenly
bodies ; but of the nature of light, and of the laws of
the reflection and refraction of its rays. He may un-
derstand distinctly how those laws produce the phaenom-
ena of the rainbow, the prism, the camera obscura,
and the magic lanthorn, and all the powers of the micro-
scope and telescope. This is a fact sufficiently attested
by experience.

In order to perceive the reason of it, we must distin-
guish the appearance that objects make to the eye, from

SEC. II.] THE PHILOSOPHY OF REID. 165

the things suggested by that appearance ; and again, in
the visible appearance of objects, we must distinguish
the appearance of colour from the appearance of exten-
sion, figure, and motion. First, then, as to the visible
appearance of the figure, and motion, and extension of
bodies, I conceive that a man born blind may have a
distinct notion, if not of the very things, at least of some-
thing extremely like to them. May not a blind man be
made to conceive that a body moving directly from the
eye, or directly towards it, may appear to be at rest ? and
that the same motion may appear quicker or slower, ac-
cording as it is nearer to the eye or farther off, more
direct or more oblique ? May he not be made to con-
ceive, that a plain surface, in a certain position, may ap-
pear as a straight line, and vary its visible figure, as its
position, or the position of the eye, is varied? — that
a circle seen obliquely will appear an ellipse ; and a
square, a rhombus, or an oblong rectangle ? Dr. Saun-
derson understood the projection of the sphere, and the
common rules of perspective ; and if he did, he must
have understood all that I have mentioned. If there
were any doubt of Dr. Saunderson's understanding these
things, I could mention my having heard him say in
conversation, that he found great difficulty in under-
standing Dr. Halley's demonstration of that proposition,
that the angles made by the circles of the sphere, are
equal to the angles made by their representatives in the
stereographic projection ; but, said he, when I laid aside
that demonstration, and considered the proposition in
my own way, I saw clearly that it must be true. Another
gentleman, of undoubted credit and judgment in these
matters, who had part in this conversation, remembers
it distinctly.

As to the appearance of colour, a blind man must be
more at a loss ; because he hath no perception that resem-
bles it. Yet he may, by a kind of analogy, in part supply
this defect. To those who see, a scarlet colour signifies

r66 THE PHILOSOPHY OF REID. [C». VI.

an unknown quality in bodies, that makes to the eye an
appearance which they are well acquainted with and
have often observed — to a blind man, it signifies an un-
known quality, that makes to the eye an appearance
which he is unacquainted with. But he can conceive
the eye to be variously affected by different colours, as
the nose is by different smells, or the ear by different
sounds. Thus he can. conceive scarlet to differ from
blue, as the sound of a trumpet does from that of a drum;
or as the smell of an orange differs from that of an ap-
ple. It is impossible to know whether a scarlet colour
has the same appearance to me which it hath to another
man ; and, if the appearance of it to different persons
differed as much as colour does from sound, they might
never be able to discover this difference. Hence it ap-
pears obvious, that a blind man might talk long about
colours distinctly and pertinently; and, if you were to
examine him in the dark about the nature, composition,
and beauty of them, he might be able to answer, so as
not to betray his defect.

We have seen how far a blind man may go in the
knowledge of the appearances which things make to the
eye. As to the things which are suggested by them or
inferred from them, although he could never discover them
of himself, yet he may understand them perfectly by the
information of others. And everything of this kind that
enters into our minds by the eye, may enter into his by
the ear. Thus, for instance, he could never, if left to
the direction of his own faculties, have dreamed of any
such thing as light ; but he can be informed of every-
thing we know about it. He can conceive, as distinctly
as we, the minuteness and velocity of its rays, their vari-
ous degrees of refrangibility and reflexibility, and all the
magical powers and virtues of that wonderful element.
He could never of himself have found out, that there are
such bodies as the sun, moon, and stars ; but he may be
informed of all the noble discoveries of astronomers,

SEC. II.] THE PHILOSOPHY OF REID. 167

about their motions, and the laws of nature by which
they are regulated. Thus, it appears, that there is very
little knowledge got by the eye, which may not be com-
municated by language to those who have no eyes.

If we should suppose that it were as uncommon for
men to see as it is to be born blind, would not the few
who had this rare gift appear as prophets and inspired
teachers to the many ? We conceive inspiration to give
a man no new faculty, but to communicate to him, in a
new way, and by extraordinary means, what the facul-
ties common to mankind can apprehend, and what he
can communicate to others by ordinary means. On the
supposition we have made, sight would appear to the
blind very similar to this ; for the few who had this gift,
could communicate the knowledge acquired by it tc
those who had it not. They could not, indeed, convey
to the blind any distinct notion of the manner in which
they acquired this knowledge. A ball and socket would
seem, to a blind man, in this case, as improper an instru-
ment for acquiring such a variety and extent of know-
ledge, as a dream or a vision. The manner in which a
man who sees, discerns so many things by means of the
eye, is as unintelligible to the blind, as the manner in
which a man may be inspired with knowledge by the
Almighty, is to us. Ought the blind man, therefore,
without examination, to treat all pretences to the gift of
seeing as imposture ? Might he not, if he were candid
and tractable, find reasonable evidence of the reality of
this gift in others, and draw great advantages from it to
himself?

The distinction we have made between the visible ap-
pearances of the objects of sight, and things suggested
by them, is necessary to give us a just notion of the in-
tention of nature in giving us eyes. If we attend duly
to the operation of our mind in the use of this faculty,
we shall perceive that the visible appearance of objects is
hardly ever regarded by us. It is not at all made an

l68 THE PHILOSOPHY OF REID. [Cn. VI.

object of thought or reflection, but serves only as a sign
to introduce to the mind something else, which may be
distinctly conceived by those who never saw.

Thus, the visible appearance of things in my room
varies almost every hour, according as the day is clear
or cloudy, as the sun is in the east, or south, or west,
and as my eye is in one part of the room or in another ;
but I never think of these variations, otherwise than as
signs of morning, noon, or night, of a clear or cloudy
sky. A book or a chair has a different appearance to
the eye, in every different distance and position ; yet we
conceive it to be still the same; and, overlooking the
appearance, we immediately conceive the real figure, dis-
tance, and position of the body, of which its visible or
perspective appearance is a sign and indication.

When I see a man at the distance of ten yards, and
afterwards see him at the distance of a hundred yards,
his visible appearance, in its length, breadth, and all its
linear proportions, is ten times less in the last case than
it is in the first ; yet I do not conceive him one inch di-
minished by thjs diminution of his visible figure. Nay,
I do not in the least attend to this diminution, even when
I draw from it the conclusion of his being at a greater
distance. For such is the subtilty of the mind's opera-
tion in this case, that we draw the conclusion, without
perceiving that ever the premises entered into the mind.
A thousand such instances might be produced, in order
to shew that the visible appearances of objects are in-
tended by nature only as signs or indications ; and that
the mind passes instantly to the things signified, without
making the least reflection upon the sign, or even per-
ceiving that there is any such thing. It is in a way some-
what similar, that the sounds of a language, after it is be-
come familiar, are overlooked, and we attend only to
the things signified by them.

It is therefore a just and important observation of the
Bishop of Cloyne, That the visible appearance of objects

Sec. III.] THE PHILOSOPHY OF REID. 169

is a kind of language used by nature, to inform us of
their distance, magnitude, and figure. And this obser-
vation hath been very happily applied by that ingenious
writer, to the solution of some phenomena in optics,
which had before perplexed the greatest masters in that
science. The same observation is further improved by
the judicious Dr. Smith, in his Optics, for explaining the
apparent figure of the heavens, and the apparent distances
and magnitudes of objects seen with glasses, or by the
naked eye.

Avoiding as much as possible the repetition of what
hath been said by these excellent writers, we shall avail
ourselves of the distinction between the signs that nature
useth in this visual language, and the things signified by
them; and in what remains to be said of sight, shall first
make some observations upon the signs.

Section III.

OF THE VISIBLE APPEARANCES OF OBJECTS.

In this section we must speak of things which are
never made the object of reflection, though almost
every moment presented to the mind. Nature intended
them only for signs ; and in the whole course of life they
are put to no other use. The mind has acquired a con-
firmed and inveterate habit of inattention to them ; for
they no sooner appear, than quick as lightning the thing
signified succeeds, and engrosses all our regard. They
have no name in language ; and, although we are con-
scious of them when they pass through the mind, yet
their passage is so quick and so familiar, that it is abso-
lutely unheeded ; nor do they leave any footsteps of them-
selves, either in the memory or imagination. That this
is the case with regard to the sensations of touch, hath
been shewn in the last chapter ; and it holds no less with
regard to the visible appearances of objects.

170 THE PHILOSOPHY OF REID. [Cn. VI.

I cannot therefore entertain the hope of being intelligi-
ble to those readers who have not, by pains and prac-
tice, acquired the habit of distinguishing the appearance
of objects to the eye, from the judgment which we form
by sight of their colour, distance, magnitude, and figure.

The only profession in life wherein it is necessary to
make this distinction, is that of painting. The painter
hath occasion for an abstraction, with regard to visible
objects, somewhat similar to that which we here require :
and this indeed is the most difficult part of his art. For
it is evident, that, if he could fix in his imagination the
visible appearance of objects, without confounding it with
the things signified by that appearance, it would be as
easy for him to paint from the life, and to give every
figure its proper shading and relief, and its perspective
proportions, as it is to paint from a copy. Perspective,
shading, giving relief, and colouring, are nothing else
but copying the appearance which things make to the
eye. We may therefore borrow some light on the subject
of visible appearance from this art.

Let one look upon any familiar object, such as a book,
at different distances and in different positions : is he not
able to affirm, upon the testimony of his sight, that it is
the same book, the same object, whether seen at the dis-
tance of one foot or of ten, whether in one position or
another ; that the colour is the same, the dimensions the
same, and the figure the same, as far as the eye can
judge ? This surely must be acknowledged. The same
individual object is presented to the mind, only placed
at different distances and in different positions. Let me
ask, in the next place, Whether this object has the same
appearance to the eye in these different distances ? In-
fallibly it hath not. For,

First, However certain our judgment may be that the
colour is the same, it is as certain that it hath not the
same appearance at different distances. There is a cer-
tain degradation of the colour, and a certain confusion

SBC. III.] THE PHILOSOPHY OF REID. 1^1

and indistinctness of the minute parts, which is the natu-
ral consequence of the removal of the object to a greater
distance. Those that are not painters, or critics in
painting, overlook this ; and cannot easily be persuaded,
that the colour of the same object hath a different appear-
ance at the distance of one foot and of ten, in the
shade and in the light But the masters in painting
know how, by the degradation of the colour and the
confusion of the minute parts, figures which are upon
the same canvas, and at the same distance from the eye,
may be made to represent objects which are at the most
unequal distances. They know how to make the ob-
jects appear to be of the same colour, by making their
pictures really of different colours, according to their
distances or shades.

Secondly, Every one who is acquainted with the rules
of perspective, knows that the appearance of the figure
of the book must vary in every different position: yet if
you ask a man that has no notion of perspective, whether
the figure of it does not appear to his eye to be the same
in all its different positions ? he can with a good con-
science affirm that it does. He hath learned to make
allowance for the variety of visible figure arising from
the difference of position, and to draw the proper con-
clusions from it. But he draws these conclusions so
readily and habitually, as to lose sight of the premises :
and therefore where he hath made the same conclusion,
he conceives the visible appearance must have been the
same.

Thirdly, Let us consider the apparent magnitude or
dimensions of the book. Whether I view it at the dis-
tance of one foot or of ten feet, it seems to be about seven
inches long, five broad, and one thick. I can judge of
these dimensions very nearly by the eye, and I judge
them to be the same at both distances. But yet it is
certain, that, at the distance of one foot, its visible length
and breadth is about ten times as great as at the distance of

172 THE PHILOSOPHY OF REID. [Cn. VI.

ten feet ; and consequently its surface is about a hun-
dred times as great This great change of apparent
magnitude is altogether overlooked, and every man is
apt to imagine, that it appears to the eye of the same
size at both distances. Further, when I look at the book,
it seems plainly to have three dimensions, of length,
breadth, and thickness : but it is certain that the visible
appearance hath no more than two, and can be exactly
represented upon a canvas which hath only length and
breadth.

In the last place, does not every man, by sight, per-
ceive the distance of the book from his eye ? Can he
not affirm with certainty, that in one case it is not above
one foot distant, that in another it is ten ? Nevertheless,
it appears certain, that distance from the eye is no im-
mediate object of sight. There are certain things in
the visible appearance, which are signs of distance from
the eye, and from which, as we shall afterwards shew, we
learn by experience to judge of that distance within cer-
tain limits ; but it seems beyond doubt, that a man born
blind, and suddenly made to see, could form no judg-
ment at first of the distance of the objects which he saw.

The young man couched by Cheselden thought, at
first, that everything he saw touched his eye, and learned
only by experience to judge of the distance of visible
objects.

I have entered into this long detail, in order to shew
that the visible appearance of an object is extremely
different from the notion of it which experience teaches
us to form by sight ; and to enable the reader to attend
to the visible appearance of colour, figure, and extension,
in visible things, which is no common object of thought,
but must be carefully attended to by those who would
enter into the philosophy of this sense, or would com-
prehend what shall be said upon it. To a man newly
made to see, the visible appearance of objects would be
the same as to us ; but he would see nothing at all of

SEC. IV.] THE PHILOSOPHY OF REID. 173

their real dimensions, as we do. He could form no
conjecture, by means of his sight only, how many inches
or feet they were in length, breadth, or thickness. He
could perceive little or nothing of their real figure ; nor
could he discern that this was a cube, that a sphere; that
this was a cone, and that a cylinder. His eye could
not inform him that this object was near, and that more
remote. The habit of a man or of a woman, which
appeared to us of one uniform colour, variously folded
and shaded, would present to his eye neither fold nor
shade, but variety of colour. In a word, his eyes,
though ever so perfect, would at first give him almost no
information of things without him. They would indeed
present the same appearances to him as they do to us,
and speak the same language ; but to him it is an un-
known language; and, therefore, he would attend only
to-the signs, without knowing the signification of them,
whereas to us it is a language perfectly familiar ; and,
therefore, we take no notice of the signs, but attend
only to the thing signified by them.

Section IV.

THAT COLOUR IS A QUALITY OF BODIES, NOT A SENSATION
OF THE MIND.

BY colour, all men, who have not been tutored by
modern philosophy, understand, not a sensation of the
mind, which can have no existence when it is not per-
ceived, but a quality or modification of bodies, which
continues to be the same whether it is seen or not.
The scarlet-rose which is before me, is still a scarlet-rose
when I shut my eyes, and was so at midnight when no
eye saw it. The colour remains when the appearance
ceases; it remains the same when the appearance
changes. For when I view this scarlet-rose through
a pair of green spectacles, the appearance is changed;

174 THE PHILOSOPHY OF REID. [CH.V1.

but I do not conceive the colour of the rose changed.
To a person in the jaundice, it has still another appear-
ance; but he is easily convinced that the change is in his
eye, and not in the colour of the object. Every differ-
ent degree of light makes it have a different appearance,
and total darkness takes away all appearance, but makes
not the least change in the colour of the body. We may,
by a variety of optical experiments, change the appear-
ance of figure and magnitude in a body, as well as that
of colour; we may make one body appear to be ten.
But all men believe, that, as a multiplying glass does not
really produce ten guineas out of one, nor a microscope
turn a guinea into a ten-pound piece, so neither does a
coloured glass change the real colour of the object seen
through it, when it changes the appearance of that col-
our.

The common language of mankind shews evidently,
that we ought to distinguish between the colour of a
body, which is conceived to be a fixed and permanent
quality in the body, and the appearance of that colour
to the eye, which may be varied a thousand ways, by a
variation of the light, of the medium, or of the eye it-
self. The permanent colour of the body is the cause
which, by the mediation of various kinds or degrees of
light, and of various transparent bodies interposed, pro-
duces all this variety of appearances. When a coloured
body is presented, there is a certain apparition to the eye,
or to the mind, which we have called the appearance of col-
our. Mr. Locke calls it an idea; and, indeed, it may be
called so with the greatest propriety. This idea can
have no existence but when it is perceived. It is a kind
of thought, and can only be the act of a percipient or
thinking being. By the constitution of our nature, we
are led to conceive this idea as a sign of something ex-
ternal, and are impatient till we learn its meaning. A
thousand experiments for this purpose are made every
day by children, even before they come to the use of rea-

SEC. IV.] THE PHILOSOPHY OF REID. 175

son. They look at things, they handle them, they put
them in various positions, at different distances, and in
different lights. The ideas of sight, by these means,
come to be associated with, and readily to suggest, things
external, and altogether unlike them. In particular,
that idea which we have called the appearance of colour,
suggests the conception and belief of some unknown
quality in the body which occasions the idea; and it is
to this quality, and not to the idea, that we give the
name of colour. * The various colours, although in their
nature equally unknown, are easily distinguished when
we think or speak of them, by being associated with the
ideas which they excite. In like manner, gravity, mag-
netism, and electricity, although all unknown qualities,
are distinguished by their different effects. As we grow
up, the mind acquires a habit of passing so rapidly from
the ideas of sight to the external things suggested by
them, that the ideas are not in the least attended to, nor
have they names given them in common language.

When we think or speak of any particular colour,
however simple the notion may seem to be which is pre-
sented to the imagination, it is really in some sort com-
pounded. It involves an unknown cause and a known
effect. The name of colour belongs indeed to the cause
only, and not to the effect. But as the cause is unknown,
we can form no distinct conception of it but by its rela-
tion to the known effect; and, therefore, both go together
in the imagination, and are so closely united, that they
are mistaken for one simple object of thought.* When I

* It is justly observed by Mr. Stewart, that these passages seem
inconsistent with each other. If in the perception of colour, the sen-
sation and the quality "be so closely united as^o be mistaken for
one simple object of thought," does it not obviously follow, that it
is to this compounded notion the name of colour must in general be
given ? On the other hand, when it is said that the name of colour is
never given to the sensation, but to the quality only, does not this
imply, that every time the word is pronounced, the quality is sepa-
rated from the sensation, even in the imagination of the vulgar ?—H.

176 THE PHILOSOPHY OF REID. [CH.V1.

would conceive those colours of bodies which we call scar-
let and blue — if I conceived them only as unknown quali-
ties, I could perceive no distinction between the one
and the other. I must, therefore, for the sake of dis-
tinction, join to each of them, in my imagination, some
effect or some relation that is peculiar; and the most
obvious distinction is, the appearance which one and the
other makes to the eye. Hence the appearance is, in
the imagination, so closely united with the quality called
a scarlet-colour, that they are apt to be mistaken for one
and the same thing, although they are in reality so differ-
ent and so unlike, that one is an idea in the mind, and the
other is a quality of body.

I conclude, then, that colour is not a sensation, but a
secondary quality of bodies, in the sense we have already
explained; that it is a certain power or virtue in bodies,
that in fair daylight exhibits to the eye an appearance
which is very familiar to us, although it hath no name.
Colour differs from other secondary qualities in this,
that, whereas the name of the quality is sometimes given
to the sensation which indicates it, and is occasioned by
it, we never, as far as I can judge, give the name of col-
our to the sensation, but to the quality only. * Perhaps
the reason of this may be,, that the appearances of the
same colour are so various and changeable, according to
the different modifications of the light, of the medium,
and of the eye, that language could not afford names for
them. And, indeed, they are so little interesting that
they are never attended to, but serve only as signs to in-
troduce the things signified by them. Nor ought it to
appear incredible, that appearances so frequent and so
familiar should have no names, nor be made objects of
thought; since we have before shewn that this is true of
many sensations of touch, which are no less frequent nor
less familiar.

* See note on p. 175.

SEC. V.I THE PHILOSOPHY OF REID. 177

Section V.

AN INFERENCE FROM THE PRECEDING.

From what hath been said about colour, we may in-
fer two things. The first is, that one of the most re-
markable paradoxes of modern philosophy, which hath
been universally esteemed as a great discovery, is, in
reality, when examined to the bottom, nothing else but
an abuse of words. The paradox I mean is, That col-
our is not a quality of bodies, but only an idea in the
mind. We have shewn, that the word colour, as used by
the vulgar, cannot signify an idea in the mind, but a
permanent quality of body. We have shewn that there is
really a permanent quality of body, to which the common
use of this word exactly agrees. Can any stronger proof
be desired, that this quality is that to which the vulgar
give the name of colour? If it should be said, that this
quality, to which we give the name of colour, is unknown
to the vulgar, and, therefore, can have no name among
them, I answer, it is, indeed, known only by its effects
— that is, by its exciting a certain idea in us; but are
there not numberless qualities of bodies which are known
only by their effects, to which, notwithstanding, we find
it necessary to give names ? Medicine alone might fur-
nish us with a hundred instances of this kind. Do not
the words astringent, narcotic, epispastic, caustic, and innu-
merable others, signify qualities of bodies, which are
known only by their effects upon animal bodies ? Why,
then, should not the vulgar give a name to a quality,
whose effects are every moment perceived by their eyes ?
We have all the reason, therefore, that the nature of the
thing admits, to think that the vulgar apply the name of
colour to that quality of bodies which excites in us what
the philosophers call the idea of colour. And that
there is such a quality in bodies, all philosophers.

1 78 THE PHILOSOPHY OF REID. [Ca. VI.

allow, who allow that there is any such thing as body.
Philosophers have thought fit to leave that quality of
bodies which the vulgar call colour, without a name, and
to give the name of colour to the idea or appearance, to
which, as we have shewn, the vulgar give no name, be-
cause they never make it an object of thought or reflec-
tion. Hence it appears, that when philosophers affirm
that colour is not in bodies, but in the mind, and the
vulgar affirm that colour is not in the mind, but is a
quality of bodies, there is no difference between them
about things, but only about the meaning of a word.

The vulgar have undoubted right to give names to
things which they are daily conversant about; and phi-
losophers seem justly chargeable with an abuse of lan-
guage, when they change the meaning of a common
word, without giving warning.

If it is a good rule, to think with philosophers and
speak with the vulgar, it must be right to speak with the
vulgar when we think with them, and not to shock them
by philosophical paradoxes, which, when put into com-
mon language, express only the common sense of man-
kind.

If you ask a man that is no philosopher, what colour
is, or what makes one body appear white, another scar-
let, he cannot tell. He leaves that inquiry to philos-
ophers, and can embrace any hypothesis about it, ex-
cept that of our modern philosophers, who affirm that
colour is not in body, but only in the mind.

Nothing appears more shocking to his apprehension,
than that visible objects should have no colour, and that
colour should be in that which he conceives to be invisi-
ble. Vet this strange paradox is not only universally re-
ceived, but considered as one of the noblest discoveries
of modern philosophy. The ingenious Addison, in the
Spectator, No. 413, speaks thus of it: — "I have here
supposed that my reader is acquainted with that great
modern discovery, which is at present universally ac-

SEC. V.] THE PHILOSOPHY OF REID. 179

knowledged by all the inquirers into natural philoso-
phy— namely, that light and colours, as apprehended
by the imagination, are only ideas in the mind, and not
qualities that have any existence in matter. As this is a
truth which has been proved incontestably by many
modern philosophers, and is, indeed, one of the finest
speculations in that science, if the English reader would
see the notion explained at large, he may find it in the
eighth chapter of the second book of Locke's Essay on
Human Understanding.'"

Mr. Locke and Mr. Addison are writers who have de-
served so well of mankind, that one must feel some un-
easiness in differing from them, and would wish to
ascribe all the merit that is due to a discovery upon
which they put so high a value. And, indeed, it is just
to acknowledge that Locke, and other modern philoso-
phers, on the subject of secondary qualities, have the
merit of distinguishing more accurately than those that
went before them, between the sensation in the mind,
and that constitution or quality of bodies which gives
occasion to the sensation. They have shewn clearly
that these two things are not only distinct, but altogether
unlike: that there is no similitude between the effluvia of
an odorous body and the sensation of smell, or between
the vibrations of a sounding body and the sensation of
sound: that there can be no resemblance between the
feeling of heat, and the constitution of the heated body
which occasions it; or between the appearance which a
coloured body makes to the eye, and the texture of the
body which causes that appearance.

Nor was the merit small of distinguishing these things
accurately; because, however different and unlike in
their nature, they have been always so associated in the
imagination, as to coalesce, as it were, into one two-
faced form, which, from its amphibious nature, could
not justly be appropriated either to body or mind; and,
until it was properly distinguished into its different con-

l8o THE PHILOSOPHY OF REID. [Cn. VI.

stituent parts, it was impossible to assign to either their
just shares in it. None of the ancient philosophers had
made this distinction. * The followers of Democritus and
Epicurus conceived the forms of heat, and sound, and
colour, to be in the mind only; but that our senses fal-
laciously represented them as being in bodies. The
Peripatetics imagined that those forms are really in
bodies; and that the images of them are conveyed to the
mind by our senses, f

The one system made the senses naturally fallacious
and deceitful; the other made the qualities of body to
resemble the sensations of the mind. Nor was it possi-
ble to find a third, without making the distinction we
have mentioned; by which, indeed, the errors of both
these ancient systems are avoided, and we are not left
under the hard necessity of believing, either, on the one
hand, that our sensations are like to the qualities of
body, or, on the other, that God hath given us one faculty
to deceive us, and another to detect the cheat.

We desire, therefore, with pleasure, to do justice to
the doctrine of Locke, and other modern philosophers,
with regard to colour and other secondary qualities, and
to ascribe to it its due merit, while we beg leave to cen-
sure the language in which they have expressed their
doctrine. When they had explained and established the
distinction between the appearance which colour makes
to the eye, and the modification of the coloured body
which, by the laws of nature, causes that appearance,
the question was, whether to give the name of colour to

* This is inaccurate. The distinction was known to the ancient
philosophers; and Democritus was generally allowed to be its author.
This Reid himself elsewhere indeed admits. — (See above, pp. 140
156, 157).— H.

\ These statements concerning both classes of philosophers are
vague and incorrect. The latter, in general, only allowed species
for two senses, Sight and Hearing; few admitted them in Feeling;
and some rejected them altogether. — H.

SEC. VI.] THE PHILOSOPHY OF REID. l8l

the cause or to the effect ? By giving it, as they have
done, to the effect, they set philosophy apparently in
opposition to common sense, and expose it to the ridi-
cule of the vulgar. But had they given the name of
colour to the cause, as they ought to have done, they
must then have affirmed, with the vulgar, that colour is
a quality of bodies; and that there is neither colour nor
anything like it in the mind. Their language, as well
as their sentiments, would have been perfectly agreeable
to the common apprehensions of mankind, and true
Philosophy would have joined hands with Common
Sense. As Locke was no enemy to common sense, it
may be presumed, that, in this instance, as in some
others, he was seduced by some received hypothesis; and
that this was actually the case, will appear in the follow-
ing section.

Section VI.

THAT NONE OF OUR SENSATIONS ARE RESEMBLANCES OF ANT
OF THE QUALITIES OF BODIES.

A second inference is, that, although colour is really
a quality of body, yet it is not represented to the mind
by an idea or sensation that resembles it; on the contrary,
it is suggested by an idea which does not in the least
resemble it. And this inference is applicable, not to
colour only, but to all the qualities of body which we
have examined.

It deserves to be remarked, that, in the analysis we
have hitherto given of the operations of the five senses,
and of the qualities of bodies discovered by them, no in-
stance hath occurred, either of any sensation which re-
sembles any quality of body, or of any quality of body
whose image or resemblance is conveyed to the mind by
means of the senses.

There is no phsenomenon in nature more unaccounta-
ble than the intercourse that is carried on between the

182 THE PHILOSOPHY OF REID. [Cn, VI.

mind and the external world — there is no phenomenon
which philosophical spirits have shewn greater avidity to
pry into, and to resolve. It is agreed by all, that this
intercourse is carried on by means of the senses; and this
satisfies the vulgar curiosity, but not the philosophic.
Philosophers must have some system, some hypothesis,
that shews the manner in which our senses make us
acquainted with external things. All the fertility of
human invention seems to have produced only one hy-
pothesis for this purpose, which, therefore, hath been
universally received; and that is, that the mind, like a
mirror, receives the images of things from without, by
means of the senses: so that their use must be to con-
vey these images into the mind. *

Whether to these images of external things in the
mind, we give the name of sensible forms, or sensible
species, with the Peripatetics, or the name of ideas of sen-
sation, with Locke; or whether, with later philosophers,
we distinguish sensations, which are immediately conveyed
by the senses, from ideas of sensation, which are faint
copies of our sensations retained in the memory and im-
agination ; f these are only differences about words. The
hypothesis I have mentioned is common to all these
different systems.

The necessary and allowed consequence of this hypoth-
esis is, that no material thing, nor any quality of material
things, can be conceived by us, or made an object of thought,
until its image is conveyed to the mind by means of the senses.
We shall examine this hypothesis particularly afterwards,
and at this time only observe, that, in consequence

* This is incorrect, especially as it asserts that the one universal
hypothesis of philosophy was, that "the mind receives the images of
things from without," meaning by these images, immediate or rep-
resentative objects, different from the modifications of the thinking
subject itself. — H.

f He refers to Hume; Aristotle, however, and Hobbes, had pre-
viously called Imagination a decaying sense. — H.

SEC. VI.] THE PHILOSOPHY OF REID. 183

of it, one would naturally expect, that to every quality
and attribute of body we know or can conceive, there
should be a sensation corresponding, which is the image
and resemblance of that quality; and that the sensations
which have no similitude or resemblance to body, or to
any of its qualities, should give us no conception of a
material world, or of anything belonging to it These
things might be expected as the natural consequences of
the hypothesis we have mentioned.

Now, we have considered, in this and the preceding
chapters, Extension, Figure, Solidity, Motion, Hardness,
Roughness, as well as Colour, Heat, and Cold, Sound,
Taste, and Smell. We have endeavoured to shew that
our nature and constitution lead us to conceive these as
qualities of body, as all mankind have always conceived
them to be. We have likewise examined with great at-
tention the various sensations we have by means of the
five senses, and are not able to find among them all one
single image of body, or of any of its qualities. From
whence, then, come those images of body and of its qual-
ities into the mind ? Let philosophers resolve this ques-
tion. All I can say is, that they come not by the senses.
I am sure that, by proper attention and care, I may
know my sensations, and be able to affirm with certainty
what they resemble, and what they do not resemble. I
have examined them one by one, and compared them
with matter and its qualities; and I cannot find one of
them that confesses a resembling feature.

A truth so evident as this — that our sensations are not
images of matter, or of any of its qualities — ought not to
yield to a hypothesis such as that above-mentioned, how-
ever ancient, or however universally received by philos-
ophers ; nor can there be any amicable union between the
two. This will appear by some reflections upon the
spirit of the ancient and modern philosophy concerning
sensation.

During the reign of the Peripatetic philosophy, our

1 84 THE PHILOSOPHY OF REID. [CH. VI.

sensations were not minutely or accurately examined.
The attention of philosophers, as well as of the vulgar,
was turned to the things signified by them: therefore, in
consequence of the common hypothesis, it was taken for
granted, that all the sensations we have from external
things, are the forms or images of these external things.
And thus the truth we have mentioned yielded entirely to
the hypothesis, and was altogether suppressed by it.

Des Cartes gave a noble example of turning our
attention inward, and scrutinizing our sensations; and
this example hath been very worthily followed by modern
philosophers, particularly by Malebranche, Locke, Berke-
ley, and Hume. The effect of this scrutiny hath been,
a gradual discovery of the truth above-mentioned — to
wit, the dissimilitude between the sensations of our minds,
and the qualities or attributes of an insentient inert sub-
stance, such as we conceive matter to be. But this
valuable and useful discovery, in its different stages, hath
still been unhappily united to the ancient hypothesis —
and from this inauspicious match of opinions, so un-
friendly and discordant in their natures, have arisen those
monsters of paradox and scepticism with which the
modern philosophy is too justly chargeable.

Locke saw clearly, and proved incontestably, that the
sensations we have by taste, smell, and hearing, as well
as the sensations of colour, heat, and cold, are not
resemblances of anything in bodies; and in this he agrees
with Des Cartes and Malebranche. Joining this opinion
with the hypothesis, it follows necessarily, that three
senses of the five are cut off from giving us any intelligence
of the material world, as being altogether inept for that
office. Smell, and taste, and sound, as well as colour
and heat, can have no more relation to body, than anger
or gratitude ; nor ought the former to be called qualities
of body, whether primary or secondary, any more than
the latter. For it was natural and obvious to argue thus
from that hypothesis: If heat, and colour, and sound

SEC. VI.] THE PHILOSOPHY OF REID. 185

are real qualities of body, the sensations by which we
perceive them must be resemblances of those qualities ;
but these sensations are not resemblances ; therefore,
those are not real qualities of body.

We see, then, that Locke, having found that the ideas
of secondary qualities are no resemblances, was com-
pelled, by a hypothesis common to all philosophers, to
deny that they are real qualities of body. It is more
difficult to assign a reason why, after this, he should call
them secondary qualities; for this name, if I mistake not,
was of his invention.* Surely he did not mean that they
were secondary qualities of the mind ; and I do not see
with what propriety, or even by what tolerable license,
he could call them secondary qualities of body, after
finding that they were no qualities of body at all. In
this, he seems to have sacrificed to Common Sense, and
to have been led by her authority even in opposition to
his hypothesis. The same sovereign mistress of our
opinions that led this philosopher to call those things
secondary qualities of body, which, according to his
principles and reasonings, were no qualities of body at
all, hath led, not the vulgar of all ages only, but philoso-
phers also, and even the disciples of Locke, to believe
them to be real qualities of body — she hath led them to
investigate, by experiments, the nature of colour, and
sound, and heat, in bodies. Nor hath this investigation
been fruitless, as it must have been if there had been no
such thing in bodies ; on the contrary, it hath produced
very noble and useful discoveries, which make a very
considerable part of natural philosophy. If, then, natural
philosophy be not a dream, there is something in bodies
which we call colour, and heal, and sound. And if this

* The terms First and Second, or Primary and Secondary qualities,
were no more an invention of Locke than the distinction which he
applied them to denote. The terms First and Second Qualities, as I
have noticed, in the Aristotelian philosophy, marked out, however,
a different distribution of qualities than that in question. — H.

1 86 THE PHILOSOPHY OF REID. [CH. VI.

be so, the hypothesis from which the contrary is con-
cluded, must be false : for the argument, leading to a
false conclusion, recoils against the hypothesis from
which it was drawn, and thus directs its force backward.
If the qualities of body were known to us only by
sensations that resemble them, then colour, and sound,
and heat could be no qualities of body; but these are real
qualities of body ; and, therefore, the qualities of body
are not known only by means of sensations that resemble
them.

But to proceed. What Locke had proved with regard
to the sensations we have by smell, taste, and hearing,
Bishop Berkeley proved no less unanswerably with regard
to all our other sensations ; to wit, that none of them
can in the least resemble the qualities of a lifeless and
insentient being, such as matter is conceived to be.
Mr. Hume hath confirmed this by his authority and
reasoning. This opinion surely looks with a very malign
aspect upon the old hypothesis ; yet that hypothesis hath
still been retained, and conjoined with it. And what a
brood of monsters hath this produced !

The first-born of this union, and, perhaps, the most
harmless, was, that the secondary qualities of body were
mere sensations of the mind. To pass by Malebranche's
notion of seeing all things in the ideas of the divine mind,
as a foreigner, never naturalized in this island ; the next
was Berkeley's system, That extension, and figure, and
hardness, and motion — that land, and sea, and houses,
and our own bodies, as well as those of our wives, and
children, and friends — are nothing but ideas of the mind:
and that there is nothing existing in nature, but minds
and ideas.

The progeny that followed, is still more frightful ; so
that it is surprising, that one could be found who had
the courage to act the midwife, to rear it up, and to
usher it into the world. No causes nor effects ; no sub-
stances, material or spiritual ; no evidence, even in

SEC. VII.] THE PHILOSOPHY OF REID. 187

mathematical demonstration ; no liberty nor active power ;
nothing existing in nature, but impressions and ideas
following each other, without time, place, or subject.
Surely no age ever produced such a system of opinions,
justly deduced with great acuteness, perspicuity, and ele-
gance, from a principle universally received. The hy-
pothesis we have mentioned is the father of them all.
The dissimilitude of our sensations and feelings to ex-
ternal things, is the innocent mother of most of them.

As it happens sometimes, in an arithmetical operation,
that two errors balance one another, so that the con-
clusion is little or nothing affected by them; but when
one of them is corrected, and the other left, we are led
farther from the truth than by both together: so it seems
to have happened in the Peripatetic philosophy of
sensation, compared with the modern. The Peripatetics
adopted two errors; but the last served as a corrective to
the first, and rendered it mild and gentle ; so that their
system had no tendency to scepticism. The moderns
have retained the first of those errors, but have gradually
detected and corrected the last. The consequence hath
been, that the light we have struck out hath created
darkness, and scepticism hath advanced hand in hand
with knowledge, spreading its melancholy gloom, first
over the material worjd, and at last over the whole face
of nature. Such a phaenomenon as this, is apt to stagger
even the lovers of light and knowledge, while its cause is
latent ; but, when that is detected, it may give hopes that
this darkness shall not be everlasting, but that it shall be
succeeded by a more permanent light.

Section VIL

OF VISIBLE FIGURE AND EXTENSION.

Although there is no resemblance, nor, as far as we
know, any necessary connection, between that quality in
a body which we call its colour, and the appearance which

1 88 THE PHILOSOPHY OP REID. [CH. VL

that colour makes to the eye, it is quite otherwise with
regard to its figure and magnitude. • There is certainly a
resemblance, and a necessary connection, between the
visible figure and magnitude of a body, and its real figure
and magnitude ; no man can give a reason why a scarlet
colour affects the eye in the manner it does ; no man can
be sure that it affects his eye in the same manner as it
affects the eye of another, and that it has the same ap-
pearance to him as it has to another man ; — but we can
assign a reason why a circle placed obliquely to the eye,
should appear in the form of an ellipse. The visible
figure, magnitude, and position may, by mathematical
reasoning, be deduced from the real ; and it may be
demonstrated, that every eye that sees distinctly and per-
fectly, must, in the same situation, see it under this form,
and no other. Nay, we may venture to affirm, that a
man born blind, if he were instructed in mathematics,
would be able to determine the visible figure of a body
when its real figure, distance, and position, are given.
Dr. Saunderson understood the projection of the sphere,
and perspective. Now, I require no more knowledge in
a blind man, in order to his being able to determine the
visible figure of bodies, than that he can project the out-
line of a given body, upon the surface of a hollow sphere,
whose centre is in the eye. This projection is the visible
figure he wants : for it is the same figure with that which
is projected upon the tunica retina in vision.

A blind man can conceive lines drawn from every
point of the object to the centre of the eye, making an-
gles. He can conceive that the length of the object will
appear greater or less, in proportion to the angle which
it subtends at the eye ; and that, in like manner, the
breadth, and in general the distance, of any one point
of the object from any other point, will appear greater
or less, in proportion to the angles which those distances
subtend. He can easily be made to conceive, that the
visible appearance has no thickness, any more than a

SEC. VII.] THE PHILOSOPHY OF REID. 189

projection of the sphere, or a perspective draught. He
may be informed, that the eye, until it is aided by ex-
perience, does not represent one object as nearer or more
remote than another. Indeed, he would probably con-
jecture this of himself, and be apt to think that the rays
of light must make the same impression upon the eye,
whether they come from a greater or a less distance.

These are all the principles which we suppose our
blind mathematician to have ; and these he may cer-
tainly acquire by information and reflection. It is no
less certain, that, from these principles, having given the
real figure and magnitude of a body, and its position
and distance with regard to the eye, he can find out its
visible figure and magnitude. He can demonstrate in
general, from these principles, that the visible figure of
all bodies will be the same with that of their projection
upon the surface of a hollow sphere, when the eye is
placed in the centre. And he can demonstrate that their
visible magnitude will be greater or less, according as
their projection occupies a greater or less part of the
surface of this sphere.

To set this matter in another light, let us distinguish
betwixt the position of objects with regard to the eye, and
their distance from it. Objects that lie in the same right
line drawn from the centre of the eye, have the same
position, however different their distances from the eye
may be : but objects which lie in different right lines
drawn from the eye's centre, have a different position ;
and this difference of position is greater or less in pro-
portion to the angle made at the eye by the right lines
mentioned. Having thus defined what we mean by the
position of objects with regard to the eye, it is evident
that, as the real figure of a body consists in the situation
of its several parts with regard to one another, so its vis-
ible figure consists in the position of its several parts
with regard to the eye ; and, as he that hath a distinct
conception of the situation of the parts of the body with

I9 THE PHILOSOPHY OF REID. [CH. VI.

regard to one another, must have a distinct conception
of its real figure ; so he that conceives distinctly the
position of its several parts with regard to the eye, must
have a distinct conception of its visible figure. Now,
there is nothing, surely, to hinder a blind man from
conceiving the position of the several parts of a body
with regard to the eye, any more than from conceiving
their situation with regard to one another ; and, there-
fore, I conclude, that a blind man may attain a distinct
conception of the visible figure of bodies.

