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Cornell University Library 
QL 785.P53 1911 

Clever Hans 

3 1924 024 783 973 

Cornell University 

The original of tliis book is in 
tine Cornell University Library. 

There are no known copyright restrictions in 
the United States on the use of the text. 











Fellow in Psycholosy in the University of Chicago 



Professor of Psychology in the University of Chicago 




Copyright, 191 i, 




[By James R. Angell] 

The University of Chicago 

It gives me great pleasure to accept the invitation of 
the publishers to write a word of introduction for Mr. 
Rahn's excellent translation of " Der Kluge Hans ", a 
book which in the original has been but little known to 
American readers. The present wave of interest in animal 
life and behavior renders its appearance peculiarly ap- 

No more remarkable tale of credulity founded on un- 
conscious deceit was ever told, and were it offered as 
fiction, it would take high rank as a work of imagination. 
Being in reality a record of sober fact, it verges on the 
miraculous. After -reading Mr. Pfungst's story one can 
quite understand how sedate and sober Germany was for 
months thrown into a turmoil of newspaper debate, which 
for intensity and range of feeling finds its only parallel 
in a heated political campaign. That the subject of the 
controversy was the alleged ability of a trained horse to 
^olve complex arithmetical problems may excite gaiety 
and even derision, until one hears the details. Scientists 
and scholars of the highest eminence were drawn into the 
conflict, which has not yet wholly subsided, although the 
present report must be regarded as quite final in its ver- 


As for Hans himself, he has become the prototype of a 
host of less distinguished imitators representing every 
level of animal life, and when last heard from he was still 
entertaining mystified audiences by his accomplishments. 

But the permanent worth of the book is not to be found 
in its record of popular excitement, interesting as that is. 
It is a document of the very first consequence in its revela- 
tion of the workings of the animal mind as disclosed in the 
horse. Animal lovers of all kinds, whether scientists or 
laymen, will find in it material of greatest value for the 
correct apprehension of animal behavior. Moreover, it 
afiFords an illuminating insight into the technique of ex- 
perimental psychology in its study both of human and ani- 
mal consciousness. Finally, it contains a number of 
highly suggestive observations bearing on certain aspects 
of telepathy and muscle-reading. All things considered, it 
may fairly be said that few scientific books appeal to so 
various a range of interests in so vital a way.. 

Readers who wish to inform themselves of all the per- 
sonal circumstances in the case may best read the text 
just as it stands. Those who desire to get at the pith of 
the matter without reference to its historical settings, may 
be advised to omit the Introduction by Professor Stumpf 
of the University of Berlin, together with supplements 
II, III and IV. 



Prefatory Note (By James R. Angell) . . . v 

Introduction (By C. Stumpf) .... i 


I. The Problem of Animal Consciousness and " Clever 

Hans "...... 15 

II. Experiments and Observations ... 30 

III. The Author's Introspections . . . .88 

IV. Laboratory Tests ..... 102 

V. Explanation of the Observations . . . 141 

VI. Genesis of the Reaction of the Horse . . 212 
Conclusion ....... 240 

Supplements : 

I. Mr. von Osten's Method of Instruction (By C. Stumpf) 245 

II. The Report of September 12th, 1904) . . . 253 

III. An Abstract from the Records of the September 

Commission . . . . -255 

VI. The Report of December 9th, 1904 . . 261 

Table of References ... = .• 267 


[By C. Stumpf] 

A HORSE that solves correctly problems in multiplica- 
tion and division by means of tapping. Persons of unim- 
peachable honor, who in the master's absence have re- 
ceived responses, and assure us that in the process they 
have not made even the slightest sign. Thousands of 
spectators, horse-fanciers, trick-trainers of first rank, 
and not one of them during the course of many months' 
observations are able to discover any kind of regular 

That was the riddle. And its solution was found in 
the unintentional minimal movements of the horse's ques- 

Simple though it may seem, the history of the solu- 
tion is nevertheless quite complex, and one of the im- 
portant incidents in it is the appearance of the zoologist 
and African traveler. Schillings, upon the scene, and 
then there is the report of the so-called Hans-Commis- 
sion of September 12, 1904. And finally there is the 
scientific investigation, the results of which were pub- 
lished in my report of December 9, 1904. 

After a cursory inspection during the month of 
February, I again called upon Mr. von Osten in July, 
and asked him to explain to Professor Schumann and 
me just what method he had used in instructing the 
horse. We hoped in this way to gain a clue to the 


based not merely upon the fact that no such signals had 
been detected by the most expert observers, but also 
upon the character of the two men who exhibited the 
horse, upon their behavior during the entire period, and 
upon the method of instruction which Mr. von Osten 
had employed. In the case of unintentional signs, on the 
other hand, one had to deal with the fact with which 
physiologists and experimental psychologists are es- 
pecially familiar, viz., that our conscious states, without 
our willing it — indeed, even in spite of us — are accom- 
panied by bodily changes which very often can be de- 
tected only by the use of extremely fine graphic methods. 
The following is a more general instance : every mother, 
who detects the lie or divines the wish in the eyes of the 
child, knows that there are characteristic changes of 
facial expression, which are, nevertheless, very difficult 
of definition.* 

The commission did not even maintain or believe that 
unintentional signs within the realm of the senses known 
to us, were to be excluded. Professor Nagel and I 
would never have subscribed to any such conclusion. The 
sentence in question, therefore, could only be interpreted 
as follows: that signals of the kind that are used in- 

* " From the productions of the ' thought-readers ' we see how slight 
and seemingly insignificant the unconscious movements may be, which 
serve as signs for a sensitive re-agent. But in this case no contact is 
necessary. There would have to be some sort of visible or audible ex- 
pression on the part of the questioner. No proof for this has as yet 
been advanced." 

How any one possessing the power of logical thought could possibly 
infer from these words of mine (published in the above-mentioned ar- 
ticle in the " Tag "), that I denied the possibility of the occurrence of 
visual signs, is to me incomprehensible. What I did dfeny, and still 
deny, is that up to that time any had been proven to occur. 


tentionally in the training of horses, could not have oc- 
curred even as unintended signs, for otherwise Mr. 
Busch would have detected them. And in order to be 
observed by him it was immaterial whether they were 
given purposely or not. The same signs, therefore, 
which as a result of his observations were declared not to 
be present, could not be assumed to be involved as un- 

For my part I am ready to confess that at this time I 
did not expect to find the involuntary signals, if any such 
were involved, in the form of movements. I had in mind 
rather some sort of nasal whisper such as had been in- 
voked by the Danish psychologist A. Lehmann, in order 
to explain certain cases of so-called telepathy. I could 
not believe that a horse could perceive movements which 
escaped the sharp eyes of the circus-manager. To be 
sure, extremely slight movements may still be perceived 
after objects at rest have become imperceptible. But one 
would hardly expect this feat on the part of an animal, 
who was so deficient in keenness of vision, as we have 
been led, by those of presumably expert knowledge, to 
believe of the horse, — one would expect it all the less 
because Mr. von Osten and Mr. Schillings would move 
hither and thither in most irregular fashion while the 
horse was going through his tapping, and would there- 
fore make the perception of minute movements all the 
more difficult. 

Nor was there anything in the exhibitions given at the 
same time in a Berlin vaudeville by the mare " Rosa," 
whieh might have shattered this belief. For, in the case 
of f.iis rival of Hans, the movements involved were com- 
paijwtively coarse. The closing signal consisted in bend- 
ing forward on the part of the one exhibiting the mare, 


while up to that point he had stood bolt upright. Most 
persons were not aware of this, because this change in 
posture cannot be noticed from the front. I happened 
to sit to the side and caught the movement every time. 
It was the same that was noted by Dr. Miessner, an- 
other member of the commission, (see page 256), but 
concerning which he did not give me a more complete 
account. Later I learned through Professor Th. W. 
Engelmann that the very same movement was employed 
not long ago, for giving signals to a dog exhibited at 
Utrecht. This particular movement is very well adapted 
to commercial purposes, since the spectator always tries to 
view the performance from a point as nearly in front of 
the animal and its master as possible, thus making the 
detection of the trick all the more difficult. 

The details of the various experiments made by this 
commission are given in an excerpt from the records 
kept by Dr. von Hornbostel, which I showed to a small 
group of persons a few days after the 12th of September 
(Supplement III). At that time none of the particulars 
was published, because the commission wished to wait 
until some positive statement might be made. The public 
was merely to be assured that a group of reputable men, 
from different spheres of life, who could have no pur- 
pose in hazarding their reputation, believed that the case 
was one worthy of careful investigation. 

I left Berlin on September 17th and did not return 
until October 3d. In the meantime Mr. Schillings con- 
tinued the investigation, and was assisted in part by Mr, 
Oskar Pfungst, one of my co-workers at the Psycho- 
logical Institute. For the first time a number of tests 
were now made in which neither the questioner, nor any 
of those present knew the answer to the problem, i^ucli 


tests naturally were the first steps toward a positive in- 
vestigation. The results were such that Mr. Schillings 
was led to replace his hypothesis of independent concep- 
tual thinking by one of some kind of suggestion. In 
this he was strengthened somewhat by having noted 
the fact that in his questions which he put to the horse, 
he might proceed as far as to ask the impossible. He 
has always been ready to oflfer himself in the tests which 
have been undertaken since then. 

On October 13, 1904, together with the two gentlemen 
mentioned in the beginning of my report, I began my 
more detailed investigation, and finished on November 
29. We worked for several hours on the average of 
four times each week. I take this opportunity of giving 
expression of the recognition which is due to the two 
gentlemen. They were ready to go to the courtyard in 
all kinds of weather, at times they went without me, and 
they always patiently discussed the order and method 
of the experiments and the results. Dr. von Hornbostel 
had the important task of keeping the records, and Mr. 
Pfungst undertook the conduct of the experiments. It 
was he, who, soon after the blinder-tests disclosed the 
necessary presence of visual signs, discovered the nature 
of these signs. Without him we might have shown the 
horse to be dependent upon visual stimuli in general, 
but we never would have been able to gain that mass of 
detail, which makes the case valuable for human psychol- 
ogy. But I am tempted to praise not merely his patience 
and skill, but also his courage. For we must not believe 
that Mr. von Osten's horse was a " perfectly gentle " 
animal. If he stood untied and happened to be excited 
by some sudden occurrence, he would make that court- 
yard an unsafe place, and both Mr. Schillings and Mr. 


Pfungst suffered from more than one bite. In this con- 
nection I would also express my obligations to Count 
Otto zu Castell-Rudenhausen, for his frequent interces- 
sion on our behalf with the owner of the horse, and for 
his many evidences of good-will and helpfulness. 

After the publication of this report (Supplement IV), 
there was still some further discussion of the case in 
societies of various kinds and in the press, but no im- 
portant objections were raised. A hippologist thought 
that men of his calling should have been consulted, a 
telepathist believed that telepathists should have been 
called in. There was also some further talk of sugges- 
tion, will-transference, thought-reading and the occult, 
but no attempt was made to elucidate these vague terms 
with reference to their application to the case in hand. 
Others adhered to the old cry of " fraud," for a share of 
which Mr. Pfungst now fell heir. There were a few who 
felt it incumbent upon themselves to preserve their 
' priority,' and therefore stated with a show of satisfac- 
tion that I had finally ' confessed ' myself to hold their 
respective points of view. As if there were anything 
like " confessions " in science ! As if mere affirmations, 
even though sealed and deposited in treasure vaults, had 
any value with reference to a case in which every manner 
of supposition had been advanced in lieu of explanation. 
Why did they wait so long, if they had convincing proof 
for their position? 

And finally there were disappointed Darwinists who 
expressed fear lest ecclesiastical and reactionary points 
of view should derive favorable material from the con- 
clusions arrived at in my report. Needless fear. For 
lovers of truth it must always remain a matter of incon- 
sequence whether anyone is pleased or displeased with 


the truth, and whether it is enunciated by Aristotle or 

Mr. von Osten, however, continued to exhibit Hans, 
and is probably doing so still, but in what frame of mind, 
I dare not judge. The spectators continue to look on, 
they are doubly alert to catch movements, and many of 
them have learned from Mr. Schillings what kind of 
movements they are to expect. But these " initiated " 
ones regularly return and declare that there is nothing in 
the movements and that they simply could not discover 
any aids given to the horse. Nothing can so well show 
how difficult the case is, and how great the need of a 
thorough exposition of the whole matter, than the ac- 
count given in the following pages of Mr. Pfungst. Its 
publication has been delayed on account of the additional 
tests made in the laboratory, but we have reason to sup- 
pose that through these additional tests the work has 
gained in permanent value. Experimental psychologists 
will perhaps be greatly interested in the graphic regis- 
tration of the minute involuntary movements which ac- 
company the thought process, and in the artificial asso- 
ciation of a given involuntary movement with a given 
idea. Likewise the tests on sense-perception in horses, 
which have led to essential changes in hitherto current 
views, and the critical review of the comprehensive litera- 
ture on similar achievements of other animals, will be 
welcomed by many. 

Before closing these introductory remarks, I would 
make one more statement concerning Mr. von Osten. 
The reader will notice that the judgment passed upon him 
in this treatise is placed at the end, whereas in the report 
of the commission it came first. This was brought about 
by the change that was made in the way of stating the 


problem. Then the question discussed was whether 
' tricks ' were involved ; now the question is : What is the 
mechanism of the process? The question of the good 
faith of the master was taken up once more only because 
the facts that were brought to light by the later experi- 
mentation seemingly brought forward new grounds for 
distrust. But by placing this discussion toward the end 
of our report we wished to indicate that everything that 
is said of the present status of facts, is quite independent 
of the view taken concerning Mr. von Osten. Even as- 
suming that the horse had been purposely trained by him 
to respond to this kind of signal, the case would still 
deserve a place in the annals of science. For visual signs, 
planned and practiced so that they could not only be 
more readily perceived by the animal than by man, but 
could be transferred from their inventor to others without 
any betrayal of the secret, — this would be an extraor- 
dinary invention, and Mr. von Osten would then be a 
fraud, but also a genius of first rank. 