Although we think the arguments that have been
offered are sufficient to prove that a blind man may con-
ceive the visible extension and figure of bodies ; yet, in
order to remove some prejudices against this truth, it
will be of use to compare the notion which a blind
mathematician might form to himself of visible figure,
with that which is presented to the eye in vision, and to
observe wherein they differ.

First, Visible figure is never presented to the eye but
in conjunction with colour : and, although there be no
connection between them from the nature of the things,
yet, having so invariably kept company together, we are
hardly able to disjoin them even in our imagination.
What mightily increases this difficulty is, that we have
never been accustomed to make visible figure an object
of thought. It is only used as a sign, and, having
served this purpose, passes away, without leaving a trace
behind. The drawer or designer, whose business it is to
hunt this fugitive form, and to take a copy of it, finds
how difficult his task is, after many years' labour and
practice. Happy ! if at last he can acquire the art of
arresting it in his imagination, until he can delineate it.
For then it is evident that he must be able to draw as
accurately from the life as from a copy. But how few
of the professed masters of designing are ever able to
arrive at this degree of perfection ! It is no wonder,
then, that we should find so great difficulty in conceiving

SEC. VII.] THE PHILOSOPHY OF REID. 191

this form apart from its constant associate, when it is so
difficult to conceive it at all. But our blind man's no-
tion of visible figure will not be associated with colour,
of which he hath no conception, but it will, perhaps, be
associated with hardness or smoothness, with which he
is acquainted by touch. These different associations
are apt to impose upon us, and to make things seem
different, which, in reality, are the same.

Secondly, The blind man forms the notion of visible
figure to himself, by thought, and by mathematical
reasoning from principles ; whereas, the man that sees,
has it presented to his eye at once, without any labour,
without any reasoning, by a kind of inspiration. A
man may form to himself the notion of a parabola, or
a cycloid, from the mathematical definition of those
figures, although he had never seen them drawn or de-
lineated. Another, who knows nothing of the mathe-
matical definition of the figures, may see them delineated
on paper, or feel them cut out in wood. Each may have
a distinct conception of the figures, one by mathematical
reasoning, the other by sense. Now, the blind man
forms his notion of visible figure in the same manner as
the first of these formed his notion of a parabola or a
cycloid, which he never saw.

Thirdly, Visible figure leads the man that sees, directly
to the conception of the real figure, of which it is a sign.
But the blind man's thoughts move in a contrary direc-
tion. For he must first know the real figure, distance,
and situation of the body, and from thence he slowly
traces out the visible figure by mathematical reasoning.
Nor does his nature lead him to conceive this visible
figure as a sign ; it is a creature of his own reason and
imagination.

Ip2 THE PHILOSOPHY OF REID. [Cn. VI.

Section VIII.

SOME QUERIES CONCERNING VISIBLE FIGURE ANSWERED.

It may be asked, What kind of thing is this visible
figure ? Is it a Sensation, or an Idea ? If it is an idea,
from what sensation is it copied ? These questions may
seem trivial or impertinent to one who does not know
that there is a tribunal of inquisition erected by certain
modem philosophers, before which everything in nature
must answer. The articles of inquisition are few indeed,
but very dreadful in their consequences. They are only
these : Is the prisoner an Impression or an Idea ? If an
idea, from what impression copied ? Now, if it appears
that the prisoner is neither an impression, nor an idea
copied from some impression, immediately, without
being allowed to offer anything in arrest of judgment, he
is sentenced to pass out of existence, and to be, in all
time to come, an empty unmeaning sound, or the ghost
of a departed entity.

Before this dreadful tribunal, cause and effect, time
and place, matter and spirit, have been tried and cast :
how then shall such a poor flimsy form as visible figure
stand before it ? It must even plead guilty, and confess
that it is neither an impression nor an idea. For, alas !
it is notorious, that it is extended in length and breadth ;
it may be long or short, broad or narrow, triangular,
quadrangular, or circular; and, therefore, unless ideas
and impressions are extended and figured, it cannot
belong to that category.

If it should still be asked, To what category of beings
does visible figure then belong ? I can only, in answer,
give some tokens, by which those who are better ac-
quainted with the categories, may chance to find its
place. It is, as we have said, the position of the several
parts of a figured body with regard to the eye. The

SEC. VIII.] THE PHILOSOPHY OF REID. 193

different positions of the several parts of the body with
regard to the eye, when put together, make a real figure,
which is truly extended in length and breadth, and
which represents a figure that is extended in length,
breadth, and thickness. In like manner, a projection
of the sphere is a real figure, and hath length and
breadth, but represents the sphere, which hath three
dimensions. A projection of the sphere, or a perspec-
tive view of a palace, is a representative in the very same
sense as visible figure is ; and wherever they have their
lodgings in the categories, this will be found to dwell
next door to them.

It may farther be asked, Whether there be any sensa-
tion proper to visible figure, by which it is suggested in
vision ? — or by what means it is presented to the mind ?
This is a question of some importance, in order to our
having a distinct notion of the faculty of seeing : and to
give all the light to it we can, it is necessary to compare
this sense with other senses, and to make some supposi-
tions, by which we may be enabled to distinguish things
that are apt to be confounded, although they are totally
different.

There are three of our senses which give us intelli-
gence of things at a distance: smell, hearing, and sight.
In smelling and in hearing, we have a sensation or im-
pression upon the mind, which, by our constitution, we
conceive to be a sign of something external: but the po-
sition of this external thing, with regard to the organ of
sense, is not presented to the mind along with the sen-
sation. When I hear the sound of a coach, I could not,
previous to experience, determine whether the sounding
body was above or below, to the right hand or to the
left. So that the sensation suggests to me some external
object as the cause or occasion of it; but it suggests not
the position of that object, whether it lies in this direc-
tion or in that. The same thing may be said with regard
to smelling. But the case is quite different with regard

IQ4 THE PHILOSOPHY OF REID. [CH.VJ.

to seeing. When I see an object, the appearance which
the colour of it makes, may be called the sensation, which
suggests to me some external thing as its cause; but it
suggests likewise the individual direction and position of
this cause with regard to the eye. I know it is precisely
in such a direction, and in no other. At the same time,
I am not conscious of anything that can be called sensa-
tion, but the sensation of colour. The position of the
coloured thing is no sensation; but it is by the laws of
my constitution presented to the mind along with the
colour, without any additional sensation.

Let us suppose that the eye were so constituted that
the rays coming from any one point of the object were
not, as they are in our eyes, collected in one point of the
retina,\)\\t diffused over the whole: it is evident to those
who understand the structure of the eye, that such an
eye as we have supposed, would shew the colour of a
body as our eyes do, but that it would neither shew
figure nor position. The operation of such an eye would
be precisely similar to that of hearing and smell; it would
give no perception of figure or extension, but merely of
colour. Nor is the supposition we have made altogether
imaginary: for it is nearly the case of most people who
have cataracts, whose crystalline, as Mr. Cheselden ob-
serves, does not altogether exclude the rays of light, but
diffuses them over the retina, so that such persons see
things as one does through a glass of broken gelly: they
perceive the colour, but nothing of the figure or magni-
tude of objects.

Again, if we should suppose that smell and sound
were conveyed in right lines from the objects, and that
every sensation of hearing and smell suggested the pre-
cise direction or position of its object; in this case, the
operations of hearing and smelling would be similar
to that of seeing: we should smell and hear the figure
of objects, in the same sense as now we see it; and
every smell and sound would be associated with some

SEC. VIII.] THE PHILOSOPHY OF REID. 195

figure in the imagination, as colour is in our present
state.

We have reason to believe, that the rays of light make
some impression upon the retina; but we are not con-
,scious of this impression; nor have anatomists or philos-
ophers been able to discover the nature and effects of it;
whether it produces a vibration in the nerve, or the mo-
tion of some subtile fluid contained in the nerve, or
something different from either, to which we cannot give
a name. Whatever it is, we shall call it the material im-
pression ; remembering carefully, that it is not an impres-
sion upon the mind, but upon the body; and that it is
no sensation, nor can resemble sensation, any more than
figure or motion can resemble thought. Now, this ma-
terial impression, made upon a particular point of the
retina, by the laws of our constitution, suggests two
things to the mind — namely, the colour an i the position
of some external object. No man can give a reason why
the same material impression might not have suggested
sound, or smell, or either of these, along with the posi-
tion of the object. That it should suggest colour and
position, and nothing else, we can resolve only into our
constitution, or the will of our Maker. And since there
is no necessary connection between these two things sug-
gested by this material impression, it might, if it had so
pleased our Creator, have suggested one of them without
the other. Let us suppose, therefore, since it plainly
appears to be possible, that our eyes had been so framed
as to suggest to us the position of the object, without
suggesting colour, or any other quality: What is the con-
sequence of this supposition ? It is evidently this, that
the person endued with such an eye, would perceive the
visible figure of bodies, without having any sensation or
impression made upon his mind. The figure he per-
ceives is altogether external; and therefore cannot be
called an impression upon the mind, without the gross-
est abuse of language. If it should be said, that it is

196 THE PHILOSOPHY OF REID. [CH. VI.

impossible to perceive a figure, unless there be some im-
pression of it upon the mind, I beg leave not to admit
the impossibility of this without some proof: and I can
find none. Neither can I conceive what is meant by an
impression of figure upon the mind. I can conceive an
impression of figure upon wax, or upon any body that is
fit to receive it; but an impression of it upon the mind, is
to me quite unintelligible; and, although I form the most
distinct conception of the figure, I cannot, upon the
strictest examination, find any impression of it upon my
mind.

If we suppose, last of all, that the eye hath the power
restored of perceiving colour, I apprehend that it will be
allowed, that now it perceives figure in the very same
manner as before, with this difference only, that colour
is always joined with it.

In answer, therefore, to the question proposed, there
seems to be no sensation that is appropriated to visible
figure, or whose office it is to suggest it. It seems to be
suggested immediately by the material impression upon
the organ, of which we are not conscious: and why may
not a material impression upon the retina suggest visible
figure, as well as the material impression made upon the
hand, when we grasp a ball, suggests real figure ? In
the one case, one and the same material impression,
suggests both colour and visible figure; and in the other
case, one and the same material impression suggests hard-
ness, heat, or cold, and real figure, all at the same
time.

We shall conclude this section with another question
upon this subject. Since the visible figure of bodies is a
real and external object to the eye, as their tangible fig-
ure is to the touch, it may be asked, Whence arises the
difficulty of attending to the first, and the facility of at-
tending to the last ? It is certain that the first is more
frequently presented to the eye, than the last is to the
touch; the first is as distinct and determinate an object

SEC. VIII.] THE PHILOSOPHY OF REID. 197

as the last, and seems in its own nature as proper for
speculation. Yet so little hath it been attended to, that
it never had a name in any language, until Bishop Berke-
ley gave it that which we have used after his example,
to distinguish it from the figure which is the object of
touch.

The difficulty of attending to the visible figure of
bodies, and making it an object of thought, appears so
similar to that which we find in attending to our sensa-
tions, that both have probably like causes. Nature in-
tended the visible figure as a sign of the tangible figure
and situation of bodies, and hath taught us, by a kind
of instinct, to put it always to this use. Hence it hap-
pens, that the mind passes over it with a rapid motion,
to attend to the things signified by it. It is as unnatu-
ral to the mind to stop at the visible figure, and attend
to it, as it is to a spherical body to stop upon an inclined
plane. There is an inward principle, which constantly
carries it forward, and which cannot be overcome but by
a contrary force.

There are other external things which nature intended
for signs; and we find this common to them all, that the
mind is disposed to overlook them, and to attend only
to the things signified by them. Thus there are certain
modifications of the human face, which are natural signs
of the present disposition of the mind. Every man un-
derstands the meaning of these signs, but not one of a hun-
dred ever attended to the signs themselves, or knows
anything about them. Hence you may find many an ex-
cellent practical physiognomist who knows nothing of
the proportions of a face nor can delineate or describe
the expression of any one passion.

An excellent painter or statuary can tell, not only what
are the proportions of a good face, but what changes
every passion makes in it. This, however, is one of the
chief mysteries of his art, to the acquisition of which in-
finite labour and attention, as well as a happy genius,

198 THE PHILOSOPHY OF REID. ICH. VI.

are required ; but when he puts his art in practice, and
happily expresses a passion by its proper signs, every
one understands the meaning of these signs, without art,
and without reflection.

What has been said of painting, might easily be ap-
plied to all the fine arts. The difficulty in them all con-
sists in knowing and attending to those natural signs
whereof every man understands the meaning.

We pass from the sign to the thing signified, with ease,
and by natural impulse ; but to go backward from the
thing signified to the sign, is a work of labour and diffi-
culty. Visible figure, therefore, being intended by nature
to be a sign, we pass on immediately to the thing signi-
fied, and cannot easily return to give any attention to the
sign.

Nothing shews more clearly our indisposition to at-
tend to visible figure and visible extension than this —
that, although mathematical reasoning is no less appli-
cable to them, than to tangible figure and extension, yet
they have entirely escaped the notice of mathematicians.
While that figure and that extension which are objects
of touch, have been tortured ten thousand ways for
twenty centuries, and a very noble system of science has
been drawn out of them, not a single proposition do we
find with regard to the figure and extension which are
the immediate objects of sight !

When the geometrician draws a diagram with the most
perfect accuracy — when he keeps his eye fixed upon it,
while he goes through a long process of reasoning, and
demonstrates the relations of the several parts of his fig-
ure— he does not consider that the visible figure pre-
sented to his eye, is only the representative of a tangible
figure, upon which all his attention is fixed ; he does not
consider that these two figures have really different pro-
perties ; and that, what he demonstrates to be true of
the one, is not true of the other.

This, perhaps, will seem so great a paradox, even to

SEC. IX.] THE PHILOSOPHY OF REID. 199

mathematicians, as to require demonstration before it
can be believed. Nor is the demonstration at all diffi-
cult, if the reader will have patience to enter but a little
into the mathematical consideration of visible figure,
which we shall call the geometry of visibles.

Section IX.

OF THE GEOMETRY OF VISIBLES.*

In this geometry, the definitions of a point ; of a line,
whether straight or curve ; of an angle, whether acute,
or right, or obtuse; and of a circle — are the same as in
common geometry. The mathematical reader will easily
enter into the whole mystery of this geometry, if he at-
tends duly to these few evident principles.

1. Supposing the eye placed in the centre of a sphere,
every great circle of the sphere will have the same ap-
pearance to the eye as if it was a straight line ; for the
curvature of the circle being turned directly toward the
eye, is not perceived by it. And, for the same reason,
any line which is drawn in the plane of a great circle of
the sphere, whether it be in reality straight or curve, will
appear straight to the eye.

2. Every visible right line will appear to coincide with
some great circle of the sphere ; and the circumference
of that great circle, even when it is produced until it
returns into itself, will appear to be a continuation of
the same visible right line, all the parts of it being visi-
bly in directum. For the eye, perceiving only the posi-
tion of objects with regard to itself, and not their dis-
tance, will see those points in the same visible place
which have the same position with regard to the eye,

* How does this differ from a doctrine of Perspective ? —At any
rate, the notion is Berkeley's. Compare " New Theory of Vision,"
§§ 153- '59-— H.

2OO THE PHILOSOPHY OF REID. [CH. VI.

how different soever their distances from it may be.
Now, since a plane passing through the eye and a given
visible right line, will be the plane of some great circle
of the sphere, every point of the visible right line will
have the same position as some point of the great circle;
therefore, they will both have the same visible place, and
coincide to the eye ; and the whole circumference of the
great circle, continued even until it returns into itself,
will appear to be a continuation of the same visible right
line.

Hence it follows —

3. That every visible right line, when it is continued
in directum, as far as it may be continued, will be rep-
resented by a great circle of a sphere, in whose centre
the eye is placed. It follows —

4. That the visible angle comprehended under two
visible right lines, is equal to the spherical angle com-
prehended under the two great circles, which are the
representatives of these visible lines. For, since the vis-
ible lines appear to coincide with the great circles, the
visible angle comprehended under the former must be
equal to the visible angle comprehended under the latter.
But the visible angle comprehended under the two great
circles, when seen from the centre, is of the same mag-
nitude with the spherical angle which they really com-
prehend, as mathematicians know ; therefore, the visi-
ble angle made by any two visible lines is equal to the
spherical angle made by the two great circles of the
sphere which are their representatives.

5. Hence it is evident, that every visible right-lined
triangle will coincide in all its parts with some spherical
triangle. The sides of the one will appear equal to the
sides of the other, and the angles of the one to the an-
gles of the other, each to each : and, therefore, the whole
of the one triangle will appear equal to the whole of the
other. In a word, to the eye they will be one and the
same, and have the same mathematical properties. The

SEC. IX.] THE PHILOSOPHY OF REID. 2OI

properties, therefore, of visible right-lined triangles are
not the same with the properties of plain triangles, but
are the same with those of spherical triangles.

6. Every lesser circle of the sphere will appear a cir-
cle to the eye, placed, as we have supposed all along, in
the centre of the sphere ; and, on the other hand, every
visible circle will appear to coincide with some lesser cir-
cle of the sphere.

7. Moreover, the whole surface of the sphere will rep-
resent the whole of visible space ; for, since every visible
point coincides with some point of the surface of the
sphere, and has the same visible place, it follows, that all
the parts of the spherical surface taken together, will
represent all possible visible places — that is, the whole
of visible space. And from this it follows, in the last
place —

8. That every visible figure will be represented by that
part of the surface of the sphere on which it might be
projected, the eye being in the centre. And every such
visible figure will bear the same ratio to the whole of visi-
ble space, as the part of the spherical surface which rep-
resents it, bears to the whole spherical surface.

The mathematical reader, I hope, will enter into these
principles with perfect facility, and will as easily per-
ceive that the following propositions with regard to visi-
ble figure and space, which we offer only as a specimen,
may be mathematically demonstrated from them, and are
not less true nor less evident than the propositions of
Euclid, with regard to tangible figures.

Prop. i. Every right line being produced, will at last
return into itself.

2. A right line returning into itself, is the longest
possible right line ; and all other right lines bear a finite
ratio to it.

3. A right line returning into itself, divides the whole
of visible space into two equal parts, which will both be
comprehended under this right line.

202 THE PHILOSOPHY OF REID. [C». VI.

4. The whole of visible space bears a finite ratio to
any part of it.

5. Any two right lines being produced, will meet in
two points, and mutually bisect each other.

6. If two lines be parallel — that is, everywhere equally
distant from each other — they cannot both be straight.

7. Any right line being given, a point may be found,
which is at the same distance from all the points of the
given right line.

8. A circle may be parallel to a right line — that is,
may be equally distant from it in all its parts.

9. Right-lined triangles that are similar, are also
equal.

10. Of every right-lined triangle, the three angles taken
together, are greater than two right angles.

11. The angles of a right-lined [triangle, may all be
right angles, or all obtuse angles.

12. Unequal circles are not as the squares of their
diameters, nor are their circumferences in the ratio of
their diameters.

This small specimen of the geometry of visibles, is in-
tended to lead the reader to a clear and distinct con-
ception of the figure and extension which is presented to
the mind by vision ; and to demonstrate the truth of
what we have affirmed above — namely, that those figures
and that extension which are the immediate objects of
sight, are not the figures and the extension about which
common geometry is employed ; that the geometrician,
while he looks at his diagram, and demonstrates a
proposition, hath a figure presented to his eye, which is
only a sign and representative of a tangible figure : that
he gives not the least attention to the first, but attends
only to the last ; and that these two figures have differ-
ent properties, so that what he demonstrates of the one,
is not true of the other.

It deserves, however, to be remarked, that, as a small
part of a spherical surface differs not sensibly from a

SEC. IX. THE PHILOSOPHY OF REID. 203

plain surface, so a small part of visible extension differs
very little from that extension in length and breadth,
which is the object of touch. And it is likewise to be ob-
served, that the human eye is so formed, that an object
which is seen distinctly and at one view, can occupy but
a small part of visible space ; for we never see distinctly
what is at a considerable distance from the axis of the
eye ; and, therefore, when we would see a large object
at one view, the eye must be at so great a distance, that
the object occupies but a small part of visible space.
From these two observations, it follows, that plain fig-
ures which are seen at one view, when their planes are
not oblique, but direct to the eye, differ little from the
visible figures which they present to the eye. The sev-
eral lines in the tangible figure, have very nearly the same
proportion to each other as in the visible ; and the an-
gles of the one are very nearly, although not strictly and
mathematically, equal to those of the other. Although,
therefore, we have found many instances of natural signs
which have no similitude to the things signified, this is
not the case with regard to visible figure. It hath, in
all cases, such a similitude to the thing signified by it,
as a plan or profile hath to that which it represents ;
and, in some cases, the sign and thing signified have to
all sense the same figure and the same proportions. If
we could find a being endued with sight only, without
any other external sense, and capable of reflecting and
reasoning upon what he sees, the notions and philoso-
phical speculations of such a being, might assist us in
the difficult task of distinguishing the perceptions which
we have purely by sight, from those which derive their
origin from other senses. Let us suppose such a being,
and conceive, as well as we can, what notion he would
have of visible objects, and what conclusions he would
deduce from them. We must not conceive him dis-
posed by his constitution, as we are, to consider the
visible appearance as a sign of something else : it is no

504 THE PHILOSOPHY OF REID. |CH. VI.

sign to him, because there is nothing signified by it ; and,
therefore, we must suppose him as much disposed to at-
tend to the visible figure and extension of bodies, as we
are disposed to attend to their tangible figure and ex-
tension.

If various figures were presented to his sense, he
might, without doubt, as they grow familiar, compare
them together, and perceive wherein they agree, and
wherein they differ. He might perceive visible objects
to have length and breadth, but could have no notion of
a third dimension, any more than we can have of a fourth.
All visible objects would appear to be terminated by
lines, straight or curve; and objects terminated by the
same visible lines, would occupy the same place, and
fill the same part of visible space. It would not be
possible for him to conceive one object to be be-
hind another, or one to be nearer, another more dis-
tant.

To us, who conceive three dimensions, a line may be
conceived straight; or it may be conceived incurvated in
one dimension, and straight in another; or, lastly, it may
be incurvated in two dimensions. Suppose a line to be
drawn upwards and downwards, its length makes one
dimension, which we shall call upwards and downwards;
and there are two dimensions remaining, according to
which it may be straight or curve. It may be bent to
the right or to the left, and, if it has no bending either
to right or left, it is straight in this dimension. But
supposing it straight in this dimension of right and left,
there is still another dimension remaining, in which it
may be curve; for it may be bent backwards or forwards.
When we conceive a tangible straight line, we exclude
curvature in either of these two dimensions: and as what is
conceived to be excluded, must be conceived, as well as
what is conceived to be included, it follows that all the
three dimensions enter into our conception of a straight
line. Its length is one dimension, its straightnessintwo

SEC. IX'.] THE PHILOSOPHY OF REID. 20$

other dimensions is included, or curvature in these two
dimensions excluded, in the conception of it.

The being we have supposed, having no conception
of more than two dimensions, of which the length of a
line is one, cannot possibly conceive it either straight or
curve in more than one dimension; so that, in his con-
ception of a right line, curvature to the right hand or
left is excluded; but curvature backwards or forwards
cannot be excluded, because he neither hath, nor can
have any conception of such curvature. Hence we see
the reason that a line which is straight to the eye, may
return into itself; for its being straight to the eye, implies
only straightness in one dimension; and a line which is
straight in one dimension may, notwithstanding, be
curve in another dimension, and so may return into it-
self.

To us, who conceive three dimensions, a surface is
that which hath length and breadth, excluding thickness;
and a surface may be either plain in this third dimension,
or it maybe incurvated: so that the notion of a third
dimension enters into our conception of a surface; for it
is only by means of this third dimension that we can
distinguish surfaces into plain and curve surfaces; and
neither one nor the other can be conceived without con-
ceiving a third dimension.

The being we have supposed, having no conception
of a third dimension, his visible figures have length and
breadth indeed; but thickness is neither included nor ex-
cluded, being a thing of which he has no conception.
And, therefore, visible figures, although they have length
and breadth, as surfaces have, yet they are neither plain
surfaces nor curve surfaces. For a curve surface implies
curvature in a third dimension, and a plain surface im-
plies the want of curvature in a third dimension; and
such a being can conceive neither of these, because he
has no conception of a third dimension. Moreover, al-
though he hath a distinct conception of the inclination

206 THE PHILOSOPHY OF REID. [Cn. VI.

of two lines which make an angle, yet he can neither
conceive a plain angle nor a spherical angle. Even
his notion of a point is somewhat less determined than
ours. In the notion of a point, we exclude length,
breadth, and thickness; he excludes length and breadth,
but cannot either exclude, or include thickness, because
he hath no conception of it.

Having thus settled the notions which such a being
as we have supposed might form of mathematical points,
lines, angles, and figures, it is easy to see, that, by com-
paring these together, and reasoning about them, he
might discover their relations, and form geometrical
conclusions built upon self-evident principles. He
might likewise, without doubt, have the same notions
of numbers as we have, and form a system of arithmetic.
It is not material to say in what order he might proceed
in such discoveries, or how much time and pains he
might employ about them, but what such a being, by rea-
son and ingenuity, without any materials of sensation
but those of sight only, might discover.

As it is more difficult to attend to a detail of possibilities
than of facts, even of slender authority, I shall beg leave
to give an extract from the travels of Johannes Rudolphus
Anepigraphus, a Rosicrucian philosopher, who having,
by deep study of the occult sciences, acquired the art of
transporting himself to various sublunary regions, and
of conversing with various orders of intelligences, in the
course of his adventures became acquainted with an or-
der of beings exactly such as I have supposed.

How they communicate their sentiments to one an-
other, and by what means he became acquainted with
their language, and was initiated into their philosophy;
as well as of many other particulars, which might have
gratified the curiosity of his readers, and, perhaps, added
credibility to his relation, he hath not thought fit to in-
form us; these being matters proper for adepts only to
know.

SEC. IX.] THE PHILOSOPHY OF REID. 207

His account of their philosophy is as follows: —
' ' The Idomenians, " saith he, " are many of them very
ingenious, and much given to contemplation. In arith-
metic, geometry, metaphysics, and physics, they have
most elaborate systems. In the two latter, indeed, they
have had many disputes carried on with great subtilty,
and are divided into various sects; yet in the two former
there hath been no less unanimity than among the hu-
man species. Their principles relating to numbers and
arithmetic, making allowance for their notation, differ in
nothing from ours — but their geometry differs very con-
siderably."

As our author's account of the geometry of the Ido-
menians agrees in everything with the geometry of visibles,
of which we have already given a specimen, we shall pass
over it. He goes on thus: — "Colour, extension, and fig-
ure, are conceived to be the essential properties of body. A
very considerable sect maintains, that colour is the essence
of body. If there had been no colour, say they, there
had been no perception or sensation. Colour is all
that we perceive, or can conceive, that is peculiar to
body; extension and figure being modes common to
body and to empty space. And if we should suppose a
body to be annihilated, colour is the only thing in it that
can be annihilated; for its place, and consequently the fig-
ure and extension of that place, must remain, and can-
not be imagined not to exist. These philosophers hold
space to be the place of all bodies, immovable and in-
destructible, without figure and similar in all its parts,
incapable of increase or diminution, yet not unmeasura-
ble; for every the least part of space bears a finite ratio to
the whole. So that with them the whole extent of space
is the common and natural measure of everything that
hath length and breadth; and the magnitude of every
body and of every figure is expressed by its being such a
part of the universe. In like manner, the common and
natural measure of length is an infinite right line, which,

208 THE PHILOSOPHY OF REID. [Cu. Vl.

as hath been before observed, returns into itself, and hath
no limits, but bears a finite ratio to every other line.

" As to their natural philosophy, it is now acknow-
ledged by the wisest of them to have been for many ages
in a very low state. The philosophers observing, that
body can differ from another only in colour, figure, or
magnitude, it was taken for granted, that all their particu-
lar qualities must arise from the various combinations of
these their essential attributes; and, therefore, it was
looked upon as the end of natural philosophy, to shew
how the various combinations of these three qualities in
different bodies produced all the phaenomena of nature.
It were endless to enumerate the various systems that
were invented with this view, and the disputes that were
carried on for ages; the followers of every system ex-
posing the weak sides of other systems, and palliating
those of their own with great art.

' ' At last, some free and facetious spirits, wearied with
eternal disputation, and the labour of patching and
propping weak systems, began to complain of the sub-
tilty of nature; of the infinite changes that bodies under-
go in figure, colour, and magnitude; and of the difficulty
of accounting for these appearances — making this a pre-
tence for giving up all inquiries into the causes of things,
as vain and fruitless.

" These wits had ample matter of mirth and ridicule
in the systems of philosophers; and, finding it an easier
task to pull down than to build or support, and that
every sect furnished them with arms and auxiliaries to
destroy another, they began to spread mightily, and
went on with great success. Thus philosophy gave way
to scepticism and irony, and those systems which had
been the work of ages, and the admiration of the learned,
became the jest of the vulgar: for even the vulgar readily
took part in the triumph over a kind of learning which
they had long suspected, because it produced nothing
but wrangling and altercation. The wits, having now

SEC. EX.] THE PHILOSOPHY OF REID. 209

acquired great reputation, and being flushed with suc-
cess, began to think their triumph incomplete, until
every pretence to knowledge was overturned ; and ac-
cordingly began their attacks upon arithmetic, geometry,
and even upon the common notions of untaught Ido-
menians. So difficult it hath always been," says
our author, "for great conquerors to know where to
stop.

' ' In the meantime, natural philosophy began to rise
from its ashes, under the direction of a person of great
genius, who is looked upon as having had something in
him above Idomenian nature. He observed, that the
Idomenian faculties were certainly intended for con-
templation, and that the works of nature were a nobler
subject to exercise them upon, than the follies of systems,
or the errors of the learned ; and being sensible of the
difficulty of finding out the causes of natural things, he
proposed, by accurate observation of the phaenomena of
nature, to find out the rules according to which they
happen, without inquiring into the causes of those rules.
In this he made considerable progress himself, and
planned out much work for his followers, who call them-
selves inductive philosophers. The sceptics look with envy
upon this rising sect, as eclipsing their reputation, and
threatening to limit.their empire; but they are at a loss
on what hand to attack it. The vulgar begin to reverence
it as producing useful discoveries.

"It is to be observed, that every Idomenian firmly
believes, that two or more bodies may exist in the same
place. For this they have the testimony of sense, and
they can no more doubt of it, than they can doubt
whether they have any perception at all. They often see
two bodies meet and coincide in the same place, and
separate again, without having undergone any change in
their sensible qualities by this penetration. When two
bodies meet, and occupy the same place, commonly one
only appears in that place, and the other disappears.

210 THE PHILOSOPHY OF REID. [Cn. VI.

That which continues to appear is said to overcome, the
other to be overcome."

To this quality of bodies they gave a name, which our
author tells us hath no word answering to it in any hu-
man language. And, therefore, after making a long
apology, which I omit, he begs leave to call it the over-
coming quality of bodies. He assures us, that " the spec-
ulations which had been raised about this single quality
of bodies, and the hypotheses contrived to account for
it, were sufficient to fill many volumes. Nor have there
been fewer hypotheses invented by their philosophers, to
account for the changes of magnitude and figure; which,
in most bodies that move, they perceive to be in a
continual fluctuation. The founder of the inductive sect,
believing it to be above the reach of Idomenian faculties,
to discover the real causes of these phsenomena, applied
himself to find from observation, by what laws they are
connected together ; and discovered many mathematical
ratios and relations concerning the motions, magnitudes,
figures, and overcoming quality of bodies, which con-
stant experience confirms. But the opposers of this
sect choose rather to content themselves with feigned
causes of these phaenomena, than to acknowledge the
real laws whereby they are governed, which humble their
pride, by being confessedly unaccountable. ''

Thus far Johannes Rudolphus Anepigraphus. Whe-
ther this Anepigraphus be the same who is recorded
among the Greek alchemistical writers not yet published,
by Borrichius, Fabricius, and others, I do not pretend
to determine. The identity of their name, and the simil-
itude of their studies, although no slight arguments, yet
are not absolutely conclusive. Nor will I take upon me
to judge of the narrative of this learned traveller, by the
external marks of his credibility ; I shall confine myself
to those which the critics call internal. It would even
be of small importance to inquire, whether the Idome-
nians have a real, or only an ideal existence; since this

SEC. X.] THE PHILOSOPHY OF REID. 211

is disputed among the learned with regard to things with
which we are more nearly connected. The important
question is, whether the account above given, is a just
account of their geometry and philosophy ? We have all
the faculties which they have, with the addition of others
which they have not; we may, therefore, form some
judgment of their philosophy and geometry, by separat-
ing from all others, the perceptions we have by sight and
reasoning upon them. As far as I am able to judge in
this way, after a careful examination, their geometry
must be such as Anepigraphus hath described. Nor
does his account of their philosophy appear to contain
any evident marks of imposture; although here, no
doubt, proper allowance is to be made for liberties
which travellers take, as well as for involuntary mistakes
which they are apt to fall into.

Section X.

OF THE PARALLEL MOTION OF THE EYES.

Having explained, as distinctly as we can, visible fig-
ure, and shewn its connection with the things signified
by it, it will be proper next to consider some phaenom-
ena of the eyes, and of vision, which have commonly
been referred to custom, to anatomical or to mechanical
causes ; but which, as I conceive, must be resolved into
original powers and principles of the human mind ; and,
therefore, belong properly to the subject of this inquiry.

The first is the parallel motion of the eyes ; by which,
when one eye is turned to the right or to the left, up-
wards or downwards, or straight forwards, the other al-
ways goes along with it in the same direction. We see
plainly, when both eyes are open, that they are always
turned the same way, as if both were acted upon by the
same motive force ; and if one eye is shut, and the hand

212 THE PHILOSOPHY OF REID. [Cn. VI.

laid upon it, while the other turns various ways, we feel
the eye that is shut turn at the same time, and that whether
we will or not. What makes this phenomenon surprising
is, that it is acknowledged, by all anatomists, that the
muscles which move the two eyes, and the nerves which
serve these muscles, are entirely distinct and unconnected.
It would be thought very surprising and unaccountable
to see a man, who, from his birth, never moved one
arm, without moving the other precisely in the same
manner, so as to keep them always parallel — yet it
would not be more difficult to find the physical cause of
such motion of the arms, than it is to find the cause of
the parallel motion of the eyes, which is perfectly simi-
lar.

The only cause that hath been assigned of this parallel
motion of the eyes, is custom. We find by experience,
it is said, when we begin to look at objects, that, in
order to have distinct vision, it is necessary to turn both
eyes the same way ; therefore, we soon acquire the habit
of doing it constantly, and by degrees lose the power of
doing otherwise.

This account of the matter seems to be insufficient ;
because habits are not got at once ; it takes time to ac-
quire and to confirm them ; and if this motion of the
eyes were got by habit, we should see children, when
they are born, turn their eyes different ways, and move
one without the other, as they do their hands or legs.
I know some have affirmed that they are apt to do so.
But I have never found it true from my own observation,
although I have taken pains to make observations of
this kind, and have had good opportunities. I have
likewise consulted experienced midwives, mothers, and
nurses, and found them agree, that they had never ob-
served distortions of this kind in the eyes of children,
but when they had- reason to suspect convulsions, or
some preternatural cause.

It seems, therefore, to be extremely probable, that,

SEC. X.] THE PHILOSOPHY OF REID. 213

previous to custom, there is something in the constitu-
tion, some natural instinct, which directs us to move
both eyes always the same way.

We know not how the mind acts upon the body, nor
by what power the muscles are contracted and relaxed —
but we see that, in some of the voluntary, as well as in
some of the involuntary motions, this power is so di-
rected, that many muscles which have no material tie
or connection, act in concert, each of them being taught
to play its part in exact time and measure. Nor doth a
company of expert players in a theatrical performance,
or of excellent musicians in a concert, or of good dancers
in a country dance, with more regularity and order,
conspire and contribute their several parts, to produce
one uniform effect, than a number of muscles do, in
many of the animal functions, and in many voluntary
actions. Yet we see such actions no less skilfully
and regularly performed in children, and in those who
know not that they have such muscles, than in the most
skilful anatomist and physiologist.

Who taught all the muscles that are concerned in
sucking, in swallowing our food, in breathing, and in
the several natural expulsions, to act their part in such
regular order and exact measure ? It was not custom
surely. It was that same powerful and wise Being who
made the fabric of the human body, and fixed the laws
by which the mind operates upon every part of it, so that
they may answer the purposes intended by them. And
when we see, in so many other instances, a system of
unconnected muscles conspiring so wonderfully in their
several functions, without the aid of habit, it needs
not be thought strange, that the muscles of the eyes
should, without this aid, conspire to give that direction
to the eyes, without which they could not answer their
end.

We see ~ like conspiring action in the muscles which
contract the pupils of the two eyes ; and in those mus-

214 THE PHILOSOPHY OF REID. [Cn. VI.

cles, whatever they be, by which the conformation of
the eyes is varied according to the distance of objects.

It ought, however, to be observed, that, although it
appears to be by natural instinct that both eyes are al-
ways turned the same way, there is still some latitude
left for custom.

What we have said of the parallel motion of the eyes,
is not to be understood so strictly as if nature directed
us to keep their axes always precisely and mathemati-
cally parallel to each other. Indeed, although they are
always nearly parallel, they hardly ever are exactly so.
When we look at an object, the axes of the eyes meet
in that object : and, therefore, make an angle, which is
always small, but will be greater or less, according as
the object is nearer or more remote. Nature hath very
wisely left us the power of varying the parallelism of
our eyes a little, so that we can direct them to the same
point, whether remote or near. This, no doubt, is
learned by custom : and accordingly we see, that it is
a long time before children get this habit in perfection.

This power of varying the parallelism of the eyes is
naturally no more than is sufficient for the purpose in-
tended by it ; but by much practice and straining, it may
be increased. Accordingly, we see, that some have ac-
quired the power of distorting their eyes into unnatural
directions, as others have acquired the power of distort-
ing their bodies into unnatural postures.

Those who have lost the sight of an eye, commonly
lose what they had got by custom, in the direction of
their eyes, but retain what they had by nature ; that is,
although their eyes turn and move always together, yet,
when they look upon an object, the blind eye will often
have a very small deviation from it ; which is not per-
ceived by a slight observer, but may be discerned by one
accustomed to make exact observations in these matters.

SEC. XI.] THE PHILOSOPHY OF REID. 21$

Section XL

OF OUR SEEING OBJECTS ERECT BY INVERTED IMAGES.

Another phenomenon which hath perplexed philoso-
phers, is our seeing objects erect, when it is well known
that their images or pictures upon the tunica retina of the
eye are inverted.

The sagacious Kepler first made the noble discovery,
that distinct but inverted pictures of visible objects are
formed upon the retina by the rays of light coming
from the object. The same great philosopher demon-
strated, from the principles of optics, how these pictures
are formed — to wit, That the rays coming from any one
point of the object, and falling upon the various parts of
the pupil, are, by the cornea and crystalline, refracted
so as to meet again in one point of the retina, and there
paint the colour of that point of the object from which
they come. As the rays from different points of the ob-
ject cross each other before they come to the retina, the
picture they form must be inverted; the upper part of the
object being painted upon the lower part of the retina,
the right side of the object upon the left of the retina, and
so of the other parts.

This philosopher thought chat we see objects erect by
means of these inverted pictures, for this reason, that,
as the rays from different points of the object cross each
other before they fall upon the retina, we conclude that
the impulse which we feel upon the lower part of the
retina comes from above, and that the impulse which we
feel upon the higher part comes from below.

Des Cartes afterwards gave the same solution of this
phaenomenon, and illustrated it by the judgment which
we form of the position of objects which we feel with our
arms crossed, or with two sticks that cross each other.

But we cannot acquiesce in this solution. First, Be-

2l6 THE PHILOSOPHY OF REID. [Cn. VI.

cause it supposes our seeing things erect, to be a deduc-
tion of reason, drawn from certain premises: whereas it
seems to be an immediate perception. And, secondly,
Because the premises from which all mankind are sup-
posed to draw this conclusion, never entered into the
minds of the far greater part, but are absolutely un-
known to them. We have no feeling or perception of
the pictures upon the retina, and as little surely of the
position of them. In order to see objects erect, accord-
ing to the principles of Kepler or Des Cartes, we must
previously know that the rays of light come from the ob-
ject to the eye in straight lines; we must know that the
rays from different points of the object cross one another
before they form the pictures upon the retina; and, lastly,
we must know that these pictures are really inverted.
Now, although all these things are true, and known to
philosophers, yet they are absolutely unknown to the far
greatest part of mankind: nor is it possible that they who
are absolutely ignorant of them, should reason from
them, and build conclusions upon them. Since, there-
fore, visible objects appear erect to the ignorant as well
as to the learned, this cannot be a conclusion drawn from
premises which never entered into the minds of the ig-
norant. We have indeed had occasion to observe many
instances of conclusions drawn, either by means of
original principles, or by habit, from premises which
pass through the mind very quickly, and which are
never made the objects of reflection; but surely no man
will conceive it possible to draw conclusions from prem-
ises which never entered into the mind at all.