In truth he probably was neither,, but I was brief 
in my report, for otherwise I would have been obliged 
to go into more detail than the case warranted. And a 
judgment passed upon a human personality is quite a 
different matter from a judgment upon a horse. If it is 
unscientific to make unqualified statements concerning: 
a horse after the performance of only a few experimental 
tests, it is certainly an unwarranted thing to pass a moral 
judgment upon a man upon the basis of meagre material. 
Anyone who would assume the role of judge should bear 
in mind that here too we have more than a hundredfoli 
the material which they could bring forward, and among 
it some which, if taken alone, would be more unfavorable 
than any that they had. But here all things should be 


weighed -together, and not in isolation. A former in- 
structor of mathematics in a German gymnasium, a pas- 
sionate horseman and hunter, extremely patient and at 
the same time highly irrascible, liberal in permitting the 
use of the horse for days at a time and again tyrannical 
in the insistence upon foolish conditions, clever in his 
method of instruction and yet at the same time possessing 
not even the slightest notion of the most elementary con- 
ditions of scientific procedure, — all this, and more, goes 
to make up the man. He is fanatic in his conviction, he 
has an eccentric mind which is crammed full of theories 
from the phrenology of Gall to the belief that the horse 
is capable of inner speech and thereby enunciates in- 
wardly the number as it proceeds with the tapping. From 
theories such as these, and on the basis of all sorts of 
imagined emotional tendencies in the horse, he also 
managed to formulate an explanation for the failure of 
the tests in which none of the persons present knew the 
answer to the problem given the horse, and also for the 
failure of those tests in which the large blinders were 
applied. And he would often interfere with or hinder 
other tests which, according to his point of view, were 
likely to lead us astray. And yet, when the first tests 
with the blinders did turn out as unmistakably sheer 
failures, there was such genuine surprise, such tragi- 
comic rage directed against the horse, that we finally 
believed that his views in the matter would be changed 
beyond a doubt. " The gentlemen must admit," he said 
at the time, " that after seeing the objective success of 
my efforts at instruction, I was warranted in my belief 
in the horse's power of independent thought." Never- 
theless, upon the following day he was as ardent an ex- 


ponent of the belief in the horse's intelligence as he ever 
had been. 

And finally, after I could no longer keep from him the 
results of our investigation, I received a letter from him 
in which he forbade further experimentation with the 
horse. The purpose of our inquiries, he said, had been to 
corroborate his theories. On account of his withdrawal 
of the horse a few experimental series unfortunately 
could not be completed, but happily the major portion of 
our task had been accomplished. 




If we would appreciate the interest that has been 
aroused everywhere by the wonderful horse solving 
arithmetical problems, we must first consider briefly the 
present state of the problem of animal consciousness.* 
Animal consciousness cannot be directly gotten at, and 
the psychologist must therefore seek to appreciate it on 
the basis of the animal's behavior and with the assistance 
of conceptions borrowed from human psychology. 
Hence it is that animal psychology rests upon uncertain 
foundations with the result that the fundamental prin- 
ciples have been repeatedly questioned and agreement 
has not yet been attained. The most important of these 
questions is, " Does the animal possess consciousness, 
and is it like the human consciousness ? " Comparative 
psychologists divide into three groups on this question. 

The one group allows consciousness to the lower 
forms, but emphasizes the assertion that between the 
animal and the human consciousness there is an impassable 

* Since the present treatise is intended for the larger public, this 
brief resume will probably be welcome to many. 



gap. The animal may have sensations and memory- ' 
images of sensations which may become associated in 
manifold combinations. Both sensations and memory 
images are believed to be accompanied by conditions of 
pleasure and of pain (so-called sensuous feelings), and 
these in turn, become the mainsprings of desire. The 
possession of memory gives the power of learning 
through experience. But with this, the inventory of the 
content of animal consciousness is exhausted. The 
ability to form concepts * and with their aid to make 
judgments and draw conclusions is denied the lower 
forms. All the higher intellectual, aesthetic and moral 
feelings, as well as volition guided by motives, are also 
denied. Among the ancients this view was held by Aris- 
totle and the Stoics ; and following them it was taught 
by the Christian Church. It pervaded all mediaeval 
philosophy, which grew out of the teachings of Aristotle 
and the Church. It is this philosophy, in the form of 
Neo-Thomism, which still obtains in the Catholic world. 
During the 17th century, even though temporarily, an- 
other conception of the consciousness of lower forms 
came to prevail and was introduced by Descartes, the 
" Father " of modern philosophy. Far more radical than 
the earlier conception, it denied to animals not only the 

* Ideas are copies of fonner sensations, feelings and other psychic 
experiences and retain also the accidental signs which belonged to those 
earlier experiences. They are images in the concrete, such as the 

memory of a certain horse in a certain definite situation say a 

well-fed, long-tailed one standing at a manger. A concept, on the other 
hand, is a mental construct which has its rise in ideas, or memory- 
images, in that their essential characteristics are abstracted. For this 
reason the concept has not a definite image<ontent. (Thus the thought 
of " horse " in general, is a concept. Not so the thought of a certain 
individual horse, that is an idea, with a definite image-content.) 


power of abstract thought, but every form of psychic 
life whatever, and reduced the lower form to a machine, 
which automatically reacted upon external stimuli. This 
daring view, however, prevailed for only a comparatively 
short period; but owing to the opposition which it 
aroused, it gave a tremendous impetus to the study of 
animal consciousness. Most of the great philosophers 
following Descartes, such as Locke, Leibniz, Kant, and 
Schopenhauer, however greatly they may have differed 
in other points, in this one returned to the Aristotelian 
point of view. 

A third belief avers that animal and human conscious- 
ness do not differ in essentials, but only in degree. This 
conclusion is regularly arrived at by those who regard 
so-called abstract thought itself, as simply a play of in- 
dividual sensations and sensation-images, as did the 
French and British associationists (Condillac and the 
Mills). The superiority of man accordingly consisted 
in his ability to form more intricate ideational complexes. 
Again, this conception of the essential similarity of the 
human and the animal psyche has also always been ar- 
rived at by the materialists (from Epicurus to C. Vogt 
and Biichner) who impute reason to the animal form as 
well as to man. The same position is, furthermore, taken 
by the evolutionists, including those who do not subscribe 
to the doctrines of materialism. It has almost become 
dogma with them that there exists an unbroken chain 
of psychic life from the lowest protozoa to man. 
Haeckel, preeminently, though not always convincingly, 
sought to establish such a graded series and thus to 
bridge the chasm between the human and the animal 

Two tendencies, therefore, are discernible in animal 


psychology. The one seeks to remove the animal psyche 
farther away from the human, the other tries to bring 
the two closer together. It is undoubtedly true that many 
acts of the lower forms reveal nothing of the nature of 
conceptual thinking. But that others might thus be 
interpreted cannot be denied. But need they be thus in- 
terpreted ? — There lies the dispute. A single incontrovert- 
ible fact which would fulfil this demand, [i.e., proof of 
conceptual thinking] , would, at a stroke, decide the ques- 
tion in favor of those who ascribe the power of thought 
to the lower forms. 

At last the thing so long sought for, was apparently 
found : A horse that could solve arithmetical problems — 
an animal which, thanks to long training, mastered not 
merely rudiments, but seemingly arrived at a power of 
abstract thought and which surpassed, by far, the highest 
expectations of th* greatest enthusiast. 

And now what was it that this wonderful horse could 
do? The reader may accompany us to an exhibition 
which was given daily before a select company at about 
the noon hour in a paved courtyard surrounded by high 
apartment houses in the northern part of Berlin. No 
fee was ever taken. The visitor might walk about freely 
and if he wished, might closely approach the horse and 
its master, a man between sixty and seventy years of age. 
His white head was covered with a black, slouch hat. 
To his left the stately animal, a Russian trotting horse, 
stood like a docile pupil, managed not by means of the 
whip, but by gentle encouragement and frequent reward 
of bread or carrots. He would answer correctly, nearly 
all of the questions which were put to him in German. 
If he understood a question, he immediately indicated 
this by a nod of the head; if he failed to grasp its im- 


port, he communicated the fact by a shake of the head. 
We were told that the questioner had to confine himself 
to a certain vocabulary, but this was comparatively rich 
and the horse widened its scope daily without special 
instruction, but by simple contact with his environment. 
His master, to be sure, was usually present whenever 
questions were put to the horse by others, but in the 
course of time, he gradually responded to a greater and 
greater number of persons. Even though Hans did not 
appear as willing and reliable in the case of strangers 
as in the case of his own master, this might easily be 
explained by the lack of authoritativeness on their part 
and of affection on the part of Hans, who for the last 
four years had had intercourse only with his master. 

Our intelligent horse was unable to speak, to be sure. 
His chief mode of expression was tapping with his right 
forefoot. A good deal was also expressed by means of 
movements of the head. Thus " yes " was expressed by 
a nod, " no " by a deliberate movement from side to 
side; and "upward," "upper," "downward," "right," 
" left," were indicated by turning the head in these di- 
rections. In this he showed an astonishing ability to 
put himself in the place of his visitors. Upon being 
asked which arm was raised by a certain gentleman op- 
posite him, Hans promptly answered by a movement to 
the right, even though seen from his own side, it would 
appear to be the left. Hans would also walk toward the 
persons or things that he was asked to point out, and he 
would bring from a row of colored cloths, the piece of the 
particular color demanded. Taking into account his 
limited means of expression, his master had translated a 
large number of concepts into numbers ; e. g. : — the letters 
of the alphabet, the tones of the scale, and the names of 


the playing cards were indicated by taps. In the case of 
playing cards one tap meant " ace," two taps " king," 
three " queen," etc. 

Let us turn now to some of his specific accomplish- 
ments. He had, apparently, completely mastered the 
cardinal numbers from i to loo and the ordinals to lo, at 
least. Upon request he would count objects of all sorts, 
the persons present, even to distinctions of sex. Then 
hats, umbrellas, and eyeglasses. Even the mechanical 
activity of tapping seemed to reveal a measure of in- 
telligence. Small numbers were given with a, slow 
tapping of the right foot. With larger numbers he 
would increase his speed, and would often tap very 
rapidly right from the start, so that one might have 
gained the impression that knowing that he had a large 
number to tap, he desired to hasten the monotonous 
activity. After the final tap, he would return his right 
foot — which he used in his counting — to its original 
position, or he would make the final count with a very 
energetic tap of the left foot, — to underscore it, as it 
were. " Zero " was expressed by a shake of the head. 

But Hans could not only count, he could also solve 
problems in arithmetic. The four fundamental pro- 
cesses were entirely familiar to him. Common fractions 
he changed to decimals, and vice versa; he could solve 
problems in mensuration — and all with such ease that it 
was difficult to follow him if one had become somewhat 
rusty in these branches. The following problems are 
illustrations of the kind he solved.* " How much is f 
plus J^ ? " Answer : A- (In the case of all fractions Hans 
would first tap the numerator, then the denominator; in 

* All examples mentioned are cited from extant works of various 


this case, therefore, first 9, then 10). Or again: " I have 
a number in mind. I subtract 9, and have 3 as a re- 
mainder. What is the number I had in mind?" — 12. 
" What are the factors of 28 ? " — Thereupon Hans tapped 
consecutively 2, 4, 7, 14, 28. " In the number 365287149 
I place a decimal point after the 8. How many are there 
now in the hundreds place ? " — 5. " How many in the 
ten thousandths place ? " — 9. It will be noticed, there- 
fore, that he was able to operate with numbers far ex- 
ceeding 100, indeed he could manipulate those of six 
places. We were told that this, however, was no longer 
arithmetical computation iii the true sense of the term; 
Hans merely knew after the analogy of 10 and 100 that 
the thousands take the fourth place, the ten-thousands 
the fifth, etc. If an error entered into Hans' answer, he 
could nearly always correct it immediately upon being 
asked : " By how many units did you go wrong ? " 

Hans, furthermore, was able to read the German read- 
ily, whether written or printed. Mr. von Osten, how- 
ever, taught him only the small letters, not the capitals. 
If a series of placards with written words were placed 
before the horse, he could step up and point with his 
nose to any of the words required of him. He could 
even spell some of the words. This was done by the aid 
of a table devised by Mr. von Osten, in which every 
letter of the alphabet, as well as a number of diphthongs 
had an appropriate place which the horse could designate 
by means of a pair of numbers. Thus in the fifth hori- 
zontal row " s " had first place ; " sch " second, " ss," 
third, etc.; so that the horse would indicate the letter 
"s" by treading first 5, then i, "sch," by 5 and 2, 
" ss " by 5 and 3. Upon being asked " What is this 
woman holding in her hand?" Hans spelled without 


hesitation: 3, 2; 4, 6; 3, 7; i.e., " S chirm " (parasol). 
At another time a picture of a horse standing at a manger 
was shown him and he was asked, " What does this 
represent?" He promptly spelled "Pferd" (horse) 
and then " Krippe " (manger) . 

He, moreover, gave evidence of an excellent memory. 
In passing we might also mention that he knew the value 
of all the German coins. But most astonishing of all was 
the following: Hans carried the entire yearly calendar 
in his head ; he could give you not only the date for each 
day without having been previously taught anew, but 
he could give you the date of any day you might mention. 
He could also answer such inquiries as this : " If the 
eighth day of a month comes on Tuesday, what is the 
date for the following Friday ? " He could tell the time 
to the minute by a watch and could answer off-hand the 
question, " Between what figures is the small hand of a 
watch at 5 minutes after half-past seven ? " or, " How 
many minutes has the large hand to travel between seven 
minutes after a quarter past the hour, and three quarters . 
past ? " Tasks that were given him but once would 
be repeated correctly upon request. The sentence: 
" Brticke und Weg sind vom Feinde besetzt " (The 
bridge and the road are held by the enemy), was given 
to Hans one day and upon the following day he tapped 
consecutively the 58 numbers which were necessary for a 
correct response. He recognized persons after having 
seen them but once — yes, even their photographs taken 
in previous years and bearing but slight resemblance. 

A corresponding high degree of sensory activity 
seemed to accompany these astonishing feats of memory 
and reason. Although the horse is not usually credited 
with a very keen sense of vision, Hans was able to count 


the windows of distant houses and the street urchins 
cHmbing about on neighboring roofs. He had an ear 
for the most subtle nuances of the voice. He caught 
every word, — no matter how softly it was spoken — so 
that we were not allowed to whisper the answer to a 
problem, even when standing at a distance of several 
yards, since it would be equivalent — so Mr. von Osten 
declared — to giving the result to the horse. 

Musical ability also comes into the category of Hans' 
accomplishments. He possessed, not only an absolute 
tone consciousness — a gift granted to few of us in the 
human world — which enabled him to recognize a note 
sounded or sung to him as c, d, etc. (within the once 
accented scale of c-major), but also an infallible feeling 
for intervals, and could therefore determine whether two 
tones, sounded simultaneously, composed a third or fifth, 
etc. Without difficulty he analyzed compound clangs into 
their components ; he indicated their agreeableness or 
disagreeableness and could inform us which tones must be 
eliminated to make consonance out of dissonance. C, d 
and e were given simultaneously and Hans was asked: 
" Does that sound pleasant ? " He shook his head. 
" What tone must be omitted to make it pleasant? " Hans 
trod twice — indicating tone " d." When the seventh 
chord, d-f-a-c, was sounded, he shook his head disap- 
provingly. He evidently was old-fashioned in his musical 
tastes and not agreeably disposed toward modern music, 
so he indicated by tapping that the seventh, c, would 
have to be eliminated ; thus changing the seventh chord 
to a minor chord in order to obtain harmony. When 
asked what tones might not be given simultaneously 
with the fourth and sixth, Hans indicated consecutively 
the third, fifth and seventh ; that the first might be added, 


he was ready to admit. Finally, he was familiar with not 
less than thirteen melodies and their time. 

Not only in the high degree of development of the 
senses and the intellect, but also in that of the feeling and 
the will, did Hans possess a decided individuality. Being 
of a high-strung and nervous temperament and governed 
by moods, he evinced strong likes and dislikes, and fre- 
quently displayed an annoying stubbornness, — a fact often 
dwelt upon by Mr. von Osten. He had never felt the 
whip, and therefore often persisted in wilfully answering; 
the simplest questions incorrectly and a moment later 
would solve, with the greatest ease, some of the most 
difficult problems. Whenever any one asked a question 
without himself knowing the answer, Hans would in- 
dulge in all sorts of sport at the questioner's expense. 
We were told that the sensitive animal could easily per- 
ceive the questioner's ignorance and would therefore 
lose confidence in, and respect for, him. It was felt to 
be desirable, however, to have just such cases with cor- 
rect responses. Often, too, Hans would persist in giving 
what seemed an incorrect reply, but which was later dis-. 
covered to be correct. On the other hand it was useless 
to try to get answers upon topics of which he knew 
nothing. Thus he ignored questions put in French or 
Latin and became fidgety, thereby showing the genuine- 
ness of his achievements ; but upon topics with which 
he was familiar he could not be led astray. Indeed, 
there was nothing but language lacking to make him 
almost human and the intelligent animal was declared 
by experienced educators to be at about the stage of 
development of a child of 13 or 14 years. 

This wonderful horse, which in the opinion of its 
friends was the means of deciding in the affirmative the 


old, old, question of the rationality of the lower forms 
and thus changing radically the existing Weltan- 
schauung, aroused world-wide interest. A flood of ar- 
ticles appeared in the newspapers and magazines, two 
monograph^''' attempts at explanation were devoted to 
him.* He was made the subject of popular couplets, and 
his name was sung on the vaudeville stage. He appeared 
upon picture post-cards and upon liquor labels, and his 
popularity was shown by his reincarnation in the form 
of children's playthings. Many personages of note who 
had seen the horse's exhibitions, declared, some of them 
in public statements, that they were now convinced. 
Among these, besides Mr. Schillings, were naturalists 
of note ; e. g. : the African explorer Prof. G. Schwein- 
furth. Dr. Heinroth and Dr. Schaff, the director of the 
zoological garden in Hanover; there were likewise 
horse-fanciers of first-rank, such as General Zobel, and 
the well-known hippological writer Major R. Schoen- 
beck. Again, the well-known zoologist, K. Mobius, 
writing in the " National-zeitung " declared he was 
convinced of the horse's power to count and to solve 
arithmetical problems. He also said that he believed 
the horse's memory and acute power of sense-dis- 
crimination to be at the root of the matter. Those 
who gleaned all their knowledge of the horse from news- 
paper reading were satisfied to arrest judgment, or, on 
the other hand, became indignant at the supposed im- 
position on the part of the gentleman of leisure and at the 
gullibility of the public. Some would of course attempt 
explanations on the basis of older facts. Here we have 
two points of view. 

» The works referred to in the text are to be found listed on pages 
267 ff. 


Some tried to explain the whole thing on the basis of 
purely mechanical memory and would thus allow the 
title " learned " but not " intelligent " Hans. If, for in- 
stance, he was able to indicate the component of a clang 
of three tones, it was not because he had the power to 
analyze the tone-complex, but because he was able to 
see the stops of the harmonica and was accustomed to 
give one tap for every stop which was closed. If he 
was able to tell time by the watch, it was not because 
he read it, but because he was always asked at the same 
hour of the day (which, of course, was contrary to fact) 
and because he had learned by heart the necessary 
number of taps. They also said that his manifold arith- 
metical achievements were merely the expression of a 
remarkable memory; that in the animal brain, lying 
fallow for centuries, there was stored up a tremendous 
amount of energy, which here had been suddenly 
released. They justified their point by calling to mind, 
in this connection, the wonderful memory of primitive 
races. The authors of the two monographs already, 
mentioned, Zell and Freund, adopted this ' mnemo- 
technic ' interpretation, and the latter considered that he 
had disposed definitely of the problem in designating the 
horse — a " four-legged computing machine." 

Another group would not even allow Hans the glory 
of a wonderful memory. He knew nothing. Rather 
was he to be regarded as a stupid Hans, and totally 
dependent upon signs or helps given by his master. 
Only a very few believed, however, that such signs — the 
nature of which was quite unknown or regarding which 
only vague unsubstantiated suppositions were advanced 
— were given unintentionally. Most of the critics openly 
averred that we here had to do with intentional control,' 


in other words, with tricks. But not Only did stupid 
orthodoxy dispose of the matter in this way, but also the 
enlightened, who believe everything unusual to be con- 
trary to reason. They put the Hans problem on a level 
with spiritualism, and were convinced that if the veil 
were removed a crass imposition would be revealed. 
Professional trainers who regarded themselves as well 
informed did not hesitate to give expression to this same 
view, even though they had observed Hans inad- 
equately or not at all. 

The defenders of this second point of view were not 
at a loss to point out the signs supposed to be given to 
Hans. One of these believed he had discovered the 
primary means for giving these signs in the slouch hat 
of Mr. von Osten. It was no accident, they said, that 
Mr. Schillings wore a slouch hat when he experimented 
with the horse. It is sufficient to note that Mr. Schil- 
lings was usually bare-headed or wore only a cap when 
he tested the horse. Another accused, in like fashion, 
the long coat of the experimenter ; a third, who " had 
had opportunity to observe Hans on several occasions," 
declared with equal certainty that the cue lay in the 
movements of the hand as it was thrust into the pocket 
filled with carrots. One circus-star declared, that the 
trick lay in eye movements, another such star declared it 
lay in the movements of the hand. A sixth discovered 
that the signs were " manifold " and adds, " to be sure, the 
trainer must have a fund of such signs in order to prevent 
embarrassment." Such a hypothesis is itself, it would 
seem, one of embarrassment. On the other hand, there 
were many first-class observers who vainly tried to dis- 
cover regularly recurring signs; among them the only 
professional trainer, — who had devoted any satisfactory 


length of time to the horse and had also sought diligently ? 
for the signs in question— said, " I was fully convinced 
that I would be able to explain the problem in this way, 
but I was mistaken." The president of the "Inter- 
nationale Artisten Genossenschaft," a person who knew 
all the usual means of' control in trick performances, went 
over to the other side as a result of his observations. 

There were others who sought for auditory signs. The 
opinion was expressed that " Hans was unable to answer 
the simplest question such as 'What is two plus three?' 
whenever the questioner's tone of voice differed from 
that of the master's." Another put chief stress upon the 
changing inflection ; furthermore, a " high degree of 
auditory sensitivity " was often offered in explanatibn. f 

The sense of smell was also made to bear some bur- 
dens. With its help, for instance, Hans was believed to 
be able to recognize the photograph of some one present, 
supposing, of course, that the person had carried the 
picture about with him, thus allowing it to be impreg- 
nated with his peculiar personal odor. One even sug- 
gested that the heat radiating from the questioner's body 
and the electric stimulus conducted underground to 
Hans's foot were sufficient explanation for his remark- 
able feats. 

Even the so-called N-rays, of one-day fame, which 
were supposed to radiate from the human brain when in 
activity, were offered as a solution. A similar thing may 
have been in the mind of the " natural philosopher " who 
even after the publication of the December report, wrote ' 
as follows in one of the journals : " On the basis of most 
careful control, I have come to the conclusion, that the 
brain of the horse receives the thought-waves which radi- 
ate from the brain of his master; for mental work is, 


according to the judgment of science, physical work." 
Of the same character are the explanations of two others, 
one of whom declares that Hans was acting " under the 
magnetic influence of man ", while the other declared that 
" hypnotic suggestion is involved ", and, ignoring attested 
facts, tells us that, " The horse can execute the com- 
mands of another only when the master, with whom it is 
' en rapport ', wills that it shall obey." We may close 
the catalogue of explanations with one more, which, in 
spite of its vagueness, found many defenders, viz: sug- 
gestion. Without defining this conception more specifi- 
cally and without the slightest notion of the peculiar diffi- 
culties which it involves (L. Loewenfeld in his " Hand- 
buch des Hypnotismus " [Wiesbaden, 1901, pp. 35ff.] 
cites twenty different definitions of the term given by as 
many authors) a critic writes: "The astounding phenom- 
enon of an animal apparently possessing human reason 
is to be attributed solely to suggestion ". Having re- 
ferred to a dog trained for the vaudeville-stage, the gen- 
tleman concludes that, " our intelligent horse, as well as 
the dog, is simply of fine nervous organization and hence 
highly susceptible to suggestions ". 

What was to be done, with this mass of conflicting ex- 
planations? Everyone considered his own opinion the 
only correct one, without, however, being able to con- 
vince anyone else. The need here was not simple affirma- 
tion, but proof. 



A. Experimental Conditions 

The observations on the horse under ordinary condi- 
tions would have been quite insufficient for arriving at a 
decision as to the tenability of the several possible ex- 
planations. For this purpose experimentation with con- 
trolled conditions was necessary. 

It was necessary, first, that the place in which the 
experiments were performed should be guarded against 
sources of error and interruptions. Several diffi- 
culties stood in the way of the removal of the horse to a 
more convenient place. Therefore, a large canvas tent 
was erected within the courtyard of Mr. von Osten. This 
afforded the necessary isolation without hindering the 
free movements of the horse. After the essential part of 
the experiment had been completed and the problem had 
been practically solved, experimentation was sometimes 
conducted in the open courtyard. A number of the ex- 
periments were also performed in the horse's stall. 

The choice of proper persons to experiment with the 
horse required careful consideration. In so far as ob- 
servations were to be made upon the questioner, Mr. 
von Osten was of course indispensable. But to obviate 
every objection he, as well as Mr. Schillings, had to be 
excluded from the greater part of the experiments, and 



other persons had to be selected who could learn to handle 
the horse. Now one would have thought that the horse 
would respond to any moderately efficient examiner. But 
as a matter of fact it was found that the horse would not 
react at all in the case of the greater number of persons. 
Again, in the case of others he would respond once or 
twice, but would then cease. All told, Hans responded 
more or less readily to forty persons, but it was only when 
he worked with Mr. von Osten or with Mr. Schillings, 
that his responses were at all dependable. For this reason 
I undertook to befriend the horse, and by happy chance it 
came to pass in a short time he responded as readily to 
my questions as to those of the two gentlemen. In a few 
of these experiments the Count zu Castell, Count R. von 
Matuschka and Mr. Schillings undertook the role of 
questioner. Where these are not mentioned in the re- 
sults here published, I myself did the questioning. 