Bishop Berkeley having justly rejected this solution,
gives one founded upon his own principles; wherein he
is followed by the judicious Dr. Smith, in his "Optics; "
and this we shall next explain and examine.

That ingenious writer conceives the ideas of sight to
be altogether unlike those of touch. And, since the
notions we have of an object by these different senses

SEC. XL] THE PHILOSOPHY OF REID. 2I/

have no similitude, we can learn only by experience how
one sense will be affected, by what, in a certain manner,
affects the other. Figure, position, and even number,
in tangible objects, are ideas of touch; and, although
there is no similitude between these and the ideas of
sight, yet we learn by experience, that a triangle affects
the sight in such a manner, and that a square affects it
in such another manner — hence we judge that which af-
fects it in the first manner, to be a triangle, and that
which affects it in the second, to be a square. In the
same way, finding, from experience, that an object in an
erect position affects the eye in one manner, and the
same object in an inverted position affects it in another,
we learn to judge, by the manner in which the eye is
affected, whether the object is erect or inverted. In a
word, visible ideas, according to this author, are signs of
the tangible; and the mind passeth from the sign to the
thing signified, not by means of any similitude between
the one and the other, nor by any natural principle, but
by having found them constantly conjoined in experi-
ence, as the sounds of a language are with the things
they signify: so that, if the images upon the retina had
been always erect, they would have shewn the objects
erect, in the manner as they do now that they are in-
verted— nay, if the visible idea which we now have from
an inverted object, had been associated from the begin-
ning with the erect position of that object, it would
have signified an erect position, as readily as it now sig-
nifies an inverted one. And, if the visible appearance
of two shillings had been found connected from the be-
ginning with the tangible idea of one shilling, that
appearance would as naturally and readily have sig-
nified the unity of the object as now it signifies its
duplicity.

This opinion is, undoubtedly, very ingenious : and,
if it is just, serves to resolve not only the phaenomenon
now under consideration, but likewise that which we

2l8 THE PHILOSOPHY OF REID. |CH. VI.

shall next consider — our seeing objects single with two
eyes.

It is evident that, in this solution, it is supposed that
we do not originally, and previous to acquired habits,
see things either erect or inverted, of one figure or
another, single or double ; but learn, from experience,
to judge of their tangible position, figure, and number,
by certain visible signs.

Indeed, it must be acknowledged to be extremely diffi-
cult to distinguish the immediate and natural objects of
sight, from the conclusions which we have been accus-
tomed from infancy to draw from them. Bishop Berkeley
was the first that attempted to distinguish the one from
the other, and to trace out the boundary that divides
them. And if, in doing so, he hath gone a little to the
right hand or to the left, this might be expected in a sub-
ject altogether new, and of the greatest subtilty. The
nature of vision hath received great light from this dis-
tinction ; and many phaenomena in optics, which before
appeared altogether unaccountable, have been clearly and
distinctly resolved by it. It is natural, and almost un-
avoidable, to one who hath made an important discovery
in philosophy, to carry it a little beyond its sphere, and
to apply it to the resolution of phaenomena which do
not fall within its province. Even the great Newton,
when he had discovered the universal law of gravitation,
and observed how many of the phaenomena of nature
depend upon this, and other laws of attraction and re-
pulsion, could not help expressing his conjecture, that
all the phaenomena of the material world depend upon
attracting and repelling forces in the particles of matter.
And I suspect that the ingenious Bishop of Cloyne, having
found so many phaenomena of vision reducible to the con-
stant association of the ideas of sight and touch, carried
this principle a little beyond its just limits.

In order to judge as well as we can whether it is so,
let us suppose such a blind man as Dr. Saunderson,

SEC. XL] THE PHILOSOPHY OF REID. 210

having all the knowledge and abilities which a blind
man may have, suddenly made to see perfectly. Let us
suppose him kept from all opportunities of associating
his ideas of sight with those of touch, until the former
become a little familiar; and the first surprise, occa-
sioned by objects so new, being abated, he has time to
canvass them, and to compare them, in his mind, with
the notions which he formerly had by touch; and, in
particular, to compare, in his mind, that visible exten-
sion which his eyes present, with the extension in length
and breadth with which he was before acquainted.

We have endeavoured to prove, that a blind man may
form a notion of the visible extension and figure of bod-
ies, from the relation which it bears to their tangible
extension and figure. Much more, when this visible
extension and figure are presented to his eye, will he be
able to compare them with tangible extension and figure,
and to perceive that the one has length and breadth as
well as the other; that the one may be bounded by lines,
either straight or curve, as well as the other. And,
therefore, he will perceive that there may be visible as
well as tangible circles, triangles, quadrilateral and mul-
tilateral figures. And, although the visible figure is
coloured, and the tangible is not, they may, notwith-
standing, have the same figure; as two objects of touch
may have the same figure, although one is hot and the
other cold.

We have demonstrated, that the properties of visible
figure differ from those of the plain figures which they
represent; but it was observed, at the same time, that
when the object is so small as to be seen distinctly at
one view, and is placed directly before the eye, the dif-
ference between the visible and the tangible figure is too
small to be perceived by the senses Thus, it is true,
that, of every visible triangle, the three angles are greater
than two right angles; whereas, in a plain triangle, the
three angles are equal to two right angles; but when the

220 THE PHILOSOPHY OF fcEtD. [Cn. VI.

visible triangle is small, its three angles will be so nearly
equal to two right angles, that the sense cannot discern
the difference. In like manner, the circumferences of
unequal visible circles are not, but those of plain circles
are, in the ratio of their diameters; yet, in small visible
circles, the circumferences are very nearly in the ratio of
their diameters; and the diameter bears the same ratio to
the circumference as in a plain circle, very nearly.

Hence it appears, that small visible figures (and such
only can be seen distinctly at one view) have not only a
resemblance to the plain tangible figures which have the
same name, but are to all senses the same: so that if
Dr. Saunderson had been made to see, and had atten-
tively viewed the figures of the first book of Euclid, he
might, by thought and consideration, without touching
them, have found out that they were the very figures he
was before so well acquainted with by touch.

When plain figures are seen obliquely, their visible
figure differs more from the tangible ; and the representa-
tion which is made to the eye, of solid figures, is still
more imperfect ; because visible extension hath not three,
but two dimensions only. Yet, as it cannot be said that
an exact picture of a man hath no resemblance of the
man, or that a perspective view of a house hath no resem-
blance of the house, so it cannot be said, with any pro-
priety, that the visible figure of a man or of a house hath
no resemblance of the objects which they represent.

Bishop Berkeley therefore proceeds upon a capital mis-
take, in supposing that there is no resemblance betwixt
the extension, figure, and position which we see, and
that which we perceive by touch.

We may further observe, that Bishop Berkeley's sys-
tem, with regard to material things, must have made him
see this question, of the erect appearance of objects, in
a very different light from that in which it appears to
those who do not adopt his system.

In his theory of vision, he seems indeed to allow, that

SEC. XI.] THE PHILOSOPHY OF REID. Ml

there is an external material world: but he believed that
this external world is tangible only, and not visible ; and
that the visible world, the proper object of sight, is not ex-
ternal, but in the mind. If this is supposed, he that
affirms that he sees things erect and not inverted, affirms
that there is a top and a bottom, a right and a left in the
mind. Now, I confess I am not so well acquainted with
the topography of the mind, as to be able to affix a
meaning to these words when applied to it.

We shall therefore allow, that, if visible objects were
not external, but existed only in the mind, they could
have no figure, or position, or extension ; and that it
would be absurd to affirm, that they are seen either erect
or inverted, or that there is any resemblance between
them and the objects of touch. But when we propose
the question, why objects are seen erect and not inverted,
we take it for granted, that we are not in Bishop Berke-
ley's ideal world, but in that world which men who yield
to the dictates of common sense, believe themselves to
inhabit. We take it for granted, that the objects both
of sight and touch, are external, and have a certain figure,
and a certain position with regard to one another, and
with regard to our bodies, whether we perceive it or not.

When I hold my walking-cane upright in my hand,
and look at it, I take it for granted that I see and handle
the same individual object. When I say that I feel it
erect, my meaning is, that I feel the head directed from
the horizon, and the point directed towards it ; and when
I say that I see it erect, I mean that I see it with the head
directed from the horizon, and the point towards it. I
conceive the horizon as a fixed object both of sight and
touch, with relation to which, objects are said to be high
or low, erect or inverted ; and when the question is
asked, why I see the object erect, and not inverted, it is
the same as if you should ask, why I see it in that posi-
tion which it really hath, or why the eye shews the real
position of objects, and doth not shew them in an in-

222 THE PHILOSOPHY OF REID. [CH. VI.

verted position, as they are seen by a common astronom-
ical telescope, or as their pictures are seen upon the
retina of an eye when it is dissected.

Section XII.

THE SAME SUBJECT CONTINUED.

It is impossible to give a satisfactory answer to this
question, otherwise than by pointing out the laws of
nature which take place in vision ; for by these the phae-
nomena of vision must be regulated.

Therefore, I answer, First, That, by a law of nature,
the rays of light proceed from every point of the object
to the pupil of the eye, in straight lines ; Secondly, That,
by the laws of nature, the rays coming from any one
point of the object to the various parts of the pupil, are
so refracted as to meet again in one point of the retina ;
and the rays from different points of the object, first
crossing each other, and then proceeding to as many
different points of the retina, form an inverted picture of
the object.

So far the principles of optics carry us ; and experience
further assures us, that, if there is no such picture upon
the retina, there is no vision ; and that such as the picture
on the retina is, such is the appearance of the object, in
colour and figure, distinctness or indistinctness, bright-
ness or faintness.

It is evident, therefore, that the pictures upon the ret-
ina are, by the laws of nature, a mean of vision; but in
what way they accomplish their end, we are totally
ignorant. Philosophers conceive, that the impression
made on the retina by the rays of light, is communicated
to the optic nerve, and by the optic nerve conveyed to
some part of the brain, by them called the sensorium;
and that the impression thus conveyed to the sensorium

SEC. XII.] THE PHILOSOPHY OF REID. 223

is immediately perceived by the mind, which is supposed
to reside there. But we know nothing of the seat of the
soul: and we are so far from perceiving immediately
what is transacted in the brain, that of all parts of the
human body we know least about it. It is indeed very
probable, that the optic nerve is an instrument of vision
no less necessary than the retina; and that some impres-
sion is made upon it, by means of the pictures on the
retina. But of what kind this impression is, we know
nothing.

There is not the least probability that there is any
picture or image of the object either in the optic nerve
or brain. The pictures on the retina are formed by the
rays of light; and, whether we suppose, with some, that
their impulse upon the retina causes some vibration of
the fibres of the optic nerve, or, with others, that it gives
motion to some subtile fluid contained in the nerve,
neither that vibration nor this motion can resemble the
visible object which is presented to the mind. Nor is
there any probability that the mind perceives the pictures
upon the retina. These pictures are no more objects of
our perception, than the brain is, or the optic nerve.
No man ever saw the pictures in his own eye, nor in-
deed the pictures in the eye of another, until it was
taken out of the head and duly prepared.

It is very strange, that philosophers, of all ages, should
have agreed in this notion, that the images of external
objects are conveyed by the organs of sense to the brain,
and are there perceived by the mind. Nothing can be
more unphilosophical. For, First, This notion hath no
foundation in fact and observation. Of all the organs of
sense, the eye only, as far as we can discover, forms any
kind of image of its object; and the images formed by
the eye are not in the brain, but only in the bottom of
the eye; nor are they at all perceived or felt by the mind.
Secondly, It is as difficult to conceive how the mind
perceives images in the brain, as how it perceives things

224 THE PHILOSOPHY OF REID. [Cn. VI.

more distant. If any man will shew how the mind may
perceive images in the brain, I will undertake to shew
how it may perceive the most distant objects; for, if we
give eyes to the mind, to perceive what is transacted at
home in its dark chamber, why may we not make these
eyes a little longer-sighted ? and then we shall have no
occasion for that unphilosophical fiction of images in the
brain. In a word, the manner and mechanism of the
mind's perception is quite beyond our comprehension;
and this way of explaining it, by images in the brain,
seems to be founded upon very gross notions of the
mind and its operations; as if the supposed images in
the brain, by a kind of contact, formed similar impres-
sions or images of objects upon the mind, of which im-
pressions it is supposed to be conscious,

We have endeavoured to shew, throughout the course
of this inquiry, that the impressions made upon the mind
by means of the five senses, have not the least resem-
blance to the objects of sense; and, therefore, as we see
no shadow of evidence that there are any such images in
the brain, so we see no purpose, in philosophy, that the
supposition of them can answer. Since the picture upon
the retina, therefore, is neither itself seen by the mind,
nor produces any impression upon the brain or sensorium,
which is seen by the mind, nor makes any impression
upon the mind that resembles the object, it may still be
asked, How this picture upon the retina causes vision ?

Before we answer this question, it is proper to observe,
that, in the operations of the mind, as well as in those of
bodies, we must often be satisfied with knowing that cer-
tain things are connected, and invariably follow one
another, without being able to discover the chain that
goes between them. It is to such connections that we
give the name of laws of nature; and when we say that
one thing produces another by a law of nature, this sig-
nifies no more, but that one thing, which we call in
popular language the cause, is constantly and invariably

SEC. XII.] THE PHILOSOPHY OF REID. 22$

followed by another, which we call the effect; and that
we know not how they are connected. Thus, we see it
is a fact, that bodies gravitate towards bodies; and that
this gravitation is regulated by certain mathematical pro-
portions, according to the distances of the bodies from
each other, and their quantities of matter. Being un-
able to discover the cause of this gravitation, and pre-
suming that it is the immediate operation, either of the
Author of nature, or of some subordinate cause, which
we have not hitherto been able to reach, we call it a law'
of nature. If any philosopher should hereafter be so
happy, as to discover the cause of gravitation, this can
only be done by discovering some more general law of
nature, of which the gravitation of bodies is a necessary
consequence. In every chain of natural causes, the
highest link is a primary law of nature, and the highest
link which we can trace, by just induction, is either this
primary law of nature, or a necessary consequence of it.
To trace out the laws of nature, by induction from the
phenomena of nature, is all that true philosophy aims at,
and all that it can ever reach.

There are laws of nature by which the operations of the
mind are regulated, there are also laws of nature that
govern the material system ; and, as the latter are the ulti-
mate conclusions which the human faculties can reach in
the philosophy of bodies, so the former are the ultimate
conclusions we can reach in the philosophy of minds.

To return, therefore, to the question above proposed,
we may see, from what hath been just now observed, that
it amounts to this — By what law of nature is a picture
upon the retina the mean or occasion of my seeing an ex-
ternal object of the same figure and colour in a contrary
position, and in a certain direction from the eye ?

It will, without doubt, be allowed that I see the whole
object in the same manner and by the same law by which
I see any one point of it. Now I know it to be a fact,
that, in direct vision, I see every point of the object in the

226 THE PHILOSOPHY OF REID. [Cn. VI.

direction of the right line that passeth from the centre of
the eye to that point of the object. And I know, like-
wise, from optics, that the ray of light that comes to the
centre of my eye, passes on to the retina in the same
direction. Hence, it appears to be a fact, that every point
of the object is seen in the direction of a right line passing
from the picture of that point on the retina, through the
centre of the eye. As this is a fact that holds universally
and invariably, it must either be a law of nature or the
necessary consequence of some more general law of
nature; and, according to the just rules of philosophising,
we may hold it for a law of nature, until some more
general law be discovered, whereof it is a necessary con-
sequence— which, I suspect, can never be done.

Thus, we see that the phaenomena of vision lead us by
the hand to a law of nature, or a law of our constitution,
of which law, our seeing objects erect by inverted images,
is a necessary consequence. For it necessarily follows,
from the law we have mentioned, that the object whose
picture is lowest on the retina must be seen in the highest
direction from the eye; and that the object whose picture
is on the right of the retina must be seen on the left; so
that, if the pictures had been erect in the retina, we
should have seen the object inverted. My chief intention
in handling this question, was to ^oint out this law of
nature, which, as it is a part of the constitution of the
human mind, belongs properly to the subject of this
inquiry. For this reason, I shall make some farther
remarks upon it, after doing justice to the ingenious Dr.
Porterfield, who long ago, in the " Medical Essays," or,
more lately, in his " Treatise of the Eye," pointed out,
as a primary law of our nature, That a visible object ap-
pears in the direction of a right line perpendicular to the
retina at that point where its image is painted. If lines
drawn from the centre of the eye to all parts of the retina
be perpendicular to it, as they must be very nearly, this
coincides with the law we have mentioned, and is the

SEC. XII.] THE PHILOSOPHY OF REID. 227

same in other words. In order, therefore, that we may
have a more distinct notion of this law of our constitution,
we may observe —

1. That we can give no reason why the retina is, of all
parts of the body, the only one on which pictures made
by the rays of light cause vision; and, therefore, we must
resolve this solely into a law of our constitution. We
may form such pictures by means of optical glasses,
upon the hand, or upon any other part of the body; but
they are not felt, nor do they produce anything like
vision. A picture upon the retina is as little felt as one
upon the hand; but it produces vision, for no other
reason that we know, but because it is destined by the
wisdom of nature to this purpose. The vibrations of the
air strike upon the eye, the palate, and the olfactory
membrane, with the same force as upon the membrani
tympani of the ear. The impression they make upon the
last produces the sensation of sound; but their impres-
sion upon any of the former produces no sensation at all.
This may be extended to all the senses, whereof each
hath its peculiar laws, according to which the impres-
sions made upon the organ of that sense, produce sensa-
tions or perceptions in the mind, that cannot be pro-
duced by impressions made upon any other organ.

2. We may observe, that the laws of perception, by
the different senses, are very different, not only in re-
spect of the nature of the objects perceived by them, but
likewise in respect of the notices they give us of the dis-
tance and situation of the object. In all of them the
object is conceived * to be external, and to have real
existence, independent of our perception : but in one,
the distance, figure, and situation of the object, are all

* The common sense of mankind assures us that the object of
sense, is not merely conceived to be external, but pe re eived in its ex-
ternality; that we know the Non-Ego, not merely mediately, by a
representation in the Ego, but immediately, as existing though only
as existing in relation to our organs. — H.

228 THE PHILOSOPHY OF REID. [CH. VI.

presented to the mind: in another, the figure and situa-
tion, but not the distance; and in others, neither figure,
situation, nor distance. In vain do we attempt to ac-
count for these varieties in the manner of perception by
the different senses, from principles of anatomy or natural
philosophy. They must at last be resolved into the will
of our Maker, who intended that our powers of percep-
tion should have certain limits, and adapted the organs
of perception, and the laws of nature by which they
operate, to his wise purposes.

When we hear an unusual sound, the sensation indeed
is in the mind, but we know that there is something ex-
ternal that produced this sound. At the same time, our
hearing does not inform us whether the sounding body
is near or at a distance, in this direction or that ; and
therefore we look round to discover it.

If any new phenomenon appears in the heavens, we
see exactly its colour, its apparent place, magnitude, and
figure; but we see not its distance. It may be in the at-
mosphere, it may be among the planets, or it may be in
the sphere of the fixed stars, for anything the eye can de-
termine.

The testimony of the sense of touch reaches only to
objects that are contiguous to the organ, but, with re-
gard to them, is more precise and determinate. When
we feel a body with our hand, we know the figure, dis-
tance, and position of it, as well as whether it is rough
or smooth, hard or soft, hot or cold.

The sensations of touch, of seeing, and hearing, are
all in the mind, and can have no existence but when
they are perceived. How do they all constantly and in-
variably suggest the conception and belief of external
objects, which exist whether they are perceived or not ?
No philosopher can give any other answer to this, but
that such is the constitution of our nature. How do we
know that the object of touch is at the finger's end, and
nowhere else ? — that the object of sight is in such a di-

SEC. XII.] THE PHILOSOPHY OF REID. 22g

rection from the eye, and in no other, but maybe at any
distance ? — and that the object of hearing may be at any
distance, and in any direction ? Not by custom surely
— not by reasoning, or comparing ideas — but by the
constitution of our nature. How do we perceive visible
objects in the direction of right lines perpendicular to
that part of the retina on which the rays strike, while we
do not perceive the objects of hearing in lines perpendic-
ular to the membrana tympani upon which the vibrations
of the air strike ? Because such are the laws of our na-
ture. How do we know the parts of our bodies affected
by particular pains ? Not by experience or by reason-
ing, but by the constitution of nature. The sensation of
pain is, no doubt, in the mind, and cannot be said to
have any relation, from its own nature, to any part of
the body; but this sensation, by our constitution, gives a
perception of some particular part of the body, whose
disorder causes the uneasy sensation. If it were not so,
a man who never before felt either the gout or the tooth-
ache,, when he is first seized with the gout in his toe,
might mistake it for the toothache.

Every sense, therefore, hath its peculiar laws and
limits, by the constitution of our nature; and one of the
laws of sight is, that we always see an object in the di-
rection of a right line, passing from its image on the ret-
ina through the centre of the eye.

3. Perhaps some readers will imagine that it is easier,
and will answer the purpose as well, to conceive a law
of nature, by which we shall always see objects in the
place in which they are, and in their true position, with-
out having recourse to images on the retina, or to the
optical centre of the eye.

To this I answer, that nothing can be a law of nature
which is contrary to fact. The laws of nature are the
most general facts we can discover in the operations of
nature. Like other facts, they are not to be hit upon by
a happy conjecture, but justly deduced from observation;

230 THE PHILOSOPHY OF REID. [CH. VI.

like other general facts, they are not to be drawn from a
few particulars, but from a copious, patient, and cautious
induction. That we see things always in their true
place and position, is not fact; and therefore it can be
no law of nature. In a plain mirror, I see myself, and
other things, in places very different from those they
really occupy. And so it happens in every instance
wherein the rays coming from the object are either re-
flected or refracted before falling upon the eye. Those
who know anything of optics, know that, in all such
cases, the object is seen in the direction of a line passing
from the centre of the eye, to the point where the rays
were last reflected or refracted; and that upon this all the
powers of the telescope and microscope depend.

Shall we say, then, that it is a law of nature, that the
object is seen in the direction which the rays have when
they fall on the eye, or rather in the direction contrary
to that of the rays when they fall upon the eye ? No.
This is not true; and therefore it is no law of nature.
For the rays, from any one point of the object, come to
all parts of the pupil; and therefore must have different
directions: but we see the object only in one of these di-
rections —to wit, in the direction of the rays that come
to the centre of the eye. And this holds true, even
when the rays that should pass through the centre are
stopped, and the object is seen by rays that pass at a dis-
tance from the centre.

Perhaps it may still be imagined, that, although we
are not made so as to see objects always in their true
place, nor so as to see them precisely in the direction of
the rays when they fall upon the cornea; yet we may be
so made as to see the object in the direction which the
rays have when they fall upon the retina, after they have
undergone all their refractions in the eye — that is, in the
direction in which the rays pass from the crystalline to
the retina. But neither is this true ; and consequently it
is no law of our constitution. In order to see that it is

Sac. XII.] THE PHILOSOPHY OF REID. 231

not true, we must conceive all the rays that pass from
the crystalline to one point of the retina, as forming a
small cone, whose base is upon the back of the crystal-
line, and whose vertex is a point of the retina. It is evi-
dent that the rays which form the picture in this point,
have various directions, even after they pass the crystal-
line: yet the object is seen only in one of these directions
— to wit, in the direction of the rays that come from the
centre of the eye. Nor is this owing to any particular
virtue in the central rays, or in the centre itself; for the
central rays may be stopped. When they are stopped,
the image will be formed upon the same point of the
retina as before, by rays that are not central, nor have
the same direction which the central rays had: and in
this case the object is seen in the same direction as be-
fore, although there are now no rays coming in that di-
rection.

From this induction we conclude, That our seeing an
object in that particular direction in which we do see it,
is not owing to any law of nature by which we are made
to see it in the direction of the rays, either before their
refractions in the eye, or after, but to a law of our na-
ture, by which we see the object in the direction of the
right line that passeth from the picture of the object upon
the retina to the centre of the eye.

The facts upon which I ground this induction, are
taken from some curious experiments ofScheiner, in his
"Fundamentum Opticum," quoted by Dr. Porterfield,
and confirmed by his experience. I have also repeated
these experiments, and found them to answer. As they
are easily made, and tend to illustrate and confirm the
law of nature I have mentioned, I shall recite them as
briefly and distinctly as I can.

Experiment i. Let a very small object, such as the
head of a pin, well illuminated, be fixed at such a dis-
tance from the eye as to be beyond the nearest limit and
within the farthest limit of distinct vision. For a young

232 THE PHILOSOPHY OF REID. [Cn. VI.

eye, not near-sighted, the object may be placed at the
distance of eighteen inches. Let the eye be kept steadily
in one place, and take a distinct view of the object.
We know, from the principles of optics, that the rays
from any one point of this object, whether they pass
through the centre of the eye, or at any distance from
the centre which the breadth of the pupil will permit, do
all unite again in one point of the retina. We know,
also, that these rays have different directions, both be-
fore they fall upon the eye, and after they pass through
the crystalline.

Now, we can see the object by any one small parcel
of these rays, excluding the rest, by looking through a
small pin-hole in a card. Moving this pin-hole over
the various parts of the pupil, we can see the object,
first by the rays that pass above the centre of the eye,
then by the central rays, then by the rays that pass
below the centre, and in like manner by the rays that
pass on the right and left of the centre. Thus, we view
this object, successively, by rays that are central, and by
rays that are not central; by rays that have different di-
rections, and are variously inclined to each other, both
when they fall upon the cornea, and when they fall upon
the retina; but always by rays which fall upon the same
point of the retina. And what is the event ? It is this —
that the object is seen in the same individual direction,
whether seen by all these rays together, or by any one
parcel of them.

Experiment 2. Let the object above mentioned be
now placed within the nearest limit of distinct vision —
that is, for an eye that is not near-sighted, at the dis-
tance of four or five inches. We know that, in this case,
the rays coming from one point of the object do not
meet in one point of the retina, but spread over a small
circular spot of it; the central rays occupying the centre
of this circle, the rays that pass above the centre occupy-
ing the upper part of the circular spot, and so of the rest.

S&c. Xtl.J THE PHILOSOPHY OF REID. 233

And we know that the object is, in this case, seen con-
fused; every point of it being seen, not in one, but in va-
rious directions. To remedy this confusion, we look at
the object through the pin-hole, and while we move the
pin-hole over the various parts of the pupil, the object
does not keep its place, but seems to move in a contrary
direction.

It is here to be observed, that, when the pin-hole is
carried upwards over the pupil, the picture of the object
is carried upwards upon the retina, and the object, at
the same time, seems to move downwards, so as to be
always in the right line, passing from the picture through
the centre of the eye. It is likewise to be observed, that
the rays which form the upper and the lower pictures
upon the retina do not cross each other, as in ordinary
vision ; yet, still, the higher picture shews the object
lower, and the lower picture shews the object higher,
in the same manner as when the rays cross each other.
Whence we may observe, by the way, that this phaenom-
enon of our seeing objects in a position contrary to that
of their pictures upon the retina, does not depend upon
the crossing of the rays, as Kepler and Des Cartes con-
ceived.

Experiment 3. Other things remaining as in the last
experiment, make three pin-holes in a straight line, so
near that the rays coming from the object through all
the holes may enter the pupil at the same time. In this
case, we have a very curious phsenomenon ; for the ob-
ject is seen triple with one eye. And if you make more
holes within the breadth of the pupil, you will see as
many objects as there are holes. However, we shall sup-
pose them only three — one on the right, one in the mid-
dle and one on the left ; in which case you see three ob-
jects standing in a line from right to left.

It is here to be observed, that there are three pictures
on the retina ; that on the left being formed by the rays
which pass on the left of the eye's centre, the middle

234 THE PHILOSOPHY OF REID. [C». Vt.

picture being formed by the central rays, and the right-
hand picture by the rays which pass on the right of the
eye's centre. It is farther to be observed, that the ob-
ject which appears on the right, is not that which is seen
through the hole on the right, but that which is seen
through the hole on the left ; and, in like manner, the
left-hand object is seen through the hole on the right,
as is easily proved by covering the holes successively : so
that, whatever is the direction of the rays which form the
right-hand and left-hand pictures, still the right-hand
picture shews a left-hand object, and the left-hand pict-
ure shews a right-hand object.

Experiment 4. It is easy to see how the two last ex-
periments may^ be varied, by placing the object beyond
the farthest limit of distinct vision. In order to make
this experiment, I looked at a candle at the distance of
ten feet, and put the eye of my spectacles behind the
card, that the rays from the same point of the object
might meet and cross each other, before they reached
the retina. In this case, as in the former, the candle
was seen triple through the three pin-holes ; but the
candle on the right was seen through the hole on the
right ; and, on the contrary, the left-hand candle was
seen through the hole on the left. In this experiment it
is evident, from the principles of optics, that the rays
foYming the several pictures on the retina cross each
other a little before they reach the retina ; and, therefore,
the left-hand picture is formed by the rays which pass
through the hole on the right : so that the position of
the pictures is contrary to that of the holes by which
they are formed ; and, therefore, is also contrary to that
of their objects — as we have found it to be in the former
experiments.

These experiments exhibit several uncommon phae-
nomena, that regard the apparent place, and the direc-
tion of visible objects from the eye ; phenomena that
seem to be most contrary to the common rules of vision.

SEC. XII.] THE PHILOSOPHY OF REID. 235

When we look at the same time through three holes that
are in a right line, and at certain distances from each
other, we expect that the objects seen through them
should really be, and should appear to be, at a distance
from each other. Yet, by the first experiment, we may,
through three such holes, see the same object, and the
same point of that object ; and through all the three it
appears in the same individual place and direction.

When the rays of light come from the object in right
lines to the eye, without any reflection, inflection, or
refraction, we expect that the object should appear in
its real and proper direction from the eye ; and so it
commonly does. But in the second, third, and fourth
experiments, we see the object in a direction which is
not its true and real direction from the eye, although the
rays come from the object to the eye, without any in-
flection, reflection, or refraction.

When both the object and the eye are fixed without
the least motion, and the medium unchanged, we expect
that the object should appear to rest, and keep the same
place. Yet, in the second and fourth experiments, when
both the eye and the object are at rest, and the medium
unchanged, we make the object appear to move upwards
or downwards, or in any direction we please.

When we look, at the same time and with the same
eye, through holes that stand in a line from right to left,
we expect that the object seen through the left-hand hole
should appear on the left, and the object seen through
the right-hand hole should appear on the right. Yet, in
the third experiment, we find the direct contrary.

Although many instances occur in seeing the same ob-
ject double with two eyes, we always expect that it should
appear single when seen only by one eye. Yet, in the
second and fourth experiments, we have instances
wherein the same object may appear double, triple, or
quadruple to one eye, without the help of a polyhedron or
multiplying glass.

236 THE PHILOSOPHY OF REID. [Cn. VI.

All these extraordinary phenomena, regarding the di-
rection of visible objects from the eye, as well as those
that are common and ordinary, lead us to that law of
nature which I have mentioned, and are the necessary
consequences of it. And, as there- is no probability that
we shall ever be able to give a reason why pictures upon
the retina make us see external objects, any more than
pictures upon the hand or upon the cheek ; or, that we
shall ever be able to give a reason, why we see the ob-
ject in the direction of a line passing from its picture
through the centre of the eye, rather than in any other
direction — I am, therefore, apt to look upon this law as
a primary law of our constitution.

To prevent being misunderstood, I beg the reader to
observe, that I do not mean to affirm that the picture
upon the retina will make us see an object in the direc-
tion mentioned, or in any direction, unless the optic
nerve, and the other more immediate instruments of vis-
ion, be sound, and perform their function. We know
not well what is the office of the optic nerve, nor in what
manner it performs that office ; but that it hath some
part in the faculty of seeing, seems to be certain ; be-
cause, in an amaurosis, which is believed to be a dis-
order of the optic nerve, the pictures on the retina are
clear and distinct, and yet there is no vision. '

We know still less of the use and function of the
choroid membrane ; but it seems likewise to be neces-
sary to vision : for it is well known, that pictures upon
that part of the retina where it is not covered by the
choroid — I mean at the entrance of the optic nerve —
produce no vision any more than a picture upon the
hand. We acknowledge, therefore, that the retina is not
the last and most immediate instrument of the mind in
vision. There are other material organs, whose oper-
ation is necessary to seeing, even after the pictures upon
the retina are formed. If ever we come to know the
structure and use of the choroid membrane, the optic

THE PHILOSOPHY OF REID. 237

nerve, and the brain, and what impressions are made
upon them by means of the pictures on the retina,
some more links of the chain may be brought within our
view, and a more general law of vision discovered ; but,
while we know so little of the nature and office of these
more immediate instruments of vision, it seems to be im-
possible to trace its laws beyond the pictures upon the
retina.

Neither do I pretend to say, that there may not be
diseases of the eye, or accidents, which may occasion
our seeing objects in a direction somewhat different from
that mentioned above. I shall beg leave to mention one
instance of this kind that concerns myself.

In May, 1761, being occupied in making an exact
meridian, in order to observe the transit of Venus, I
rashly directed to the sun, by my right eye, the cross
hairs of a small telescope. I had often done the like in
my younger days with impunity ; but I suffered by it at
last, which I mention as a warning to others.

I soon observed a remarkable dimness in that eye; and
for many weeks, when I was in the dark, or shut my
eyes, there appeared before the right eye a lucid spot,
which trembled much like the image of the sun seen
by reflection from water. This appearance grew fainter,
and less frequent, by degrees ; so that now there are
seldom any remains of it. But some other very sensible
effects of this hurt still remain. For, First, The sight
of the right eye continues to be more dim than that of
the left Secondly, The nearest limit of distinct vision
is more remote in the right eye than in the other ; al-
though, before the time mentioned, they were equal in
both these respects, as I had found by many trials. But,
thirdly, what I chiefly intended to mention is, That a
straight line, in some circumstances, appears to the right
eye to have a curvature in it. Thus, when I look upon
a music book, and, shutting my left eye, direct the right
to a point of the middle line of the five which compose

238 THE PHILOSOPHY OF REID. [Cn. VI.

the staff of music, the middle line appears dim, indeed,
at the point to which the eye is directed, but straight; at
the same time, the two lines above it, and the two below
it, appear to be bent outwards, and to be more distant
from each other and from the middle line, than at other
parts of the staff, to which the eye is not directed.
Fourthly, Although I have repeated this experiment
times innumerable, within these sixteen months, I do
not find that custom and experience takes away this ap-
pearance of curvature in straight lines. Lastly, This ap-
pearance of curvature is perceptible when I look with
the right eye only, but not when I look with both eyes;
yet I see better with both eyes together, than even with
the left eye alone.

I have related this fact minutely as it is, without re-
gard to any hypothesis; because I think such uncommon
facts deserve to be recorded. I shall leave it to others
to conjecture the cause of this appearance. To me it
seems most probable, that a small part of the retina
toward the centre is shrunk, and that thereby the contig-
uous parts are drawn nearer to the centre, and to one an-
other, than they were before; and that objects whose im-
ages fall on these parts, appear at that distance from each
other which corresponds, not to the interval of the parts
in their present preternatural contraction, but to their in-
terval in their natural and sound state.

Section XIII.

OF SEEING OBJECTS SINGLE WITH TWO EYES.

Another phsenomenon of vision which deserves atten-
tion, is our seeing objects single with two eyes. There
are two pictures of the object, one on each retina, and
each picture by itself makes us see an object in a certain
direction from the eye; yet both together commonly

SEC. XIII.] THE PHILOSOPHY OF REID. 2$9

make us see only one object. All the accounts or solu-
tions of this phaenomenon given by anatomists and phi-
losophers seem to be unsatisfactory. I shall pass over
the opinions of Galen, of Gassendus, of Baptista Porta,
and of Rohault. The reader may see these examined
and refuted by Dr. Porterfield. I shall examine Dr.
Porterfield's own opinion, Bishop Berkeley's, and some
others. But it will be necessary first to ascertain the
facts; for, if we mistake the phaenomena of single and
double vision, it is ten to one that this mistake will lead
us wrong in assigning the causes. This likewise we
ought carefully to attend to, which is acknowledged in
theory by all who have any true judgment or just taste
in inquiries of this nature, but is very often overlooked
in practice — namely, that, in the solution of natural
phaenomena, all the length that the human faculties can
carry us, is only this, that, from particular phaenomena,
we may, by induction, trace out general phaenomena, of
which all the particular ones are necessary consequences.
And when we have arrived at the most general phenom-
ena we can reach, there we must stop. If it is asked,
Why such a body gravitates towards the earth ? all the
answer that can be given is, Because all bodies gravitate
towards the earth. This is resolving a particular phae-
nomenon into a general one. If it should again be asked,
Why do all bodies gravitate toward the earth ? we can
give no other solution of this phaenomenon, but that all
bodies whatsoever gravitate towards each other. This is
^resolving a general phaenomenon into a more general
one. If it should be asked, Why all bodies gravitate to
one another? we cannot tell; but, if we could tell, it
could only be by resolving this universal gravitation of
bodies into some other phaenomenon still more general,
and of which the gravitation of all bodies is a particular
instance. The most general phaenomena we can reach,
are what we call laws of nature; so that the laws of na-
ture are nothing else but the most general facts relating

24O THE PHILOSOPHY OF REID. [CM. VI.

to the operations of nature, which include a great many
particular facts under them. And if, in any case, we
should give the name of a law of nature to a general
phaenomenon, which human industry shall afterwards
trace to one more general, there is no great harm done.
The most general assumes the name of a law of nature
when it is discovered, and the less general is contained
and comprehended in it. Having premised these things,
we proceed to consider the phaenomena of single and
double vision, in order to discover some general princi-
ple to which they all lead, and of which they are the
necessary consequences. If we can discover any such
general principle, it must either be a law of nature,
or the necessary consequence of some law of nature;
and its authority will be equal whether it is the first or
the last.

1. We find that, when the eyes are sound and perfect,
and the axes of both directed to one point, an object
placed in that point is seen single — and here we observe,
that in this case the two pictures which shew the object
single, are in the centres of the retina. When two pict-
ures of a small object are formed upon points of the
retina, if they shew the objects single, we shall, for the
sake of perspicuity, call such two points of the retina,
corresponding points; and where the object is seen double,
we shall call the points of the retina on which the pict-
ures are formed, points that do not correspond. Now, in
this first phaenomenon, it is evident, that the two centres
of the retina are corresponding points.

2. Supposing the same things as in the last phaenomenon,
other objects at the same distance from the eyes as that to
which their axes are directed, do also appear single. Thus,
if I direct my eyes to a candle placed at the distance of
ten feet, and, while I look at this candle, another stands at
the same distance from my eyes, within the field of vision,
1 can, while I look at the first candle, attend to the ap-
pearance which the second makes to the eye; and I find

SEC. XIIL] THE PHILOSOPHY OF REID. 241

that in this case it always appears single. It is here
to be observed, that the pictures of the second candle
do not fall upon the centres of the retince, but they
both fall upon the same side of the centres — that is,
both to the right, or both to the left; and both are
at the same distance from the centres. This might
easily be demonstrated from the principles of optics.
Hence it appears, that in this second phaenomenon
of single vision, the corresponding points are points of
the two retina, which are similarly situate with respect
to the two centres, being both upon the same side of the
centre, and at the same distance from it. It appears
likewise, from this phaenomenon, that every point in one
retina corresponds with that which is similarly situate
in the other.

3. Supposing still the same things, objects which are
much nearer to the eyes, or much more distant from
them, than that to which the two eyes are directed,
appear double. Thus, if the candle is placed at the
distance of ten feet, and I hold my finger at arms-
length between my eyes and the candle — when I look at
the candle, I see my finger double; and when I look at
my finger, I see the candle double; and the same thing
happens with regard to all other objects at like distances
which fall within the sphere of vision. In this phaenom-
enon, it is evident to those who understand the princi-
ples of optics, that the pictures of the objects which are
seen double, do not fall upon the points of the retince
which are similarly situate, but that the pictures of the
objects seen single do fall upon points similarly situate.
Whence we infer, that, as the points of the two retince,
which are similarly situate with regard to the centres, do
correspond, so those which are dissimilarly situate do
not correspond.

4. It is to be observed, that, although, in such cases
as are mentioned in the last phaenomenon, we have been
accustomed from infancy to see objects double which

242 THE PHILOSOPHY OF REID. [CH. VI.

we know to be single; yet custom, and experience of the
unity of the object, never take away this appearance of
duplicity.

5. It may, however, be remarked that the custom of
attending to visible appearances has a considerable ef-
fect, and -makes the phaenomenon of double vision to
be more or less observed and remembered. Thus you
may find a man that can say, with a good conscience, that
he never saw things double all his life; yet this very man,
put in the situation above mentioned, with his finger be-
tween him and the candle, and desired to attend to the
appearance of the object which he does not look at, will,
upon the first trial, see the candle double, when he looks
at his finger; and his finger double, when he looks at the
candle. Does he now see otherwise than he saw before?
No; surely; but he now attends to what he never attended
to before. The same double appearance of an object
hath been a thousand times presented to his eye before
now, but he did not attend to it; and so it is as little an
object of his reflection and memory, as if it had never
happened.

When we look at an object, the circumjacent objects
may be seen at the same time, although more obscurely
and indistinctly: for the eye hath a considerable field of
vision, which it takes in at once. But we attend only
to the object we look at. The other objects which fall
within the field of vision, are not attended to; and there-
fore are as if they were not seen. If any of them draws
our attention, it naturally draws the eyes at the same
time : for, in the common course of life, the eyes always
follow the attention : or if at any time, in a revery, they
are separated from it, we hardly at that time see what is
directly before us. Hence we may see the reason why
the man we are speaking of thinks that he never before
saw an object double. When he looks at any object, he
sees it single, and takes no notice of other visible objects
at that time, whether they appear single or double. If

SEC. XIII.] THE PHILOSOPHY OF REID. 243

any of them draws his attention, it draws his eyes at the
same time ; and, as soon as the eyes are turned towards
it, it appears single. But, in order to see things double
— at least, in order to have any reflection or remembrance
that he did so — it is necessary that he should look at one
object, and at the same time attend to the faint appear-
ance of other objects which are within the field of vision.
This is a practice which perhaps he never used, nor at-
tempted ; and therefore he does not recollect that ever
he saw an object double. But when he is put upon giv-
ing this attention, he immediately sees objects double,
in the same manner, and with the very same circum-
stances, as they who have been accustomed, for the
greatest part of their lives, to give this attention.

There are many phenomena of a similar nature, which
shew that the mind may not attend to, and thereby, in
some sort, not perceive objects that strike the senses. I
had occasion to mention several instances of this in the
second chapter; and I have been assured, by persons of
the best skill in music, that, in hearing a tune upon the
harpsichord, when they give attention to the treble, they
do not hear the bass; and when they attend to the bass,
they do not perceive the air of the treble. Some persons
are so near-sighted, that, in reading, they hold the book
to one eye, while the other is directed to other objects.
Such persons acquire the habit of attending, in this case,
to the objects of one eye, while they give no attention to
those of the other.

6. It is observable, that, in all cases, wherein we see
an object double, the two appearances have a certain
position with regard to one another, and a certain ap-
parent or angular distance. This apparent distance is
greater or less in different circumstances ; but, in the same
circumstances, it is always the same, not only to the
same, but to different persons.

Thus, in the experiment above mentioned, if twenty
different persons, who see perfectly with both eyes, shall

244 THE PHILOSOPHY OF REID. [Cn. VI.

place their finger and the candle at the distances above
expressed, and hold their heads upright, looking at the
finger, they will see two candles, one on the right, another
on the left. That which is seen on the right, is seen by
the right eye, and that which is seen on the left, by the
left eye; and they will see them at the same apparent dis-
tance from each other. If, again, they look at the candle,
they will see two fingers, one on the right, and the other
on the left ; and all will see them at the same apparent
distance ; the finger towards the left being seen by the
right eye, and the other by the left. If the head is laid
horizontally to one side, other circumstances remaining
the same, one appearance of the object seen double, will
be directly above the other. In a word, vary the cir-
cumstances as you please, and the appearances are varied
to all the spectators in one and the same manner.

7. Having made many experiments in order to as-
certain the apparent distance of the two appearances of an
object seen double, I have found that in all cases this
apparent distance is proportioned to the distance between
the point of the retina, where the picture is made in one
eye, and the point which is situated similarly to that on
which the picture is made on the other eye ; so that, as
the apparent distance of two objects seen with one eye,
is proportioned to the arch of the retina, which lies be-
tween their pictures, in like manner, when an object is
seen double with the two eyes, the apparent distance of
the two appearances is proportioned to the arch of either
retina, which lies between the picture in that retina, and
the point corresponding to that of the picture in the
other retina.

8. As, in certain circumstances, we invariably see one
obect appear double, so, in others, we as invariably see
two objects unite into one, and, in appearance, lose their
duplicity. This is evident in the appearance of the
binocular telescope. And the same thing happens when
any two similar tubes are applied to the two eyes in a

SEC. XIII.] THE PHILOSOPHY OF REID. 245

parallel direction; for, in this case, we see only one tube.
And if two shillings are placed at the extremities of the
two tubes, one exactly in the axis of one eye, and the
other in the axis of the other eye, we shall see but one
shilling. If two pieces of coin, or other bodies, of dif-
ferent colour, and of different figure be properly placed
in the two axes of the eyes, and at the extremities of the
tubes, we shall see both the bodies in one and the same
place, each as it were spread over the other, without hid-
ing it ; and the colour will be that which is compounded
of the two colours.

9. From these phsenomena, and from all the trials I
have been able to make, it appears evidently, that, in
perfect human eyes, the centres of the two retince cor-
respond and harmonize with one another, and that every
other point in one retina doth correspond and harmonize
with the point which is similarly situate in the other-
in such manner, that pictures falling on the corresponding
points of the two retince, shew only one object, even when
there are really two; and pictures falling upon points of
the refines which do not correspond, shew us two visible
appearances, although there be but one object: so that
pictures, upon corresponding points of the two retince,
present the same appearance to the mind as if they had
both fallen upon the same point of one retina; and
pictures upon points of the two retince, which do not
correspond, present to the mind the same apparent dis-
tance and position of two objects, as if one of those
pictures was carried to the point corresponding to it in
the other retina. This relation and sympathy between
corresponding points of the two retince, I do not advance
as an hypothesis, but as a general fact or phenomenon
of vision. All the phenomena before mentioned, of
single or double vision, lead to it, and are necessary
consequences of it. It holds true invariably in all per-
fect human eyes, as far as I am able to collect from in-
numerable trials of various kinds made upon my own

246 THE PHILOSOPHY OF REID. [Cn. VI.

eyes, and many made by others at my desire. Most of
the hypotheses that have been contrived to resolve the
phenomena of single and double vision, suppose this
general fact, while their authors were not aware of it.
Sir Isaac Newton, who was too judicious a philosopher,
and too accurate an observer, to have offered even a
conjecture which did not tally with the facts that had
fallen under his observation, proposes a query with re-
spect to the cause of it — " Optics, " Query, 15. The judi-
cious Dr. Smith, in his "Optics," Book I, § 137, hath
confirmed the truth of this general phenomenon from
his own experience, not only as to the apparent unity of
objects whose pictures fall upon the corresponding points
of the retitue, but also as to the apparent distance of the
two appearances of the same object when seen double.

This general phenomenon appears, therefore, to be
founded upon a very full induction, which is all the evi-
dence we can have for a fact of this nature. Before we
make an end of this subject, it will be proper to inquire,
First, Whether those animals whose eyes have an adverse
position in their heads, and look contrary ways, have
such corresponding points in their retina? Secondly,
What is the position of the corresponding points in im-
perfect human eyes — I mean in those that squint ? And,
in the last place, Whether this harmony of the corre-
sponding points in the retince, be natural and original, or
the effect of custom ? And, if it is original, Whether it
can be accounted for by any of the laws of nature al-
ready discovered ? or whether it is itself to be looked
upon as a law of nature, and a part of the human con-
stitution ?

Section XIV.

OF THE LAWS OF VISION IN BRUTE ANIMALS.

It is the intention of nature, in giving eyes to animals,
that they may perceive the situation of visible objects,
or the direction in which they are placed — it is probable,

Stc. XIV.] THE PHILOSOPHY OF REID. 247

therefore, that, in ordinary cases, every animal, whether
it has many eyes or few, whether of one structure or of
another, sees objects single, and in their true and pro-
per direction. And, since there is a prodigious variety
in the structure, the motions, and the number of eyes in
different animals and insects, it is probable that the laws
by which vision is regulated, are not the same in all, but
various, adapted to the eyes which nature hath given
them.

Mankind naturally turn their eyes always the same
way, so that the axes of the two eyes meet in one point.
They naturally attend to, or look at that object only
which is placed in the point where the axes meet. And
whether the object be more or less distant, the configu-
ration of the eye is adapted to the distance of the object,
so as to form a distinct picture of it.

When we use our eyes in this natural way, the t\vo
pictures of the object we look at are formed upon the
centres of the two retince; and the two pictures of any
contiguous object are formed upon the points of the
retina which are similarly situate with regard to the
centres. Therefore, in order to our seeing objects single,
and in their proper direction, with two eyes, it is suffi-
cient that we be so constituted, that objects whose pictures
are formed upon the centres of the two retince, or upon
points similarly situate with regard to these centres, shall
be seen in the same visible place. And this is the con-
stitution which nature hath actually given to human
eyes.

When we distort our eyes from their parallel direction,
which is an unnatural motion, but may be learned by
practice; or when we direct the axes of the two eyes to
one point, and at the same time direct our attention to
some visible object much nearer or much more distant
than that point, which is also unnatural, yet may be
learned: in these cases, and in these only, we see one ob-
ject double, or two objects confounded in one. In these

248 THE PHILOSOPHY OF REID. [Cn. VI.

cases, the two pictures of the same object are formed
upon points of the retince which are not similarly sit-
uate, and so the object is seen double; or the two pic-
tures of different objects are formed upon points of the
retince which are similarly situate, and so the two ob-
jects are seen confounded in one place.

Thus it appears, that the laws of vision in the human
constitution are wisely adapted to the natural use of
human eyes, but not to that use of them which is un-
natural. We see objects truly when we use our eyes in
the natural way; but have false appearances presented to
us when we use them in a way that is unnatural. We
may reasonably think that the case is the same with
other animals. But is it not unreasonable to think, that
those animals which naturally turn one eye towards one
object, and another eye towards another object, must
thereby have such false appearances presented to them,
as we have when we do so against nature ?

Many animals have their eyes by nature placed ad-
verse and immovable, the axes of the two eyes being
always directed to opposite points. Do objects painted
on the centres of the two retince appear to such animals
as they do to human eyes, in one and the same visible
place ? I think it is highly probable that they do not ;
and that they appear, as they really are, in opposite places.

If we judge from analogy in this case, it will lead us
to think that there is a certain correspondence between
points of the two retince in such animals, but of a differ-
ent kind from that which we have found in human eyes.
The centre of one retina will correspond with the centre
of the other, in such manner that the objects whose pic-
tures are formed upon the secorresponding points, shall
appear not to be in the same place, as in human eyes,
but in opposite places. And in the same manner will
the superior part of one retina correspond with the in-
ferior part of the other, and the anterior part of one with
the posterior part of the other.

SEC. XV.] THE PHILOSOPHY OF REID. 24$

Some animals, by nature, turn their eyes with equal
facility, either the same way or different ways, as we turn
our hands and arms. Have such animals corresponding
points in their retina, and points which do not corre-
spond, as the human kind has ? I think it is probable
that they have not; because such a constitution in them
could serve no other purpose but to exhibit false appear-
ances.

If we judge from analogy, it will lead us to think,
that, as such animals move their eyes in a manner sim-
ilar to that in which we move our arms, they have an
immediate and natural perception of the direction they
give to their eyes, as we have of the directions we give to
our arms; and perceive the situation of visible objects
by their eyes, in a manner similar to that in which we
perceive the situation of tangible objects with our hands.

We cannot teach brute animals to use their eyes in
any other way than in that which nature hath taught
them; nor can we teach them to communicate to us the
appearances which visible objects make to them, either
in ordinary or in extraordinary cases. We have not,
therefore, the same means of discovering the laws of
vision in them, as in our own kind, but must satisfy
ourselves with probable conjectures; and what we have
said upon this subject, is chiefly intended to shew, that
animals to which nature hath given eyes differing in
their number, in their position, and in their natural
motions, may very probably be subjected to different
laws of vision, adapted to the peculiarities of their organs
of vision.

Section XV.

SQUINTING CONSIDERED HYPOTHETICALLY.

Whether there be corresponding points in the retina,
of those who have an involuntary squint ? and if there
are, whether they be situate in the same manner as in

2$0 THE PHILOSOPHY OF REID. [CH. VI.

those who have no squint ? are not questions of mere
curiosity. They are of real importance to the physician
who attempts the cure of a squint, and to the patient who
submits to the cure. After so much has been said of the
strabismus, or squint, both by medical and by optical
writers, one might expect to find abundance of facts for
determining these questions. Yet, I confess, I have
been disappointed in this expectation, after taking some
pains both to make observations, and to collect those
which have been made by others.

Nor will this appear very strange, if we consider, that
to make the observations which are necessary for deter-
mining these questions, knowledge of the principles of
optics, and of the laws of vision, must concur with
opportunities rarely to be met with.

Of those who squint, the far greater part have no dis-
tinct vision with one eye. When this is the case, it is
impossible, and indeed of no importance, to determine
the situation of the corresponding points. When both
eyes are good, they commonly differ so much in their
direction, that the same object cannot be seen by both
at the same time; and, in this case, it will be very diffi-
cult to determine the situation of the corresponding
points; for such persons will probably attend only to the
objects of one eye, and the objects of the other will be
as little regarded as if they were not seen.

We have before observed, that, when we look at a
near object, and attend to it, we do not perceive the
double appearances of more distant objects, even when
they are in the same direction, and are presented to the
eye at the same time. It is probable that a squinting
person, when he attends to the objects of one eye, will,
in like manner, have his attention totally diverted from
the objects of the other; and that he will perceive them
as little as we perceive the double appearances of objects
when we use our eyes in the natural way. Such a per-
son, therefore, unless he is so much a philosopher as to

SEC. XV.] THE PHILOSOPHY OF REID. $$t

have acquired the habit of attending very accurately to
the visible appearances of objects, and even of objects
which he does not look at, will not be able to give any
light to the questions now under consideration.

It is very probable that hares, rabbits, birds, and fishes,
whose eyes are fixed in an adverse position, have the
natural faculty of attending at the same time to visible
objects placed in different, and even in contrary direc-
tions; because, without this faculty, they could not have
those advantages from the contrary direction of their
eyes, which nature seems to have intended. But it is
not probable that those who squint have any such natural
faculty; because we find no such faculty in the rest
of the species. We naturally attend to objects placed in
the point where the axes of the two eyes meet, and to
them only. To give attention to an object in a different
direction is unnatural and not to be learned without
pains and practice.

A very convincing proof of this may be drawn from a
fact now well known to philosophers : when one eye is
shut, there is a certain space within the field of vision,
where we can see nothing at all — the space which is di-
rectly opposed to that part of the bottom of the eye
where the optic nerve enters. This defect of sight, in
one part of the eye, is common to all human eyes, and
hath been so from the beginning of the world; yet it
was never known, until the sagacity of the Abb6 Mari-
otte discovered it in the last century. And now when
it is known, it cannot be perceived, but by means of
some particular experiments, which require care and at-
tention to make them succeed.

What is the reason that so remarkable a defect of
sight, common to all mankind, was so long unknown,
and is now perceived with so much difficulty ? It is
surely this — That the defect is at some distance from the
axis of the eye, and consequently in a part of the field
of vision to which we never attend naturally, and to

252 THE PHILOSOPHY OF REID. [Cu. VI.

which we cannot attend at all, without the aid of some
particular circumstances.

From what we have said, it appears, that, to deter-
mine the situation of the corresponding points in the
eyes of those who squint, is impossible, if they do not
see distinctly with both eyes; and that it will be very
difficult, unless the two eyes differ so little in their di-
rection, that the same object may be seen with both at
the same time. Such patients I apprehend are rare; at
least there are very few of them with whom I have had
the fortune to meet: and therefore, for the assistance of
those who may have happier opportunities, and inclina-
tion to make the proper use of them, we shall consider
the case of squinting, hypothetically, pointing out the
proper articles of inquiry, the observations that are
wanted, and the conclusions that may be drawn from them.

1. It ought to be inquired, Whether the squinting
person sees equally well with both eyes ? and, if there
be a defect in one, the nature and degree of that defect
ought to be remarked. The experiments by which this
may be done, are so obvious, that I need not mention
them. But I would advise the observer to make the
proper experiments, and not to rely upon the testimony
of the patient; because I have found many instances,
both of persons that squinted, and others who were
found, upon trial, to have a great defect in the sight of
one eye, although they were never aware of it before.
In all the following articles, it is supposed that the patient
sees with both eyes so well as to be able to read with
either, when the other is covered.

2. It ought to be inquired, Whether, when one eye
is covered, the other is turned directly to the object ?
This ought to be tried in both eyes successively. By
this observation, as a touchstone, we may try the hy-
pothesis concerning squinting, invented by M. de la
Hire, and adopted by Boerhaave, and many others of
the medical faculty.

SEC. XV.] THE PHILOSOPHY OF REID. 253

The hypothesis is, That, in one eye of a squinting
person, the greatest sensibility and the most distinct
vision is not, as in other men, in the centre of the retina,
but upon one side of the centre ; and that he turns the
axis of this eye aside from the object, in order that the
picture of the object may fall upon the most sensible part
of the retina, and thereby give the most distinct vision.
If this is the cause of squinting, the squinting eye will be
turned aside from the object, when the other eye is covered,
as well as when it is not.

A trial so easy to be made, never was made for more
than forty years ; but the hypothesis was very generally
received — so prone are men to invent hypotheses, and so
backward to examine them by facts. At last, Dr. Jurin
having made the trial, found that persons who squint turn
the axis of the squinting eye directly to the object, when
the other eye is covered. This fact is confirmed by Dr.
Porterfield ; and I have found it verified in all the in-
stances that have fallen under my observation.

3. It ought to be inquired, Whether the axes of the
two eyes follow one another, so as to have always the
same inclination, or make the same angle, when the
person looks to the right or to the left, upward or down-
ward, or straight forward. By this observation we may
judge whether a squint is owing to any defect in the
muscles which move the eye, as some have supposed. In
the following articles, we suppose that the inclination
of the axes of the eyes is found to be always the
same.

4. It ought to be inquired, Whether the person that
squints sees an object single or double*

If he sees the object double, and if the two appear-
ances have an angular distance, equal to the angle which
the axes of his eyes make with each other, it may be con-
cluded that he hath corresponding points in the retince of
his eyes, and that they have the same situation as in those
who have no squint If the two appearances should

254 THE PHILOSOPHY OF REID. [Ca. VI.

have an angular distance which is always the same, but
manifestly greater or less than the angle contained under
the optic axes, this would indicate corresponding points
in the retince, whose situation is not the same as in those
who have no squint ; but it is difficult to judge accurately
of the angle which the optic axes make.

A squint too small to be perceived, may occasion
double vision of objects : for, if we speak strictly, every
person squints more or less, whose optic axes do not
meet exactly in the object which he looks at. Thus, if
a man can only bring the axes of his eyes to be parallel,
but cannot make them converge in the least, he must
have a small squint in looking at near objects, and will
see them double, while he sees very distant objects single.
Again, if the optic axes always converge, so as to meet
eight or ten feet before the face at farthest, such a person
will see near objects single ; but when he looks at very
distant objects, he will squint a little, and see them
double.

An instance of this kind is related by Aguilonius in
his "Optics," who says, that he had seen a young man to
whom near objects appeared single, but distant objects
appeared double.

Dr. Briggs, in his " Nova Visionis Theoria," having col-
lected from authors several instances of double vision,
quotes this from Aguilonius, as the most wonderful and
unaccountable of all, insomuch that he suspects some im-
position on the part of the young man: but to those who
understand the laws by which single and double vision are
regulated, it appears to be the natural effect of a very
small squint.

Double vision may always be owing to a small squint,
when the two appearances are seen at a small angular
distance, although no squint was observed : and I do
not remember any instances of double vision recorded by
authors, wherein any account is given of the angular dis-
tance of the appearances.

SEC. XV.] THE PHILOSOPHY OF REID. 25$

In almost all the instances of double vision, there is
reason to suspect a squint or distortion of the eyes, from
the concomitant circumstances, which we find to be one
or other of the following — the approach of death or of a
deliquium, excessive drinking or other intemperance, vio-
lent headache, blistering the head, smoking tobacco,
blows or wounds in the head. In all these cases, it is
reasonable to suspect a distortion of the eyes, either from
spasm, or paralysis in the muscles that move them. But,
although it be probable that there is always a squint
greater or less where there is double vision, yet it is
certain that there is not double vision always where
there is a squint. I know no instance of double vision
that continued for life, or even for a great number of
years. We shall therefore suppose, in the following arti-
cles, that the squinting person sees objects single.

5. The next inquiry, then, ought to be, Whether the
object is seen with both eyes at the same time, or only
with the eye whose axes is directed to it ? It hath been
taken for granted, by the writers upon the strabismus, be-
fore Dr. Jurin, that those who squint commonly see ob-
jects single with both eyes at the same time ; but I know
not one fact advanced by any writer which proves it. Dr.
Jurin is of a contrary opinion ; and, as it is of conse-
quence, so it is very easy, to determine this point, in
particular instances, by this obvious experiment. While
the person that squints looks steadily at an object, let the
observer carefully remark the direction of both his eyes,
and observe their motions ; and let an opaque body be
interposed between the object and the two eyes succes-
sively. If the patient, notwithstanding this interposition,
and without changing the direction of his eyes, continues
to see the object all the time, it may be concluded that
he saw it with both eyes at once. But, if the interposi-
tion of the body between one eye and the object makes it
disappear, then we may be certain that it was seen by
that eye only. In the two following articles, we shall

2$6 THE PHILOSOPHY OF REID. |CH. VI.

suppose the first to happen, according to the common
hypothesis.

6. Upon this supposition, it ought to be inquired,
Whether the patient sees an object double in those cir-
cumstances wherein it appears double to them who have
no squint? Let him, for instance, place a candle at the
distance of ten feet ; and holding his finger at arm's-
length between him and the candle, let him observe,
when he looks at the candle, whether he sees his finger
with both eyes, and whether he sees it single or double;
and when he looks at his finger, let him observe whether
he sees the candle with both eyes and whether single or
double.

By this observation, it may be determined, whether to
this patient, the phaenomena of double as well as of sin-
gle vision are the same as to them who have no squint.
If they are not the same — if he sees objects single with
two eyes, not only in the cases wherein they appear sin-
gle, but in those also wherein they appear double to other
men — the conclusion to be drawn from this supposition
is, that his single vision does not arise from corresponding
points in the retince of his eyes : and that the laws of vis-
ion are not the same in him as in the rest of mankind.

7. If, on the other hand, he sees objects double in
those cases wherein they appear double to others, the
conclusion must be, that he hath corresponding points
in the retina of his eyes, but unnaturally situate. And
their situation may be thus determined.

When he looks at an object, having the axis of one eye
directed to it, and the axis of the other turned aside from it,
let us suppose a right line to pass from the object through
the centre of the diverging eye. We shall, for the sake
of perspicuity, call this right line, the natural axis of the
eye; and it will make an angle with the real axis, greater
or less, according as his squint is greater or less. We
shall also call that point of the retina in which the natural
axis cuts it, the natural centre of the retina ; which will

SEC. XV.] THE PHILOSOPHY OF REID. 257

be more or less distant from the real centre, according
as the squint is greater or less.

Having premised these definitions, it will be evident
to those who understand the principles of optics, that in
this person the natural centre of one retina corresponds
with the real centre of the other, in the very same man-
ner as the two real centres correspond in perfect eyes ; and
that the points similarly situate with regard to the real
centre in one retina, and the natural centre in the other,
do likewise correspond, in the very same manner as the
points similarly situate with regard to the two real cen-
tres correspond in perfect eyes.

If it is true, as has been commonly affirmed, that one
who squints sees an object with both eyes at the same
time, and yet sees it single, the squint will most probably
be such as we have described in this article. And we
may further conclude, that, if a person affected with such
a squint as we have supposed, could be brought to the
habit of looking straight, his sight would thereby be
greatly hurt ; for he would then see everything double
which he saw with both eyes at the same time ; and ob-
jects distant from one another would appear to be con-
founded together. His eyes are made for squinting, as
much as those of other men are made for looking straight;
and his sight would be no less injured by looking straight,
than that of another man by squinting. He can never
see perfectly when he does not squint, unless the corre-
sponding points of his eyes should by custom change
their place ; but how small the probability of this is will
appear in the iyth section.

Those of the medical faculty who attempt the cure of
a squint, would do well to consider whether it is attended
with such symptoms as are above described. If it is,
the cure would be worse than the malady: for, everyone
will readily acknowledge that it is better to put up with
the deformity of a squint, than to purchase the cure by
the loss of perfect and distinct vision.

258 THE PHILOSOPHY OF REID. [CH. VI.

8. We shall now return to Dr. Jurin's hypothesis, and
suppose that our patient, when he saw objects single
notwithstanding his squint, was found, upon trial, to have
seen them only with one eye.

We would advise such a patient to endeavor, by re-
peated efforts, to lessen his squint, and to bring the axes
of his eyes nearer to a parallel direction. We have natu-
rally the power of making small variations in the inclina-
tion of the optic axes ; and this power may be greatly in-
creased by exercise.

In the ordinary and natural use of our eyes, we can
direct their axes to a fixed star; in this case they must
be parallel: we can direct them also to an object six
inches distant from the eye; and in this case the axes
must make an angle of fifteen or twenty degrees. We
see young people in their frolics learn to squint, making
their eyes either converge or diverge, when they wil^ to
a very considerable degree. Why should it be more
difficult for a squinting person to learn to look straight
when he pleases? If once, by an effort of his will, he
can but lessen his squint, frequent practice will make it
easy to lessen it, and will daily increase his power. So
that, if he begins this practice in youth, and perseveres in
it, he may probably, after some time, learn to direct both
his eyes to one object.

When he hath acquired this power, it will be no diffi-
cult matter to determine, by proper observations, whether
the centres of the retina, and other points similarly sit-
uate with regard to the centres, correspond, as in other
men.

9. Let us now suppose that he finds this to be the
case ; and that he sees an object single with both eyes,
when the axes of both are directed to it. It will then
concern him to acquire the habit of looking straight, as
he hath got the power, because he will thereby not only
remove a deformity, but improve his sight ; and I con-
ceive this habit, like all others, may be got by frequent

SEC. XV.] THE PHILOSOPHY OF REID. 259

exercise. He may practise before a mirror when alone,
and in company he ought to have those about him who
will observe and admonish him when he squints.

10. What is supposed in the 9th article is not merely
imaginary ; it is really the case of some squinting per-
sons, as will appear in the next section. Therefore, it
ought further to be inquired, How it comes to pass that
such a person sees an object which he looks at, only
with one eye, when both are open ? In order to answer
this question, it may be observed, first, Whether, when
he looks at an object, the diverging eye is not drawn so
close to the nose, that it can have no distinct images ?
Or, secondly, whether the pupil of the diverging eye is not
covered wholly, or in'part, by the upper eyelid ? Dr. Jurin
observed instances of these cases in persons that squinted,
and assigns them as causes of their seeing the object only
with one eye. Thirdly, it may be observed, whether the
diverging eye is not so directed, that the picture of the
object falls upon that part of the retina where the optic
nerve enters, and where there is no vision ? This will
probably happen in a squint wherein the axes of the eyes
converge so as to meet about six inches before the nose.

11. In the last place, it ought to be inquired, Whether
such a person hath any distinct vision at all with the di-
verging eye, at the time he is looking at an object with
the other ?

It may seem very improbable that he should be able
to read with the diverging eye when the other is covered,
and yet, when both are open, have no distinct vision with
it at all. But this, perhaps, will not appear so improb-
able if the following considerations are duly attended to.

Let us suppose that one who saw perfectly, gets, by
a blow on the head, or some other accident, a perma-
nent and involuntary squint. According to the laws of
vision, he will see objects double, and will see objects
distant from one another confounded together ; but,
such vision being very disagreeable, as well as incon-

260 THE PHILOSOPHY OF REID. [CH. VI.

venient, he will do everything in his power to remedy it.
For alleviating such distresses, nature often teaches men
wonderful expedients, which the sagacity of a philoso-
pher would be unable to discover. Every accidental
motion, every direction or conformation of his eyes,
which lessens the evil, will be agreeable ; it will be re-
peated until it be learned to perfection,, and become ha-
bitual, even without thought or design. Now, in this
case, what disturbs the sight of one eye is the sight of
the other ; and all the disagreeable appearances in vision
would cease if the light of one eye was extinct. The
sight of one eye will become more distinct and more
agreeable, in the same proportion as that of the other
becomes faint and indistinct. It may, therefore, be ex-
pected, that every habit will, by degrees, be acquired
which tends to destroy distinct vision in one eye while
it is preserved in the other. These habits will be greatly
facilitated if one eye was at first better than the other ;
for, in that case, the best eye will always be directed to
the object which he intends to look at, and every habit
will be acquired which tends to hinder his seeing it at all,
or seeing it distinctly by the other at the same time.

I shall mention one or two habits that may probably
be acquired in such a case ; perhaps there are others
which we cannot so easily conjecture. First, By a small
increase or diminution of his squint, he may bring it to
correspond with one or other of the cases mentioned in
the last article. Secondly, The diverging eye may be
brought to such a conformation as to be extremely
short-sighted, and consequently to have no distinct vision
of objects at a distance. I knew this to be the case of
one person that squinted ; but cannot say whether the
short-sightedness of the diverging eye was original, or
acquired by habit.

We see, therefore, that one who squints, and originally
saw objects double by reason of that squint, may acquire
such habits that, when he looks at an object, he shall see

SEC. XVI.] THE PHILOSOPHY OF REID. 261

it only with one eye ; nay, he may acquire such habits
that, when he looks at an object with his best eye, he
shall have no distinct vision with the other at all.
Whether this is really the case — being unable to deter-
mine in the instances that have fallen under my observa-
tion— I shall leave to future inquiry.

I have endeavoured, in the foregoing articles, to de-
lineate such a process as is proper in observing the phse-
nomena of squinting. I know well by experience, that
this process appears more easy in theory than it will be
found to be in practice; and that, in order to carry it on
with success, some qualifications of mind are neces-
sary in the patient, which are not always to be met with.
But, if those who have proper opportunities and incli-
nation to observe such phenomena, attend duly to this
process, they may be able to furnish facts less vague and
uninstructive than those we meet with, even in authors
of reputation. By such facts, vain theories may be ex-
ploded, and our knowledge of the laws of nature, which
regard the noblest of our senses, enlarged.

Section XVI.

FACTS RELATING TO SQUINTING.

Having considered the phenomena of squinting,
hypothetically, and their connection with correspond-
ing points in the retina. I shall now mention the facts I
have had occasion to observe myself, or have met with
in authors, that can give any light to this subject.

Having examined above twenty persons that squinted,
I found in all of them a defect in the sight of one eye.
Four only had so much of distinct vision in the weak eye,
as to be able to read with it, when the other was cov-
ered. The rest saw nothing at all distinctly with one
eye.

Dr. Porterfield says, that this is generally the case of

262 THE PHILOSOPHY OF REID. rCn. VI.

people that squint ; and I suspect it is so more generally
than is commonly imagined. Dr. Jurin, in a very judi-
cious dissertation upon squinting, printed in Dr. Smith's
"Optics," observes, that those who squint, and see with
both eyes, never see the same object with both at the
same time ; that, when one eye is directed straight for-
ward to an object, the other is drawn so close to the nose
that the object cannot at all be seen by it, the images
being too oblique and too indistinct to affect the eye.
In some squinting persons, he observed the diverging
eye drawn under the upper eyelid, while the other was
directed to the object. From these observations, he
concludes that " the eye is thus distorted, not for the
sake of seeing better with it, but rather to avoid seeing
at all with it as much as possible. " From all the ob-
servations he had made, he was satisfied that there is
nothing peculiar in the structure of a squinting eye ;
that the fault is only in its wrong direction ; and that
this wrong direction is got by habit. Therefore, he
proposes that method of cure which we have described
in the eighth and ninth articles of the last section. He
tells us, that he had attempted a cure, after this method,
upon a young gentleman, with promising hopes of suc-
cess ; but was interrupted by his falling ill of the small-
pox, of which he died.

It were to be wished that Dr. Jurin had acquainted us
whether he ever brought the young man to direct the axes
of both eyes to the same object, and whether, in that case,
he saw the object single, and saw it with both eyes ; and
that he had likewise acquainted us, whether he saw ob-
jects double when his squint was diminished. But as to
these facts he is silent.

I wished long for an opportunity of trying Dr. Jurin's
method of curing a squint, without finding one ; having
always, upon examination, discovered so great a defect
in the sight of one eye of the patient as discouraged the
attempt.

SEC. XVI.) THE PHILOSOPHY OF REID. 263

But I have lately found three young gentlemen, with
whom I am hopeful this method may have success, if
they have patience and perseverance in using it. Two
of them are brothers, and, before I had access to ex-
amine them, had been practising this method by the di-
rection of their tutor, with such success, that the elder
looks straight when he is upon his guard ; the younger
can direct both his eyes to one object ; but they soon
return to their usual squint.

A third young gentleman, who had never heard of this
method before, by a few days' practice, was able to di-
rect both his eyes to one object, but could not keep them
long in that direction. All the three agree in this, that,
when both eyes are directed to one object, they see it
and the adjacent objects single ; but, when they squint,
they see objects sometimes single and sometimes double.
I observed of all the three, that when they squinted most
— that is, in the way they had been accustomed to — the
axes of their eyes converged so as to meet five or six
inches before the nose. It is probable that, in this case,
the picture of the object in the diverging eye, must fall
upon that part of the retina where the optic nerve enters;
and therefore, the object could not be seen by the eye.

All the three have some defect in the sight of one eye,
which none of them knew until I put them upon making
trials; and when they squint, the best eye is always
directed to the object, and the weak eye is that which
diverges from it. But when the best eye is covered, the
weak eye is turned directly to the object. Whether this
defect of sight in one eye, be the effect of its having been
long disused, as it must have been when they squinted;
or whether some original defect in one eye might be the
occasion of their squinting, time may discover. The
two brothers have found the sight of the weak eye im-
proved by using to read with it while the other is covered.
The elder can read an ordinary print with the weak eye •
the other, as well as the third gentleman, can only read

264 THE PHILOSOPHY OF REID. [Cn. VI.

a large print with the weak eye. I have met with one
other person only who squinted, and yet could read a large
print with the weak eye. He is a young man, whose
eyes are both tender and weak-sighted, but the left much
weaker than the right. When he looks at any object, he al-
ways directs the right eye to it, and then the left is turned
towards the nose so much that it is impossible for him
to see the same object with both eyes at the same time.
When the right eye is covered, he turns the left directly
to the object; but he sees it indistinctly, and as if it had
a mist about it.

I made several experiments, some of them in the com-
pany and with the assistance of an ingenious physician,
in order to discover whether objects that were in the axes
of the two eyes, were seen in one place confounded to-
gether, as in those who have no involuntary squint. The
object placed in the axis of the weak eye was a lighted
candle, at the distance of eight or ten feet. Before the
other eye was placed a printed book, at such a distance
as that he could read upon it. He said, that while he
read upon the book, he saw the candle but very faintly.
And from what we could learn, these two objects did
not appear in one place, but had all that angular dis-
tance in appearance which they had in reality.

If this was really the case, the conclusion to be drawn
from it is, that the corresponding points in his eyes are
not situate in the same manner as in other men; and
that, if he could be brought to direct both eyes to one
object, he would see it double. But, considering that
the young man had never been accustomed to observa-
tions of this kind, and that the sight of one eye was so
imperfect, I do not pretend to draw this conclusion with
certainty from this single instance.

All that can be inferred from these facts is, that, of
four persons who squint, three appear to have nothing
preternatural in the structure of their eyes. The cen-
tres of their retince, and the points similarly situate with

SEC. xvii.] THE PHILOSOPHY OF REID. 265

regard to the centres, do certainly correspond in the same
manner as in other men — so that, if they can be brought
to the habit of directing their eyes right to an object,
they will not only remove a deformity, but improve their
sight. With regard to the fourth, the case is dubious,
with some probability of a deviation from the usual
course of nature in the situation of the corresponding
points of his eyes.

Section XVII.

OF THE EFFECT OF CUSTOM IN SEEING OBJECTS SINGLE.

It appears from the phenomena of single and double
vision, recited in § 13, that our seeing an object single
with two eyes, depends upon these two things: — First,
Upon that mutual correspondence of certain points of
the retina which we have often described; Secondly, Upon
the two eyes being directed to the object so accurately
that the two images of it fall upon corresponding points.
These two things must concur in order to our seeing an
object single with two eyes; and, as far as they depend
upon custom, so far only can single vision depend upon
custom.

With regard to the second — that is, the accurate direc-
tion of both eyes to the object — I think it must be ac-
knowledged that this is only learned by custom. Na-
ture hath wisely ordained the eyes to move in such man-
ner that their axes shall always be nearly parallel; but
hath left it in our power to vary their inclination a lit-
tle, according to the distance of the object we look at.
Without this power, objects could appear single at one
particular distance only; and, at distances much less or
much greater, would always appear double. The wis-
dom of nature is conspicuous in giving us this power,
and no less conspicuous in making the extent of it
exactly adequate to the end.

266 THE PHILOSOPHY Of REID. [CH. VI.

The parallelism of the eyes, in general, is therefore
the work of nature; but that precise and accurate direc-
tion, which must be varied according to the distance of
the object, is the effect of custom. The power which
nature hath left us of varying the inclination of the optic
axes a little, is turned into a habit of giving them always
that inclination which is adapted to the distance of the
object.

But it may be asked, What gives rise to this habit ?
The only answer that can be given to this question is,
that it is found necessary to perfect and distinct vision.
A man who hath lost the sight of one eye, very often
loses the habit of directing it exactly to the object he looks
at, because that habit is no longer of use to him. And
if he should recover the sight of his eye, he would re-
cover this habit, by finding it useful. No part of the
human constitution is more admirable than that whereby
we acquire habits which are found useful, without any
design or intention. Children must see imperfectly at
first; but, by using their eyes, they learn to use them in
the best manner, and acquire, without intending it, the
habits necessary for that purpose. Every man becomes
most expert in that kind of vision which is most useful
to him in his particular profession and manner of life. A
miniature painter, or an engraver, sees very near objects
better than a sailor; but the sailor sees very distant ob-
jects much better than they. A person that is short-
sighted, in looking at distant objects, gets the habit of
contracting the aperture of his eyes, by almost closing
his eyelids. Why ? For no other reason, but because
this makes him see the object more distinct. In like
manner, the reason why every man acquires the habit
of directing both eyes accurately to the object, must
be, because thereby he sees it more perfectly and dis-
tinctly.

It remains to be considered, whether that correspond-
ence between certain points of the retince, which is like-

SEC. XVII.] THE PHILOSOPHY OF REID. 267

wise necessary to single vision, be the effect of custom,
or an original property of human eyes.

A strong argument for its being an original property,
may be drawn from the habit, just now mentioned, of
directing the eyes accurately to an object. This habit
is got by our finding it necessary to perfect and distinct
vision. But why is it necessary ? For no other reason
but this, because thereby the two images of the object
falling upon corresponding points, the eyes assist each
other in vision, and the object is seen better by both to-
gether, than it could be by one; but when the eyes are
not accurately directed, the two images of an object fall
upon points that do not correspond, whereby the sight
of one eye disturbs the sight of the other, and the object
is seen more indistinctly with both eyes than it would be
with one. Whence it is reasonable to conclude, that
this correspondence of certain points of the refines, is
prior to the habits we acquire in vision, and consequently
is natural and original. We have all acquired the habit
of directing our eyes always in a particular manner,
which causes single vision. Now, if nature hath ordained
that we should have single vision only, when our eyes
are thus directed, there is an obvious reason why all
mankind should agree in the habit of directing them in
this manner. But, if single vision is the effect of cus-
tom, any other habit of directing the eyes would have
answered the purpose; and no account can be given why
this particular habit should be so universal; and it must
appear very strange, that no one instance hath been
found of a person who had acquired the habit of seeing
objects single with both eyes, while they were directed in
any other manner.

The judicious Dr. Smith, in his excellent system of
optics, maintains the contrary opinion, and offers some
reasonings and facts in proof of it. He agrees with
Bishop Berkeley in attributing it entirely to custom,
that we see objects single with two eyes, as well as that

268 THE PHILOSOPHY OF REID. [CH. VI.

we see objects erect by inverted images. Having con-
sidered Bishop Berkeley's reasonings in the nth section,
we shall now beg leave to make some remarks on what
Dr. Smith hath said upon this subject, with the respect
due to an author to whom the world owes, not only many
valuable discoveries of his own, but those of the brightest
mathematical genius of this age, which, with great labour,
he generously redeemed from oblivion.