With regard to the number of experiments and their 
performance, the following precautions were observed. 
A sufficiently large number of tests was made in each 
series in order to obviate the possibility of the contention 
that the horse's errors were due to chance. The condi- 
tions of experimentation were such that the further con- 
tention that he happened to be tired or otherwise indis- 
posed, whenever the reactions seemed to be inadequate, 
could not be offered. The possibility of confusing the 
horse by means of unwonted conditions also had to be 
avoided. For this reason it was necessary to alternate the 
trial in which procedure was with the knowledge of the 
answer on the part of the questioner, with the trial in 
which the procedure was without such knowledge. Such 
precautions had hitherto been neglected, and therefore 
those negative results which had been occasionally ob- 


tained in single trials, could not claim objective validity, 
even though the persons making the tests were subject-; 
ively convinced. 

The course of the experiments was determined by the 
nature of the problem itself. By means of a very simple 
test it was possible to discover whether or not Hans was 
able to think independently. He was confronted with 
problems in which the procedure was without knowledge" 
of the answer on the part of the questioner. If under" 
these conditions he could respond with the correct an- 
swer — which could be the result of a rational process 
only — then the conclusion that he could think independ- 
ently, was warranted. The examination would be closed 
and Mr. von Osten would be justified in all he claimed 
for the horse. If, however, Hans should fail in this test, 
then the conclusion that he could think was by no means 
warranted, but rather the inference that he was dependent 
upon certain stimuli received from the questioner or the 
environment. Further investigation would be for the pur- 
pose of discovering the nature of these stimuli. 

To ascertain by means of which sense organ or organs 
the horse might receive these necessary stimuli, the 
method of elimination was employed. We began by ex- 
cluding visual stimuli by means of a pair of very large 
blinders. Should this investigation be without results, 
then we would proceed to test the sense of hearing. The 
elimination of auditory stimulations would be more diffi- 
cult, because ear-caps or the closing of the passage by 
means of cotton would not give sufficient assurance that 
the sound-waves were being interrupted, even if the horse 
were docile enough to sufifer these appliances. There- 
upon would follow the testing of the sense of smell and 
of the skin-senses. And finally there might be involved 


another still unknown sense, such as seems to exist in the 
lower animal-forms. The reader therefore can readily see 
that the investigation might possibly have become very 
complex, and that the investigator had to be prepared for 
all of these possibilities. 

The results of the experiments and the essential cir- 
cumstances under which they were conducted, were in 
every case recorded immediately. 

It goes without saying that in the final formulation of 
the results, all values — including those which were not 
consonant with the majority — were to be used. 

B. Experimental Results 

During the course of these experiments Hans wore 
his accustomed trappings, i. e., a girdle, light headgear 
and snaffle, and he either stood alone, untied, or was held 
loosely by the bridle either by the questioner or (though 
only in a few instances) by his attendant. The ques- 
tioner always stood to the right of the horse, as Mr. von 
Osten had been accustomed to do. As reward for correct 
responses Hans received from the questioner * — and from 
him only — a bit of bread or carrot, and at times also a 
square of sugar. Never was a whip applied. From time 
to time the horse was led about the courtyard or was al- 
lowed to run loose in order to secure the needful respite. 
Besides myself there was usually present Prof. Stumpf 
and Dr. von Hornbostel, who kept the records, and fre- 
quently also Mr. von Osten. Several times I worked 
alone with the horse. The results obtained in the horse's 
stall were in no respect different from those got in the 

* The expressions questioner and experimenter are used interchange- 
ably in this treatise. 


course of the experiments carried on in the courtyard. 
Whenever a doubt arose as to the number of taps made 
by the horse (though this did not frequently occur), then 
the series in question was immediately repeated. 

In this report of the results of our experiments, the 
reader must bear in mind that it was impossible to adhere 
to that order and distribution of tests which we are wont 
to require in the case of psychophysical experiments con- 
ducted under regular laboratory conditions. All sorts of 
difficulties had to be overcome: unfavorable weather, the 
crowds of curious ones, certain peculiarities of the horse 
— such as shying whenever the wind rippled the canvas 
of the tent — and last but not least, the idiosyncrasies of 
Mr. von Osten who repeatedly attempted to interrupt the 
progress of the experiments. 

Since it was evident that different kinds of processes 
were involved in solving the problems and since the solu- 
tions would be indicated by tapping, or by movements of 
the head, or by walking over to the object to be desig- 
nated, the results of these three sets of experiments have 
been grouped under three corresponding heads. 

/. Problems solved by tapping 

The following tests were made in which the method 
was such that when the problem was presented to the 
horse, the correct solution was known to none of those 
present, least of all to the questioner. This method we 
shall designate in the following report as "procedure 
without knowledge " whereas we shall call the method in 
which the answer was known to the questioner, "pro- 
cedure with knowledge ". 

In order to discover if the horse could read numbers, 


a series of cards on which numerals were blazoned, were 
exposed to the horse's view in such a way that none of 
those present was able to see them, and the horse was 
asked to tap the numbers as they were shown. This ex- 
periment was repeated at different times and in all there 
were 49 tests in which procedure was without knowledge, 
and 42 in which procedure was with knowledge. In the 
case of the former there were 8% correct responses, 
whereas in the case of the latter 98% of the answers were 
right. As an example of the course which the series 
tended to take, we insert the following, in which Mr. von 
Osten himself acted as questioner. 


No. exposed. 

No. tapped. 








































3 etc. 

Whenever the questioner knew the solution, nearly all 
of the horse's answers were correct; but when the an- 
swers were unknown to the questioner, the horse's re- 
sponses were, with only a few exceptions, quite unsuc- 
cessful. Since the few exceptional cases must be re- 
garded as fortuitous, the conclusion is warranted that the 
horse was unable to read numerals without assistance. 

In order to discover whether the horse could read 
words such as "Hans" or "Stall" or the names 
of colors, they were written upon placards and hung 


up in a row before the horse in such a way that the 
questioner could see the individual word but could not 
immediately recognize the particular place that each one 
occupied in the series. The horse was then asked: 
" Upon which placard is the word ' Hans ' ?, " On which 
is the word ' Stall ' ? ", etc. In order to make sure, he 
was required to repeat each answer. 

Then the experimenter would determine for himself 
the place of the word in the series and would ask the 
question again. Fourteen such tests, in which the pro- 
cedure was with knowledge on the part of the ques- 
tioner, were interspersed with twelve in which the pro- 
cedure was without such knowledge. With the latter 
there were no correct responses, whereas in the cases of 
procedure with knowledge ioo% of the answers were 
correct. Evidently the horse could not read words. 

Three words were thereupon whispered in his ear, 
which he was asked to spell in accordance with the method 
described on page 21. Since he had to indicate first the 
row, and then the place in the row occupied by the letter, 
it took two answers to indicate the position of each letter. 
I acted as questioner. The ordering of the table of let- 
ters was unknown to me, except the position of the letter 
" a ", which naturally came first, and the place of the 
letter " s ", concerning whose position I had purposely 
inquired. The words chosen for this experiment were 
" Arm ", " Rom " (Rome) and " Hans ". The horse re- 
sponded incorrectly in the case of every letter which was 
unknown to the questioner. " A " and " s " alone were 
given correctly. Thus in spelling the word " Rom " the 
horse responded with the series 3, 4 ; 3. 4 ; 5, 4 ; 5, 4 ; i. e. 
" j jst ", instead of the correct series : 4, 6 ; 4, 2 ; 3, 7. I 
later selected three other words, the spelling of which in- 


volved the tapping of thirty-two numbers on the part of 
Hans, and whose position I had carefully ascertained be- 
forehand. When these were given to the horse to spell, 
he responded promptly without a single error. Evidently 
Hans was unable to spell without assistance of some sort 
from the questioner. 

The horse's reputed aptitude in computation was tested 
in the following way. Mr. von Osten whispered a num- 
ber in the horse's ear so that none of the persons present 
could hear. Thereupon I did likewise. Hans was asked 
to add the two. Since each of the experimenters knew 
only his own number, the sum, if known to anyone, could 
be known to Hans alone. Every such test was imme- 
diately repeated with the result known to the experi- 
menters. In 31 tests. in which the method was procedure 
without knowledge, 3 of the horse's answers were correct, 
whereas in the 31 tests in which the method was pro- 
cedure with knowledge, 29 of his responses were correct. 
Since the three correct answers in the cases in which pro- 
cedure was without knowledge evidently were accidental, 
the results of this series of experiments show that Hans 
was unable to solve arithmetical problems. 

For the purpose of discovering whether the horse could 
at least count, the Russian kindergarten device, which Mr. 
von Osten had used in training^ was utilized. The ma- 
chine was placed before the horse, but the experimenter 
turned his back upon it. Before each test, a number of 
balls were pushed to one side and Hans's problem was to 
indicate the number thus separated. Each test was re- 
peated with procedure with knowledge. Of eight such 
experiments Hans responded successfully every time pro- 
cedure was with knowledge but failed every time pro- 
cedure was without knowledge. Thus 7 balls were at one 


time designated as 9 and later as 14, while 6 were at first 
designated as 12, and later as 10. Since all these errors 
could not be accounted for on the ground of miscounts 
on the part of the horse, it was evident that Hans is quite 
unable to count. 

The memory-test was conducted in the following man- 
ner. In the absence of the questioner a number or the 
name of some day of the week was spoken to the horse. 
The experimenter would then return and question him. 
Of 10 responses 2 were correct, 8 incorrect. Among the 
correct answers were the number 3, a number which, as 
we shall see, Hans was prone to give under all sorts of 
conditions, and which therefore meant very little when 
given as a correct response. The number 2, on the other 
hand, was consecutively indicated by 7, 9, 5, and 3, 8 was 
given as 5, 6, 4, and 6, consecutively ; and finally Wednes- 
day was indicated as the fourteenth day of the week. 
After this we undertook the test the horse's far-famed 
knowledge of the calendar. Dates, such as Feb. 29, 
Nov. 12, etc., were given to Hans and he was asked 
to indicate on which day of the week they fell. Sunday 
was to be indicated by i, Monday by 2, etc. Of 14 such 
tests, 10 were unsuccessful, 4 successful. But in the case 
of these 4 something very interesting occurred. It hap- 
pened that during this series the keeper of the horse was 
present, and he happened to know the days on which 
these dates fell, — as he himself testified. The dates in 
question were also little more than a week or so from the 
day of the experiment, so they could easily be deter- 
mined. But as soon as we took more remote dates both 
man and beast were hopelessly lost. It was certain that 
Hans had no knowledge of the calendar. It is needless 
to say anything of -his supposed knowledge of cards and 


coins. Hans plainly was incapable of the astonishing 
feats of memory which had been claimed for him. 

Finally we investigated Hans' musical ability. In a 
room adjoining the horse's stall there was a small har- 
monica, which spanned the once accented octave. On this 
one or more tones were played. The horse was required 
to indicate the tone played, the number of tones played 
and their relation to one another. For testing his general 
hearing 20 tests were given in which the method was pro- 
cedure without knowledge. Of the responses only one 
was correct, and that one was the tone e, for which the 
proper response was three taps, but we must bear in mind 
what has already been said of the number 3. The tone 
b was indicated by 11 taps, although Hans had only 
learned a scale of one octave and therefore could respond 
to only seven tones. In the tests in which the method 
was procedure with knowledge, he again, without excep- 
tion, was successful. Similar results were obtained in the 
analysis of compound clangs. In the cases of procedure 
without knowledge (although the experimenter here 
knew the correct responses, he purposely refrained from 
thinking of them) not a single response was correct; 
while in the cases of procedure with knowledge, all but 
one were correct. The following were typical re- 
sponses: Three tones were played and the question was 
asked, " How many tones were played ? " Hans re- 
sponded first with 4 taps and then with i. The tones 
c, e, g, a, (i, 3, 5, 6) were struck and the question asked, 
" Which tone must be eliminated to make the complex a 
chord?" In the tests in which the method had been 
procedure with knowledge, this question had always been 
answered correctly, but when procedure was without 
knowledge the responses were first 13, a tone which does 


not exist for Hans, then 2, a tone which was not given 
in the clang to be analyzed, and finally 3, which was not 
the discordant tone. Hans's far-famed musical ability 
was an illusion. 

Taking the results of all the tests into consideration, 
we find that in the case of procedure with knowledge, 
90 to 100% of the responses of the various series were 
correct, whereas, in those series of procedure without 
knowledge 10%, at most, of the responses were correct. 
Under the conditions prevailing during these latter tests, 
even these 10% must be regarded as due to chance. To 
be sure Mr. Grabow, a member of the school board and 
an enthusiastic follower of Mr. von Osten (Zeitschrift 
fiir Padagogische Psychologic, Pathologic und Hygiene, 
Berlin, 1904, Jahrg. 6, Heft. 6, S. 470), mentions a large 
number of successful tests, which were supposedly made 
in accordance with the method of procedure without 
knowledge. A thorough analysis of his experiments was 
not possible, because the conditions under which they 
were conducted were not adequately specified. But I 
have no doubt that' the successful responses of the horse 
were due solely to the absence of precautionary meas- 
ures. I, too, could cite a number of seemingly correct 
responses which demonstrably were due to the absence 
of adequate precautionary measures. I therefore repeat :;j 
Hans can neither read, count nor make calculations. He 
knows, nothing of coins or cards, calendars or clocks, nor 
can he respond, by tapping or otherwise, to a number 
spoken to him but a moment before. Finally, he has not 
a trace of musical ability. 

After all this experimentation it was evident that the 
horse was unable to work alone, but was dependent upon 
certain stimuli from its environment. The question^ 


therefore arose : does the horse get these stimuli while 
the question is being put, or during his responses, i. e., 
during the process of tapping. 