He observes, that the question, Why we see objects
single with two eyes ? is of the same sort with this, Why
we hear sounds single with two ears ? — and that the
same answer must serve both. The inference intended
to be drawn from this observation is, that, as the second
of these phenomena is the effect of custom, so likewise
is the first.

Now, I humbly conceive that the questions are not so
much of the same sort, that the same answer must serve
for both; and, moreover, that our hearing single with
two ears, is not the effect of custom.

Two or more visible objects, although perfectly "simi-
lar, and seen at the very same time, may be distinguished
by their visible places; but two sounds perfectly similar,
and heard at the same time, cannot be distinguished; for,
from the nature of sound, the sensations they occasion
must coalesce into one, and lose all distinction. If, there-
fore, it is asked, Why we hear sounds single with two
ears ? I answer, Not from custom ; but because two
sounds which are perfectly like and synchronous, have
nothing by which they can be distinguished. But will
this answer fit the other question ? I think not.

The object makes an appearance to each eye, as the
sound makes an impression upon each ear: so far the
two senses agree. But the visible appearances may be
distinguished by place, when perfectly like in other re-
spects; the sounds cannot be thus distinguished: and
herein the two senses differ. Indeed, if the two appear-
ances have the same visible place, they are, in that case,

SEC. XVII.) THE PHILOSOPHY OF REID. 269

as incapable of distinction as the sounds were, and we
see the object single. But when they have not the same
visible place, they are perfectly distinguishable, and we
see the object double. We see the object single only,
when the eyes are directed in one particular manner;
while there are many other ways of directing them within
the sphere of our power, by which we see the object
double.

Dr. Smith justly attributes to custom that well-known
fallacy in feeling, whereby a button pressed with two
opposite sides of two contiguous ringers laid across, is
felt double. I agree with him, that the cause of this
appearance is, that those opposite sides of the fingers have
never been used to feel the same object, but two different
objects, at the same time. And I beg leave to add, that,
as custom produces this phenomenon, so a contrary cus-
tom destroys it; for, if a man frequently accustoms him-
self to feel the button with his fingers across, it will at
last be felt single ; as I have found by experience.

It may be taken for a general rule, that things which
are produced by custom, may be undone or changed by
disuse, or by a contrary custom. On the other hand, it
is a strong argument, that an effect is not owing to cus-
tom, but to the constitution of nature, when a contrary
custom, long continued, is found neither to change nor
weaken it. I take this to be the best rule by which we
can determine the question presently under consideration.
I shall, therefore, mention two facts brought by Dr.
Smith, to prove that the corresponding points of the
retince have been changed by custom; and then I shall
mention some facts tending to prove, that there are cor-
responding points of the retina of the eyes originally, and
that custom produces no change in them.

"One fact is related upon the authority of Martin
Folkes, Esq., who was informed by Dr. Hepburn of
Lynn, that the Rev. Mr. Foster of Clinchwharton, in that
neighbourhood, having been blind for some years of a

270 THE PHILOSOPHY OF REID. |CH. VI.

gulta serena, was restored to sight by salivation; and that,
upon his first beginning to see, all objects appeared to
him double; but afterwards, the two appearances ap-
proaching by degrees, he came at last to see single, and
as distinctly as he did before he was blind."

Upon this case, I observe, First, That it does not prove
any change of the corresponding points of the eyes, un-
less we suppose, what is not affirmed, that Mr. Foster
directed his eyes to the object at first, when he saw double,
with the same accuracy, and in the same manner, that he
did afterwards, when he saw single. Secondly, If we
should suppose this, no account can be given, why at
first the two appearances should be seen at one certain
angular distance rather than another; or why this angular
distance should gradually decrease, until at last the ap-
pearances coincided. How could this effect be produced
by custom ? But, Thirdly, Every circumstance of this
case may be accounted for on the supposition that Mr.
Foster had corresponding points in the retina of his eyes
from the time he began to see, and that custom made no
change with regard to them. We need only further sup-
pose, what is common in such cases, that, by some years'
blindness, he had lost the habit of directing his eyes ac-
curately to an object, and that he gradually recovered
this habit when he came to see.

The second fact mentioned by Dr. Smith, is taken from
Mr. Cheselden's "Anatomy," and is this: — "A gentle-
man who, from a blow on the head, had one eye dis-
torted, found every object appear double; but, by de-
grees, the most familiar ones became single; and, in time,
all objects became so without any amendment of the dis-
tortion. "

I observe here, that it is not said that the two appear-
ances gradually approached, and at last united, without
any amendment of the distortion. This would indeed
have been a decisive proof of a change in the correspond-
ing points of the retina;, and yet of such a change as

SEC. xvn.j THE PHILOSOPHY OF REID. 271

could not be accounted for from custom. Bu, this is
not said; and, if it had been observed, a circumstance so
remarkable would have been mentioned by Mr. Cheselden,
as it was in the other case by Dr. Hepburn. We may,
therefore, take it for granted, that one of the appearances
vanished by degrees, without approaching to the other.
And this I conceive might happen several ways. First,
The sight of the distorted eye might gradually decay by
the hurt; so the appearances presented by that eye would
gradually vanish. Secondly, A small and unperceived
change in the manner of directing the eyes, might oc-
casion his not seeing the object with the distorted eye, as
appears from § 15, Art. 10. Thirdly, By acquiring the
habit of directing one and the same eye always to the ob-
ject, the faint and oblique appearance presented by the
other eye, might be so little attended to when it became
familiar, as not to be perceived. One of these causes, or
more of them concurring, might produce the effect
mentioned, without any change of the corresponding
points of the eyes.

For these reasons, the facts mentioned by Dr. Smith,
although curious, seem not to be decisive.

The following facts ought to be put in the opposite
scale. First, in the famous case of the young gentleman
couched by Mr. Cheselden, after having had cataracts on
both eyes until he was [above] thirteen years of age, it
appears that he saw objects single from the time he be-
gan to see with both eyes. Mr. Chesel den's words are,
"And now, being lately couched of his other eye, he
says, that objects, at first, appeared large to this eye, but
not so large as they did at first to the other ; and, looking
upon the same object with both eyes, he thought it looked
about twice as large as with the first couched eye only,
but not double, that we can anywise discover."

Secondly, The three young gentlemen mentioned in
the last section, who had squinted, as far as I know,
from infancy, as soon as they learned to direct both eyes

272 THE PHILOSOPHY OF REID. [Ca. VI.

to an object, saw it single. In these four cases, it ap-
pears evident that the centres of the retina corresponded
originally, and before custom could produce any such
effect ; for Mr. Cheselden's young gentleman had never
been accustomed to see at all before he was couched; and
the other three had never been accustomed to direct the
axes of both eyes to the object.

Thirdly, from the facts recited in § 13, it appears,
that, from the time we are capable of observing the phse-
nomena of single and double vision, custom makes no
change in them.

I have amused myself with such observations for more
than thirty years ; and in every case wherein I saw the
object double at first, I see it so to this day, notwith-
standing the constant experience of its being single. In
other cases, where I know there are two objects, there
appears only one, after thousands of experiments.

Let a man look at a familiar object through a poly-
hedron, or multiplying-glass, every hour of his life, the
number of visible appearances will be the same at last as
at first ; nor does any number of experiments, or length
of time, make the least change.

Effects produced by habit, must vary according as the
acts by which the habit is acquired are more or less fre-
quent; but the phaenomena of single and double vision
are so invariable and uniform in all men, are so exactly
regulated by mathematical rules, that I think we have
good reason to conclude that they are not the effect of
custom, but of fixed and immutable laws of nature.

Section XVIII.
OF DR. PORTERFIELD'S ACCOUNT OF SINGLE AND DOUBLE VISION.

Bishop Berkeley and Dr. Smith seem to attribute too
much to custom in vision, Dr. Porterfield too little.
This ingenious writer thinks, that, by an original law

SEC. XVIII.] THE PHILOSOPHY OF REID. 273

of our nature, antecedent to custom and experience, we
perceive visible objects in their true place, not only as to
their direction, but likewise as to their distance from the
eye; and, therefore, he accounts for our seeing objects
single, with two eyes, in this manner. Having the
faculty of perceiving the object with each eye in its
true place, we must perceive it with both eyes in the
same place ; and, consequently, must perceive it sin-
gle.

He is aware that this principle, although it accounts
for our seeing objects single with two eyes, yet does not
at all account for our seeing objects double ; and, where-
as other writers on this subject take it to be a sufficient
cause for double vision that we have two eyes, and only
find it difficult to assign a cause for single vision, on the
contrary, Dr. Porterfield's principle throws all the diffi-
culty on the other side.

Therefore, in order to account for the phenomena of
double vision, he advances another principle, without
signifying whether he conceives it to be an original law
of our nature, or the effect of custom. It is, That our
natural perception of the distance of objects from the eye,
is not extended to all the objects that fall within the field
of vision, but limited to that which we directly look at ;
and that the circumjacent objects, whatever be their real
distance, are seen at the same distance with the object
we look at ; as if they were all in the surface of a sphere,
whereof the eye is the centre.

Thus, single vision is accounted for by our seeing the
true distance of an object which we look at ; and double
vision, by a false appearance of distance in objects which
we do not directly look at.

We agree with this learned and ingenious author, that
it is by a natural and original principle that we see vis-
ible objects in a certain direction from the eye, and
honour him as the author of this discovery: but we can-
not assent to either of those principles by which he ex-

274 THE PHILOSOPHY OF REID. [CH. VI.

plains single and double vision — for the following rea-
sons:—

1. Our having a natural and original perception of
the distance of objects from the eye, appears contrary to
a well-attested fact: for the young gentleman couched by
Mr. Cheselden imagined, at first, that whatever he saw
touched his eye, as what he felt touched his hand.

2. The perception we have of the distance of objects
from the eye, whether it be from nature or custom, is
not so accurate and determined as is necessary to pro-
duce single vision. A mistake of the twentieth or thir-
tieth part of the distance of a small object, such as a pin,
ought, according to Dr. Porterfield's hypothesis, to make
it appear double. Very few can judge of the distance of
a visible object with such accuracy. Yet we never find
double vision produced by mistaking the distance of the
object. There are many cases in vision, even with the
naked eye, wherein we mistake the distance of an object
by one half or more: why do we see such objects single ?
When I move my spectacles from my eyes toward a
small object, two or three feet distant, the object seems
to approach, so as to be seen at last at about half its real
distance; but it is seen single at that apparent distance,
as well as when we see it with the naked eye at its real
distance. And when we look at an object with a binoc-
ular telescope, properly fitted to the eyes, we see it sin-
gle, while it appears fifteen or twenty times nearer than
it is. There are then few cases wherein the distance of
an object from the eye is seen so accurately as is neces-
sary for single vision, upon this hypothesis: this seems
to be a conclusive argument against the account given
of single vision. We find, likewise, that false judgments
or fallacious appearances of the distance of an object, do
not produce double vision: this seems to be a conclusive
argument against the account given of double vision.

3. The perception we have of the linear distance of
objects seems to be wholly the effect of experience.

SEC. XVIII.] THE PHILOSOPHY OF REID. 275

This, I think, hath been proved by Bishop Berkeley
and by Dr. Smith ; and when we come to point out
the means of judging of distance by sight, it will appear
that they are all furnished by experience.

4. Supposing that, by a law of our nature, the distance
of objects from the eye were perceived most accurately, as
well as their direction, it will not follow that we must
see the object single. Let us consider what means such
a law of nature would furnish for resolving the question,
Whether the objects of the two eyes are in one and the
same place, and consequently are not two, but one ?

Suppose then, two right lines, one drawn from the centre
of one eye to its object, the other drawn, in like man-
ner, from the centre of the other eye to its object. This
law of nature gives us the direction or position of each
of these right lines, and the length of each ; and this is
all that it gives. These are geometrical data, and we
may learn from geometry what is determined by their
means. Is it, then, determined by these data, Whether
the two right lines terminate in one and the same point,
or not ? No, truly. In order to determine this, we
must have three other data. We must know whether the
two right lines are in one plane ; we must know what
angle they make ; and we must know the distance be-
tween the centres of the eyes. And when these things
are known, we must apply the rules of trigonometry, be-
fore we can resolve the question, Whether the objects of
the two eyes are in one and the same place; and, conse-
quently, whether they are two or one ?

5. That false appearance of distance into which double
vision is resolved, cannot be the effect of custom, for
constant experience contradicts it. Neither hath it the
features of a law of nature, because it does not answer
any good purpose, nor, indeed, any purpose at all, but
to deceive us. But why should we seek for arguments,
in a question concerning what appears to us, or does not
appear ? The question is, At what distance do the ob-

276 THE PHILOSOPHY OF REID. [Cu. VI.

jects now in my eye appear ? Do they all appear at one
distance, as if placed in the concave surface of a sphere,
the eye being in the centre ? Every man, surely, may
know this with certainty ; and, if he will but give atten-
tion to the testimony of his eyes, needs not ask a philoso-
pher how visible objects appear to him. Now, it is very
true, that, if I look up to a star in the heavens, the other
stars that appear at the same time, do appear in this man-
ner: yet this phenomenon does not favour Dr. Porter-
field's hypothesis ; for the stars and heavenly bodies do
not appear at their true distances when we look directly
to them, any more than when they are seen obliquely :
and if this phaenomenon be an argument for Dr. Porter-
field's second principle, it must destroy the first. I

The true cause of this phaenomenon will be given after-
wards ; therefore, setting it aside for the present, let us
put another case. I sit in my room, and direct my
eyes to the door, which appears to be about sixteen feet
distant : at the same time, I see many other objects
faintly and obliquely — the floor, floor-cloth, the table
which I write upon, papers, standish, candle, &c. Now,
do all these objects appear at the same distance of six-
teen feet ? Upon the closest attention I find they do
not

Section XIX.

OP DR BRIGGS'S THEORY AND SIR ISAAC NEWTON'S CONJECTURE
ON THIS SUBJECT.

I am afraid the reader, as well as the writer, is already
tired of the subject of single and double vision. The
multitude of theories advanced by authors of great name,
and the multitude of facts, observed without sufficient
skill in optics, or related without attention to the most
material and decisive circumstances, have equally con-
tributed to perplex it

SEC. XVIII.] THE PHILOSOPHY OF REID. 277

In order to bring it to some issue, I have, in the i3th
section, given a more full and regular deduction than
had been given heretofore, of the phenomena of single
and double vision, in those whose sight is perfect ; and
have traced them up to one general principle, which ap-
pears to be a law of vision in human eyes that are perfect
and in their natural state.

In the 1 4th section, I have made it appear, that this
law of vision, although excellently adapted to the fab-
ric of human eyes, cannot answer the purposes of vision
in some other animals ; and therefore, very probably is
not common to all animals. The purpose of the I5th
and i6th sections is, to inquire, Whether there be any
deviation from this law of vision in those who squint ? —
a question which is of real importance in the medical art,
as well as in the philosophy of vision ; but which, after
all that hath been observed and written on the subject,
seems not to be ripe for a determination, for want of prop-
er observations. Those who have had skill to make
proper observations, have wanted opportunities ; and
those who have had opportunities, have wanted skill or
attention. I have therefore thought it worth while to
give a distinct account of the observations necessary for
the determination of this question, and what conclusions
may be drawn from the facts observed. I have likewise
collected, and set in one view, the most conclusive facts
that have occurred in authors, or have fallen under my
own observation.

It must be confessed that these facts, when applied to
the question in hand, make a very poor figure ; and the
gentlemen of the medical faculty are called upon, for the
honour of their profession, and for the benefit of man-
kind, to add to them.

All the medical, and all the optical writers upon the
strabismus that I have met with, except Dr. Jurin, either
affirm, or take it for granted, that squinting persons see
the object with both eyes, and yet see it single. Dr.

278 THE PHILOSOPHY OF REID. [Ca. VI.

Jurin affirms that squinting persons never see the object
with both eyes ; and that, if they did, they would see
it double. If the common opinion be true, the cure of
a squint would be as pernicious to the sight of the patient,
as the causing of a permanent squint would be to one
who naturally had no squint; and therefore, no physician
ought to attempt such a cure, no patient ought to sub-
mit to it. But, if Dr. Jurin's opinion be true, most
young people that squint may cure themselves, by tak-
ing some pains ; and may not only remove the deform-
ity, but, at the same time, improve their sight. If the
common opinion be true, the centres, and other points
of the two retince, in squinting persons, do not corre-
spond, as in other men, and Nature, in them, deviates
from her common rule. But, if Dr. Jurin's opinion be
true, there is reason to think that the same general law
of vision, which we have found in perfect human eyes, ex-
tends also to those which squint.

It is impossible to determine, by reasoning, which of
these opinions is true ; or whether one may not be found
true in same patients, and the other in others. Here,
experience and observation are our only guides ; and a de-
duction of instances is the only rational argument. It
might, therefore, have been expected, that the patrons of
the contrary opinions should have given instances in sup-
port of them that are clear and indisputable ; but I have
not found one such instance on either side of the ques-
tion, in all the authors I have met with. I have given
three instances from my own observation, in confirmation
of Dr. Jurin's opinion, which admit of no doubt ; and
one which leans rather to the other opinion, but is du-
bious. And here I must leave the matter to further ob-
servation.

In the i yth section, I have endeavoured to shew that
the correspondence and [or] sympathy of certain points
of the two refines, into which we have resolved all the
phenomena of single and double vision, is not, as Dr.

SEC. XIX.] THE PHILOSOPHY OF REID. 279

Smith conceived, the effect of custom, nor can [it] be
changed by custom, but is a natural and original prop-
erty of hitman eyes; and, in the last section, that it is
not owing to an original and natural perception of the
true distance of objects from the eye, as Dr. Porterfield
imagined. After this recapitulation, which is intended
to relieve the attention of the reader, shall we enter into
more theories upon this subject ?

That of Dr. Briggs — first published in English, in the
"Philosophical Transactions," afterwards in Latin,
under the title of "Nova Visionis Theoria," with a pref-
atory epistle of Sir Isaac Newton to the author — amounts
to this, That the fibres of the optic nerves, passing from
corresponding points of the retintsio the thalami nervorum
opticorum, having the same length, the same tension, and
a similar situation, will have the same tone; and, there-
fore, their vibrations, excited by the impression of the
rays of light, will be like unisons in music, and will pre-
sent one and the same image to the mind: but the fibres
passing from parts of the retina which do not correspond,
having different tensions and tones, will have discordant
vibrations; and, therefore, present different images to the
mind.

I shall not enter upon a particular examination of this
theory. It is enough to observe, in general, that it is a
system of conjectures concerning things of which we are
entirely ignorant; and that all such theories in philosophy
deserve rather to be laughed at, than to be seriously
refuted.

From the first dawn of philosophy to this day, it hath
been believed that the optic nerves are intended to carry
the images of visible objects from the bottom of the eye to
the mind; and that the nerves belonging to the organs of
the other senses have a like office. But how do we know
this ? We conjecture it; and, taking this conjecture for
a truth, we consider how the nerves may best answer this
purpose. The system of the nerves, for many ages, was

280 THE PHILOSOPHY OF REID. [Cn. VI.

taken to be a hydraulic engine, consisting of a bundle of
pipes, which carried to and fro a liquor called animal
spirits. About the time of Dr. Briggs, it was thought
rather to be a stringed instrument, composed of vibrat-
ing chords, each of which had its proper tension and
tone. But some, with as great probability, conceived it
to be a wind instrument, which played its part by the
vibrations of an elastic aether in the nervous fibrils.

These, I think, are all the engines into which the nerv-
ous system hath been- moulded by philosophers, for
conveying the images of sensible things from the organ
to the sensorium. And, for all that we know of the mat-
ter, every man may freely choose which he thinks fittest
for the purpose; for, from fact and experiment, no one
of them can claim preference to another. Indeed, they
all seem so unhandy engines for carrying images, that a
man would be tempted to invent a new one.

Since, therefore, a blind man may guess as well in the
dark as one that sees, I beg leave to offer another con-
jecture touching the nervous system, which, I hope, will
answer the purpose as well as those we have mentioned,
and which recommends itself by its simplicity. Why
may not the optic nerves, for instance, be made up of
empty tubes, opening their mouths wide enough to re-
ceive the rays of light which form the image upon the
retina, and gently conveying them safe, and in their prop-
er order, to the very seat of the soul, until they flash in
her face ? It is easy for an ingenious philosopher to fit
the caliber of these empty tubes to the diameter of the
particles of light, so as they shall receive no grosser kind
of matter; and, if these rays should be in danger of
mistaking their way, an expedient may also be found to
prevent this; for it requires no more than to bestow upon
the tubes of the nervous system a peristaltic motion, like
that of the alimentary tube.

It is a peculiar advantage of this hypothesis, that,
although all philosophers believe that the species or

SEC. XIX.] THE PHILOSOPHY OF REID. 28 1

images of things are conveyed by the nerves to the soul,
yet none of their hypotheses shew how this may be done.
For how can the images of sound, taste, smell, colour,
figure, and all sensible qualities, be made out of the
vibrations of musical chords, or the undulations of
animal spirits, or of aether ? We ought not to suppose
means inadequate to the end. Is it not as philosophi-
cal, and more intelligible, to conceive, that, as the
stomach receives its food, so the soul receives her images
by a kind of nervous deglutition ? I might add, that we
need only continue this peristaltic motion of the nervous
tubes from the sensorium to the extremities of the nerves
that serve the muscles, in order to account for muscular
motion.

Thus Nature will be consonant to herself: and, as sen-
sation will be the conveyance of the ideal aliment to the
mind, so muscular motion will be the expulsion of the
recrementitious part of it. For who can deny, that the
images of things conveyed by sensation, may, after due
concoction, become fit to be thrown off by muscular
motion ? I only give hints of these things to the ingen-
ious, hoping that in time this hypothesis may be wrought
up into a system as truly philosophical as that of animal
spirits, or the vibration of nervous fibres.

To be serious: In the operations of nature, I hold the
theories of a philosopher, which are unsupported by fact,
in the same estimation with the dreams of a man asleep,
or the ravings of a madman. We laugh at the Indian
philosopher, who, to account for the support of the earth,
contrived the hypothesis of a huge elephant, and, to sup-
port the elephant, a huge tortoise. If we will candidly
confess the truth, we know as little of the operation of
the nerves, as he did of the manner in which the earth
is supported; and our hypotheses about animal spirits, or
about the tension and vibrations of the nerves, are as
like to be true, as his about the support of the earth.
His elephant was a hypothesis, and our hypotheses are

282 THE PHILOSOPHY Of REID. [Cn. VI.

elephants. Every theory in philosophy, which is built
on pure conjecture, is an elephant ; and every theory
that is supported partly by fact, and partly by conject-
ure, is like Nebuchadnezzar's image, whose feet were
partly of iron and partly of clay.

The great Newton first gave an example to philoso-
phers, which always ought to be, but rarely hath been
followed, by distinguishing his conjectures from his con-
clusions, and putting the former by themselves, in the
modest form of queries. This is fair and legal; but all
other philosophical traffic in conjecture ought to be held
contraband and illicit. Indeed, his conjectures have
commonly more foundation in fact, and more verisimili-
tude, than the dogmatical theories of most other philos-
ophers; and, therefore, we ought not to omit that which
he hath offered concerning the cause of our seeing ob-
jects single with two eyes, in the i5th query annexed to
his "Optics."

"Are not the species of objects seen with both eyes,
united where the optic nerves meet before they come
into the brain, the fibres on the right side of both nerves
uniting there, and after union going thence into the
brain in the nerve which is on the right side of the head,
and the fibres on the left side of both nerves uniting in
the same place, and after union going into the brain in
the nerve which is on the left side of the head, and these
two nerves meeting in the brain in such a manner that
their fibres make but one entire species or picture, half
of which on the right side of the sensorium comes from
the right side of both eyes through the right side of both
optic nerves, to the place where the nerves meet, and
from thence on the right side of the head into the brain,
and the other half on the left side of the sensorium comes,
in like manner, from the left side of both eyes ? For the
optic nerves of such animals as look the same way with
both eyes (as men. dogs, sheep, oxen, &c.) meet before
they come into the brain; but the optic nerves of such

SEC. XIX.] THE PHILOSOPHY OF REID. 283

animals as do not look the same way with both eyes (as
of fishes, and of the chameleon) do not meet, if I am
rightly informed."

I beg leave to distinguish this query into two, which
are of very different natures; one being purely anatomi-
cal, the other relating to the carrying species or pictures
of visible objects to the sensorium.

The first question is, Whether the fibres coming from
corresponding points of the two retince do not unite at
the place where the optic nerves meet, and continue
united from thence to the brain; so that the right optic
nerve, after the meeting of the two nerves, is composed
of the fibres coming from the right side of both retince,
and the left, of the fibres coming from the left side of
both retince?

This is undoubtedly a curious and rational question ;
because, if we could find ground from anatomy to"
answer it in the affirmative, it would lead us a step
forward in discovering the cause of the correspondence
and sympathy which there is between certain points of
the two retince. For, although we know not what is the
particular function of the optic nerves, yet it is probable
that some impression made upon them, and communi-
cated along their fibres, is necessary to vision; and,
whatever be the nature of this impression, if two fibres
are united into one, an impression made upon one of
them, or upon both, may probably produce the same
effect. Anatomists think it a sufficient account of a
sympathy between two parts of the body, when they are
served by branches of the same nerve; we should, there-
fore, look upon it as an important discovery in anatomy,
if it were found that the same nerve sent branches to the
corresponding points of the retince.

But hath any such discovery been made ? No, not so
much as in one subject, as far as I can learn; but, in
several subjects, the contrary seems to have been dis-
covered. Dr. Porterfield hath given us two cases at

284 THE PHILOSOPHY OF REID. [On. VI.

length from Vesalius, and one from Caesalpinus, wherein
the optic nerves, after touching one another as usual,
appeared to be reflected back to the same side whence
they came, without any mixture of their fibres. Each of
these persons had lost an eye some time before his death,
and the optic nerve belonging to that eye was shrunk,
so that it could be distinguished from the other at the
place where they met. Another case, which the same
author gives from Vesalius, is still more remarkable; for
in it the optic nerves did not touch at all; and yet, upon
inquiry, those who were most familiar with the person in
his lifetime, declared that he never complained of any
defect of sight, or of his seeing objects double. Diemer-
broeck tells us, that Aquapendens [abAquapendente] and
Valverda likewise affirm, that they have met with sub-
jects wherein the optic nerves did not touch.

As these observations were made before Sir Isaac New-
ton put this query, it is uncertain whether he was
ignorant of them, or whether he suspected some inaccu-
racy in them, and desired that the matter might be more
carefully examined. But, from the following passage of
the most accurate Winslow, it does not appear that later
observations have been more favorable to his conjecture.
"The union of these (optic) nerves, by the small curva-
tures of their cornua, is very difficult to be unfolded in
human bodies. This union is commonly found to be
very close ; but, in some subjects, it seems to be no more
than a strong adhesion — in others, to be partly made by
an intersection or crossing of fibres. They have been
found quite separate ; and, in other subjects, one of them
has been found to be very much altered both in size and
colour through its whole passage, the other remaining in
its natural state."

When we consider this conjecture of Sir Isaac Newton
by itself, it appears more ingenious, and to have more
verisimilitude, than anything that has been offered upon
the subject ; and we admire the caution and modesty of

SEC. XIX.] THE PHILOSOPHY OF REID. 285

the author, in proposing it only as a subject of inquiry:
but when we compare it with the observations of anato-
mists which contradict it, we are naturally led to this
reflection, That, if we trust to the conjectures of men of
the greatest genius in the operations of nature, we have
only the chance of going wrong in an ingenious manner.

The second part of the query is, Whether the two
species of objects from the two eyes are not, at the place
where the optic nerves meet, united into one species or
picture, half of which is carried thence to the sensorium
in the right optic nerve, and the other half in the left ?
and whether these two halves are not so put together
again at the sensorium, as to make one species or
picture ?

Here it seems natural to put the previous question,
What reason have we to believe that pictures of objects
are at all carried to the sensorium, either by the optic
nerves, or by any other nerves ? Is it not possible that
this great philosopher, as well as many of a lower form,
having been led into this opinion at first by education,
may have continued in it, because lie never thought of
calling it in question ? I confess this was my own case
for a considerable part of my life. But since I was led
by accident to think seriously what reason I had to believe
it, I could find none at all. It seems to be a mere
hypothesis, as much as the Indian philosopher's elephant.
I am not conscious of any pictures of external objects in
my sensorinm, any more than in my stomach : the things
which I perceive by my senses, appear to be external,
and not in any part of the brain; and my sensations,
properly so called, have no resemblance of external
objects.

The conclusion from all that hath been said, in no less
than seven sections, upon our seeing objects single with
two eyes, is this — That, by an original property of human
eyes, objects painted upon the centres of the two reiince,
or upon points similarly situate with regard to the centres,

286 THE PHILOSOPHY OF REID. [CH. VI.

appear in the same visible place; that the most plausible
attempts to account for this property of the eyes, have
been unsuccessful; and, therefore, that it must be either
a primary law of our constitution, or the consequence of
some more general law, which is not yet discovered.

We have now finished what we intended to say, both
of the visible appearances of things to the eye, and of the
laws of our constitution by which those appearances are
exhibited. But it was observed, in the beginning of this
chapter, that the visible appearances of objects serve only
as signs of their distance, magnitude, figure, and other
tangible qualities. The visible appearance is that which
is presented to the mind by nature, according to those
laws of our constitution which have been explained. But
the thing signified by that appearance, is that which is
presented to the mind by custom.

When one speaks to us in a language that is familiar,
we hear certain sounds, and this is all the effect that his
discourse has upon us by nature; but by custom we
understand the meaning of these sounds; and, therefore,
we fix our attention, not upon the sounds, but upon the
things signified by them. In like manner, we see only
the visible appearance of objects by nature; but we learn
by custom to interpret these appearances, and to under-
stand their meaning. And when this visual language is
learned, and becomes familiar, we attend only to the
things signified ; and cannot, without great difficulty,
attend to the signs by which they are presented. The
mind passes from one to the other so rapidly and so
familiarly, that no trace of the sign is left in the memory,
and we seem immediately, and without the intervention
of any sign, to perceive the thing signified.

When I look at the apple-tree which stands before my
window, I perceive, at the first glance, its distance and
magnitude, the roughness of its trunk, the disposition of
its branches, the figure of its leaves and fruit. I seem to
perceive all these things immediately. The visible ap-

SEC. XX.] THE PHILOSOPHY OF REID. 287

pearance which presented them all to the mind, has
entirely escaped me ; I cannot, without great difficulty,
and painful abstraction, attend to it, even when it stands
before me. Yet it is certain that this visible appearance
only is presented to my eye by nature, and that I learned
by custom to collect all the rest from it. If I had never
seen before now, I should not perceive either the distance
or tangible figure of the tree; and it would have required
the practice of seeing for many months, to change that
original perception which nature gave me by my eyes,
into that which I now have by custom.

The objects which we see naturally and originally, as
hath been before observed, have length and breadth, but
no thickness nor distance from the eye. Custom, by a
kind of legerdemain, withdraws gradually these original
and proper objects of sight, and substitutes in their place
objects of touch, which have length, breadth, and thick-
ness, and a determinate distance from the eye. By what
means this change is brought about, and what principles
of the human mind concur in it, we are next to inquire.

Section XX.

OF PERCEPTION IN GENERAL.

Sensation, and the perception * of external objects by
the senses, though very different in their nature, have
commonly been considered as one and the same thing, f

* On the distinction of Sensation proper, from Perception proper,
see " Essays on the Intellectual Powers," Essay II., chap. 16. Reid
himself, especially in this work, has not been always rigid in observ-
ing their discrimination. — II.

•f- Not only are they different, but — what has escaped our philos-
ophers— the law of their manifestation is, that, while both are co-ex-
istent, each is always in the inverse ratio of the other. Perception
is the objective, Sensation the subjective, element. This by the
way. — H.

288 THE PHILOSOPHY OF REID. [Cn. VI.

The purposes of common life do not make it necessary to
distinguish them, and the received opinions of philos-
ophers tend rather to confound them; but, without at-
tending carefully to this distinction, it is impossible to
have any just conception of the operations of our senses.
The most simple operations of the mind, admit not of a
logical definition: all we can do is to describe them, so as
to lead those who are conscious of them in themselves, to
attend to them, and reflect upon them; and it is often
very difficult to describe them so as to answer this
intention.

The same mode of expression is used to denote sensation
and perception; and, therefore, we are apt to look upon
them as things of the same nature. Thus, I feel a pain;
I see a tree: the first denoteth a sensation, the last a per-
ception. The grammatical analysis of both expressions
is the same: for both consist of an active verb and an ob-
ject. But if we attend to the things signified by these
expressions, we shall find that, in the first, the distinction
between the act and the object is not real but grammatical ;
in the second, the distinction is not only grammatical
but real.

The form of the expression, I feel pain, might seem
to imply that the feeling is something distinct from the
pain felt; yet, in reality, there is no distinction. As
thinking a thought is an expression which could signify
no more than thinking, so feeling a pain signifies no more
than being pained. What we have said of pain is applica-
ble to every other mere sensation. It is difficult to give
instances, very few of our sensations having names; and,
where they have, the name being common to the sensa-
tion, and to something else which is associated with it.
But, when we attend to the sensation by itself, and sep-
arate it from other things which are conjoined with it in
the imagination, it appears to be something which can
have no existence but in a sentient mind, no distinction
from the act of the mind by which it is felt

SEC. XX.] THE PHILOSOPHY OF REID. 289

Perception, as we here understand it, hath always an
object distinct from the act by which it is perceived; an
object which may exist whether it be perceived or not.
I perceive a tree that grows before my window; there is
here an object which is perceived, and an act of the
mind by which it is perceived; and these two are not
only distinguishable, but they are extremely unlike in
their natures. The object is made up of a trunk,
branches, and leaves; but the act of the mind by which
it is perceived hath neither trunk, branches, nor leaves.
I am conscious of this act of my mind, and I can reflect
upon it; but it is too simple to admit of an analysis,
and I cannot find proper words to describe it. I find
nothing that resembles it so much as the remembrance of
the tree, or the imagination of it. Yet both these differ
essentially from perception: they differ likewise one
from another. It is in vain that a philosopher assures
me, that the imagination of the tree, the remembrance of
it, and the perception of it, are all one, and differ only
in degree of vivacity. I know the contrary; for I am as
well acquainted with all the three as I am with the apart-
ments of my own house. I know this also, that the
perception of an object implies both a conception of its
form, and a belief of its present existence.* I know,
moreover, that this belief is not the effect of argumenta-

* It is to be observed that Reid himself does not discriminate percep-
tion and imagination by any essential difference. According to him,
perception is only the conception (imagination) of an object, ac-
companied with a belief of its present existence; and even this last
distinction, a mere "faith without knowledge," is surrendered by
Mr. Stewart. Now, as conception (imagination) is only immedi-
ately cognisant of the ego, so must perception on this doctrine be a
knowledge purely stibjective. Perception must be wholly different
in kind from Conception, if we are to possess a faculty informing us
of the existence and qualities of an external world; and, unless we
are possessed of such a faculty, we shall never be competent to vin-
dicate more than an ideal reality to the objects of our cognitions. — H.

290 THE PHILOSOPHY OF REID. [Cn. VI.

tion and reasoning; it is the immediate effect of my
constitution.

I am aware that this belief which I have in perception
stands exposed to the strongest batteries of scepticism.
But they make no great impression upon it. The scep-
tic asks me, Why do you believe the existence of the
external object which you perceive? This belief, sir,
is none of my manufacture; it came from the mint of
Nature; it bears her image and superscription; and, if
it is not right, the fault is not mine: I even took it upon
trust, and without suspicion. Reason, says the sceptic,
is the only judge of truth, and you ought to throw off
every opinion and every belief that is not grounded on
reason. Why, sir, should I believe the faculty of rea-
son more than that of perception ? — they came both out
of the same shop, and were made by the same artist;
and if he puts one piece of false ware into my hands,
what should hinder him from putting another ? *

"Perhaps the sceptic will agree to distrust reason,
rather than give any credit to perception. For, says
he, since, by your own concession, the object which you
perceive, and that act of your mind by which you per-
ceive it, are quite different things, the one may exist
without the other; and, as the object may exist without
being perceived, so the perception may exist without an
object. There is nothing so shameful in a philosopher
as to be deceived and deluded; and, therefore, you
ought to resolve firmly to withhold assent, and to throw
off this belief of external objects, which may be all delu-
sion. For my part, I will never attempt to throw it off;
and, although the sober part of mankind will not be

* This argument would be good in favour of our belief, that we
are really percipient of a non-ego: it is not good in favour of our
belief that a non-ego really exists, our perception of its real existence
being abandoned. Mankind have the latter belief only as they have
the former; and, if we are deceived by our Nature touching the one,
it is absurd to appeal to her veracity in proof of the other. — H.

SEC. XX.] THE PHILOSOPHY OF REID. 291

very anxious to know my reasons, yet, if they can be of
use to any sceptic, they are these: —

First, because it is not in my power: why, then, should
I make a vain attempt ? It would be agreeable to fly
to the moon, and to make a visit to Jupiter and Saturn;
but, when I know that Nature has bound me down by
the law of gravitation to this planet which I inhabit, I
rest contented, and quietly suffer myself to be carried
along in its orbit. My belief is carried along by per-
ception, as irresistibly as my body by the earth. And
the greatest sceptic will find himself to be in the same
condition. He may struggle hard to disbelieve the in-
formations of his senses, as a man does to swim against
a torrent; but, ah ! it is in vain. It is in vain that he
strains every nerve, and wrestles with nature, and with
every object that strikes upon his senses. For, after all,
when his strength is spent in the fruitless attempt, he
will be carried down the torrent with the common herd
of believers.

Secondly, I think it would not be prudent to throw
off this belief, if it were in my power. If Nature in-
tended to deceive me, and impose upon me by false ap-
pearances, and I, by my great cunning and profound
logic, have discovered the imposture, prudence would
dictate to me, in this case, even to put up [with] this
indignity done me, as quietly as I could, and not to call
her an impostor to her face, lest she should be even
with me in another way. For what do I gain by resent-
ing this injury ? You ought at least not to believe what
she says. This indeed seems reasonable, if she intends
to impose upon me. But what is the consequence ?
I resolve not to believe my senses. I break my nose
against a post that comes in my way; I step into a dirty
kennel; and, after twenty such wise and rational actions,
I am taken up and clapped into a mad-house. Now, I
confess I would rather make one of the credulous fools
whom Nature imposes upon, than of those wise and ra-

2Q2 THE PHILOSOPHY OF REID. [CH. VI.

tional philosophers who resolve to withhold assent at all
this expense. If a man pretends to be a sceptic with
regard to the informations of sense, and yet prudently
keeps out of harm's way as other men do, he must
excuse my suspicion, that he either acts the hypocrite, or
imposes upon himself. For, if the scale of his belief
were so evenly poised as to lean no more to one side
than to the contrary, it is impossible that his actions
could be directed by any rules of common prudence.*

Thirdly, Although the two reasons already mentioned
are perhaps two more than enough, I shall offer a third.
I gave implicit belief to the informations of Nature by
my senses, for a considerable part of my life, before I
had learned so much logic as to be able to start a doubt
concerning them. And now, when I reflect upon what
is past, I do not find that I have been imposed upon by
this belief. I find that without it I must have perished by
a thousand accidents. I find that without it I should
have been no wiser now than when I was born. I should
not even have been able to acquire that logic which sug-
gests these sceptical doubts with regard to my senses.
Therefore, I consider this instinctive belief as one of
the best gifts of Nature. I thank the Author of my
being, who bestowed it upon me before the eyes of my
reason were opened, and still bestows it upon me, to be
my guide where reason leaves me in the dark. And
now I yield to the direction of my senses, not from in-
stinct only, but from confidence and trust in a faithful
and beneficent Monitor, grounded upon the experience
of his paternal care and goodness.

In all this, I deal with the Author of my being, no
otherwise than I thought it reasonable to deal with my
parents and tutors. I believed by instinct whatever they
told me, long before I had the idea of a lie, or thought

* This is not a fair consequence of Idealism ; therefore, it is not a
reductio ad absurdum. — H.

SEC. XX.] THE PHILOSOPHY OF REID. 293

of the possibility of their deceiving me. Afterwards,
upon reflection, I found they had acted like fair and hon-
est people, who wished me well. I found that, if I had
not believed what they told me, before I could give a
reason of my belief, I had to this day been little better
than a changeling. And although this natural credulity
hath sometimes occasioned my being imposed upon by
deceivers, yet it hath been of infinite advantage to me
upon the whole; therefore, I consider it as another
good gift of Nature. And I continue to give that
credit, from reflection, to those of whose integrity and
veracity I have had experience, which before I gave from
instinct.