If Mr. von Osten's opinion was correct, then the 
process of questioning played an important part in the 
success of the experiment. Of course, as he said, it was 
not necessary to ask the question aloud ; it was suiiScient 
— curiously enough — that it be inwardly spoken, thanks 
to the horse's extraordinary auditory sensitivity. If, how- 
ever, conditions were made such that the auditory sense 
was eliminated, then the animal would be unable to re- 
spond. Such a theory is not quite as absurd as it might 
seem at first blush. For Hansen and Lehmann have shown 
that an acute auditory organ is able to respond to such 
delicate stimulation as is involved in the softest whisper, 
or even in the so-called nasal whisper in which the lips 
are tightly closed.^ They have attempted thus to ex- 
plain any modes of supposed " thought-transference ", 
(cf. page 7). Since experts on horses agree that the 
horse has acute auditory sensitivity, Mr. von Osten 
seized upon this fact and tried to establish his theory in 
the following manner. No response was successfully 
made on the part of the horse, he said, when the sound 
waves caused by his (Mr. von Osten's) inner speech were 
deflected from the ear of the horse. This was the case 
when he closed nose and motith while inwardly putting 
the question, or deflected the waves from the horse's ear 
by means of a placard held before his mouth while speak- 
ing, or finally by applying lined ear-muffs to the horse's 
ears. If, on the other hand, he closed only his nose and 
not his mouth while thus inwardly putting the question, 
or if he held the placard so that there was a possibility of 
deflecting the sounds to the horse's ear, or if the ear- 


muffs were of too sheer a material, then Hans could hear 
and answer the questions which for human ears were 
inaudible. He demonstrated all this by means of experi- 
ments and of 20 tests of the first kind, in which auditory 
sensations were supposedly eliminated, 95% of the re- 
sponses were incorrect (Hans would always tap too great 
a number) ; whereas of 28 tests of the second kind, not 
a single answer was wrong, just as had been predicted. 
Now I have repeated both kinds of tests, but have al- 
ways found some correct responses in those cases in 
which the horse, supposedly, was unable to hear, a thing 
which greatly astonished Mr. von Osten. In fact, the 
responses of the horse were quite as correct when I did 
not even whisper the question inwardly. It was quite 
clear that putting the question in any form whatever was 
wholly unnecessary. Mr. von Osten's demonstrations to 
the contrary, which were based upon erroneous physical 
principles, are to be explained as cases of vivid auto- 
suggestions, (but of this, more in Chapter V). After 
all this experimentation, it was manifest that the cue was 
not given to the horse while the question was being put; 
it occurred, therefore, at some time during the process of 
tapping. But by means of which sense organ was it 
received by the horse? 

We began by examining the sense of vision, and in the 
following manner. Blinders were applied, and it is 
worthy of mention that Hans made no attempt to resist. 
The questioner stood to the right of the horse, so that 
the animal knew him to be present and could hear, but 
not see him. Hans was requested to tap a certain num- 
ber. Then the experimenter would step forward into the 
horse's field of vision and would put the same problem 
again. Since, in the tests of the first kind, Hans would 


always make the most strenuous efforts to get a view of 
the questioner, and since he would rave and tear at the 
lines whenever the attempt was made to tie him, — a thing 
which he had never done hitherto, — it was impossible to 
determine in some cases whether or not he had seen the 
questioner during the process of tapping. I am using, 
therefore, in the following exposition, besides the two 
categories of " not seen " and " seen ", a third which I 
have called " undecided ". A total of 102 tests were made 
in which large blinders were used. In 35 of these, the 
experimenter certainly was " not seen " in 56 cases he 
was " seen " and the remaining 1 1 are " undecided ". 
Under the first of these categories 6% of Hans's answers 
were correct (i. e. only two), under the second head 89% 
were correct and under the third 18% were right. In 
other words, the horse was at a loss the moment he was 
prevented from seeing the questioner; whereas his re- 
sponses were nearly always correct when the experi- 
menter was in sight, certain proof that the horse's failures 
are to be attributed to the elimination of visual stimuli 
and not to the general inconvenience occasioned by the 
blinders. It is evident therefore, that the horse required 
certain visual stimuli or signs in order to make a correct 

* Throughout this treatise I am using the word " sign," or " signal," 
whereas all other writers who have touched upon the Hans-problem, 
have always spoken of " aids." Following von Sanden,* however, I 
would distinguish clearly between the two. I would designate as aids 
all immediate stimulations of the horse's body (i. e. by means of con- 
tact), which have been designed with reference to the animal's physio- 
logical movement-mechanism in such a way that they truly ' aid ' him. 
in the production of the required movements. I would regard as signs 
on the other hand, all stimulations (whether mediate or immediate) 
which are selected without especial regard to the anatomy or physiology 


Such unequivocal results, however, were only obtained 
after we had provided blinders of sufficient size (15 X 15 
centimeters). Mr. von Osten believing that the horse 
would not suffer these to be applied, had at first proposed 
other measures. He held a slate before his face. Some 
of the horse's responses were right, others wrong. The 
tests were repeated and were successful as long as I, my- 
self, held the slate before my face, but not a single one 
of the responses was correct when another would attempt 
to hold the slate before me. Mr. von Osten then brought 
forth a kind of bolster which he fastened on the right 
side of the horse's face, — the side which was turned to- 
ward the questioner. But this also gave uncertain re- 
sults. Finally he agreed to apply blinders. But these 
were much too small and projected at a great angle from 
the head (Mr. von Osten had cut the straps, for he 
thought they worried the animal). The result was that 
only the posterior part of the horse's normal field of vision 
was obstructed. Therefore, one could never be quite 
sure whether Hans, who — it will be borne in mind — made 
every attempt to see the questioner, had not perhaps after 
all been able to peer over the edge of the blinder. The 
number of " undecided " tests, therefore, became very 
great. Of 108 tests, only 25 could be placed in the 

of the horse, and bear no inseparable relation to the thing to be done 
but are associated with it at the will of the trainer. The rider's use 
of reins, and control by means of leg-pressure and manner of sit- 
ting in the saddle, and the driver's use of the lines, all these, then 

are aids. A simple pull at the reins, however, is not an aid, but a sign. 

The whip may be used for giving signs as well as aids, the latter, 

when it does the work of the spur or of the pressure with the 
knees, as is the case with ladies' riding-horses and in lunging. All calls 
and all movements of the hand or head merely, on the part of the 
trainer, are to be regarded as signs. 


category of " not seen ", 44 in the " seen ", and 39, i. e., 
a third of the total, in the " undecided." The percentage 
of correct answers for these three categories were, respec- 
tively: 24%, 82% and 72%. Here we have once more 
approximately the same ratio between the categories of 
" seen " and " not seen " as in the case of the tests with 
the smaller blinders. If we were to count the cases 
which we had put under the head of " undecided," in the 
same category as those in which vision had been ex- 
cluded — as Mr. von Osten had done — then one would 
have been led to the conclusion that the horse did not 
need visual signs. Several observers had thus been led 
astray : e. g.. General Zobel writes in the " National- 
Zeitung" (Aug. 28, 1904), that upon request Mr. von 
Osten had covered Hans's right eye " by means of some 
sort of blinder, so that he was unable to see his in- 
structor ", and that Hans did not fail to respond cor- 
rectly. We evidently have here to do with the unreliable 
bolster mentioned above. Furthermore, Mr. Schillings 
made a number of tests with the small blinders, in which 
50% of the answers were correct, and probably in the 
same manner were obtained the results published in one 
of the daily papers (the " Berliner Tageblatt ", Dec. 12, 
1904), several days after the publication of the December 
report, and reading as follows : " Tests have been made 
upon Hans with blinders over his eyes and it is to be 
noted that, in spite of these, he still responds correctly." 
Mention is also made of the experiments noted in Supple- 
ment III (page 257), in which Mr. von Osten hid be- 
hind the questioner and merely encouraged the animal 
by occasional exhortations, but it is not possible to say 
with any degree of certainty in how far he was really 
hidden from the horse's view. 


I would add that the horse— in so far as it was at all 
possible to decide — never looked at the persons or the ob- 
jects which he was to count, or at the words which he 
was to read, yet he nevertheless gave the proper responses. 
But he would always make the most strenuous efforts to 
see the questioner. (See page 43). I would further- 
more add that several experiments, in which Mr. von 
Osten and the horse were separated from each other by 
means of the canvas tent, failed completely, and that, on 
the other hand, all tests were successful in which the ques- 
tioner was present in the feed-room and the door between 
this and the horse's stall was opened wide enough for him 
to be seen by the horse. I would also mention that to- 
ward evening the responses became less and less accurate. 
The conclusion that visual stimuli were here operative 
cannot be gainsaid. 

It was possible, to be sure, that other senses might also 
be involved, but it was certain that auditory sensations 
did not enter it. This is shown by the fact that one might 
remain just as silent while the horse was tapping his 
answer as during the putting of the question and yet 
obtain a correct response. Hans, furthermore, could 
scarcely be distracted by auditory stimulations. If either 
the experimenter or anyone else present sought, at a given 
moment, to interrupt him by such calls as " Hah ", 
" Wrong ", etc., while he was going through the process 
of tapping, they very seldom succeeded in their attempt. 
Even though such interruption did succeed in seven out 
of the twenty-one cases in which it was tried, the assump- 
tion is well grounded that the success was due entirely 
or almost entirely to minimal movements involuntarily 
executed by those attempting the interruption. It is to 
such minimal movements that the horse, as we shall 


see later, promptly reacted. When the experimenter 
(Pfungst), himself, made the interjections, which cer- 
tainly should have been more effective, we found that the 
horse was actually disturbed in only two of the fourteen 
cases; and finally in ten consecutive cases of attempted 
interruption not a single one was successful. There was 
almost a complete absence of any ear movements on the 
part of the horse, a fact in which I have been borne out 
by Mr. Henry Suermondt, the distinguished horseback 
rider. Indeed, I cannot recall that Hans ever turned his 
ears toward me, a fact which is strikingly curious in the 
case of a horse so attentive and so spirited in temper. 

Finally, I might also mention that the breathing of the 
experimenter in no wise influenced the outcome of the 
experiment. Whether he held his breath or breathed on 
the leg or body of the horse, made no difference. 

Investigations of the other senses became needless, for 
I had, in the meantime, succeeded in discovering the es- 
sential and effective signs in the course of my observa- 
tions of Mr. von Osten. These signs are minimal move- 
ments of the head on the part of the experimenter. As 
soon as the experimenter had given a problem to the 
horse, he, involuntarily, bent his head and trunk slightly 
forward and the horse would then put the right foot for- 
ward and begin to tap, without, however, returning it 
each time to its original position. As soon as the desired 
number of taps was given, the questioner would make a 
slight upward jerk of the head. Thereupon the horse 
would immediately swing his foot in a wide circle, bring- 
ing it back to its original position. (This movement, 
which in the following exposition we shall designate as 
"the back step", was never included in the count.) 


Now after Hans had ceased tapping, the questioner would 
raise his head and trunk to their normal position. This 
second, far coarser movement was not the signal for the 
back-step, but always followed it. But whenever this 
second movement was omitted, Hans, who had already 
brought back his foot to the original position and had 
thereby put it out of commission, as it were, would give 
one more tap with his left foot. 

If it was true that these movements of the questioner 
guided the horse in his tapping, then the following must 
be shown : First, that the same movements were observed 
in Mr. von Osten in every case of successful response; 
secondly, that they recurred in the same order or with 
only slight individual changes in the case of all who were 
able to obtain successful responses from the horse, and 
that they were absent or occurred at the wrong time in 
all cases of unsuccessful response. Furthermore, it was 
observed that it was possible to bring about unsuccessful 
reactions on the part of the horse as soon as the move- 
ments were voluntarily suppressed, and conversely, that 
by voluntarily giving the necessary signs the horse might 
be made to respond at pleasure ; so that anyone who pos- 
sessed the knowledge of the proper signs could thereby 
gain control over the process of response on the part of 
the horse. These requirements have all been fulfilled, as 
we shall see in the following pages. 

With regard to the regular recurrence of the move- 
ments noticed in the case of Mr. von Osten, I was, after 
some practice, able to note carefully their peculiar char- 
acteristics. This was rather difficult, not only on account 
of their extreme minuteness, but also because that very 
vivacious gentleman made sundry accompanying move- 


ments and was constantly moving back and forth. To 
abstract from these the essential and really effective 
movements was truly difiScult. It was much easier to 
observe these movements in the case of Mr. Schillings, 
probably on account of the fewer accompanying move- 
ments and perhaps on account of their greater distinct- 
ness. Usually he would raise the entire trunk a trifle, so 
that the movements could be noticed from behind. Be- 
sides these, I had an opportunity to observe the Count 
zu Castell, Mr. Hahn and the Count Matuschka. All 
three made the same movements, though somewhat more 
minutely than Mr. Schillings, yet none was as slight as 
those of Mr. von Osten.* I further noticed that Count 
Matuschka and Mr. Schillings often showed a tetidency 
to accompany every tap of the horse with a slight nod 
of the head, the last being accompanied by a more pro- 
nounced nod and then followed by the upward jerk of the 
head, in other words, they beat time with the horse. In 
the case of the last three mentioned, for whom the horse 
responded far less effectively than for Mr. von Osten or 
Mr. Schillings, belated or precipitate jerks would fre- 
quently occur. This was found to be true in the case of 
all other persons who had failed to elicit adequate re- 

* During the tests Mr. von Osten neariy always wore a slouch hat 
with a wide rim. The rim, of course, always moved with the head, and 
made the movements appear on a larger scale, (in the ratio of about 
3 : 2, as I was able to ascertain later by graphic methods). But obser- 
vation was successful, even at a distance of a meter and a half, when he 
worked with head uncovered. And even if head and forehead were 
covered entirely, it was still possible to note the movements by watch- 
ing the eye-brows. When Mr. Schillings and the rest of us worked 
with the horse, we either went bare-headed or wore only a very small 


sponses from the horse. Often, in both cases, a com- 
plete absence of any kind of minimal movement had been 
noted. The accuracy of these observations in the case 
of Mr. von Osten is attested by Mr. Stumpf and Mr. von 
Hornbostel, and by these same gentlemen and Prof. F. 
Schumann in the case of Mr. Schillings and myself. 
They also found these movements to be most minute in 
the case of Mr. von Osten. In my case also they pro- 
nounced them " minimal, and often quite imperceptible ". 
All other persons who have seen me work with the horse, 
but who were not familiar with the nature of these move- 
ments, never perceived them, no matter how closely they 
observed me. 

Since the doubt was expressed that these movements 
did not precede but followed closely upon the back-step of 
the horse (i. e', that an error with regard to the time- 
element was involved), it became important that time 
measurements be taken. This was done in the following 
manner : The questioner asked the horse to tap numbers 
from 5 to 20, seldom higher. He purposely refrained 
from pronouncing the number, but recorded it after each 
test had been completed. This was a matter of indiffer- 
ence to the horse (see page 42), and had the advantage 
that the measurement was not influenced by knowledge 
on the part of the time-keeper. Two observers were 
required, one watching the horse, the other the questioner. 
Both observers had fifth-second stop-watches. The larger 
face of this watch shows the fifth-second and a hand 
on the smaller face indicates the minute. Bv pressing 
upon the stem the watch may be set in motion at any 
moment desired, and by pressing it once more it may 
be instantly stopped, and the time clasping between 


the setting in motion and the stopping may be read on the 
face. By pressing upon the stem a third time the hands 
are brought back to zero, and the watch is ready for 
another test. At a moment agreed upon beforehand — 
usually the third tap of the horse — both observers started 
their watches. Practice tests had shown that this could 
be done with all the accuracy necessary in this case. As 
soon as the observer of the questioner noticed the latter's 
head movement he stopped his watch, and as soon as the 
observer of the horse noticed the latter's back-step he 
stopped his watch. Since the movement of the horse's 
foot does not occur as a jerk, but is of greater extent than 
a jerk would be, it was agreed that the observer was to 
stop the watch as soon as he recognized the back-step as 
such, not when the foot was being raised from the 
ground, because it was not then evident whether the horse 
would bring it back to the original position or whether 
he was preparing to give another tap, nor when he had 
brought his foot completely back, but at the moment in 
which it was evident that the horse intended to make the 
back-step. Experimentation had shown that an agree- 
ment as to this moment was possible. A tap with the 
left foot, which might possibly follow upon the back-step, 
could be left out of account. The difference in time be- 
tween the two watches would show the time between the 
head-jerk of the questioner and the back-step of the 
horse,* and if the back-step was indeed a reaction upon 

* For the benefit of those who are familiar with reaction-time ex- 
periments of this kind, I would state the following : The reaction to the 
head-jerk, on account of the minuteness of the latter, was sensory 
throughout, and therefore all precipitate reactions are entirely wanting. 
The reaction to the back-step was, like the preceding one, a reaction 


the head-jerk, then the watches would have to show a later 
time for the back-step than for the head-jerk. 

Measurements of this kind were taken for Mr. von 
Osten, Mr. Schillings and myself. In the case of the 
first two it was taken without any knowledge on their 
part. They did not even know that they were being ob- 
served, having been told that the measurements were for 
the sake of determining the horse's rate. In my case, to 
be sure, the time could not be taken without my knowl- 
edge. I succeeded, however, in eliminating the effect of 
this knowledge on my part. (Cf. pages 88 and 145.) 
Since the results obtained in the case of Mr. Schillings 
quite agree with those obtained in my case, it is evident 
they may be considered as being of equal value. 

With regard to the number of tests the following table 
may be referred to. The first vertical column gives the 

to a visual cue. (Hans's tapping was almost quite inaudible). Both 
stop-watches were carefully regulated. In order to eliminate also the 
constant error which might possibly arise as a result of some difference 
in the functioning of their pressure-mechanism, the two watches were 
always exchanged in the different series of tests, by the observer of the 
man and the observer of the horse. The two time-measurements ob 
tained by the two observers contained, of course, the reaction-times of 
the observers themselves. In order to equalize the constant error which 
thereby arose, it was arranged that each observer should react alternately 
now to the man, now to the horse. In order to be perfectly safe, the 
reaction-times of those concerned, (von Hornbostel, Pfungst, Schumann 
and Stumpf), were later determined in the laboratory by means of the 
carefully regulated Hipp chronoscope. Separate determinations were 
made of the reactions to the head-jerk and to an imitation of the horse's 
back-step. Then the time which one observer took to react upon a 
head-jerk, was compared vrith the reaction-times of the other observers 
to the back-step. Since the greatest difference which was found in this 
comparison, did not exceed one-tenth second, the results obtained in the 
courtyard required no correction. 


name of the questioner, i. e. the person operating with 
the horse. The four other columns give the number of 
tests made upon each of these. The name of the person 
who made the observation in each series is indicated at 
the head of the column. It is unnecessary to give the 
name of the observer of the horse, for the only difficulty 
lay in the observation of the questioner. The numerals 
I and II indicate two series taken at different times. 

V. H. 









V. Osten 

9 'S 

■ 34 17 

- — 

8 27 

- — 

19 17 

6 16 

Pf ungst 

6 13 

— — 

9 — 

We have omitted from this table several tests in which 
the observer of the questioner noticed no head jerks 
whatever, and therefore could not arrest his stop-watch, 
although the horse responded correctly. Four tests of 
this kind were made by Mr. von Hornbostel, two by Mr. 
Pflingst, two by Mr. Schumann and five by Mr. Stumpf. 
In the case of Mr. Pfungst the horse gave the unusually 
high number of fifty taps. The attention of the observer 
had been taxed too long and had failed him (two seconds 
is the most favorable time). The head-jerk of Mr. von 
Osten evidently occurred during a lapse in Mr. Pfungst's 
attention and therefore remained unnoticed. 















V. Osten. 








100^ 22ir 






100^ — 

o^ - 











The results of the experiments are given in the second 
table. The general arrangement corresponds to that of 
the first table. Even though the absolute number of tests 
was small, yet for the sake of giving a better general 
view, all values are given in percentages. The tests in 
which the movement of the questioner had preceded that 
of the horse — as had been anticipated — are recorded 
under "R" (right); under " W" (wrong), we have 
recorded those cases in which the testimony of the stop- 
watches — contrary to our expectation — indicated that the 
reverse order prevailed. Finally, those cases which would 
complete the 100%, i. e. those in which the watches in- 
dicate simultaneity of the movements in question, are not 

From this table we may note the following: The time- 
measurements for Mr. Schillings and Mr. Pfungst are 
quite in agreement and go to show that the order in time 
of the head movement of the questioner and the back- 


step of the horse was exactly what had been expected. 
The few contradictory cases which occur in Series I of 
the observations upon Mr. Schillings are to be accounted 
for by the fact that he was here for the first time the 
subject of observation, whereas the recorded time-meas- 
urements in the case of Mr. Pfungst had been preceded 
by a number of practice tests. The results of the meas- 
urements taken in the case of Mr. von Osten were far 
less satisfactory. Even if one were to allow a series con- 
taining barely more than 50% of " right " cases as suf- 
ficient proof of the correctness of our expectation regard- 
ing the order of the movements of the questioner and the 
horse, only three of the six series obtained with Mr. von 
Osten as subject, would satisfy this expectation. How- 
ever, since four of the six series show a greater number 
of cases of simultaneity (their percentage may be easily 
deduced by referring to the per cent of " right " and 
"wrong" cases), the proposed method would give a dis- 
torted view, and therefore it appears that the more cor- 
rect method would be to consider simply the numerical 
ratio of the " right " and " wrong " cases. Since, further- 
more. Series II shows, in every case, a decided change 
which is similar for all observers (note especially 
Pfungst), there can be no doubt but that practice is here 
involved, and that Series II is to be regarded as the true 
standard. Throughout this series we find a preponder- 
ance of " right " cases. Therefore, the table unmistaka- 
bly confirms the expected order in time. That there were 
more "wrong" cases with Mr. von Osten as subject than 
with the other questioners is to be explained by the fact 
that the decisive movements were far less easily observed 
in this case, than in that of the other questioners. (See 
page 49.) We expect that Series III would show the 


same results, or approximately the same results in the 
case of Mr. von Osten that it did for Mr. Pfungst and 
Mr. Schillings, but unfortunately he declined to act as 
subject. In the meantime, however, new and decisive 
proof presented itself which destroyed all possible doubt. 

Before adverting to it, let us consider in a few words 
the reaction-time of the horse, — the time elapsing between 
the final sign of the questioner and the reaction of the 
horse (i. e., the back-step). Unfortunately this time can- 
not be directly determined. All that can be ascertained 
from our time-measurements, is the time intervening 
between the moment of the head-jerk and the moment in 
which the reaction of the horse is noted. (See page 51). 
This time averaged, for the 127 measurements, .45 sec- 
onds. If we stated the unavoidable error, (obtained on 
the basis of extended supplementary measurements which 
it is not necessary to consider here) as .15 seconds, and 
apply it to the value found above, we obtain .3 seconds 
as the probable reaction-time of the horse.* 

That the tapping — as well as all other movements of the 
horse — was nothing other than a reaction upon certain 
visual stimuli, was proved beyond a doubt by the fact that 
the voluntary execution of the head-jerk and of other 
movements — which we will describe in more detail later 
on, — ^brought about all the proper responses on the part of 
the horse. Thus, artificial synthesis became the test 
of the correctness of analytical observation. 

To elucidate ; if the questioner retained the erect posi- 
tion he elicited no response from the horse, say what he 

* See page 126 on the corresponding reaction-time in the case of man. 
Similar tests have been made in the case of animals in only one instance, 
and that for dogs, by E. W. Weyer.' But, as might have been expected, 
they did not yield any satisfactory results. 


would. If, however, he stooped over slightly, Hans would 
immediately begin to tap, whether or not he had been 
asked a question. It seems almost ridiculous that this 
should never have been noticed before, but it is easily 
understood, for as soon as the questioner gave the problem 
he bent forward — ^be it ever so slightly — in order to 
observe the horse's foot the more closely, for the foot was 
the horse's organ of speech. Hans would invariably 
begin to tap when I stooped to jot down some note I 
wished to make. Even to lower the head a little was 
sufficient to elicit a response, even though the body itself 

Fig. I. 

might remain completely erect. Of thirty tests made in 
this position, twenty-nine were successful. Hans would 
continue to tap until the questioner again resumed a com- 
pletely erect posture. If, for instance, I stooped forward 
after having told the horse to tap 13, and if I purposely 
remained in this position until I had counted 20, he would, 
without any hesitation, tap 20. If I asked him to add 3 
and 4, but did not move until 14 was reached, he would 
tap 14. Twenty-six such tests gave similar results. 

The reaction of the horse upon such a signal for 
stopping showed slight modifications according to the 


time which elapsed between the last tap and the signal 
for stopping. These modifications, which had hitherto 
been paraded as expressions of the horse's psychical power 
may be illustrated by the following schematic figures 
'(Figures i — 4). In all of them the dotted line c-d rep- 
resents the ground level ; d shows where the horse's right 
forefoot was located before he began tapping; a and c, 
respectively, indicate the place to "which the foot is lowered 
during the process of tapping. The unbroken line gives 
the direction of the back-step. 

If Hans, having raised his foot from a to b — prepara- 

FlG. 2. 

tory to tapping, — receives the signal at or just before the 
moment he lowers the foot, he immediately swings it in a 
wide circle from c back to its original position at d, 
(Fig. i). As a matter of fact a and c coincide, but are 
juxtaposed in the diagram for the sake of schematic 
utility.) This was the usual form of the back-step. 

If the signal for stopping is given a little after the 
last tap (Fig. 2), i. e., at the time that the foot is already 
being raised for another tap, then the back-step occurs 
as a-b-d. The horse thus gives, at the moment it receives 
the signal for stopping, a changed impulse to the moving 


foot. The curve, therefore, has a kink at b, and the back- 
step occurs with seeming hesitancy, — Hans appears not 
quite certain of his result. 

If the signal be given somewhat later still (Fig. 3), i. e., 
when the foot is being lowered to complete a tap, Hans is 
still able to put on the brakes — as it were — and draw back 
his foot before it reaches the ground. The whole process 
gives the impression that the horse was just about to make 
a " mistake " of one unit, but at the last moment had 
bethought himself of the correct answer. 

Finally, if the signal be deferred still longer, it becomes 

Fig. 3. 

impossible to prevent the extra tap. The back-step again 
has the same form as in figure i ; Hans has made a 
" mistake " in his answer by one unit too many. 

Conversely, if the head-jerk of the questioner occurs too 
soon ; i. e., at the moment the horse has raised his foot for 
the final tap to the height b, (Fig. 4), then the tap is not 
completed, — but the foot, without touching the ground, 
makes the curve b c^ d, back to its original position. 
Hans has again made a " mistake " in his answer,— this 
time by one unit too few. 

All these variations go to show one thing : Hans never 


knows in advance which tap is to be the final one. These 
variations in his reactions occurred often without having 
been intended by the questioner. But to bring them 
about at will required skill, on account of the shortness of 
the time involved in the reaction. 