There is a much greater similitude than is commonly
imagined, between the testimony of nature given by our
senses, and the testimony of men given by language.
The credit we give to both is at first*the effect of instinct
only. When we grow up, and begin to reason about
them, the credit given to human testimony is restrained
and weakened, by the experience we have of deceit.
But the credit given to the testimony of our senses, is
established and confirmed by the uniformity and con-
stancy of the laws of nature.

Our perceptions are of two kinds: some are natural
and original; others acquired, and the fruit of experi-
ence. When I perceive that this is the taste of cyder,
that of brandy; that this is the smell of an apple, that of
an orange; that this is the noise of thunder, that the ring-
ing of bells; this the sound of a coach passing, that the
voice of such a friend: these perceptions, and others of the
same kind, are not original — they are acquired. But
the perception which I have, by touch, of the hardness
and softness of bodies, of their extension, figure, and
motion, is not acquired — it is original.

In all our senses, the acquired perceptions are many
more than the original, especially in sight. By this sense
we perceive originally the visible figure and colour of

294 THE PHILOSOPHY OF REID. [CH. VI.

bodies only, and their visible place: * but we learn to
perceive by the eye, almost everything which we can per-
ceive by touch. The original perceptions of this sense
serve only as signs to introduce the acquired.

The signs by which objects are presented to us in per-
ception, are the language of Nature to man ; and as, in
many respects, it hath great affinity with the language of
man to man, so particularly in this, that both are partly
natural and original, partly acquired by custom. Our
original or natural perceptions are analogous to the natu-
ral language of man to man, of which we took notice in
the fourth chapter ; and our acquired perceptions are an-
alogous to artificial language, which, in our mother-
tongue, is got very much in the same manner with our
acquired perceptions — as we shall afterwards more fully
explain.

Not only men, buf children, idiots, and brutes, acquire
by habit many perceptions which they had not originally.
Almost every employment in life hath perceptions of
this kind that are peculiar to it. The shepherd knows
every sheep of his flock, as we do our acquaintance, and
can pick them out of another flock one by one. The
butcher knows by sight the weight and quality of his
beeves and sheep before they are killed. The farmer
perceives by his eye, very nearly, the quantity of hay in
a rick, or of corn in a heap. The sailor sees the burthen,
the built, and the distance of a ship at sea, while she is
a great way off. Every man accustomed to writing, dis-
tinguishes his acquaintance by their handwriting, as he
does by their faces. And the painter distinguishes, in
the works of his art, the style of all the great masters. In
a word, acquired perception is very different in different
persons, according to the diversity of objects about which
they are employed, and the application they bestow in
observing them.

* In this passage Reid admits Figure and Place (consequently,
Extension) to be original perceptions of vision.

SEC. XX.] THE PHILOSOPHY OF REID. 29$

Perception ought not only to be distinguished from
sensation, but likewise from that knowledge of the objects
of sense which is got by reasoning. There is no reason-
ing in perception, as hath been observed. The belief
which is implied in it, is the effect of instinct. But there
are many things, with regard to sensible objects, which
we can infer from what we perceive ; and such conclu-
sions of reason ought to be distinguished from what is
merely perceived. When I look at the moon, I perceive
her to be sometimes circular, sometimes horned, and
sometimes gibbous. This is simple perception, and is
the same in the philosopher and in the clown: but from
these various appearances of her enlightened part, I infer
that she is really of a spherical figure. This conclusion
is not obtained by simple perception, but by reasoning.
Simple perception has the same relation to the conclu-
sions of reason drawn from our perceptions, as the axioms
in mathematics have to the propositions. I cannot de-
monstrate that two quantities which are equal to the same
quantity, are equal to each other ; neither can I demon-
strate that the tree which I perceive, exists. But, by the
constitution of my nature, my belief is irresistibly car-
ried along by my apprehension of the axiom ; and, by
the constitution of my nature, my belief is no less irre-
sistibly carried along by my perception of the tree. All
reasoning is from principles. The first principles of ma-
thematical reasoning are mathematical axioms and def-
initions ; and the first principles of all our reasoning
about existences, are our perceptions. The first princi-
ples of every kind of reasoning are given us by Nature,
and are of equal authority with the faculty of reason it-
self, which is also the gift of Nature. The conclusions
of reason are all built upon first principles, and can have
no other foundation. Most justly, therefore, do such"
principles disdain to be tried by reason, and laugh at all
the artillery of the logician, when it is directed against
them.

296 THE PHILOSOPHY OF REID. [Cn. VI.

When a long train of reasoning is necessary in demon-
strating a mathematical proposition, it is easily distin-
guished from an axiom ; and they seem to be things of
a very different nature. But there are some propositions
which lie so near to axioms, that it is difficult to say
whether they ought to be held as axioms, or demonstrated
as propositions. The same thing holds with regard to
perception, and the conclusions drawn from it. Some
of these conclusions follow our perceptions so easily, and
are so immediately connected with them, that it is diffi-
cult to fix the limit which divides the one from the
other.

Perception, whether original or acquired, implies no
exercise of reason ; and is common to men, children,
idiots, and brutes. The more obvious conclusions drawn
from our perceptions, by reason, make what we call com-
mon understanding; by which men conduct themselves in
the common affairs of life, and by which they are dis-
tinguished from idiots. The more remote conclusions
which are drawn from our perceptions, by reason, make
what we commonly call science in the various parts of na-
ture, whether in agriculture, medicine, mechanics, or in
any part of natural philosophy. When I see a garden
in good order, containing a great variety of things of the
best kinds, and in the most flourishing condition, I im-
mediately conclude from these signs the skill and indus-
try of the gardener. A farmer, when he rises in the
morning, and perceives that the neighbouring brook
overflows his field, concludes that, a great deal of rain
hath fallen in the night. Perceiving his fence broken,
and his corn trodden down, he concludes that some of
his own or his neighbours' cattle have broke loose. Per-
ceiving that his stable-door is broke open, and some of
his horses gone, he concludes that a thief has carried
them off. He traces the prints of his horses' feet in the
soft ground, and by them discovers which road the thief
hath taken. These are instances of common understand-

SEC. XXI.] THE PHILOSOPHY OF REID. 2g7

ing, which dwells so near to perception that it is difficult
to trace the line which divides the one from the other.
In like manner the science of nature dwells so near to
common understanding that we cannot discern where the
latter ends and the former begins. I perceive that bodies
lighter than water swim in water, and that those which
are heavier sink. Hence I conclude, that, if a body re-
mains wherever it is put under water, whether at the top
or bottom, it is precisely of the same weight with water.
If it will rest only when part of it is above water, it is
lighter than water. And the greater the part above water
is, compared with the whole, the lighter is the body. If
it had no gravity at all, it would make no impression
upon the water, but stand wholly above it. Thus, every
man, by common understanding, has a rule by which he
judges of the specific gravity of bodies which swim in
water ; and a step or two more leads him into the science
of hydrostatics.

All that we know of nature, or of existences, may be
compared to a tree, which hath its root, trunk, and
branches. In this tree of knowledge, perception is the
root, common understanding is the trunk, and the sci-
ences are the branches.

Section XXL

OF THE PROCESS OF NATURE IN PERCEPTION.

Although there is no reasoning in perception, yet there
are certain means and instruments, which, by the ap-
pointment of nature, must intervene between the object
and our perception of it : and, by these, our perceptions
are limited and regulated. First, if the object is not in con-
tact with the organ of sense, there must be some medium
which passes between them. Thus, in vision, the rays
of light ; in hearing, the vibrations of elastic air ; in
smelling, the effluvia of the body smelled — must pass

298 THE PHILOSOPHY OF REID. |CH. VI.

from the object to the organ ; otherwise we have no per-
ception.* Secondly, There must be some action or im-
pression upon the organ of sense, either by the immedi-
ate application of the object, or by the medium that goes
between them. Thirdly, The nerves which go from the
brain to the organ must receive some impression by
means of that which was made upon the organ ; and,
probably, by means of the nerves, some impression must
be made upon the brain. Fourthly, The impression
made upon the organ, nerves, and brain, is followed by
a sensation. And, last of all, This sensation is followed
by the perception of the object.

Thus, our perception of objects is the result of a train
of operations ; some of which affect the body only, others
affect the mind. We know very little of the nature of
some of these operations ; we know not at all how they
are connected together, or in what way they contribute
to that perception which is the result of the whole ; but,
by the laws of our constitution, we perceive objects in
this and in no other way.

There may be other beings who can perceive external
objects without rays of light, or vibrations of air, or efflu-
via of bodies — without impressions on bodily organs, or
even without sensations; but we are so framed by the
Author of Nature, that even when we are surrounded by ex-
ternal objects, we may perceive none of them Our faculty
of perceiving an object lies dormant, until it is roused and
stimulated by a certain corresponding sensation. Nor is
this sensation always at hand to perform its office ; for it
enters into the mind only in consequence of a certain
corresponding impression made on the organ of sense by
the object.

* The only object of perception is the immediate object. The
distant reality — the mediate object, or object simply of Reid and
other philosophers — is unknown to the perception of sense, and only
reached by reasoning. — H.

SEC. XXI.] THE PHILOSOPHY OP REID. 299

Let us trace this correspondence of impressions, sen-
sations, and perceptions, as far as we can — beginning with
that which is first in order, the impression made upon
the bodily organ. But, alas ! we know not of what na-
ture these impressions are, far less how they excite sensa-
tions in the mind.

We know that one body may act upon another by
pressure, by percussion, by attraction, by repulsion, and,
probably, in many other ways which we neither know nor
have names to express. But in which of these ways ob-
jects, when perceived by us, act upon the organs of sense,
these organs upon the nerves, and the nerves upon the
brain, we know not. Can any man tell me how in vis-
ion, the rays of light act upon the retina, how the retina
acts upon the optic nerve, and how the optic nerve acts
upon the brain ? No man can. When I feel the pain
of the gout in my toe, I know that there is some un-
usual impression made upon that part of my body. But
of what kind is it? Are the small vessels distended with
some redundant elastic, or unelastic fluid ? Are the fi-
bres unusually stretched? Are they torn asunder by force,
or gnawed and corroded by some acrid humour ? I can
answer none of these questions. All that I feel is pain,
which is not an impression upon the body, but upon the
mind ; and all that I perceive by this sensation is, that
some distemper in my toe occasions this pain. But as I
know not the natural temper and texture of my toe when
it is at ease, I know as little what change or disorder of
its parts occasions this uneasy sensation. In like manner,
in every other sensation, there is, without doubt, some
impression made upon the organ of sense ; but an im-
pression of which we know not the nature. It is too
subtile to be discovered by our senses, and we may make
a thousand conjectures without coming near the truth.
If we understood the structure of our organs of sense so
minutely as to discover what effects are produced upon
them by external objects, this knowledge would contrib-

300 THE PHILOSOPHY OF REIt). [CH. VI.

ute nothing to our perception of the object ; for they
perceive as distinctly who know least about the manner
of perception, as the greatest adepts. It is necessary that
the impression be made upon our organs, but not that
it be known. Nature carries on this part of the process
of perception, without our consciousness or concurrence.

But we cannot be unconscious of the next step in this
process — the sensation of the mind, which always im-
mediately follows the impression made upon the body.
It is essential to a sensation to be felt, and it can be
nothing more than we feel it to be. If we can only
acquire the habit of attending to our sensations, we may
know them perfectly. But how are the sensations of
the mind produced by impressions upon the body ? Of
this we are absolutely ignorant, having no means of
knowing how the body acts upon the mind, or the mind
upon the body. When we consider the nature and at-
tributes of both, they seem to be so different, and so
unlike, that we can find no handle by which the one may
lay hold of the other. There is a deep and a dark gulf
between them, which our understanding cannot pass;
and the manner of their correspondence and intercourse
is absolutely unknown.

Experience teaches us, that certain impressions upon
the body are constantly followed by certain sensations of
the mind; and that, on the other hand, certain deter-
minations of the mind are constantly followed by cer-
tain motions in the body; but we see not the chain that
ties these things together. Who knows but their con-
nection may be arbitrary, and owing to the will of our
Maker ? Perhaps the same sensations might have been
connected with other impressions, or other bodily organs.
Perhaps we might have been so made as to taste with
our fingers, to smell with our ears, and to hear by the
nose. Perhaps we might have been so made as to have
all the sensations and perceptions which we have, with-
out any impression made upon our bodily organs at all.

SEC. XXI.] THE PHILOSOPHY OF REID. 30 1

However these things may be, if Nature had given us
nothing more than impressions made upon the body, and
sensations in our minds corresponding to them, we
should, in that case, have been merely sentient, but not
percipient beings. We should never have been able to
form a conception of any external object, far less a be-
lief of its existence. Our sensations have no resemblance
to external objects; nor can we discover, by our reason,
any necessary connection between the existence of the
former, and that of the latter.

We might, perhaps, have been made of such a con-
stitution as to have our present perceptions connected
with other sensations. We might, perhaps, have had
the perception of external objects, without either impres-
sions upon the organs of sense, or sensations. Or, lastly,
The perceptions we have, might have been immediately
connected with the impressions upon our organs, with-
out any intervention of sensations. This last seems
really to be the case in one instance — to wit, in our per-
ception of the visible figure of bodies, as was observed in
the eighth section of this chapter.

The process of Nature, in perception by the senses,
may, therefore, be conceived as a kind of drama, wherein
some things are performed behind the scenes, others are
represented to the mind in different scenes, one succeed-
ing another. The impression made by the object upon
the organ, either by immediate contact or by some in-
tervening medium, as well as the impression made upon
the nerves and brain, is performed behind the scenes,
and the mind sees nothing of it. But every such im-
pression, by the laws of the drama, is followed by a sen-
sation, which is the first scene exhibited to the mind;
and this scene is quickly succeeded by another, which
is the perception of the object.

In this drama, Nature is the actor, we are the specta-
tors. We know nothing of the machinery by means of
which every different impression upon the organ, nerves,

302 THE PHILOSOPHY OF REID. [CH.VI.

and brain, exhibits its corresponding sensation; or of the
machinery by means of which each sensation exhibits its
corresponding perception. We are inspired with the
sensation, and we are inspired with the corresponding
perception, by means unknown.* And, because the
mind passes immediately from the sensation to that con-
ception and belief of the object which we have in percep-
tion, in the same manner as it passes from signs to the
things signified by them, we have, therefore, called our
sensations signs of external objects; finding no word more
proper to express the function which Nature hath
assigned them in perception, and the relation which they
bear to their corresponding objects.

There is no necessity of a resemblance between the
sign and the thing signified ; and indeed no sensation
can resemble any external object. But there are two
things necessary to our knowing things by means of signs.
First, That a real connection between the sign and thing
signified be established, either by the course of nature,
or by the will and appointment of men. When they are
•connected by the course of nature, it is a natural sign;
when by human appointment, it is an artificial sign.
Thus, smoke is a natural sign of fire; certain features are
natural signs of anger: but our words, whether ex-
pressed by articulate sounds or by writing, are artificial
signs of our thoughts and purposes.

Another requisite to our knowing things by signs is,
that the appearance of the sign to the mind, be followed
by the conception and belief of the thing signified.
Without this, the sign is not understood or interpreted;
and, therefore, is no sign to us, however fit in its own
nature for that purpose.

Now, there are three ways in which the mind passes
from the appearance of a natural sign to the conception

* On perception as a revelation — "a miraculous revelation " — see
Jacobi's " David Hume."— H.

SBC. XXII.] THE PHILOSOPHY OF REID. 303

and belief of the thing signified — by original principles of
our constitution, by custom and by reasoning.

Our original perceptions are got in the first of these
ways, our acquired perceptions in the second, and all
that reason discovers of the course of nature, in the third.
In the first of these ways, Nature, by means of the sensa-
tions of touch, informs us of the hardness and softness
of bodies; of their extension, figure, and motion; and of
that space in which they move and are placed — as hath
been already explained in the fifth chapter of this inquiry.
And, in the second of these ways, she informs us, by
means of our eyes, of almost all the same things which
originally we could perceive only by touch.

In order, therefore, to understand more particularly
how we learn to perceive so many things by the eye,
which originally could be perceived only by touch, it will
be proper, First, To point out the signs by which those
things are exhibited to the eye, and their connection with
the things signified by them; and, Secondly, To consider
how the experience of this connection produces that
habit by which the mind, without any reasoning or re-
flection, passes from the sign to the conception and be-
lief of the thing signified.

Of all the acquired perceptions which we have by sight,
the most remarkable is the perception of the distance of
objects from the eye; we shall, therefore, particularly
consider the signs by which this perception is exhibited,
and only make some general remarks with regard to the
signs which are used in other acquired perceptions.

Section XXII.

OF THE SIGNS BY WHICH WE LEARN TO PERCEIVE DISTANCE
FROM THE EYE.

It was before observed in general, that the original
perceptions of sight are signs which serve to introduce

304 THE PHILOSOPHY OF REID. [Cn. VI.

those thaf are acquired; but this is not to be understood
as if no other signs were employed for that purpose.
There are several motions of the eyes, which, in order to
distinct vision, must be varied, according as the object
is more or less distant; and such motions being by habit
connected with the corresponding distances of the object,
become signs of those distances. These motions were at
first voluntary and unconfined; but, as the intention of
nature was to produce perfect and distinct vision by their
means, we soon learn by experience to regulate them
according to that intention only, without the least reflec-
tion.

A ship requires a different trim for every variation of
the direction and strength of the wind; and, if we may
be allowed to borrow that word, the eyes require a differ-
ent trim for every degree of light, and for every variation
of the distance of the object, while it is within certain
limits. The eyes are trimmed for a particular object, by
contracting certain muscles and relaxing others; as the
ship is trimmed for a particular wind by drawing certain
ropes and slackening others. The sailor learns the trim
of his ship, as we learn the trim of our eyes, by expe-
rience. A ship, although the noblest machine that hu-
man art can boast, is far inferior to the eye in this re-
spect, that it requires art and ingenuity to navigate her;
and a sailor must know what ropes he must pull, and
what he must slacken, to fit her to a particular wind;
but with such superior wisdom is the fabric of the eye,
and the principles of its motion contrived, that it requires
no art nor ingenuity to see by it. Even that part of
vision which is got by experience, is attained by idiots.
We need not know what muscles we are to contract, and
what we are to relax, in order to fit the eye to a particu-
lar distance of the object.

But, although we are not conscious of the motions we
perform, in order to fit the eyes to the distance of the
object, we are conscious of the effort employed in pro-

SEC. XXII.] THE PHILOSOPHY OF REID. 305

f

ducing these motions; and probably have some sensation
which accompanies them, to which we give as little at-
tention as to other sensations. And thus, an effort con-
sciously exerted, or a sensation consequent upon that
effort, comes to be conjoined with the distance of the
object which gave occasion to it, and by this- conjunc-
tion becomes a sign of that distance. Some instances
of this will appear in considering the means or signs by
which we learn to see the distance of objects from the
eye. In the enumeration of these, we agree with Dr.
Porterfield, notwithstanding that distance from the eye,
in his opinion, is perceived originally, but, in our opin-
ion, by experience only.

In general, when a near object affects the eye in one
manner, and the same object, placed at a greater dis-
tance, affects it in a different manner, these various
affections of the eye become signs of the corresponding
distances. The means of perceiving distance by the eye
will therefore be explained by shewing in what various
ways objects affect the eye differently, according to their
proximity or distance.

i. It is well known, that, to see objects distinctly at
various distances, the form of the eye must undergo
some change : and nature hath given us the power of
adapting it to near objects, by the contraction of certain
muscles, and to distant objects by the contraction of
other muscles. As to the manner in which this is done,
and the muscular parts employed, anatomists do not al-
together agree. The ingenious Dr. Jurin, in his excel-
lent essay on distinct and indistinct vision, seems to
have given the most probable account of this matter; and
to him I refer the reader.

But, whatever be the manner in which this change of
the form of the eye is effected, it is certain that young
people have commonly the power of adapting their eyes
to all distances of the object, from six or seven inches,
to fifteen or sixteen feet ; so as to have perfect and dis-

306 THE PHILOSOPHY OF REID. [Cn. VI.

tinct vision at any distance within these limits. From
this it follows, that the effort we consciously employ to
adapt the eye to any particular distance of objects within
these limits, will be connected and associated with that
distance, and will become a sign of it. When the object
is removed beyond the farthest limit of distinct vision, it
will be seen indistinctly; but, more or less so, according
as its distance is greater or less ; so that the degrees of
indistinctness of the object may become the signs of dis-
tances considerably beyond the farthest limit of distinct
Vision.

If we had no other mean but this, of perceiving dis-
tance of visible objects, the most distant would not ap-
pear to be above twenty or thirty feet from the eye, and
the tops of houses and trees would seem to touch the
clouds; for, in that case, the signs of all greater distances
being the same, fhey have the same signification, and
give the same perception of distance.

But it is of more importance to observe, that, because
the nearest limit of distinct vision in the time of youth,
when we learn to perceive distance by the eye, is about
six or seven inches, no object seen distinctly ever appears
to be nearer than six or seven inches from the eye. We
can, by art, make a small object appear distinct, when
it is in reality not above half an inch from the eye;
either by using a single microscope, or by looking
through a small pin-hole in a card. When, by either of
these means, an object is made to appear distinct, how-
ever small its distance is in reality, it seems to be re-
moved at least to the distance of six or seven inches —
that is, within the limits of distinct vision.

This observation is the more important, because it
affords the only reason we can give why an object is
magnified either by a single microscope, or by being seen
through a pin-hole; and the only mean by which we can
ascertain the degree in which the object will be magni-
fied by either. Thus, if the object is really half an inch

SEC. XXII.] THE PHILOSOPHY OF REID. 307

distant from the eye, and appears to be seven inches dis-
tant, its diameter will seem to be enlarged in the same pro-
portion as its distance — that is, fourteen times.

2. In order to direct both eyes to an object, the optic
axes must have a greater or less inclination, according as
th& object is nearer or more distant And, although we'
are not conscious of this inclination, yet we are con-
scious of the effort employed in it. By this mean
we perceive small distances more accurately than we
could do by the conformation of the eye only. And,
therefore, we find, that those who have lost the sight of
one eye are apt, even within arms-length, to make mis-
takes in the distance of objects, which are easily avoided
by those who see with both eyes. Such mistakes are of-
ten discovered in snuffing a candle, in threading a nee-
dle, or in filling a tea-cup.

When a picture is seen with both eyes, and at no
great distance, the representation appears not so natural
as when it is seen only with one. The intention of
painting being to deceive the eye, and to make things
appear at different distances which in reality are upon
the same piece of canvass, this deception is not so easily
put upon both eyes as upon one; because we perceive
the distance of visible objects more exactly and deter-
minately with two eyes than with one. If the shading
and relief be executed in the best manner, the picture
may have almost the same appearance to one eye as the
objects themselves would have; but it cannot have the
same appearance to both. This is not the fault of the
artist, but an unavoidable imperfection in the art. And
it is owing to what we just now observed, that the per-
ception we have of the distance of objects by one eye is
more uncertain, and more liable to deception, than that
which we have by both.

The great impediment, and I think the only invinci-
ble impediment, to that agreeable deception of the eye
which the painter aims at, is the perception which wq

308 THE PHILOSOPHY OF REID. [CH. VI.

have of the distance of visible objects from the eye, part-
ly by means of the conformation of the eye, but chiefly
by means of the inclination of the optic axes. If this
perception could be removed, I see no reason why a
picture might not be made so perfect as to deceive the
eye in reality, and to be mistaken for the original object.
Therefore, in order to judge of the merit of a picture,
we ought, as much as possible, to exclude these two
means of perceiving the distance of the several parts of it.

In order to remove this perception of distance, the
connoisseurs in painting use a method which is very
proper. They look at the picture with one eye, through
a tube which excludes the view of all other objects. By
this method, the principal mean whereby we perceive the
distance of the object — to wit, the inclination of the op-
tic axes — is entirely excluded. I would humbly pro-
pose, as an improvement of this method of viewing pic-
tures, that the aperture of the tube next to the eye should
be very small. If it is as small as a pin-hole, so much
the better, providing there be light enough to see the
picture clearly. The reason of this proposal is, that,
when we look at an object through a small aperture, it
will be seen distinctly, whether the conformation of the
eye be adapted to its distance or not ; and we have no
mean left to judge of the distance, but the light and
colouring, which are in the painter's power. If, there-
fore, the artist performs his part properly, the picture
will by this method affect the eye in the same manner
that the object represented would do; which is the per-
fection of this art.

Although this second mean of perceiving the distance
of visible objects be more determinate and exact than
the first, yet it hath its limits, beyond which it can be
of no use. For when the optic axes directed to an ob-
ject are so nearly parallel that, in directing them to an
object yet more distant, we are not conscious of any new
effort, nor have any different sensation, there our per-

SEC. XXII.? THE PHILOSOPHY OF REID. 309

ception of distance stops; and, as all more distant ob-
jects affect the eye in the same manner, we perceive them
to be at the same distance. This is the reason why the
sun, moon, planets, and fixed stars, when seen not near
the horizon, appear to be all at the same distance, as if
they touched the concave surface of a great sphere. The
surface of this celestial sphere is at that distance beyond
which all objects affect the eye in the same manner.
Why this celestial vault appears more distant towards
the horizon, than towards the zenith, will afterwards ap-
pear.

3. The colours of objects, according as they are more
distant, become more faint and languid, and are tinged
more with the azure of the intervening atmosphere: to
this we may add, that their minute parts become more
indistinct, and their outline less accurately defined. It is
by these means chiefly, that painters can represent objects
at very different distances, upon the same canvass. And
the diminution of the magnitude of an object would not
have the effect of making it appear to be at a great dis-
tance, without this degradation of colour, and indistinct-
ness of the outline, and of the minute parts. If a
painter should make a human figure ten times less than
other human figures that are in the same piece, having
the colours as bright, and the outline and minute parts
as accurately defined, it would not have the appearance
of a man at a great distance, but of a pigmy or Lilipu-
tian.

When an object hath a known variety of colours, its
distance is more clearly indicated by the gradual dilution
of the colours into one another, than when it is of one
uniform colour. In the steeple which stands before me
at a small distance, the joinings of the stones are clearly
perceptible; the grey colour of the stone, and the white
cement are distinctly limited : when I see it at a greater
distance, the joinings of the stones are less distinct, and
the colours of the stone and of the cement begin to di-

310 THE PHILOSOPHY OF REID. [Cn. VI.

lute into one another: at a distance still greater, the join-
ings disappear altogether, and the variety of colour van-
ishes.

In an apple-tree which stands at the distance of about
twelve feet, covered with flowers, I can perceive the
figure and the color of the leaves and petals ; pieces of
branches, some larger, others smaller, peeping through
the intervals of the leaves — some of them enlightened by
the sun's rays, others shaded ; and some openings of the
sky are perceived through the whole. When I gradu-
ally remove from this tree, the appearance, even as to
colour, changes every minute. First, the smaller parts,
then the larger, are gradually confounded and mixed.
The colours of leaves, petals, branches, and sky, are
gradually diluted into each other, and the colour of the
whole becomes more and more uniform. This change
of appearance, corresponding to the several distances,
marks the distance more exactly than if the whole ob-
ject had been of one colour.

Dr. Smith, in his " Optics," gives us a very curious
observation made by Bishop Berkeley, in his travels
through Italy and Sicily. He observed, That, in those
countries, cities and palaces seen at a great distance ap-
peared nearer to him by several miles than they really
were : and he very judiciously imputed it to this cause.
That the purity of the Italian and Sicilian air, gave to
very distant objects that degree of brightness and dis-
tinctness which, in the grosser air of his own country,
was to be seen only in those that are near. The purity
of the Italian air hath been assigned as the reason why
the Italian painters commonly give a more lively colour
to the sky than the Flemish. Ought they not, for the
same reason, to give less degradation of the colours, and
less indistinctness of the minute parts, in the represen-
tation of very distant objects ?

It is very certain that, as in air uncommonly pure, we
are apt to think visible objects nearer and less than they

SEC. XXII.] THE PHILOSOPHY OF REID. 311

really are, so, in air uncommonly foggy, we are apt to
think them more distant and larger than the truth.
Walking by the sea-side in a thick fog, I see an object
which seems to me to be a man on horseback, and at
the distance of about half a mile. My companion, who
has better eyes, or is more accustomed to see such ob-
jects in such circumstances, assures me that it is a sea-
gull, and not a man on horseback. Upon a second
view, I immediately assent to his opinion ; and now it
appears to me to be a sea-gull, and at the distance only
of seventy or eighty yards. The mistake made on this
occasion, and the correction of it, are both so sudden,
that we are at a loss whether to call them by the name
of 'judgment, or by that of simple perception.

It is not worth while to dispute about names ; but it
is evident that my belief, both first and last, was pro-
duced rather by signs than by arguments, and that the
mind proceeded to the conclusion in both cases by habit,
and not by ratiocination. And the process of the mind
seems to have been this — First, Not knowing, or not
minding, the effect of a foggy air on the visible appear-
ance of objects, the object seems to me to have that deg-
radation of colour, and that indistinctness of the out-
line, which objects have at the distance of half a mile ;
therefore, from the visible appearance as a sign, I im-
mediately proceed to the belief that the object is half a
mile distant. Then, this distance, together with the
visible magnitude, signify to me the real magnitude,
which, supposing the distance to be half a mile, must
be equal to that of a man on horseback ; and the fig-
ure, considering the indistinctness of the outline, agrees
with that of a man on horseback. Thus the deception
is brought about. But when I am assured that it is a
sea-gull, the real magnitude of a sea-gull, together with
the visible magnitude presented to the eye, immediately
suggest the distance, which, in this case, cannot be above
seventy or eighty yards : the indistinctness of the figure

3f2 THE PHILOSOPHY OF REID. [Cn. VI.

likewise suggests the fogginess of the air as its cause ;
and now the whole chain of signs, and things signified,
seems stronger and better connected than it was before ;
the half mile vanishes to eighty yards ; the man on horse-
back dwindles to a sea-gull ; I get a new perception,
and wonder how I got the former, or what is become
of it ; for it is now so entirely gone, that I cannot re-
cover it.

It ought to be observed that, in order to produce
such deceptions from the clearness or fogginess of the
air, it must be uncommonly clear or uncommonly foggy;
for we learn, from experience, to make allowance for
that variety of constitutions of the air which we have
been accustomed to observe, and of which we are
aware. Bishop Berkeley therefore committed a mistake,
when he attributed the large appearance of the horizon-
tal moon to the faintness of her light, occasioned by
its passing through a larger tract of atmosphere :* for we
are so much accustomed to see the moon in all degrees
of faintness and brightness, from the greatest to the least,
that we learn to make allowance for it; and do not
imagine her magnitude increased by the faintness of
her appearance. Besides, it is certain that the horizon-
tal moon seen through a tube which cuts off the view
of the interjacent ground, and of all terrestrial objects,
loses all that unusual appearance of magnitude.

4. We frequently perceive the distance of objects, by
means of intervening or contiguous objects, whose dis-
tance or magnitude is otherwise known. When I per-
ceive certain fields or tracts of ground to lie between
me and an object, it is evident that these may become
signs of its distance. And although we have no par-
ticular information of the dimensions of such fields or
tract, yet their similitude to others which we know,
suggests their dimensions.

* This explanation was not original to Berkeley. — H.

SEC. XXII.] THE PHILOSOPHY OF REHX 313

We are so much accustomed to measure with our eye
the ground which we travel, and to compare the judg
ments of distances formed by sight, with our experience
or information, that we learn by degrees, in this way,
to form a more accurate judgment of the distance of
terrestrial objects, than we could do by any of the means
before mentioned. An object placed upon the top of
a high building, appears much less than when placed
upon the ground, at the same distance. When it stands
upon the ground, the intervening tract of ground serves
as a sign of its distance ; and the distance, together
with the visible magnitude, serves as a sign of its real
magnitude. But when the object is placed on high, this
sign of its distance is taken away : the remaining signs
lead us to place it at a less distance : and this less dis-
tance, together with the visible magnitude, becomes a
sign of a less real magnitude.

The two first means we have mentioned, would never
of themselves make a visible object appear above a hun-
dred and fifty, or two hundred feet, distant ; because,
beyond that there is no sensible change, either of the
conformation of the eyes, or of the inclination of their
axes. The third mean is but a vague and undetermi-
nate sign, when applied to distances above two or three
hundred feet, unless we know the real colour and figure
of the object ; and the fifth mean, to be afterwards men-
tioned, can only be applied to objects which are famil-
iar, or whose real magnitude is known. Hence it
follows, that, when unknown objects, upon or near the
surface of the earth, are perceived to be at the distance
of some miles, it is always by this fourth mean that WQ
are led to that conclusion.

Dr. Smith hath observed, very justly, that the known
distance of the terrestrial objects which terminate our
view, makes that part of the sky which is towards the
horizon appear more distant than that which is towards
the zenith. Hence it comes to pass, that the apparent

314 THE PHILOSOPHY OF REID. [Cn. VI.

figure of the sky is not that of a hemisphere, but rather
a less segment of a sphere. And, hence, likewise, it
comes to pass, that the diameter of the sun or moon, or
the distance between two fixed stars, seen contiguous to
a hill, or to any distant terrestrial object, appears much
greater than when no such object strikes the eye at the
same time.

These observations have heen sufficiently explained
and confirmed by Dr. Smith. I beg leave to add, that,
when the visible horizon is terminated by very distant
objects, the celestial vault seems to be enlarged in all its
dimensions. When I view it from a confined street or
lane, it bears some proportion to the buildings that sur-
round me ; but, when I view it from a large plain, ter-
minated on all hands by hills which rise one above
another to the distance of twenty miles from the eye,
methinks I see a new heaven, whose magnificence de-
clares the greatness of its Author, and puts every human
edifice out of countenance ; for now the lofty spires and
the gorgeous palaces shrink into nothing before it, and
bear no more proportion to the celestial dome than their
makers bear to its Maker.

5. There remains another mean by which we perceive
the distance of visible objects — and that is the diminu-
tion of their visible or apparent magnitude. By experi-
ence, I know what figure a man, or any other known
object, makes to my eye at the distance of ten feet — I
perceive the gradual and proportional diminution of this
visible figure, at the distance of twenty, forty, a hundred
feet, and at greater distances, until it vanish altogether.
Hence a certain visible magnitude of a known object
becomes the sign of a certain determinate distance, and
carries along with it the conception and belief of that
distance.

In this process of the mind, the sign is not a sensation ;
it is an original perception. We perceive the visible fig-
ure and visible magnitude of the object, by the original

SEC. XXII.] THE PHILOSOPHY OF REID. 315

powers of vision ; but the visible figure is used only as
a sign of the real figure, and the visible magnitude is
used only as a sign either of the distance, or of the real
magnitude, of the object : and, therefore, these original
perceptions, like other mere signs, pass through the mind
without any attention or reflection.

This last mean of perceiving the distance of known
objects, serves to explain some very remarkable phe-
nomena, in optics, which would otherwise appear very
mysterious. When we view objects of known dimen-
sions through optical glasses, there is no other mean left
of determining their distance, but this fifth. Hence it
follows, that known objects seen through glasses, must
seem to be brought nearer, in proportion to the magni-
fying power of the glass, or to be removed to a greater
distance in proportion to the diminishing power of the
glass.

If a man who had never before seen objects through a
telescope, were told that the telescope, which he is about
to use, magnifies the diameter of the object ten times ;
when he looks through this telescope at a man six feet
high, what would he expect to see ? Surely he would
very naturally expect to see a giant sixty feet high. But
he sees no such thing. The man appears no more than
six feet high, and consequently no bigger than he really
is ; but he appears ten times nearer than he is. The
telescope indeed magnifies the image of this man upon
the retina ten times in diameter, and must, therefore,
magnify his visible figure in the same proportion; and,
as we have been accustomed to see him of this visible
magnitude when he was ten times nearer than he is pres-
ently, and in no other case, this visible magnitude, there-
fore, suggests the conception and belief of that distance
of the object with which it hath been always connected.
We have been accustomed to conceive this amplification
of the visible figure of a known object, only as the effect
or sign of its being brought nearer : and we have annexed

3r6 THE PHILOSOPHY OF REID. [Ctt.Vl.

a certain determinate distance to every degree of visible
magnitude of the object ; and, therefore, any particular
degree of visible magnitude, whether seen by the naked
eye or by glasses, brings along with it the conception
and belief of the distance which corresponds to it. This
is the reason why a telescope seems not to magnify
known objects, but to bring them nearer to the eye.

When we look through a pin-hole, or a single micro-
scope, at an object which is half an inch from the eye,
the picture of the object upon the retina is not enlarged,
but only rendered distinct ; neither is the visible figure
enlarged : yet the object appears to the eye twelve or
fourteen times more distant, and as many times larger in
diameter, than it really is. Such a telescope as we have
mentioned amplifies the image on the retina, and the
visible figure of the object, ten times in diameter, and
yet makes it seem no bigger, but only ten times nearer.
These appearances had been long observed by the writers
on topics ; they tortured their invention to find the
causes of them from optical principles ; but in vain :
they must be resolved into habits of perception, which
are acquired by custom, but are apt to be mistaken for
original perceptions. The Bishop of Cloyne first fur-
nished the world with' the proper key for opening up
these mysterious appearances ; but he made considerable
mistakes in the application of it. Dr. Smith, in his
elaborate and judicious treatise of ' ' Optics, " hath applied
it to the apparent distance of objects seen with glasses,
and to the apparent figure of the heavens, with such
happy success, that there can be no more doubt about
the causes of these phenomena.

Section XXIII.

OF THE SIGNS USED IN OTHER ACQUIRED PERCEPTIONS.

The distance of objects from the eye is the most im-
portant lesson in vision. Many others are easily learned

SEC. XXIII.] THE PHILOSOPHY OF REID. 317

in consequence of it. The distance of the object, joined
with its visible magnitude, is a sign of its real magni-
tude : and the distance of the several parts of an object,
joined with its visible figure, becomes a sign of its real
figure. Thus, when I look at a globe which stands be-
fore me, by the original powers of sight I perceive only
something of a circular form, variously coloured. The
visible figure hath no distance from the eye, no convexity,
nor hath it three dimensions ; even its length and breadth
are incapable of being measured by inches, feet, or other
linear measures. But, when I have learned to perceive
the distance of every part of this object from the eye,
this perception gives it convexity, and a spherical figure ;
and adds a third dimension to that which had but two
before. The distance of the whole object makes me
likewise perceive the real magnitude ; for, being accus-
tomed to observe how an inch or a foot of length affects
the eye at that distance, I plainly perceive by my eye
the linear dimensions of the globe, and can affirm with
certainty that its diameter is about one foot and three
inches.

It was shewn in the yth section of this chapter that
the visible figure of a body may, by mathematical rea-
soning, be inferred from its real figure, distance, and
position, with regard to the eye : in like manner, we
may, by mathematical reasoning, from the visible figure,
together with the distance of the several parts of it from
the eye, infer the real figure and position. But this last
inference is not commonly made by mathematical rea-
soning, nor, indeed, by reasoning of any kind, but by
custom.

The original appearance which the colour of an object
makes to the eye, is a sensation for which we have no
name, because it is used merely as a sign, and is never
made an object of attention in common life : but this
appearance, according to the different circumstances,
signifies various things. If a piece of cloth, of one uni-

3l8 THE PHILOSOPHY OF REID. [Cn. VI.

form colour, is laid so that part of it is in the sun, and
part in the shade, the appearance of colour, in these dif-
ferent parts, is very different : yet we perceive the colour
to be the same ; we interpret the variety of appearance
as a sign of light and shade, and not as a sign of real
difference in colour. But, if the eye could be so far de-
ceived as not to perceive the difference of light in the
two parts of the cloth, we should, in that case, interpret
the variety of appearance to signify a variety of colour in
the parts of the cloth.

Again, if we suppose a piece of cloth placed as before,
but having the shaded part so much brighter in the
colour that it gives the same appearance to the eye as
the more enlightened part, the sameness of appearance
will here be interpreted to signify a variety of colour,
because we shall make allowance for the effect of light
and shade.

When the real colour of an object is known, the ap-
pearance of it indicates, in some circumstances, the de-
gree of light or shade ; in others, the colour of the cir-
cumambient bodies, whose rays are reflected by it; and,
in other circumstances, it indicates the distance or
proximity of the object — as was observed in the last sec-
tion ; and by means of these, many other things are sug-
gested1 to the mind. Thus, an unusual appearance in
the colour of familiar objects may be the diagnostic of a
disease in the spectator. The appearance of things in
my room may indicate sunshine or cloudy weather, the
earth covered with snow or blackened with rain. It
hath been observed, that the colour of the sky, in a
piece of painting, may indicate the country of the
painter, because the Italian sky is really of a different
colour from the Flemish.