Whenever the signal for stopping — which we have 
just discussed — was followed by the complete erection of 
the head and trunk, Hans would definitely cease tapping. 
If, however, the questioner failed to assume a completely 
erect position, or if he stooped forward ever so slightly, 
the horse would follow the back-step of the right foot 

Fig. 4, 

with an extra tap of the left foot. Besides occurring in 
tests in which Mr. von Osten assumed the role of ques- 
tioner, this fact was also noted when the Count zu Castell 
and Mr. Schillings acted as subjects. Since the extra 
tap just mentioned was not given like the others with the 
right foot forward, but with the left foot upon the spot, 
it was possible for the horse to execute it with a greater 
show of energy. This simulated a high degree of mental 
certainty on the part of the horse, as if he wished to 
indicate that this was the correct solution of the problem 
and it would have to stand. In spite of all this, many 


errors would creep in. It was possible to prolong this 
extra tap and thus make it appear more dilatory. We 
need hardly add that henceforth it was within the power 
of the experimenter to have the tapping executed entirely 
with the right foot or with the final extra tap of the left 
foot. Hitherto the view had been current that this lay 
solely within the pleasure of the horse. 

If the questioner still inclined forward, still remained 
in the bent posture after Hans had given the final tap 
with his left foot, the horse would immediately begin to 
tap once more with his right foot, which had, in the mean- 
time, become ready for further action. If the head jerk 
was then made, Hans would bring his right foot back, 
give the extra tap with his left foot, then resume tapping 
with the right and thus continue until the questioner once 
more resumed the erect posture. Thus the horse on one 
occasion when I wished him to tap lOO, gave — contrary 
to my desire — the following response; 39 with the right 
foot, I with the left, 24 with the right, i with the left, 35 
with the right, and i with the left. Later it became 
possible for me to cause him to tap i right, i left, i right, 
I left, etc. I could even get him to tap exclusively with 
the left foot by standing at his left rather than at his right 
as had been customary with his questioners. These taps 
with the left foot were executed in a far less elegant 
fashion than those with the right foot, and with a great 
waste of energy. Hans had become a right-handed 
individual — as it were — as a result of long habit. 

With regard to the distance at which the experimenter 
directed the horse, the following may be said : The usual 
distance was one-quarter to one-half meter. This holds 
for all tests hitherto described. Seventy tests which were 
made for the purpose of discovering the influence of 


change in distance showed that the reaction of the horse 
upon the customary signal of the head-jerk was accurate 
up to a distance of three and one-half meters. At a 
distance of three and one-half to four meters there sud- 
denly occurred a fall of 60-70% in the number of correct 
responses. At a distance of four to four and one-half 
meters only one-third of the responses were correct, and 
at a distance beyond four and one-half meters there were 
no correct responses. The greater number of these tests 
were made in our presence by Mr. von Osten, who was 
under the impression that we were testing the accuracy of 
the horse's hearing, whereas we were really testing the 
accuracy of his perception of movements. 

With regard to the different positions which the experi- 
menter might assume with reference to the horse, the 
following may be noted : The normal position was to the 
right of the horse. If the experimenter stood immediately 
in front of Hans, the latter 's reaction would be just as 
accurate, though he would always turn his head and 
make desperate efforts to see the questioner, even though 
he was held in short by the reins. When a position im- 
mediately behind the horse was taken — a somewhat 
dangerous proceeding, since Hans would at once begin 
to kick — no response could be obtained until he succeeded 
in turning far enough around to get the questioner within 
view. If he was restrained from turning completely 
around, he would at least turn his head, — and always to 
the right. One might even turn his back upon Hans 
during the tests, for the signal for stopping was not 
obtained from the face of the questioner, but from a move- 
ment of the head. The following incident will show to 
what extent the horse had become accustomed to seeing 
the questioner in a certain definite position. For a long 


time I had been in the habit — without exception — of 
standing close to the horse's shoulder. Mr. von Osten, 
on the other hand, would stand farther back. When, on a 
certain day, I assumed the latter position, the horse would 
not suffer it, but would move backward until he had his 
accustomed view of me. 

Finally we sought to discover by what movements the 
horse could be made to cease tapping. We discovered 
that upward movements served as signals for stopping. 
The raising of the head was the most eilective, though 
the raising of the eyebrows, or the dilation of the nostrils 
— as in a sneer — seemed also to be efficacious. However, 
it was impossible for me to discover whether or not these 
latter movements were accompanied by some slight, 
involuntary upward movement of the head. The upward 
movement of the head was ineffective only when it did not 
occur as a jerk, but was executed in a circuitous form, — 
first upward and then back again. Such a movement was 
occasionally observed in the case of Mr. von Osten. The 
elevation of the arms or of the elbow nearest the horse, or 
the elevation of the entire body was also effective. Even 
if a placard, with which the experimenter tried to cover 
his face, were raised at a given moment, the horse would 
make the back-step. On the other hand, head movements 
to the right and to the left or forward and back, in fine, 
all horizontal movements, remained ineffective. We also 
found that all hand movements, including the " wonder- 
fully effective thrust of the hand into the pocket filled with 
carrots ", brought no response. I might also change my 
position and walk forward and then backward some dis- 
tance behind the horse, but the back-step would only occur 
in response to the characteristic stimulus. After what 
has been said it is easy to understand how vain were Mr. 


Schillings' attempts to disturb the horse and how naturally 
he might conclude that Hans was not influenced by visual 
signs. Mr. Schillings simply did not know which signs 
were effective. 

While the horse could thus be interrupted in the process 
of tapping by movements which were executed at the 
level of the questioner's head, yet movements below this 
level had the opposite effect. If Hans showed that he 
was about to cease tapping before it was desired, it was 
possible to cause him to continue by simply bending for- 
ward a trifle more. The greater angle at which the 
questioner's trunk was now inclined caused the horse to 
increase the rate of tapping. The rule may be stated 
thus: The greater the angle at which the body inclined 
forward, the greater the horse's rate of tapping, and vice 
versa. It was noticeable that whenever Mr. von Osten 
asked for a relatively large number — in which case he 
always bent farther forward than in the case of smaller 
numbers — Hans would immediately begin to tap very 
swiftly. Not being entirely satisfied with these observa- 
tions, the following more exact measurements were taken. 
I asked the horse to tap 20. From i to 10 I held my body 
at a certain constant angle, at 10 I suddenly bent farther 
forward and retained this posture until 20 had been 
reached. If there existed a relationship between the angle 
of inclination and the rate of tapping, then the time for 
the last ten taps ought to be less than for the first ten. 
Of 34 such tests 31 were sucessful. The following are 
two specimen series. 

The first series consisted of ten tests of 15 taps each. 
In all cases my head was bent at an angle of 30° to the 
axis of the trunk, but I constantly changed the angle of 
inclination of the trunk. It was not possible to measure 


this angle accurately on account of the rapidity with 
which the whole test had to be made. I was able, how- 
ever, to diiferentiate between them with enough accuracy 
to designate the smallest angle (about 20°) as belonging 
to Grade I, and the greatest angle (about 100°) as belong- 
ing to Grade VII. By fixing certain points in the environ- 
ment, it was possible to get approximately the same angle 
repeatedly. The time from the third to the thirteenth tap 
was, in all cases, taken by Prof. Stumpf by means of a 
stop-watch. The tests were taken in the following 
order : 

Grade of inclination : I VI II II IV V VI VII 
Time for lo taps : 5.2 4.6 5.0 5.0 4.8 4.8 4.6 4.4 sec. 

From this series it will be seen that in the case of the 
same angle of inclination (II and VI were repeated and 
III was omitted) the same rate obtained in the tapping. 
In two other tests I constantly increased the angle of 
inclination during the 15 taps, and Hans gradually 
increased the rate of tapping accordingly. 

In a second series I had the horse tap 14, five times. 
I myself took the time of the taps up to 7 by means of the 
stop-watch, while Prof. Stumpf took the time of the taps 
from 8 to 13. At 8 I suddenly bent forward a little more 
and retained this position until tap 13. The results were 
as follows : 

Taps 2 to 7 (Pf.) : 3.2 2.2-2.4 2.4 2.2-2.4 2.4 seconds. 
" 8 to 13 (St.) : 2.6 2.0 2.0 2.2 2.2 seconds. 

Such good results, however, were possible only after 
a number of preliminary practice tests had been made. 
The experiment was especially difficult because the horse 
was often on the point of stopping in the midst of a test. 
This was probably due to some unintentional movement 


on my part. In such cases I could induce him to con- 
tinue tapping only by bending forward still more, but this 
effected also, as we have seen, an increase in his rate 
of tapping. Such tests, of course, could not give 
unambiguous results. 

The rate of tapping was quite independent of my rate 
of counting. Thus, if I counted aloud rapidly, but bent 
forward only very slightly, the horse's tapping was slow 
and lagged behind my count. If I counted slowly but 
bent far forward, Hans would tap rapidly and advance 
beyond my count. Thus we see that his rate of tapping 
was in accordance with the degree of inclination of my 
body and never in accordance with the rate of my count- 
ing, i. e., it was quite independent of every sort of auditory 

Direct observation and a comparison of the records of 
the time Hans required in giving to his master responses 
involving small, medium and large numbers, with the 
records of the time which he required to respond to my 
questions when I bent only slightly, moderately or very 
far forward, proved that the increased rapidity in tapping 
in the case of large numbers, which many regarded as an 
evidence of high intelligence, (see page 20), was, as a 
matter of fact, brought about in the way described. The 
two series (in each of which the time measured was for 
ID taps) are quite in accord. The horse did not tap 
faster because he had been given a large number by Mr. 
von Osten, but because the latter had bent farther for- 

From all this it readily appears why it was possible to 
cause Hans to increase his rate of tapping but not to 
decrease it. To do the latter would involve a decrease in 
the angle of inclination of the body. This would neces- 


sitate the erection of the body. As we have seen, this 
was the signal to which Hans reacted by ceasing to tap. 
And as a matter of fact we never knew the horse to 
decrease his rate of tapping in the course of any single 
test, except in the case of very large numbers, and then 
it was probably due to fatigue. Mr. von Osten insisted 
that Hans often slowed down toward the end of a test, 
" in order to obviate mistakes ", but all the tests in which 
he tried to demonstrate this to us, were unsuccessful. In 
spite of all exhortation, Hans would tap either uniformly 
or somewhat more rapidly as soon as his master — in all 
probability unconsciously — bent somewhat lower. Only 
once was such a test successful. Mr. von Osten — upon 
our request — asked the horse to give a certain large 
number. In this instance the decrease in the rate of 
tapping was due to fatigue and had nothing whatever 
to do with the desire on the part of the horse to avoid 
error. Futhermore, Mr. Hahn, who had visited Hans 
twenty times and had made careful notes of his observa- 
tions, corroborated my statement when he said that he 
himself never noted the decrease in rate mentioned. Con- 
trary statements may perhaps be due to the fact that the 
tense state of expectancy on the part of the observer made 
the interval between the last taps appear subjectively 
somewhat longer. 

So much for the technique of the tapping. Now a 
word about the numbers which Hans tapped. (I refer 
only to the results obtained in series which involved no 
volitional control). The number i was very difficult to 
get. Hans usually tapped 2 instead. Thus even in the 
case of Mr. von Osten he responded five times with 2, 
and only in the sixth test did he react correctly. As far 
as other questioners were concerned, i was seldom ever 


obtained, except in the case of Mr. Schillings and myself. 
The numbers 2, 3 and 4, on the other hand, were very 
easily obtained and, above all, 3 seldom failed. 3 seemed 
to be the horse's favorite number and was very frequently 
given instead of other numbers. Thus, one-sixth of all 
the horse's incorrect responses which were given to me 
were in terms of the number 3. The numbers 5 and 6 were 
a little more difficult to obtain and above 10 the difficulty 
increased rapidly. Indeed, I never saw Hans respond 
with a number exceeding 20 to any questioner, Mr. 
Schillings and Mr. von Osten excepted. I saw the nine 
vain attempts of Count zu Castell to get the number 15, 
and Count Matuschka's eight unsuccessful attempts to 
obtain the number 16 as a response. But even with Mr. 
von Osten and Mr. Schillings such failures were not 
infrequent. Thus, Mr. von Osten tried five consecutive 
times to obtain the number 24. I myself did not fare 
any better at first. But the following table shows what 
practice can do. If we compare the percentage of correct 
responses (involving the numbers i to 7 — for which alone 
I have sufficient material, viz., 80 to 100 cases), obtained 
in the first half of our tests, with that of the second half, 
we get the following : 

For number : 1234567 

In first half of tests : 49, 92, 89, 86, 74, 62, S3 % 
" second " " : 92, 95, 92, 98, 97, 86, 96 % 

From this we see how hard it was at first to get the 
number i and that failure was as frequent as success, and 
how much easier it was on the other hand to get the 
numbers 2 and 3 (and which, therefore, do not show any 
great improvement in the second half of the tests). 
Beyond the 3 the percentage of correct responses de- 
creased and the number 7 stood at the same level as the 


number i. In the second half of the tests, all these 
differences disappeared and errors were infrequent and 
seldom exceeded + i or — i . These results of practice are 
not to be accredited to the horse, but to the experimenter, 
who was at first quite unskilled. This difference in results 
does not appear in the case of Mr. von Osten, for his. 
initial practice had been had many years previous. The 
values obtained in his case were very constant throughout 
our experimentation and generally showed something like 
90% of correct responses. To be sure, in his case also, 
the number i was somewhat unfavorable, (79% were 
correct responses). But the percentages obtained in his 
case showed no improvement whatever throughout our 
experimentation. We need scarcely add that with the 
voluntary control of the giving of the signs, in the case at 
least of such small numbers as are here discussed, no 
errors, whatever, occurred. 