It was already observed, that the original and acquired
perceptions which we have by our senses, are the lan-
guage of nature to man, which, in many respects, hath
a great affinity to human languages. The instances

SEC. XXIII.] THE PHILOSOPHY OF REID. 319

which we have given of acquired perceptions, suggest
this affinity — that, as, in human languages, ambiguities
are often found, so this language of nature in our ac-
quired perceptions is not exempted from them. We
have seen, in vision particularly, that the same appear-
ance to the eye, may, in different circumstances, indicate
different things. Therefore, when the circumstances are
unknown upon which the interpretation of the signs de-
pends, their meaning must be ambiguous ; and when
the circumstances are mistaken, the meaning of the signs
must also be mistaken.

This is the case in all the phenomena which we call
fallacies of the senses ; and particularly in those which
are called fallacies in vision. The appearance of things
to the eye always corresponds to the fixed laws of Na-
ture ; therefore, if we speak properly, there is no fallacy
in the senses. Nature always speaketh the same lan-
guage, and useth the same signs in the same circum-
stances ; but we sometimes mistake the meaning of the
signs, either through ignorance of the laws of Nature, or
through ignorance of the circumstances which attend the
signs.

To a man unacquainted with the principles of op-
tics, almost every experiment that is made with the
prism, with the magic lanthorn, with the telescope, with
the microscope, seems to produce some fallacy in vision.
Even the appearance of a common mirror, to one alto-
gether unacquainted with the effects of it, would seem
most remarkably fallacious. For how can a man be
more imposed upon, than in seeing that before him
which is really behind him ? How can he be more im-
posed upon, than in being made to see himself several
yards removed from himself? Yet children, even before
they can speak their mother tongue, learn not to be de-
ceived by these appearances. These, as well as all the
other surprising appearances produced by optical glasses,
are a part of the visual language, and, to those who un-

320 THE PHILOSOPHY OF REID. [CH. VI.

derstand the laws of Nature concerning light and col-
ours, are in nowise fallacious, but have a distinct and
true meaning.

Section XXIV.

OF THE ANALOGY BETWEEN PERCEPTION AND THE CREDIT
WE GIVE TO HUMAN TESTIMONY.

The objects of human knowledge are innumerable ;
but the channels by which it is conveyed to the mind
are few. Among these, the perception of external things
by our senses, and the informations which we receive
upon human testimony, are not the least considerable ;
and so remarkable is the analogy between these two, and
the analogy between the principles of the mind which
are subservient to the one and those which are subservi-
ent to the other, that, without further apology, we shall
consider them together.

In the testimony of Nature given by the senses, as well
as in human testimony given by language, things are
signified to us by signs : and in one as well as the other,
the mind, either by original principles or by custom,
passes from the sign to the conception and belief of the
things signified.

We have distinguished our perceptions into original
and acquired ; and language, into natural and artificial.
Between acquired perception and artificial language,
there is a great analogy ; but still a greater between orig-
inal perception and natural language.

The signs in original perception are sensations, of
which Nature hath given us a great variety, suited to the
variety of the things signified by them. Nature hath
established a real connection between the signs and the
things signified; and Nature hath also taught us the
interpretation of the signs — so that, previous to ex-
perience, the sign suggests the thing signified, and creates
the belief of it.

SEC. XXI V.] THE PHILOSOPHY OF REID. 32!

The signs in natural language are features of the face,
gestures of the body, and modulations of the voice; the
variety of which is suited to the variety of the things
signified by them. Nature hath established a real con-
nection between these signs, and the thoughts and dis-
positions of the mind which are signified by them; and
Nature hath taught us the interpretation of these signs; so
that, previous to experience, the signs suggest the thing
signified, and create the belief of it.

A man in company, without doing good or evil, with-
out uttering an articulate sound, may behave himselt
gracefully, civilly, politely; or, on the contrary, meanly,
rudely, and impertinently. We see the dispositions of
his mind by their natural signs in his countenance and
behavior, in the same manner as we perceive the figure
and other qualities of bodies by the sensations which
nature hath connected with them.

The signs in the natural language of the human
countenance and behaviour, as well as the signs in our
original perceptions, have the same signification in all
climates and in all nations; and the skill of interpreting
them is not acquired, but innate.

In acquired perception, the signs are either sensations,
or things which we perceive by means of sensations.
The connection between the sign and the thing signified,
is established by nature; and we discover this connection
by experience; but not without the aid of our original
perceptions, or of those which we have already acquired.
After this connection is discovered, the sign, in like
manner as in original perception, always suggests the
thing signified, and creates the belief of it.

In artificial language, the signs are articulate sounds,
whose connection with the things signified by them, is
established by the will of men; and, in learning our
mother tongue, we discover this connection by experience;
but not without the aid of natural language, or of what
we had before attained of artificial language. And. after

322 THE PHILOSOPHY OF REID. [CH. VI.

this connection is discovered, the sign, as in natural
language, always suggests the thing signified, and creates
the belief of it.

Our original perceptions are few, compared with the
acquired; but, without the former, we could not possibly
attain the latter. In like manner, natural language is
scanty, compared with artificial; but, without the former
we could not possibly attain the latter.

Our original perceptions, as well as the natural
language of human features and gestures, must be
resolved into particular principles of the human con-
stitution. Thus, it is by one particular principle of our
constitution that certain features express anger; and, by
another particular principle, that certain features express
benevolence. It is, in like manner, by one particular
principle of our constitution that a certain sensation
signifies hardness in the body which I handle; and it is
by another particular principle that a certain sensation
signifies motion in that body.

But our acquired perceptions, and the information we
receive by means of artificial language, must be resolved
into general principles of the human constitution. When
a painter perceives that this picture is the work of
Raphael, that the work of Titian; a jeweller, that this is
a true diamond, that a counterfeit; a sailor, that this is a
ship of five hundred ton, that of four hundred; these dif-
ferent acquired perceptions are produced by the same
general principles of the human mind, which have a dif-
ferent operation in the same person, according as they are
variously applied, and in different persons according to
the diversity of their education and manner of life. In
like manner, when certain articulate sounds convey to
my mind the knowledge of the battle of Pharsalia, and
others, the knowledge of the battle of Poltowa — when a
Frenchman and an Englishman receive the same in-
formation by different articulate sounds — the signs used
in these different cases, produce the knowledge and belief

SEC. XXIV.] THE PHILOSOPHY OF REID. 323

of the things signified, by means of the same general
principles of the human constitution.

Now, if we compare the general principles of our con-
stitution, which fit us for receiving information from our
fellow-creatures by language, with the general principles
which fit us for acquiring the perception of things by our
senses, we shall find them to be very similar in their
nature and manner of operation.

When we begin to learn our mother tongue, we per-
ceive, by the help of natural language, that they who
speak to us use certain sounds to express certain things,
we imitate the same sounds when we would express the
same things; and find that we are understood.

But here a difficulty occurs which merits our attention,
because the solution of it leads to some original principles
of the human mind, which are of great importance, and
of very extensive influence. We know by experience
that men have used such words to express such things;
but all experience is of the/aj/, and can, of itself, give
no notion or belief of what is future. How come we,
then, to believe, and to rely upon it with assurance, that
men, who have it in their power to do otherwise, will
continue to use the same words when they think the same
things ? Whence comes this knowledge and belief — this
foresight, we ought rather to call it — of the future and
voluntary actions of our fellow-creatures ? Have they
promised that they will never impose upon us by
equivocation or falsehood ? No, they have not. And,
if they had, this would not solve the difficulty; for such
promise must be expressed by words or by other signs;
and, before we can rely upon it, we must be assured
that they put the usual meaning upon the signs which
express that promise. No man of common sense ever
thought of taking a man's own word for his honesty; and
it is evident that we take his veracity for granted when
we lay any stress upon his word or promise. I might
add, that this reliance upon the declarations and testimony

324 THE PHILOSOPHY OF REID. [Cu.VI.

of men is found in children long before they know what
a promise is.

There is, therefore, in the human mind an early
anticipation, neither derived from experience, nor from
reason, nor from any compact or promise, that our fel-
low-creatures will use the same signs in language, when
they have the same sentiments.

This is, in reality, a kind of prescience of human
actions; and it seems to me to be an original principle of
the human constitution, without which we should be
incapable of language, and consequently incapable of
instruction.

The wise and beneficent Author of Nature, who in-
tended that we should be social creatures, and that we
should receive the greatest and most important part of
our knowledge by the information of others, hath, for
these purposes, implanted in our natures two principles
that tally with each other.

The first of these principles is, a propensity to speak
truth, and to use the signs of language so as to convey
our real sentiments. This principle has a powerful
operation, even in the greatest liars; for, where they lie
once, they speak truth a hundred times. Truth is always
uppermost, and is the natural issue of the mind. It
requires no art or training, no inducement or temptation,
but only that we yield to a natural impulse. Lying, on
the contrary, is doing violence to our nature; and is never
practised, even by the worst men, without some tempta-
tion. Speaking truth is like using our natural food,
which we would do from appetite, although it answered
no end; but lying is like taking physic, which is nauseous
to the taste, and which no man takes but for some end
which he cannot otherwise attain.

If it should be objected, That men may be influenced
by moral or political considerations to speak truth, and,
therefore, that their doing so is no proof of such an
original principle as we have mentiond — I answer, First,

SEC.XX1V.J THE PHILOSOPHY OF REID. 325

That moral or political considerations can have no
influence until we arrive at years of understanding and
reflection; and it is certain, from experience, that children
keep to truth invariably, before they are capable of being
influenced by such considerations. Secondly, When we
are influenced by moral or political considerations, we
must be conscious of that influence, and capable of per-
ceiving it upon reflection. Now, when I reflect upon my
actions most attentively, I am not conscious that, in
speaking truth, I am influenced on ordinary occasions by
any motive, moral or political. I find that truth is always
at the door of my lips, and goes forth spontaneously, if
not held back. It requires neither good nor bad intention
to bring it forth, but only that I be artless and undesign-
ing. There may indeed be temptations to falsehood,
which would be too strong for the natural principle of
veracity, unaided by principles of honor or virtue; but
where there is no such temptation, we speak truth by
instinct — and this instinct is the principle I have been
explaining.

By this instinct, a real connection is formed between
our words and our thoughts, and thereby the former
became fit to be signs of the latter, which they could not
otherwise be. And although this connection is broken
in every instance of lying and equivocation, yet these
instances being comparatively few, the authority of human
testimony is only weakened by them, but not destroyed.

Another original principle implanted in us by the
Supreme Being, is a disposition to confide in the veracity
of others, and to believe what they tell us. This is the
counterpart to the former; and, as that may be called the
principle of veracity, we shall, for want of a more proper
name, call this the principle of credulity. It is unlimited
in children, until they meet with instances of deceit and
falsehood; and it retains a very considerable degree of
strength through life.

If Nature had left the mind of the speaker in (equilibria,

326 THE PHILOSOPHY OF REID. [Cn. VI.

without any inclination to the side of truth more than to
that of falsehood, children would lie as often as they
speak truth, until reason was so far ripened as to suggest
the imprudence of lying, or conscience, as to suggest its
immorality. And if Nature had left the mind of the hearer
in cequilibrio, without any inclination to the side of belief
more than to that of disbelief, we should take no man's
word until we had positive evidence that he spoke truth.
His testimony would, in this case, have no more authority
than his dreams; which may be true or false, but no man
is disposed to believe them, on this account, that they
were dreamed. It is evident that, in the matter of
testimony, the balance of human judgment is by nature
inclined to the side of belief; and turns to that side of
itself, when there is nothing put into the opposite scale.
If it was not so, no proposition that is uttered in dis-
course would be believed, until it was examined and tried
by reason; and most men would be unable to find reasons
for believing the thousandth part of what is told them.
Such distrust and incredulity would deprive us of the
greatest benefits of society, and place us in a worse con-
dition than that of savages.

Children, on this supposition, would be absolutely in-
credulous, and, therefore, absolutely incapable of in-
struction: those who had little knowledge of human life,
and of the manners and characters of men, would be in
the next degree incredulous: and the most credulous
men would be those of greatest experience, and of
the deepest penetration; because, in many cases, they
would be able to find good reasons for believing tes-
timony, which the weak and the ignorant could not
discover.

In a word, if credulity were the effect of reasoning
and experience, it must grow up and gather strength, in
the same proportion as reason and experience do. But,
if it is the gift of Nature, it will be strongest in childhood,
and limited and restrained by experience; and the most

SEC. XXIV.] THE PHILOSOPHY OF REID. 327

superficial view of human life shews, that the last is
really the case, and not the first*

It is the intention of Nature, that we should be car-
ried in arms before we are able to walk upon our legs;
and it is likewise the intention of Nature, that our belief
should be guided by the authority and reason of others,
before it can be guided by our own reason. The weak-
ness of the infant, and the natural affection of the mother,
plainly indicate the former; and the natural credulity of
youth, and authority of age, as plainly indicate the lat-
ter. The infant, by proper nursing and care, acquires
strength to walk without support. Reason hath likewise
her infancy, when she must be carried in arms: then she
leans entirely upon authority, by natural instinct, as if
she was conscious of her own weakness; and, without
this support, she becomes vertiginous. When brought
to maturity by proper culture, she begins to feel her own
strength, and leans less upon the reason of others: she
learns to suspect testimony in some cases, and to dis-
believe it in others; and sets bounds to that authority to
which she was at first entirely subject. But still, to the
end of life, she finds a necessity of borrowing light from
testimony, where she has none within herself, and of
leaning, in some degree, upon the reason of others,
where she is conscious of her own imbecility.

And as, in many instances, Reason, even in her ma-
turity, borrows aid from testimony, so in others she mu-
tually gives aid to it,, and strengthens its authority.
For, as we find good reason to reject testimony in some
cases, so in others we find good reason to reply upon it
with perfect security, in our most important concerns.
The character, the number, and the disinterestedness of
witnesses, the impossibility of collusion, and the incredi-
bility of their concurring in their testimony without col-

* See, contra, Priestley's "Examination," p. 86. "Brown's
Lect." lect. Ixxxiv.

328 THE PHILOSOPHY OF REID. [CH. VI.

lusion, may give an irresistible strength to testimony,
compared to which its native and intrinsic authority is
very inconsiderable.

Having now considered the general principles of the
human mind which fit us for receiving information from
our fellow-creatures, by the means of language, let us
next consider the general principles which fit us for re-
ceiving the information of Nature by our acquired per-
ceptions.

It is undeniable, and indeed is acknowledged by all,
that when we have found two things to have been con-
stantly conjoined in the course of nature, the appearance
of one of them is immediately followed by the conception
and belief of the other. The former becomes a natural
sign of the latter; and the knowledge of their constant
conjunction in time past, whether got by experience or
otherwise, is sufficient to make us rely with assurance
upon the continuance of that conjunction.

This process of the human mind is so familiar that we
never think of inquiring into the principles upon which
it is founded. We are apt to conceive it as a self-evi-
dent truth, that what is to come must be similar to what
is past. Thus, if a certain degree of cold freezes water
to-day, and has been known to do so in all time past, we
have no doubt but the same degree of cold will freeze
water to-morrow, or a year hence. That this is a truth
which all men believe as soon as they understand it, I
readily admit; but the question as, Whence does its evi-
dence arise ? Not from comparing the ideas, surely.
For, when I compare the idea of cold with that of water
hardened into a transparent solid body, I can perceive
no connection between them: no man can shew the one
to be the necessary effect of the other; no man can give
a shadow of reason why Nature hath conjoined them.
But do we not learn their conjunction from experience ?
True; experience informs us that they have been con-
j oined in time/aj// but no man ever had any experience

SEC. XXIV.] THE PHILOSOPHY OF REID. 329

of what isfuiure: and this is the very question to be re-
solved, How we come to believe that the future will be
like the/aj1//3 Hath the Author of nature promised this ?
Or were we admitted to his council, when he established
the present laws of nature, and determined the time of
their continuance. No, surely. Indeed, if we believe
that there is a wise and good Author of nature, we may
see a good reason why he should continue the same laws
of nature, and the same connections of things, for a long
time: because, if he did otherwise, we could learn noth-
ing from what is past, and all our experience would be
of no use to us. But, though this consideration, when
we come to the use of reason, may confirm our belief of
the continuance of the present course of nature, it is cer-
tain that it did not give rise to this belief; for children
and idiots have this belief as soon as they know that fire
will burn them. It must, therefore, be the effect of in-
stinct, not of reason.*

The wise Author of our nature intended, that a great
and necessary part of our knowledge should be derived
from experience, before we are capable of reasoning, and
he hath provided means perfectly adequate to this inten-
tion. For, First, He governs nature by fixed laws, so
that we find innumerable connections of things which
continue from age to age. Without this stability of the
course of nature, there could be no experience; or, it
would be a false guide, and lead us into error and mis-
chief. If there were not a principle of veracity in the
human mind, men's words would not be signs of their
thoughts: and if there were no regularity in the course
of nature, no one thing could be a natural sign of an-
other. Secondly, He hath implanted in human minds

*Compare Stewart's "Elements," vol. I., chap. iv. § 5, p. 205,
sixth edition ; "Philosophical Essays," p. 74, sqq., fourth edition;
Royer Collard, in Jouffroy's " Oeuvres de Reid," t. IV. p. 279, sqq. ;
with Priestley's "Examination," p. 86. sqq. I merely refer to
works relative to Reid's doctrine. — H.

330 THE PHILOSOPHY OF REID. [Cu. VI.

an original principle by \thich we believe and expect the
continuance of the course of nature, and the continuance
of those connections which we have observed in time
past. It is by this general principle of our nature, that,
when two things have been found connected in time past,
the appearance of the one produces the belief of the other.

I think the ingenious author of the " Treatise of Hu-
man Nature " first observed, That our belief of the con-
tinuance of the laws of nature cannot be founded either
upon knowledge or probability: but, far from conceiving
it to be an original principle of the mind, he endeavours
to account for it from his favourite hypothesis, That be-
lief is nothing but a certain degree of vivacity in the idea
of the thing believed. I made a remark upon this cu-
rious hypothesis in the second chapter, and shall now
make another.

The belief which we have in perception, is a belief of
the present existence of the object; that which we have in
memory, is a belief of its past existence; the belief of
which we are now speaking is a belief of its future ex-
istence; and in imagination there is no belief at all.
Now, I would gladly know of this author, how one
degree of vivacity fixes the existence of the object
to the present moment; another carries it back to
time past; a third, taking a contrary direction, carries
it into futurity; and a fourth carries it out of ex-
istence altogether. Suppose, for instance, that I see
the sun rising out of the sea; I remember to have
seen him rise yesterday; I believe he will rise to-mor-
row near the same place; I can likewise imagine him ris-
ing in that place, without any belief at all. Now, ac-
cording to this sceptical hypothesis, this perception, this
memory, this foreknowledge, and this imagination, are
all the same idea, diversified only by different degrees of
vivacity. The perception of the sun rising is the most
lively idea; the memory of his rising yesterday is the same
idea a little more faint; the belief of his rising to-morrow

SEC. XXIV.] THE PHILOSOPHY OF REID. 331

is the same idea yet fainter; and the imagination of his
rising is still the same idea, but faintest of all. One
is apt to think, that this idea might gradually pass
through all possible degrees of vivacity without stirring
out of its place. But, if we think so, we deceive our-
selves: for no sooner does it begin to grow languid than
it moves backward into time past. Supposing this to be
granted, we expect, at least, that, as it moves backward
by the decay of its vivacity, the more that vivacity decays
it will go back the farther, until it remove quite out of
sight. But here we are deceived again; for there is a
certain period of this declining vivacity when, as if it had
met an elastic obstacle in its motion backward, it sud-
denly rebounds from the past to the future, without tak-
ing the present in its way. And now, having got into the
regions of futurity, we are apt to think that it has room
enough to spend all its remaining vigour: but still we
are deceived: for, by another sprightly bound, it mounts
up into the airy region of imagination. So that ideas, in
the gradual declension of their vivacity, seem to imitate
the inflection of verbs in grammar. They begin with
the present,, and proceed in order to the preterite, the
future, and the indefinite. This article of the scep-
tical creed is indeed so full of mystery, on whatever
side we view it, that they who hold that creed are
very injuriously charged with incredulity ; for, to me,
it appears to require as much faith as that of St. Atha-
nasius.

However, we agree with the author of the ' ' Treatise
of Human Nature," in this, That our belief of the con-
tinuance of nature's laws is not derived from reason. It
is an instinctive prescience of the operations of na-
ture very like to that prescience of human actions
which makes us rely upon the testimony of our fel-
low-creatures ; and as, without the latter, we should be
incapable of receiving information from men by lan-
guage, so, without the former, we should be incapable

332 THE PHILOSOPHY OF REID. [Cu. VI.

of receiving the information of nature by means of ex-
perience.

All our knowledge of nature beyond our original
perceptions, is got by experience, and consists in
the interpretation of natural signs. The constancy
of nature's laws connects the sign with the thing sig-
nified; and, by the natural principle just now ex-
plained, we rely upon the continuance of the connec-
tions which experience hath discovered; and thus the ap-
pearance of the sign is followed by the belief of the
thing signified.

Upon this principle of our constitution, not only
acquired perception, but all inductive reasoning, and all
our reasoning from analogy, is grounded; and, therefore,
for want of another name, we shall beg leave to call it
the inductive principle. It is from the force of this princi-
ple that we immediately assent to that axiom upon which
all our knowledge of nature is built, That effects of the
same kind must have the same cause; for effects and
causes, in the operations of nature, mean nothing but
signs and the things signified by them. We perceive
no proper causality or efficiency in any natural cause;
but only a connection established by the course of
nature between it and what is called its effect. Antece-
dently to all reasoning, we have, by our constitution, an
anticipation that there is a fixed and steady course of
nature: and we have an eager desire to discover this
course of nature. We attend to every conjunction of
things which presents itself, and expect the continuance
of that conjunction. And, when such a conjunction
has been often observed, we conceive the things to be
naturally connected, and the appearance of one, without
any reasoning or reflection, carries along with it the be-
lief of the other.

If any reader should imagine that the inductive prin-
ciple may be resolved into what philosophers usually
call the association of ideas, let him observe, that, by this

SEC. XXIV.] THE PHILOSOPHY OF REID. 333

principle, natural signs are not associated with the idea
only, but with the belief of the things signified. Now,
this can with no propriety be called an association of
ideas, unless ideas and belief be one and the same thing.
A child has found the prick of a pin conjoined with
pain ; hence he believes, and knows, that these things
are naturally connected ; he knows that the one will
always follow the other. If any man will call this only
an association of ideas, I dispute not about words,
but I think he speaks very improperly. For, if we
express it in plain English, it is a prescience that things
which he hath found conjoined in time past, will be
conjoined in time to come. And this prescience is not
the effect of reasoning, but of an original principle
of human nature, which I have called the inductive
principle.

This principle, like that of credulity, is unlimited in
infancy, and gradually restrained and regulated as we
grow up. It leads us often into mistakes; but is of in-
finite advantage upon the whole. By it, the child once
burnt shuns the fire; by it, he likewise runs away from
the surgeon by whom he was inoculated. It is better
that he should do the last, than that he should not do
the first.

But the mistakes we are led into by these two natural
principles, are of a different kind. Men sometimes lead
us into mistakes, when we perfectly understand their
language, by speaking lies. But Nature never misleads
us in this way: her language is always true; and it is
only by misinterpreting it that we fall into error. There
must be many accidental conjunctions of things, as well
as natural connections; and the former are apt to be
mistaken for the latter. Thus, in the instance above
mentioned, the child connected the pain of inoculation
with the surgeon; whereas it was really connected with
the incision only. Philosophers, and men of science
are not exempted from such mistakes; indeed, all false

334 THE PHILOSOPHY OF REID. [Cn. VI

reasoning in philosophy is owing to them; it is drawn
from experience and analogy, as well as just reasoning,
otherwise it could have no verisimilitude; but the one is
an unskilful and rash, the other a just and legitimate
interpretation of natural signs. If a child, or a man of
common understanding, were put to interpret a book of
science, written in his mother tongue, how many blun-
ders and mistakes would he be apt to fall into? Yet
he knows as much of this language as is necessary for
his manner of life.

The language of Nature is the universal study; and
the students are of different classes. Brutes, idiots, and
children employ themselves in this study, and owe to it
all their acquired perceptions. Men of common under-
standing make a greater progress, and learn, by a small
degree of reflection, many things of which children are
ignorant.

Philosophers fill up the highest form in this school,
and are critics in the language of nature. All these
different classes have one teacher — Experience, en-
lightened by the inductive principle. Take away the
light of this inductive principle, and Experience is as
blind as a mole: she may, indeed, feel what is present,
and what immediately touches her; but she sees nothing
that is either before or behind, upon the right hand or
upon the left, future or past.

The rules of inductive reasoning, or of a just interpre-
tation of Nature, as well as the fallacies by which we are
apt to misinterpret her language, have been, with
wonderful sagacity, delineated by the great genius of
Lord Bacon: so that his "Novum Organum" may justly
be called "A Grammar of the Language of Nature."
It adds greatly to the merit of this work, and atones for
its defects, that, at the time it was written, the world had
not seen any tolerable model of inductive reasoning,
from which the rules of it might be copied. The arts of
poetry and eloquence were grown up to perfection when

SEC. XXIV.] THE PHILOSOPHY OF REID. 335

Aristotle described them; but the art of interpreting
Nature was yet in embryo when Bacon delineated its
manly features and proportions. Aristotle drew his
rules from the best models of those arts that have yet
appeared; but the best models of inductive reasoning
that have yet appeared, which I take to be the third
book of the "Principia," and the "Optics," of Newton,
were drawn from Bacon's rules. The purpose of all
those rules, is to teach us to distinguish seeming, or ap-
parent connections of things, in the course of nature,
from such as are real.

They that are unskilful in inductive reasoning, are
more apt to fall into error in their reasonings from the
phaenomena of nature than in their acquired perceptions ;
because we often reason from a few instances, and there-
by are apt to mistake accidental conjunctions of things
for natural connections: but that habit of passing, with-
out reasoning, from the sign to the thing signified, which
constitutes acquired perception, must be learned by
many instances or experiments; and the number of ex-
periments serves to disjoin those things which have been
accidentally conjoined, as well as to confirm our belief
of natural connections.

From the time that children begin to use their hands,
Nature directs them to handle everything over and over,
to look at it while they handle it, and to put it in
various positions, and at various distances from the
eye. We are apt to excuse this as a childish diversion,
because they must be doing something, and have not
reason to entertain themselves in a more manly way.
But, if we think more justly, we shall find, that they are
engaged in the most serious and important study; and,
if they had all the reason of a philosopher, they could
not be more properly employed. For it is this childish
employment that enables them to make the proper use
of their eyes. They are thereby every day acquiring
habits of perception, which are of greater importance

336 THE PHILOSOPHY OF REID. [Ca.Vl.

than anything we can teach them. . The original per-
ceptions which Nature gave them are few, and insuffi-
cient for the purposes of life; and, therefore, she made
them capable of acquiring many more perceptions by
habit. And, to complete her work, she hath given them
an unwearied assiduity in applying to the exercises by
which those perceptions are acquired.

This is the education which Nature gives to her chil-
dren. And, since we have fallen upon this subject, we
may add, that another part of Nature's education is,
That, by the course of things, children must often exert
all their muscular force, and employ all their ingenuity,
in order to gratify their curiosity, and satisfy their little
appetites. What they desire is only to be obtained at
the expense of labour and patience, and many disap-
pointments. By the exercise of body and mind neces-
sary for satisfying their desires, they acquire agility,
strength, and dexterity in their motions, as well as health
and vigour to their constitutions; they learn patience
and perseverance; they learn to bear pain without dejec-
tion, and disappointment without despondence. The
education of Nature is most perfect in savages, who have
no other tutor; and we see that, in the quickness of all
their senses, in the agility of their motions, in the hardi-
ness of their constitutions, and in the strength of their
minds to bear hunger, thirst, pain, and disappointment,
they commonly far exceed the civilized. A most ingen-
ious writer, on this account, seems to prefer the savage
life to that of society. But the education of Nature
could never of itself produce a Rousseau. It is the in-
tention of Nature that human education should be joined
to her institution, in order to form the man. And she
hath fitted us for human education, by the natural prin-
ciples of imitation and credulity, which discover them-
selves almost in infancy, as well as by others which are of
later growth.

When the education which we receive from men, does

SBC. XXIV. THE PHILOSOPHY OF REID. 337

not give scope to the education of Nature, it is wrong
directed ; it tends to hurt our faculties of perception,
and to enervate both the body and mind. Nature hath
her way of rearing men, as she hath of curing their dis-
eases. The art of medicine is to follow Nature, to imi-
tate and to assist her in the cure of diseases ; and the art
of education is to follow Nature, to assist and to imi-
tate her in her way of rearing men. The ancient inhab-
itants of the Baleares followed Nature in the manner of
teaching their children to be good archers, when they
hung their dinner aloft by a thread, and left the younkers
to bring it down by their skill in archery.

The education of Nature, without any more human
care than is necessary to preserve life, makes a perfect
savage. Human education, joined to that of Nature,
may make a good citizen, a skilful artisan, or a well-
bred man ; but reason and reflection must superadd
their tutory, in order to produce a Rousseau, a Bacon, or
a Newton.

Notwithstanding the innumerable errors committed
in human education, there is hardly any education so
bad as to be worse than none. And I apprehend that,
if even Rousseau were to choose whether to educate a
son among the French, the Italians, the Chinese, or
among the Eskimaux, he would not give the preference
to the last.

When Reason is properly employed, she will confirm
the documents of Nature, which are always true and
wholesome ; she will distinguish, in the documents of
human education, the good from the bad, rejecting the
last with modesty, and adhering to the first with rever-
ence.

Most men continue all their days to be just what
Nature and human education made them. Their man-
ners, their opinions, their virtues, and their vices, are
all got by habit, imitation, and instruction ; and reason
has little or no share in forming them.

338 THE PHILOSOPHY OF REID. [CH. VII.

CHAPTER VII.
CONCLUSION.

CONTAINING REFLECTIONS UPON THE OPINIONS OF PHILOSO-
PHERS ON THIS SUBJECT.

THERE are two ways in which men may form their
notions and opinions concerning the mind, and con-
cerning its powers and operations. The first is the only
way that leads to truth ; but it is narrow and rugged,
and few have entered upon it. The second is broad
and smooth, and hath been much beaten, not only by
the vulgar, but even by philosophers ; it is sufficient for
common life, and is well adapted to the purposes of
the poet and orator : but, in philosophical disquisitions
concerning the mind, it leads to error and delusion.

We may call the first of these ways, the way of reflec-
tion. When the operations of the mind are exerted, we
are conscious of them ; and it is in our power to attend
to them ; and to reflect upon them, until they become
familiar objects of thought. This is the only way in
which we can form just and accurate notions of those
operations. But this attention and reflection is so diffi-
cult to man, surrounded on all hands by external ob-
jects which constantly solicit his attention, that it has
been very little practised, even by philosophers. In
the course of this inquiry, we have had many occasions
to shew how little attention hath been given to the most
familiar operations of the senses.

The second, and the most common way, in which
men form their opinions concerning the mind and its

CH. VII.] THE PHILOSOPHY OF REID. 339

operations, we may call the way of analogy. There is
nothing in the course of nature so singular, but we can
find some resemblance, or at least some analogy, be-
tween it and other things with which we are acquainted.
The mind naturally delights in hunting after such analo-
gies, and attends to them with pleasure. From them,
poetry and wit derive a great part of their charms ; and
eloquence, not a little of its persuasive force.

Besides the pleasure we receive from analogies, they
are of very considerable use, both to facilitate the con-
ception of things, when they are not easily apprehended
without such a handle, and to lead us to probable con-
jectures about their nature and qualities, when we want
the means of more direct and immediate knowledge.
When I consider that the planet Jupiter, in like manner
as the earth, rolls round his own axis, and revolves
round the sun, and that he is enlightened by several sec-
ondary planets, as the earth is enlightened by the moon,
I am apt to conjecture, from analogy, that, as the earth
by these means is fitted to be the habitation of various
orders of animals, so the nlanet Jupiter is, by the like
means, fitted for the same purpose ; and, having no
argument more direct and conclusive to determine me
in this point, I yield, to this analogical reasoning, a de-
gree of assent proportioned to its strength. When I
observe that the potato plant very much resembles the
solatium in its flower and fructification, and am informed
that the last is poisonous, I am apt from analogy to have
some suspicion of the former : but, in this case, I have
access to more direct and certain evidence ; and, there-
fore, ought not to trust to analogy, which would lead
me into an error.

Arguments from analogy are always at hand, and
grow up spontaneously in a fruitful imagination ; while
arguments that are more direct and more conclusive
often require painful attention and application ; and
therefore mankind in general have been very much dis-

34° THE PHILOSOPHY OF REID. [Cn. VII.

posed to trust to the former. If one attentively exam-
ines the systems of the ancient philosophers, either con-
cerning the material world, or concerning the mind, he
will find them to be built solely upon the foundation of
analogy. Lord Bacon first delineated the strict and se-
vere method of induction ; since his time, it has been
applied with very happy success in some parts of natural
philosophy — and hardly in anything else. But there is
no subject in which mankind are so much disposed to
trust to the analogical way of thinking and reasoning, as
in what concerns the mind and its operations ; because,
to form clear and distinct notions of those operations in
the direct and proper way, and to reason about them,
requires a habit of attentive reflection, of which few are
capable, and which, even by those few, cannot be at-
tained without much pains and labour.

Every man is apt to form his notions of things diffi-
cult to be apprehended, or less familiar, from their an-
alogy to things which are more familiar. Thus, if a man
bred to the seafaring life, and accustomed to think and
talk only of matters relating to navigation, enters into
discourse upon any other subject, it is well known that
the language and the notions proper to his own profes-
sion are infused into every subject, and all things are
measured by the rules of navigation ; and, if he should
take it into his head to philosophize concerning the fac-
ulties of the mind, it cannot be doubted but he would
draw his notions from the fabric of his ship, and would
find in the mind, sails, masts, rudder, and compass.*

Sensible objects, of one kind or other; do no less oc-
cupy and engross the rest of mankind, than things re-
lating to navigation the seafaring man. For a consid-
erable part of life, we can think of nothing but the
objects of sense ; and, to attend to objects of another na-

* See "Essays on the Intellectual Powers," Ess. VI., ch. viii.,
Nos. 2 and 6.— H.

CH. VII.] THE PHILOSOPHY OF REID. 341

ture, so as to form clear and distinct notions of them, is
no easy matter, even after we come to years of reflection.
The condition of mankind, therefore, affords good reason
to apprehend that their language, and their common
notions concerning the mind and its operations, will
be analogical, and derived from the objects of sense ;
and that these analogies will be apt to impose upon
philosophers, as well as upon the vulgar, and to lead
them to materialize the mind and its faculties : and
experience abundantly confirms the truth of this.

How generally men of all nations, and in all ages of
the World, have conceived the soul, or thinking princi-
ple in man, to be some subtile matter, like breath or
wind, the names given to it almost in all languages suffi-
ciently testify. We have words which are proper, and
not analogical, to express the various ways in which we
perceive external objects by the senses — such -as feeling,
sight, taste ; but we are often obliged to use these words
analogically, to express other powers of the mind which
are of a very different nature. And the powers which
imply some degree of reflection, have generally no
names but such as are analogical. The objects of
thought are said to be in the mind — to be apprehended,
comprehended, conceived, imagined, retained, weighed, ru-
minated.

It does not appear that the notions of the ancient
philosophers, with regard to the nature of the soul, were
much more refined than those of the vulgar, or thatthey
were formed in any other way. We shall distinguish the
philosophy that regards our subject into the old and the
new. The old reached down to Des Cartes, who gave
it a fatal blow, of which it has been gradually expiring
ever since, and is now almost extinct. Des Cartes Js the
father of the new philosophy that relates to this subject ;
but it hath been gradually improving since his time,
upon the principles laid down by him. The old philoso-
phy seems to have been purely analogical ; the new is

342 THE PHILOSOPHY OF REID. [CH. VII.

more derived from reflection, but still with a very con-
siderable mixture of the old analogical notions.

Because the objects of sense consist of matter and
form, the ancient philosophers conceived everything to
belong to one of these, or to be made up of both.
Some, therefore, thought that the soul is a particular
kind of subtile matter, separable from our gross bodies ;
others thought that it is only a particular form of the
body, and inseparable from it. For there seem to have
been some among the ancients, as well as among the
moderns, who conceived that a certain structure or
organization of the body, is all that is necessary to ren-
der it sensible and intelligent. The different powers of
the mind were, accordingly, by the last sect of philoso-
phers, conceived to belong to different parts of the body
— as the heart, the brain, the liver, the stomach, the
blood.

They who thought that the soul is a subtile matter,
separable from the body, disputed to which of the four
elements it belongs — whether to earth, water, air, or fire.
Of the three last, each had its particular advocates. But
some were of opinion, that it partakes of all the elements:
that it must have something in its composition similar
to everything we perceive; and that we perceive earth by
the earthly part; water, by the watery part; and fire, by
the fiery part of the soul. Some philosophers, not
satisfied with determining of what kind of matter the soul
is made, inquired likewise into its figure, which they
determined to be spherical, that it might be the more fit
for motion. The most spiritual and sublime notion con-
cerning the nature of the soul, to be met with among the
ancient philosophers, I conceive to be that of the
Platonists, who held that it is made of that celestial and
incorruptible matter of which the fixed stars were made,
and, therefore, has a natural tendency to rejoin its proper
element. I am at a loss to say, in which of these classes
of philosophers Aristotle ought to be placed. He defines

CH. VII.] THE PHILOSOPHY OF REID. 343

the soul to be, The first ivn-Xs-jiMaof a natural body which
has potential life. I beg to be excused from translating
the Greek word, because I know not the meaning
of it.

The notions of the ancient philosophers with regard to
the operations of the mind, particularly with regard to
perception and ideas, seem likewise to have been formed
by the same kind of analogy.

Plato, of the writers that are extant, first introduced the
word idea into philosophy; but his doctrine upon this
subject had somewhat peculiar. He agreed with the rest
of the ancient philosophers in this — that all things con-
sist of matter and form; and that the matter of which all
things were made, existed from eternity, without form:
but he likewise believed that there are eternal forms of all
possible things which exist, without matter; and to these
eternal and immaterial forms he gave the name of ideas;
maintaining that they are the only object of true knowl-
edge. It is of no great moment to us, whether he bor-
rowed these notions from Parmenides, or whether they
were the issue of his own creative imagination. The
latter Platonists seem to have improved upon them, in
conceiving those ideas, or eternal forms of things, to exist
not of themselves, but in the divine mind, and to be the
models and patterns according to which all things were
made: —

" Then liv'd the Eternal One; then, deep retir'd
In his unfathom'd essence, view'd at large
The uncreated images of things."

To these Platonic notions, that of Malebranche is very
nearly allied. This author seems, more than any other,
to have been aware of the difficulties attending the com-
mon hypothesis concerning ideas — to wit, That ideas
of all objects of thought are in the human mind; and,
therefore, in order to avoid those difficulties, makes the
ideas which are the immediate objects of human thought,

344 THE PHILOSOPHY OF REID. [CH, VII.

to be the ideas of things in the Divine mind, who, being
intimately present to every human mind, may discover
his ideas to it, as far as pleaseth him.

The Platonists and Malebranche excepted, all other
philosophers, as far as I know, have conceived that there
are ideas or images of every object of thought in the
human mind, or, at least, in some part of the brain,
where the mind is supposed to have its residence.

Aristotle had no good affection to the word idea, and
seldom or never uses it but in refuting Plato's notions
about ideas. He thought that matter may exist without
form; but that forms cannot exist without matter. But,
at the same time, he taught, That there can be no
sensation, no imagination, nor intellection, without
forms, phantasms, or species in the mind; and that things
sensible are perceived by sensible species, and things
intelligible by intelligible species. His followers taught,
more explicitly, that those sensible and intelligible species
are sent forth by the objects, and make their impressions
upon the passive intellect; and that the active intellect
perceives them in the passive intellect. And this seems
to have been the common opinion while the Peripatetic
philosophy retained its authority.

The Epicurean doctrine, as explained by Lucretius,
though widely different from the Peripatetic in many
things, is almost the same in this. He affirms, that
slender films or ghosts (tenuia rerum simulacra) are still
going off from all things, and flying about; and that these,
being extremely subtile, easily penetrate our gross bodies,
and, striking upon the mind, cause thought and imag-
ination.

After the Peripatetic system had reigned above a
thousand years in the schools of Europe, almost without
a rival, it sunk before that of Des Cartes; the perspicuity
of whose writings and notions, contrasted with the
obscurity of Aristotle and his commentators, created a
strong prejudice in favor of this new philosophy. The

CH. VII.] THE PHILOSOPHY OF REID. 345

characteristic of Plato's genius was sublimity, that of
Aristotle's, subtilty; but Des Cartes far excelled both in
perspicuity, and bequeathed this spirit to his successors.
The system which is now generally received, with regard
to the mind and its operations, derives not only its spirit
from Des Cartes, but its fundamental principles; and,
after all the improvements made by Malebranche, Locke,
Berkeley, and Hume, may still be called the Cartesian
system: we shall, therefore, make some remarks upon its
spirit and tendency in general, and upon its doctrine con-
cerning ideas in particular.

i. It may be observed, That the method which Des
Cartes pursued, naturally led him to attend more to the
operations of the mind by accurate reflection, and to
trust less to analogical reasoning upon this subject, than
any philosopher had done before him. Intending to
build a system upon a new foundation, he began with a
resolution to admit nothing but what was absolutely
certain and evident. He supposed that his senses, his
memory, his reason, and every other faculty to which we
trust in common life, might be fallacious; and resolved
to disbelieve everything, until he was compelled by
irresistible evidence to yield assent.

In this method of proceeding, what appeared to him,
first of all, certain and evident, was, That he thought —
that he doubted — that he deliberated. In a word, the
operations of his own mind, of which he was conscious,
must be real, and no delusion; and, though all his
other faculties should deceive him, his consciousness
could not* This, therefore, he looked upon as the first
of all truths. This was the first firm ground upon which
he set his foot, after being tossed in the ocean of scepti-
cism ; and he resolved to build all knowledge upon it,
without seeking after any more first principles.

* Des Cartes did not commit Reid's error of making conscious-
ness a co-ordinate and special faculty. — H.

346 THE PHILOSOPHY OF REID. [Cn. vn.

As every other truth, therefore, and particularly the
existence of the objects of sense, was to be deduced by a
train of strict argumentation from what he knew by con-
sciousness, he was naturally led to give attention to the
operations of which he was conscious, without borrowing
his notions of them from external things.

It was not in the way of analogy, but of attentive re-
flection, that he was led to observe, That thought, voli-
tion, remembrance, and the other attributes of the mind,
are altogether unlike to extension, to figure, and to all
the attributes of body; that we have no reason, therefore,
to conceive thinking substances to have any resemblance
to extended substances; and that, as the attributes of the
thinking substance are things of which we are conscious,
we may have a more certain and immediate knowledge
of them by reflection, than we can have of external ob-
jects by our senses.

These observations, as far as I know, were first made
by Des Cartes; and they are of more importance, and
throw more light upon the subject, than all that had been
said upon it before. They ought to make us diffident
and jealous of every notion concerning the mind and its
operations, which is drawn from sensible objects in the
way of analogy, and to make us rely only upon accu-
rate reflection, as the source of all real knowledge upon
this subject.

2. I observe that, as the Peripatetic system has a ten-
dency to materialize the mind and its operations, so the
Cartesian has a tendency to spiritualize body and its
qualities. One error, common to both systems, leads
to the first of these extremes in the way of analogy, and
to the last in the way of reflection. The error I mean
is, That we can know nothing about body, or its quali-
ties, but as far as we have sensations which resemble
those qualities. Both systems agreed in this: but
according to their differing methods of reasoning, they
drew very different conclusions from it ; the Peripatetic

CH. VIM THE PHILOSOPHY OF REID. 347

drawing his notions of sensation from the qualities of
body; the Cartesian, on the contrary, drawing his no-
tions of the qualities of body from his sensations.

The Peripatetic, taking it for granted that bodies and
their qualities do really exist, and are such as we com-
monly take them to be, inferred from them the nature of
his sensations, and reasoned in this manner: — Our sensa-
tions are the impressions which sensible objects make
upon the mind, and may be compared to the impression
of a seal upon wax: the impression is the image or form
of the seal, without the matter of it; in like manner,
every sensation is the image or form of some sensible
quality of the object. This is the reasoning of Aristotle:
and it has an evident tendency to materialize the mind
and its sensations.

The Cartesian, on the contrary, thinks that the exist-
ence of body, or of any of its qualities, is not to be
taken as a first principle ; and that we ought to admit
nothing concerning it, but what, by just reasoning, can
be deduced from our sensations; and he knows that, by
reflection, we can form clear and distinct notions of our
sensations, without borrowing our notions of them by
analogy from the objects of sense. The Cartesians,
therefore, beginning to give attention to 'their sensations,
first discovered that the sensations corresponding to
secondary qualities, cannot resemble any quality of body.
Hence, Des Cartes and Locke inferred, that sound, taste,
smell, colour, heat, and cold, which the vulgar took to
be qualities of body, were not qualities of body, but
mere sensations of the mind.* Afterwards, the ingen-

* Des Cartes and Locke made no such inference. They only
maintained (as Reid himself states) that sound, taste, &c., as sensa-
tions in us, have no resemblance to any quality in bodies. If the
names, therefore, of sound, taste, &c., were to be employed univo-
cally — i. e., to denote always things the same or similar — in that
case they argued that these terms, if properly significant of the sen-
sations, could not be properly applied to the relative qualities in ex-

348 THE PHILOSOPHY OF REID. [CH. VII.

ious Berkeley, considering more attentively the nature of
sensation in general, discovered and demonstrated, that
no sensation whatever could possibly resemble any qual-
ity of an insentient being, such as body is supposed to
be; and hence he inferred, very justly, that there is the
same reason to hold extension, figure, and all the pri-
mary qualities, to be mere sensations, as there is to hold
the secondary qualities to be mere sensations. Thus,
by just reasoning upon the Cartesian principles, matter
was stripped of all its qualities; the new system, by a
kind of metaphysical sublimation, converted all the qual-
ities of matter into sensations, and spiritualized body,
as the old had materialized spirit.

The way to avoid both these extremes, is to admit
the existence of what we see and feel as a first principle,
as well as the existence of things whereof we are con-
scious; and to take our notions of the qualities of body,
from the testimony of our senses, with the Peripatetics ;
and our notions of our sensations from the testimony
of consciousness, with the Cartesians.

ternal things. This is distinctly stated both by Des Cartes and
Locke. But Des Cartes and the Cartesians observe that the terms
in question are equivocally used; being commonly applied both to
that in things which occasions the sensation in us, and to that sen-
sation itself. Nay, the Cartesians, to avoid the ambiguity, distin-
guished the two relatives by different names. To take colour, tor
example: they called colour, as a sensation in the mind, formal
colour; colour, as a quality in bodies capable of producing the sensa-
tion, primitive or radical colour. They had likewise another dis-
tinction of less importance — that of secondary or derivative colour;
meaning thereby that which the coloured bodies impress upon the
external medium. Thus, again, primitive or radical sound was the
property of a body to determine a certain agitation in the air or
other medium; secondary or derivative sound, that agitation in the
medium itself ; formal sound, the sensation occasioned by the im-
pression made by the radical sound mediately, and by the deriva-
tive immediately, upon the organ of hearing. There is thus no
difference between Reid and the Cartesians, except that the doctrine
which he censures is in fact more precise and explicit than his
own. — H.

CH. VII.] THE PHILOSOPHY OF REID. 349

3. I observe, That the modern scepticism is the
natural issue of the new system; and that, although it
did not being forth this monster until the year 1739,* ^
may be said to have carried it in its womb from the be-
ginning.

The old system admitted all the principles of common
sense as first principles, without requiring any proof of
them; and, therefore, though its reasoning was common-
ly vague, analogical, and dark, yet it was built upon a
broad foundation, and had no tendency to scepticism.
We do not find that any Peripatetic thought it incum-
bent upon him to prove the existence of a material
world; but every writer upon the Cartesian system at-
tempted this, until Berkeley clearly demonstrated the
futility of their arguments; and thence concluded that
there was no such thing as a material world; and that
the belief of it ought to be rejected as a vulgar error.

The new system admits only one of the principles of
common sense as a first principle; and pretends, by
strict argumentation, to deduce all the rest from it.
That our thoughts, our sensations, and every thing of
which we are conscious, hath a real existence, is admitted
in this system as a first principle; but everything else
must be made evident by the light of reason. Reason
must rear the whole fabric of knowledge upon this sin-
gle principle of consciousness.

There is a disposition in human nature to reduce
things to as few principles as possible;f and this, with-
out doubt, adds to the beauty of a system, if the princi-
ples are able to support what rests upon them. The
mathematicians glory, very justly, in having raised so
noble and magnificent a system of science, upon the
foundation of a few axioms and definitions. This love

* When Hume's "Treatise of Human Nature " appeared. — H.
f See " Essays on the Intellectual Powers," p. 656, sqq. 4to edi-
tion.—H.

350 THE PHILOSOPHY OF REID. [CM. VII.

of simplicity, and of reducing things to few principles,
hath produced many a false system; but there never was
any system in which it appears so remarkably as that of
Des Cartes.* His whole system concerning matter and
spirit is built upon one axiom, expressed in one word,
cogito. Upon the foundation of conscious thought, with
ideas for his materials, he builds his system of the hu-
man understanding, and attempts to account for all
its phenomena; and having, as he imagined, from his
consciousness, proved the existence of matter; upon the
existence of matter, and of a certain quantity of motion
originally impressed upon it, he builds his system of the
material world, and attempts to account for all its phae-
nomena.

These principles, with regard to the material system,
have been found insufficient; and it has been made evi-
dent that, besides matter and motion, we must admit
gravitation, cohesion, corpuscular attraction, magnetism,
and other centripetal and centrifugal forces, by which
the particles of matter attract and repel each other.
Newton, having discovered this, and demonstrated that
these principles cannot be resolved into matter and mo-
tion, was led, by analogy and the love of simplicity, to
conjecture, but with a modesty and caution peculiar to
him, that all the phenomena of the material world de-
pended upon attracting and repelling forces in the parti-
cles of matter. But we may now venture to say, that
this conjecture fell short of the mark. For, even in the
unorganized kingdom, the powers by which salts, crys-
tals, spars, and many other bodies, concrete into regular
forms, can never be accounted for by attracting and re-
pelling forces in the particles of matter. And in the
vegetable and animal kingdoms, there are strong indica-

* We must except, however, before Reid, among others, the sys-
tem of Spinoza, and, since Reid, those of Fichte, Schelling, Hegel,
&c.— H.

CH. VII.] THE PHILOSOPHY OF REID. 351

tions of powers of a different nature from all the powers
of unorganized bodies. We see, then, that, although,
in the structure of the material world, there is, without
doubt, all the beautiful simplicity consistent with the
purposes for which it was made, it is not so simple as
the great Des Cartes determined it to be; nay, it is not so
simple as the greater Newton modestly conjectured it to
be. Both were misled by analogy, and the love of sim-
plicity. One had been much conversant about exten-
sion, figure, and motion; the other had enlarged his
views to attracting and repelling forces; and both formed
their notions of the unknown parts of nature, from those
with which they were acquainted, as the shepherd Tity-
rus formed his notion of the city of Rome from his coun-
try village: —

" Urbem quam dicunt Romam, Meliboee, putavi
Stultus ego, huic nostrae similem, quo ssepe solemus
Pastores ovium teneros depellere foetus.
. Sic canibus catulos similes, sic matribus hoedos
Noram: sic parvis componere magna solebam."

This is a just picture of the analogical way of thinking.
But to come to the system of Des Cartes, concerning
the human understanding. It was built, as we have ob-
served, upon consciousness as its sole foundation, and
with ideas * as its materials; and all his followers have
built upon the same foundation and with the same ma-
terials. They acknowledge that Nature hath given us
various simple ideas. These are analogous to the mat-
ter, of Des Cartes's physical system. They acknowledge,
likewise, a natural power, by which ideas are com-
pounded, disjoined, associated, compared. This is an-

* There is no valid ground for supposing that Des Cartes meant
by ideas aught but modifications of the mind itself. That the ma-
jority of the Cartesians did not, is certain. The case is, however,
different with regard to Malebranche and Berkeley. But of this
again. — H.

352 THE PHILOSOPHY OF REID. [Cn. VII.

alogous to the original quantity of motion in Des
Cartes's physical system. From these principles, they
attempt to explain the phaenomena of the human under-
standing, just as in the physical system the phaenomena
of nature were to be explained by matter and motion.
It must, indeed, be acknowledged, that there is great
simplicity in this system, as well as in the other. There
is such a similitude between the two, as may be expected
between children of the same father; but, as the one has
been found to be the child of Des Cartes, and not of
Nature, there is ground to think that the other is so like-
wise.

That the natural issue of this system is scepticism with
regard to everything except the existence of our ideas,
and of their necessary relations, which appear upon com-
paring them, is evident; for ideas, being the only objects
of thought, and having no existence but when we are
conscious of them, it necessarily follows that there is no
object of our thought which can have a continued and
permanent existence. Body and spirit, cause and effect,
time and space, to which we were wont to ascribe an
existence independent of our thought, are all turned out
of existence by this short dilemma. Either these things
are ideas of sensation or reflection, or they are not; if
they are ideas of sensation or reflection, they can have no
existence but when we are conscious of them; if they are
not ideas of sensation or reflection, they are words with-
out any meaning.*

Neither Des Cartes nor Locke perceived this conse-
quence of their system concerning ideas. Bishop Ber-
keley was the first who discovered it. And what followed
upon this discovery ? Why, with regard to the material
world, and with regard to space and time, he admits the
consequence, That these things are mere ideas, and have

* This dilemma applies to the sensualism of Locke, but not to the
rationalism of Des Cartes. — H.

CH.VII.] THE PHILOSOPHY OF REID. 353

no existence out in our minds; but with regard to the
existence of spirits or minds, he does not admit the con-
sequence; and, if he had admitted it, he must have been
an absolute sceptic. But how does he evade this conse-
quence with regard to the existence of spirits ? The ex-
pedient which the good Bishop uses on this occasion is
very remarkable, and shows his great aversion to scepti-
cism. He maintains that we have no ideas of spirits;
and that we can think, and speak, and reason about
them, and about their attributes, without having any
ideas of them. If this is so, my Lord, what should hin-
der as from thinking and reasoning about bodies, and
their qualities, without having ideas of them ? The
Bishop either did not think of this question, or did not
think fit to give any answer to it. However, we may
observe, that, in order to avoid scepticism, he fairly starts
out of the Cartesian system, without giving any reason
why he did so in this instance, and in no other. This,
indeed, is the only instance of a deviation from Cartesian
principles which I have met with in the successors of
Des Cartes; and it seems to have been only a sudden
start, occasioned by the terror of scepticism; for, in all
other things, Berkeley's system is founded upon Carte-
sian principles.

Thus we see that Des Cartes and Locke take the road
that leads to scepticism, without knowing the end of it;
but they stop short for want of light to carry them far-
ther. Berkeley, frighted at the appearance of the dread-
ful abyss, starts aside, and avoids it. But the author of
the "Treatise of Hum an Nature," more daring and in-
trepid, without turning aside to the right hand or to the
left, like Virgil's Alecto, shoots directly into the gulf :

" Hie specus horrendum, et ssevi spiracula Ditis
Monstrantur : ruptoque ingens Acheronte vorago
Pestiferas aperit fauces."

4. We may observe, That the account given by the
new system, of that furniture of the human understand-

354 THE PHILOSOPHY OF REID. [Cn. VII.

ing which is the gift of Nature, and not the acquisition
of our own reasoning faculty, is extremely lame and im-
perfect. *

The natura. furniture of the human understanding is
of two kinds: First, The notions or simple apprehen-
sions which we have of things; and, secondly, The judg-
ments or the belief which we have concerning them. As
to our notions, the new system reduces them to two
classes — ideas of sensation, and ideas of reflection : the
first are conceived to be copies of our sensations, re-
tained in the memory or imagination; the second, to be
copies of the operations of our minds whereof we are
conscious, in like manner retained in the memory or
imagination : and we are taught that these two compre-
hend all the materials about which the human under-
standing is, or can be employed. As to our judgment
of things, or the belief which we have concerning them,
the new system allows no part of it to be the gift of na-
ture, but holds it to be the acquisition of reason, and to
be got by comparing our ideas, and perceiving their
agreements or disagreements. Now I take this account,
both of our notions, and of our judgments or belief, to
be extremely imperfect; and I shall briefly point out
some of its capital defects.

The division of our notions into ideas of sensation, f
and ideas of reflection, is contrary to all rules of logic;
because the second member of the division includes the
first. For, can we form clear and just notions of our
sensations any other way than by reflection ? Surely we
cannot. Sensation is an operation of the mind of which
we are conscious; and we get the notion of sensation by
reflecting upon that which we are conscious of. In like
manner, doubting and believing are operations of the
mind whereof we are conscious ; and we get the notion

* The following summary refers principally to Locke. — H.
f It must be remembered that under Sensation Locke and others
included Perception proper and Sensation proper. — H.

CH. VII.] THE PHILOSOPHY OF REID. 355

of them by reflecting upon what we are conscious of.
The ideas of sensation, therefore, are ideas of reflection,
as much as the ideas of doubting, or believing, or any
other ideas whatsoever. *

But, to pass over the inaccuracy of this division, it is
extremely incomplete. For, since sensation is an opera-
tion of the mind, as well as all the other things of which
we form our notions by reflection, when it is asserted
that all our notions are either ideas of sensation or ideas
of reflection, the plain English of this is, That mankind

* I do not see how this criticism on Locke's division can be de-
fended, or even excused. It is perfectly evident that Reid here con-
founds the proper ideas of sensation — that is, the ideas of the quali-
ties of matter, about which sensation (perception) is conversant —
with the idea of sensation itself — that is, the idea of this faculty as
an attribute of mind, and which is the object of a reflex conscious-
ness. Nor would it be competent to maintain that Locke, allowing
no immediate knowledge of aught but of mind and its contents, con-
sequently reduces all our faculties to self-consciousness, and thus
abolishes the distinction of sensation (perception) and reflection, as
separate faculties, the one conversant with the qualities of the exter-
nal world, the other with the qualities of the internal. For, in the
first place, it would still be logically competent, on the hypothesis
that all our knowledge is exclusively of self, to divide the ideas we
possessed, into classes, according as these were given as representa-
tions of the non-ego by the ego, or as phaenomena of the ego itself.
In the second place, Reid's criticism does not admit of this excuse.
But, in the third, if the defence were valid in itself, and here availa-
ble, the philosophy of Reid himself would be obnoxious to a similar
criticism. For he makes perception (consequently the object known
in perception) an object of consciousness; but consciousness, in [his
yiew, is only of the phaenomena of mind itself — all consciousness is
to him self -consciousness. Thus, his perception, as contained under
his consciousness, is only cognisant of the ego. With all this, how-
ever, Reid distinguishes perception and consciousness as special and
co-ordinate faculties; perception being conversant about the qualities
of matter, as suggested — that is, as represented in the percipient sub-
ject— consciousness as conversant about perception and the other at-
tributes of mind itself. — With the preceding observations, the reader
may compare Priestley's "Examination," p. 38, and Stewart's
" Philosophical Essays," Note N. — H.

356 THE PHILOSOPHY OF REID. [Cn. VII.

neither do nor can think of anything but of the opera-
tions of their own minds. Nothing can be more con-
trary to truth, or more contrary to the experience of man-
kind. I know that Locke, while he maintained this
doctrine, believed the notions which we have of body
and of its qualities, and the notions which we have of
motion and of space, to be ideas of sensation. But why
did he believe this ? Because he believed those notions
to be nothing else but images of our sensations. If,
therefore, the notions of body and its qualities, of mo-
tion and space, be not images of our sensations, will it
not follow that those notions are not ideas of sensation ?
Most certainly. *

There is no doctrine in the new system which more
directly leads to scepticism than this. And the author
of the "Treatise of Human Nature" knew very well
how to use it for that purpose ; for, if you maintain that
there is any such existence as body or spirit, time or
place, cause or effect, he immediately catches you be-
tween the horns of this dilemma ; your notions of these
existences are either ideas of sensation, or ideas of reflec-

* I may here notice — what I shall hereafter more fully advert to —
that Reid's criticism of Locke, here and elsewhere, proceeds upon
the implication that the English philosopher attached the same re-
stricted meaning to the term Sensation that he did himself. But this
is not the case. Locke employed Sensation to denote both the idee
and the sentiment of the Cartesians — both the perception and the
sensation of Reid. To confound this distinction was, indeed, wrong,
but this is a separate and special ground of censure, and, in a general
criticism of Locke's doctrine, the fact that he did so confound percep-
tion proper and sensation proper, should always be taken into ac-
count. But, waving this, what is gained by the distinction in Reid's
hands? In his doctrine, space, motion, &c., as perceived, are only
conceptions; only modifications of self, suggested, in some unknown
way, on occasion of the impression made on the sense; consequently,
in the one doctrine as in the other, what is known is nothing beyond
the affections of the thinking subject itself; and this is the only basis
required by the idealist and sceptic for the foundation of their sys-
tems.— H.

CH. VII.] THE PHILOSOPHY OF REID. 357

tion : if of sensation, from what sensation are they
copied ? if of reflection, from what operation of the mind
are they copied ?

It is indeed to be wished that those who have written
much about sensation, and about the other operations
of the mind, had likewise thought and reflected much,
and with great care, upon those operations : but is it
not very strange that they will not allow it to be possi-
ble for mankind to think of anything else ?

The account which this system gives of our judgment
and belief concerning things, is as far from the truth as
the account it gives of our notions or simple apprehen-
sions. It represents our senses as having no other office
but that of furnishing the mind with notions or simple
apprehensions of things ; and makes our judgment and
belief concerning those things to be acquired by com-
paring our notions together, and perceiving their agree-
ments or disagreements.

We have shewn, on the contrary, that every operation
of the senses, in its very nature, implies judgment or be-
lief, as well as simple apprehension. Thus, when I feel
the pain of the gout in my toe, I have not only a notion
of pain, but a belief of its existence, and a belief of some
disorder in my toe which occasions it ; and this belief
is not produced by comparing ideas, and perceiving their
agreements and disagreements ; it is included in the very
nature of the sensation. When I perceive a tree before
me, my faculty of seeing gives me not only a notion or
simple apprehension of the tree, but a belief of its exist-
ence, and of its figure, distance, and magnitude ; and
this judgment or belief is not got by comparing ideas, it
is included in the very nature of the perception. We
have taken notice of several original principles of belief
in the course of this inquiry; and when other faculties of
the mind are examined, we shall find more, which have
not occurred in the examination of the five senses.

Such original and natural judgments are, therefore, a

358 THE PHILOSOPHY OF REID. [Cn. VII.

part of that furniture which Nature hath given to the
human understanding. They are the inspiration of the
Almighty no less than our notions or simple apprehen-
sions. They serve to direct us in the common affairs of
life, where our reasoning faculty would leave us in the
dark. They are a part of our constitution ; and all the
discoveries of our reason are grounded upon them.
They make up what is called the common sense of man-
kind; * and, what is manifestly contrary to any of those
first principles, is what we call absurd. The strength of
them is good sense, which is often found in those who
are not acute in reasoning. A remarkable deviation
from them, arising from a disorder in the constitution,
is what we call lunacy ; as when a man believes that he
is made of glass. When a man suffers himself to be
reasoned out of the principles of common sense, by
metaphysical arguments, we may call this metaphysical
lunacy ; which differs from the other species of the dis-
temper in this, that it is not continued, but intermittent:
it is apt to seize the patient in solitary and speculative
moments : but, when he enters into society, Common
Sense recovers her authority, f A clear explication and
enumeration of the principles of common sense, is one
of the chief desiderata in logic. We have only consid-
ered such of them as occurred in the examination of the
five senses.

5. The last observation that I shall make upon the
new system, is, that, although it professes to set out in
the way of reflection, and not of analogy, it hath retained
some of the old analogical notions concerning the op-
erations of the mind ; particularly, that things which do
not now exist in the mind itself, can only be perceived,

* See Note A.— H.

f No one admits this more promptly than the sceptic himself.
See Hume's "Treatise of Human Nature," Book I., Part iv., §7,
and "Enquiry Concerning Human Understanding," § 12, Part II.

— H.

CH. VII.] THE PHILOSOPHY OF REID. 359

remembered, or imagined, by means of ideas or images *
of them in the mind, which are the immediate objects of
perception, remembrance, and imagination. This doc-
trine appears evidently to be borrowed from the old sys-
tem ; which taught that external things make impres-
sions upon the mind, like the impressions of a seal upon
wax ; that it is by means of those impressions that we
perceive, remember, or imagine them ; and that those
impressions must resemble the things from which they
are taken. When we form our notions of the operations
of the mind by analogy, this way of conceiving them
seems to be very natural, and offers itself to our thoughts ;
for, as everything which is felt must make some im-
pression upon the body, we are apt to think that every-
thing which is understood must make some impression
upon the mind.

From such analogical reasoning, this opinion of the
existence of ideas or images of things in the mind, seems
to have taken its rise, and to have been so universally
received among philosophers. It was observed already,
that Berkeley, in one instance, apostatizes from this prin-
ciple of the new system, by affirming that we have no
ideas of spirits, and that we can think of them immedi-
ately, without ideas. But I know not whether in this
he has had any followers. There is some difference,
likewise, among modern philosophers with regard to the
ideas or images by which we perceive, remember, or
imagine sensible things. For, though all agree in the
existence of such images, "f they differ about their
place ; some placing them in a particular part of the

* That is, by representative entities different from the modes of
the mind itself. This doctrine, I have already noticed, is attributed
by Reid too universally to philosophers; and is also a comparatively
unimportant circumstance in reference to the Idealist and Sceptic.
See Note C.— H.

f See last note. Berkeley did hold the hypothesis of ideas as un-
derstood by Reid. — H,

360 THE PHILOSOPHY OF REID. [CH. VII.

brain, where the soul is thought to have her residence,
and others placing them in the mind itself. Des Cartes
held the first of these opinions ;* to which Newton seems
likewise to have inclined ; for he proposes this query in
his "Optics:" — "Annon sensorium animalium est
locus cui substantia sentiens adest, et in quern sensibiles
rerum species per nervos et cerebrum deferuntur, ut ibi
praesentes a praesente sentiri possint ? " But Locke seems
to place the ideas of sensible things in the mind ; f and
that Berkeley, and the author of the "Treatise of Human
Nature," were of the same opinion, is evident. The
last makes a very curious application of this doctrine,
by endeavouring to prove from it, That the mind either
is no substance, or that it is an extended and divisible
substance ; because the ideas of extension cannot be in
a subject which is indivisible and unextended.

I confess I think his reasoning in this, as in most
cases, is clear and strong. For whether the idea of ex-
tension be only another name for extension itself, as
Berkeley and this author assert ; or whether the idea of
extension be an image and resemblance of extension, as
Locke conceived ; I appeal to any man of common
sense, whether extension, or any image of extension, can
be in an unextended and indivisible subject. But while
I agree with him in his reasoning, I would make a differ-
ent application of it, He takes it for granted, that there
are ideas of extension in the mind ; and thence infers,
that, if it is at all a substance, it must be an extended

* An unqualified error, arising from not understanding the am-
biguous language of Des Cartes; who calls, by the common name
of ideas, both the organic motions in the brain, of which the mind,
in his doctrine, necessarily knows nothing, and the representations
in the mind itself, hyperphysically determined on occasion of those
motions, and of which alone the mind is cognizant. But of this un-
der the " Essays on the Intellectual Powers." — H.

•f Locke's opinion on this point is as obscure and doubtful as that
of Des Cartes is clear and certain. But Reid is probably right. — H.

CH. VII.] THE PHILOSOPHY OF RfclD. 361

and divisible substance. On the contrary, I take it for
granted, upon the testimony of common sense, that my
mind is a substance — that is, a permanent subject of
thought ; and my reason convinces me that it is an un-
extended and indivisible substance ; and hence I infer
that there cannot be in it anything that resembles ex-
tension. If this reasoning had occurred to Berkeley, it
would probably have led him to acknowledge that we
may think and reason concerning bodies, without having
ideas of them in the mind, as well as concerning spirits.

I intended to have examined more particularly and
fully this doctrine of the existence of ideas or images of
things in the mind ; and likewise another doctrine,
which is founded upon it — to wit, That judgment or be-
lief is nothing but a perception of the agreement or dis-
agreement of our ideas ; but, having already shewn,
through the course of this inquiry, that the operations
of the mind which we have examined, give no counte-
nance to either of these doctrines, and in many things
contradict them, I have thought it proper to drop this
part of my design. It may be executed with more ad-
vantage, if it is at all necessary, after inquiring into some
other powers of the human understanding.

Although we have examined only the five senses, and
the principles of the human mind which are employed
about them, or such as have fallen in our way in the
course of this examination, we shall leave the further
prosecution of this inquiry to future deliberation. The
powers of memory, of imagination, of taste, of reason-
ing, of moral perception, the will, the passions, the
affections, and all the active powers of the soul, present
a vast and boundless field of philosophical disquisition,
which the author of this inquiry is far from thinking
himself able to survey with accuracy. Many authors of
ingenuity, ancient and modern, have made excursions
into this vast territory, and have communicated useful
observations: but there is reason to believe that those

362 THE PHILOSOPHY OF REID. [CH. VII.

who have pretended to give us a map of the wnole, have
satisfied themselves with a very inaccurate and incom-
plete survey. If Galileo had attempted a complete sys-
tem of natural philosophy, he had, probably, done little
service to mankind: but by confining himself to what
was within his comprehension, he laid the foundation of
a system of knowledge, which rises by degrees, and does
honour to the human understanding. Newton, building
upon this foundation, and, in like manner, confining
his inquiries to the law of gravitation and the properties
of light, performed wonders. If he had attempted a
great deal more, he had done a great deal less, and per-
haps nothing at all. Ambitious of following such great
examples, with unequal steps, alas ! and unequal force,
we have attempted an inquiry only into one little corner
of the human mind — that corner which seems to be most
exposed to vulgar observation, and to be most easily
comprehended; and yet, if we have delineated it justly,
it must be acknowledged that the accounts heretofore
given of it were very lame, and wide of the truth.

INDEX.

Addison, conception of col-
or, 178-9.

Agnolonius, hiso ptics, 254.

Analogy, 339.

Analysis, of the human fac-
ulties necessary, 75-6.

Anatomy, mental, 72-3.

Anepigraphus, J. R., 206.

Animal spirits, theory of,
280.

Animals, laws of vision in,
246.

Apprehension, simple, 95,

95 H.

Aquapendens, 284.
Aristotle, on primary and

secondary qualities, 140,
156 ; on imagination, 182
H.; compared with Ba-
con, 335 ; definition of
the soul, 342-3 ; referred
to, 344; materialistic ten-
dency of his system, 346.
Association of ideas, 332-3.

Bacon, his services, 334.

Belief, Locke's theory of,
criticised, 95 sq.; Hume's
theory of, criticised, 96 sq.,
330 ; cannot be defined,

96 sq. ; in human testi-
mony, 323 sq.; in the con-
tinuance of the present
course of nature, 328 sq. ;
an ingredient of mental
operations, 137 sq., 228,
330.

Berkeley, relation of his
philosophy to scepticism,
81 sq., 86 sq., 349, 353 ;
ideas and spirits, 102, 186;
natural signs, 139 H. ; pri-
mary and secondary qual-
ities of matter, 140 ; qual-
ities of matter not resem-
bling sensations, 138 sq.,
T53» 158; his solution of
certain phenomena of vi-
sion examined, 218, 220
sq. ; noticed, 148, 160,
186, 199 H., 267, 272, 310,
312, 316, 345.

Body, its qualities, how ap-
prehended, 181 sq.

Borrichius, 210.

Brain, 223, 224.

Briggs, Dr., 254, 279.

Csesalpinus, 284.

Cause and effect, 332.

Cheselden, case of couch-
ing, 172, 194, 271 sq.; on
double vision, 270.

Cold, I2gsq. ; see Touch.

Color, 162 sq. ; see Seeing; a
blind man's notion of,
165 sq.

Common sense, the root of
all philosophy, 81 ; prin-
ciples of, 100, 358 ; prac-
tically acknowledged by
the idealists, 104 ; con-
trasted with the ideal phi-
losophy, 132 sq., 358.

363

364

INDEX.

Conception, distinguished
from perception, 289 H.

Consciousness, Des Cartes'
view of, 345 H., 350.

Credulity, 325.

Custom, 265 sq.

Democritus, on the qualities
of matter, 140, 157, 180,
i8oH.

Des Cartes, his doubt, 77,
345 ; misapprehended by
Reid, 77 H.; scepticism
the natural issue of his
system, 86 sq., 349; on
primary and secondary
qualities, 140, 157 ; on
seeing objects erect by in-
verted images, 215, 216 ;
the father of the new
philosophy of mind, 341 ;
remarks upon the Car-
tesian system, 345 sq. ; no-
ticed, 72, 82, 84, 103, 148,
154, 155 H., 160, 184.

Dimerbroeck, 284.

Distance, how computed by
the eye, 304 sq.

Divine veracity, 155 H.

Effluvia, 90.

'EvreA-exeta, 343.

Epicurus and the Epicu-
reans, on primary and
secondary qualities, 140,
157, 180.; theory of per-
ception, 344.

Experience, 323.

Experiment, 71.

Extension, notion of, 141-7,
187-91; see Seeing, Sight,
Touch ; Reid's and Kant's
theories contrasted, 141
H.; possibility of an a
posteriori perception of,
147 H.

Eyes, parallel motion of,
211 sq., 265 sq ; concen-
tration on one object, 263
sq. ; see Seeing.

Fabricius, 210.

Fichte, idealism, 152 H.
Figure, how perceived by

the eye, 315.
Folkes, Martin, 269.
Foster, case of, 269, 270.

Galen, 239.

Gassendi, 239.

Genius, adulterates phil^so-

phy, 76.
Geometry of visibles, 199

sq. ; see Seeing.
Grew, Dr. N., 121.

Halley, Dr., 165.

Hardness, 131, 139 sq. ; see
Touch.

Hearing, 122 sq.

Heat, 129; see Touch,

Hobbes, on imagination,
182 H.; noticed, 84.

Hume, his Treatise of Hu-
man Nature considered,
8isq.; reduces Berkeley's
system to scepticism, 86,
353; his theory of belief
examined, 96 sq, 330; his
theory of mind, 100 sq. ;
confession, 135, 358 H.;
noticed, 139, 150, 160,
184, 186, 345, 349 H, 356.

Idea, how used by Reid,
93-4; by Des Cartes, 351,
360.

Idealism, 151-2 H.

Ideal philosophy, 87 ; the
theory of sensation, mem-
ory, belief, and imagina-
tion introduced by it con-
sidered, 96; psychological
history of, 100 sq. ; re-
marks on, 153 sq.

Ideas, doctrines of ancient
philosophers about, 343
sq.

Identity, Locke's account of,
considered, 79.

Image, Reid's use of the
term, 93.

Imagination, how accom-
panied, 93 H.; view of

INDEX.

365

Aristotle and Hobbes, 182
H.; distinguished from
perception, 289 H.

Impressions, in reference to
sensations, 298 sq. ; on the
mind, the peripatetic
theory of, 347.

Inductive principle, 328 sq.

Instinct, instinctive beliefs,
291 sq. ; belief in the con-
stancy of nature, see In-
ductive principle.

Jacobi, on perception, 302

H.
Jurin, Dr.,

Kant, relation to Hume, 66
H.; held the notion of ex-
tension to be a priori, 141
H., 147 H.

Kepler, on seeing objects
erect by inverted images,
215, 216.

Laertius, 83.

Language, imperfection of,
impediment to the study
of mind, 74 sq.; natural,
etc., considered, 124-8,
136.

Laws of nature, their char-
acter, 225, 230 sq., 239
sq. ; belong to mind as
well as to matter, 225.

Light, 162; see Seeing.

Locke, his theory of person-
al identity considered, 79;
his definition of knowl-
edge criticised, 97 sq.;
quoted, 152; his doctrine
of primary and secondary
qualities discussed, 157,
179, 185; not the origina-
tor of these terms, 185 H. ;
misinterpreted by Reid,
347 H. ; noticed, 79, 82,
103, 148, 160.

Lucretius, 344.

Malebranche, his doctrine
of primary and secondary

qualities, 140, .157, 184,
186; his theory of per-
ception, 343-4; noticed,
79, 82, 103, 148, 160.

Mariotte, 251.

Memory distinguished from
perception, 330; defined,

94-

Metaphysic, 88.

Mind, importance of the
study of, 70; how to be
studied, 71, 72; impedi-
ments to our knowledge
of, 72-6; the systems of
Des Cartes, Malebranche,
and Locke, considered,
76-80; of Berkeley and
Hume, 8 1-6; its exist-
ence, how inferred, 105
sq.; in sensation, act-
ive or passive?, 116-17;
operations of, two ways
of treating, 338; names of
operations borrowed from
sensible images, 341.

Nature, the works of, 85;
our belief in the uniform-
ity of, 328 sq.

Nerves, theory of, 279.

Newton, Sir Isaac, his reg-
ular philosophy, 71; on
color, etc., 119; his
query on single vision,
246, 282; attracting and
repelling forces, 218, 350;
followed Bacon's rules of
inductive reasoning, 335;
concerning species, 360;
noticed, 113, 162, 351.

Optic nerve, 222, 336, 279.

Perception, in general, 287-
303; distinguished from
sensation, 288, 298; law
of the manifestation of
sensation and perception,
287 H.; distinguished
from imagination, 289,
289 H.; from memory,
289; what it implies, 289;

366

INDEX.

original and acquired,
293 sq.; involves no ex-
ercise of reason, 295; per-
ception of objects, the re-
sult of what, 297-303;
the true object of, im-
mediate, 298 H.; analo-
gous to testimony, 320-37.

Peripatetics, on species,
344; their tendency to
materialize mind, 346;
noticed, 183, 187.

Phantasms, 344.

Philosophers, their notions
concerning the soul, 341.

Plato, his system of ideas,
343 sq.; noticed, 104.

Platonists, their notion of
the soul, 344.

Porta, Baptista, 239.

Porterfield, Dr., on vision,
226, 231 239, 253, 261,
272 sq.

Pyrrho, the Elean, 83.

Qualities, primary and sec-
ondary, the distinction of,
140, 157, iSssq.; i8sH.

Reason, in connection with
common sense, 79 sq.,
149; inaccurate use of
term by Reid, 79 H., 149
H. ; in relation to our be-
lief in testimony, 327.

Reflection, 338; Locke's ac-
count of, 355-6.

Retina, how rays of light
affect, 194-237; see See-
ing; how objects fall
upon, 240.

Rousseau, 336-7.

Saunderson, N., 145, 165,
188, 220.

Scepticism, in philosophy of
Des Cartes, Malebranche,
Locke, and Berkeley, 82,
86 sq., 349 sq. ; animad-
verted on, 290; origin of,
351-2.

Scheiner, experiments ort
the eye, 231.

Seeing, in general, 162 sq.;
color, 173-81; visible
figure and extension, 187-
91; geometry of visibles,
199-211; certain phenom-
ena of vision examined:
the parallel motion of the
eyes, our seeing objects
erect by inverted images,
seeing objects single with
two eyes, 211 sq.

Sensation, indefinable, 96;
belongs to a sentient be-
ing, 107; what it suggests,
106; does not resemble
qualities of body, 181-7;
distinguished from per-
ception, 288, 298; sensa-
tion and reflection as the
sources of ideas, consid-
ered, 354 sq.

Sensations, distinguished
from qualities causing
them, 109 sq., 114 sq.,
129 sq., 132 sq., 157, 173
sq., 177.

Sense, testimony of, 320-37.

Senses, systems concerning,
156-61; do not deceive,

3i9-

Sensorium, denned, 222; the-
ories concerning, 280-5.

Sight, see Seeing.

Sign, connection of, with
thing signified, 135 sq.

Smelling, in general, 89-116;
the sensation considered
abstractly, 90-2; compared
with the remembrance
and imagination, 92-5; as
a quality in bodies, etc.,
109-11; the name of
smell, to what it belongs,
115-16; in sensation, the
mind active or passive?,
116-17.

Smith, Dr., his system of
optics, 216, 246, 262, 267,
268, 269, 270, 272, 275,
279. 3io, 313, 3M, 3i6.

INDEX.

367

Softness, 131; see Touch.
Soul, opinions regarding its

nature, 341 sq.
Sound, see Hearing.
Species, sensible, theories

of, 1 80, 344.
Squinting, see Seeing.
Strabismus, 277.
Suggestion, explained, 107

sq., 107-8 H.

Taste, 1 1 8-2 1.
Tertullian, 108 H.
Testimony, evidence of,

compared with that of

sense, 320-37.
Touch, analysed, 129 sq.;

heat and cold, 129 sq. ;

hardness and softness,

131 sq. ; hardness and

other primary qualities,
139 sq: extension, 141
sq.; existence of a ma-
terial world, 148 sq.
Truth, an innate principle,
324-

Valverda, 284.
Vesalius, 284.
Virgil, quoted, 351.
Visibles, geometry of, see

Seeing.
Vision, see Seeing.

Winslow, quoted, 284.
World, material, existence

of, a first principle, 148-

56, 348, 357 sq.

Zeno. 84,

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