We have discussed the influence of the experimenter, 
i. e., the one who asked the horse to tap ; now let us con- 
sider the influence of others present upon the horse. 

As a general rule, other persons had no effect upon the 
horse's responses. This appears from the failure of nearly 
all tests in which all of those present — with the exception 
of the questioner himself — knew the number which the 
horse was to tap. Even when the others concentrated 
their whole attention upon the number, it profited little as 
a close analysis of the 136 cases, which belong under this 
head in our records, go to prove. Thus, in the presence 
of a group of twenty interested persons — during the 
absence of Mr. von Osten — ^twenty-one problems were 
given to the horse, the solutions of which were known to 
everyone but myself, the questioner. Result: only two 
correct responses. Only when there was among the 


spectators someone to whom the horse was accustomed to 
respond or one from whom he regularly received his food, 
would such an influence be effective.* But such cases 

* Mr. Schillings, however, did succeed in making a number of tests 
with the co-operation of others who had never before worked with the 
horse. These tests were made under the follovring conditions: The 
horse was standing in his stall, when Mr. Schillings and another gentle 
man approached him. There was no one else present. Mr. Schillings, who 
tried to remain as passive inwardly, as possible, asked his partner to 
think consecutively of different numbers between one and 20, which thus 
were known to him alone. Hans was then commanded by Mr. Schillings 
to tap the numbers, which he did, to the great astonishment of the men, 
and especially of Mr. Schillings. In like manner Mr. Sander, a staff 
physician in the marine, received — so he writes me — three correct 
responses to four questions which he put to the horse. It happened 
also in the case of two scientific men and finally, too, in my own case 
when I first came in contact with the horse, (see page 88). The horse's 
reaction was brought about in the same way in every one of these 
instances. Mr. Schillings, in bending forward slightly, thereby started 
the horse a-tapping, and his companion — just as innocently — interrupted 
the process by means of a movement of his head, when the right number 
of taps was reached. 

I later tried similar experiments together with Mr. Hahn. I was 
aware of the answer to the riddle at the time, but he was not. Mr. 
Hahn stepped in front of the horse and thought intently of certain 
numbers. I did the questioning, that is, I got the horse to tap. In 
twelve tests Hans responded correctly in only two instances. In the 
ten others he always tapped beyond the number Mr. Hahn had in 
mind, e.g., 21 instead of 2, and was evidently awaiting a movement on 
my part. When we exchanged r61es, Mr. Hahn doing the questioning 
and I doing the " thinking," the horse would not respond at all, although 
as a rule Mr. Hahn had been fairly successful in working with him 
alone. I had gradually gained so much influence over the horse, that 
he would scarcely attend to any one else when I was about — Mr. von 
Osten hardly excepted. 

In this connection I would prefer to avoid the term " rapport," which 
may rise in the minds of many, since it has been used so much in con- 
nection with the phenomena of hypnotism, for I would not obscure a 
fact that is clear by giving it a name that is vague. 


were few. The most important were the following: 
I at one time whispered a number to Hans (on the occa- 
sion of the tests mentioned on page 37), and Mr. von 
Osten asked for it the moment I stepped aside. Hans 
answered incorrectly even though I stood close beside 
Mr. von Osten ; I did not, however, think intently of the 
number. As soon as I concentrated my attention upon 
the number he promptly responded correctly. Further 
cases are those mentioned on page 38, in which the 
keeper of the horse unintentionally aided in giving four 
dates which were unknown to all others present, including 
the questioner. This single instance shows the necessity 
of the rule that during tests in which the method is that 
of procedure without knowledge the solutions should be 
known to no one of those present. Finally the tests made 
by the September-Commission and reported in Supple- 
ment III (page 25s) may possibly belong under this head. 
Since they were not followed out any further, I am unable 
to render a definite judgment upon them. In most of 
these tests the question itself, as put by Mr. von Osten, 
was not adequately answered, but curiously enough, how- 
ever, the number which had been given to Hans in von 
Osten's absence and which formed the initial number of 
some mathematical operation, was tapped correctly. This 
may possibly be explained by the assumption that this 
initial number had been retained in the memory of some 
of those present, (see page 149, on the " perseverative 
tendency "), and that the horse, since he had been working 
with some of them, responded to one of those present. 
Chance may have played some part also. 

If the questioner knew the number of taps desired, 
(which was not the case with the tests hitherto discussed), 
then the environment had still less influence upon the 


horse — except that it caused occasional interruption. The 
horse's responses, therefore, did not tend to become more 
successful just because a number of persons were 
simultaneously concentrating upon the result desired. 
This was proven by the experiments which we repeatedly 
made for this purpose. Only one person at a time had 
any influence upon Hans. If two questioners tried to in- 
fluence the horse at the same time, — other conditions being 
the same, — success would be for the one who had the 
greater control over the animal when working alone with 
him. Prof. Stumpf and I made the following experiment. 
Both of us stood to the right of the horse, each thinking 
of a number. In ten such tests Hans always tapped my 
number. When Stumpf concentrated upon 5 and I upon 
8, the horse responded with 8, i. e., the larger number. 
When Stumpf had 7 in mind, and I had 4, the response 
would be 4, i. e., the smaller number. When Stumpf 
thought of number 6, and I had fixed upon none, Hans 
tapped 35. He was evidently awaiting my signal. When 
I went away Stumpf again demanded the number 6, and 
the horse responded properly. When I returned, Stumpf's 
attempts again failed. On another occasion Count 
Matuschka put a number of questions, while Mr. von 
Osten stood behind him. All of the horse's responses 
were correct, even the one answering the question: 
"How much is 7 times 7?", which was difficult on 
account of the great number of taps required. I was 
able to note from the direction of the horse's eyes that he 
was attending only to his master and not to the Count. 
On still another occasion Mr. Grabow sang two tones— 
the second being the fourth of the first— and asked Hans: 
"How many intervals lie between?" I was standing 
erect before the horse, and was thinking intently of the 


number 2, but without giving any voluntary sign of any 
sort Hans tapped 2, wrhereupon Mr. Grabow put a 
number of similar questions ; but I no longer thought of 
the answers, and all of Hans's responses went wrong. 

Although Hans was not influenced by others so long as 
a suitable experimenter was present, yet he might be 
disturbed and under certain conditions might be led to 
make the back-step in response to certain movements in 
his environment. The person to whom he responded 
would have to be close to the experimenter and would 
necessarily have to execute a movement greater in extent 
than the experimenter's. In such instances the raising of 
the head, arm or trunk, was a sufficient stimulus. Thus 
we made the following two series of tests. Mr. 'Stumpf 
stood with trunk bent forward before the horse, and at 
a moment decided upon beforehand, assumed an erect 
position. I myself stood beside Hans and asked him to 
tap. When I stood at the horse's neck, then Mr. Stumpf 's 
interruption was effective. When I stood at the horse's 
flank, the interruption effected only a seeming hesitation, 
and when I moved still farther back, the horse continued 
to tap despite any attempted disturbance. In the second 
series the questioner remained constantly at the right 
shoulder of the horse, while the one who attempted to dis- 
tract him, changed positions. When the latter stood to 
the right immediately in front of or beside the questioner, 
the distrubance was effective in 10 out of 13 cases. But 
when he stood back of, and to the right of, the questioner, 
the attempts at disturbance were seldom successful. If 
he chose a place before and to the left of the horse, there 
was hardly any distraction (in 4 cases only, out of 13), 
and if he stood to the left and behind the animal, he 
exerted no influence whatever. Hans manifestly turned 


his attention, almost exclusively, to the side at which the 
questioner stood. 

That knowledge of this modus operandi made it 
possible for those persons to get responses from the 
horse, who hitherto had been unsuccessful, is shown in 
the case of Mr. Stumpf when he began to control his 
movements voluntarily on the basis of observations which 
had been made. 

II. Problems which Hans solved by movements of the 


We are here concerned with the horse's head move- 
ments upward, downward, to the right and to the left, 
and also with nodding and shaking of the head to signify 
" yes " and " no ". We soon discovered that these ex- 
periments, also, were successful without an oral state- 
ment of the problem, — in other words, the auditory 
stimulus was quite superfluous. The tests with the 
blinders showed that Hans was lost as soon as his ques- 
tioner was out of his view, but responded adequately the 
moment the questioner was in sight. Hans, therefore, 
had established no idea of any sort in connection with 
the terms " up ", " down ", etc., but in these cases, like- 
wise, he reacted in response to certain visual stimuli. The 
nature of these stimuli I discovered at first in my observa- 
tions of Mr. von Osten and also of myself, when working 
with the horse. 

Above ^11 things it was necessary that the questioner, 
during these tests, should stand perfectly erect. If he 
stooped ever so slightly, the test was unsuccessful. If he 
carefully refrained from any movement whatsoever, and 
looking straight before him asked the horse, "Which 


direction is right? " or " Which way is upward? ", Hans 
would execute all sorts of head movements without rhyme 
or reason. It was evident that he noted that a head move- 
ment of some kind was expected of him, but did not know 
the particular one that was wanted. But if the questioner 
now raised his head, Hans would begin to nod and would 
continue doing so until the questioner lowered his head. 
This reaction was interpreted as signifying " yes ". Mr. 
von Osten had always asked Hans before each of the 
more difficult tests whether he had comprehended the 
meaning of the problem, and was reassured only upon 
seeing the horse's affirmative response. But contrary to 
Mr. von Osten's expectation, Hans also responded in this 
manner after a pair of ear-caps had been drawn over his 
ears. In the case of the tests described at the beginning 
of the chapter, in which the method was that of "pro- 
cedure without knowledge ", Mr. von Osten had always 
insisted that we await Hans's nod of comprehension 
before proceeding. We complied ; Hans nodded and — 
regularly disgraced himself ! 

When the questioner raised his head somewhat higher 
than normal, Hans would throw his own upward, which 
was supposed to signify " upward ". A lowering of the 
head on the part of the questioner was followed by a 
lowering on the part of Hans, which was his form of re- 
sponse for " down ". For some time I was in a quandary 
as to the difference between the questioner's signal for 
this latter response and the one which was the signal for 
the horse to begin tapping, although I had often given 
both kinds unwittingly. Further experiments showed 
that Hans r«sponded with a nod of the head whenever 
the questioner, while bending forward, chanced to stand 
in front of, or to the side of the horse's head, but that 


he would begin to tap in response to the same signal, 
as soon as the experimenter stood farther back. The 
difference in the two signals, therefore, was very slight, 
and I repeatedly noted that instead of tapping, as he had 
been requested, Hans would respond to the Count zu 
Castell's and Mr. Schillings' questions by a nod of the 

If, while standing in the customary position to the 
right of and facing the horse, the questioner would turn 
his head a little to the right — a movement which, when 
seen from the horse's position, would appear to be to the 
left, — Hans would turn his head to his left. But if on 
the other hand the questioner would turn slightly to the 
left, — i. e. seen from the horse's position, to the right, — 
then Hans would turn his head to his right. And finally, 
whenever the questioner turned his head first to the right, 
then to the left, Hans would respond by turning first to 
his left, then to his right. This, according to Mr. von 
Osten, signified " zero " or " no ". Since this movement 
could not be executed by the experimenter while in a 
stooping position, it can now readily be seen why it was 
that Hans, instead of shaking his head, always began to 
tap whenever a placard with " O " upon it, was shown to 
him in the course of the experiments in which the 
method was procedure without knowledge on the part of 
the questioner. The latter expected the horse to tap, and 
therefore bent forward. Like all of the horse's other forms 
of response, this, too, was always unsuccessful when- 
ever the questioner stepped behind the animal. Although 
Hans had always responded to Mr. von Osten and Mr. 
Schillings, and at first also to me, by means of the 
stereotyped movement of the head to the right and then 
to the left to signify " zero " or " no ", I later succeeded 


in controlling my signals so as to get the inverted order 
in the horse's response. In the case of Mr. Schillings and 
of Mr. von Osten all of the movements just described 
were very minute, and long after the movements, which 
were effective stimuli for releasing the process of tapping, 
were recognized, it was still exceedingly difificult to dis- 
cover them in these two gentlemen. The signal for 
" zero " and " no " was relatively the most pronounced of 
the group in the case of Mr. von Osten, while with Mr. 
Schillings it was the least pronounced, in comparison with 
his very strong "jerk". Yet in both cases Hans re- 
sponded wtih absolute certainty. 

It is now readily conceivable how it was possible to 
make the horse respond to all sorts of foolish questions, 
both by involuntary signs — i. e., expressions following 
upon the bare imaging of the response expected, — as well 
as by means of controlled signs. One could thus obtain 
consecutively the answers " yes " and " no " to the same 
question. Or one might ask : " Hans, where is your 
head ? ", and Hans would bend to the earth. " And 
where are your legs ? " He would look at the skies. Etc. 

Let us examine for a moment the directives which the 
horse required for the various positions. If one called 
him, while he was running about the courtyard, he paid 
no attention whatever, but if one beckoned to him, he 
came immediately. A raising of the hand brought him 
to a standstill. If one now stepped forward or pointed 
one's hand in that direction, he would step forward, or 
vice versa, he would step backward. By means of mini- 
mal movements of the head, of the arm nearest the 
horse, or of the whole body, Hans could be induced to 
assume the position one desired, without touching him or 
speaking a word. I noticed this quite early in the course 


of the investigation. Once, when intending to ask the 
horse to step backward to the right, I inadvertently said 
" Step backward to the left ! ", whereupon he stepped 
backward to the right. In spite of my verbal error, I had 
involuntarily given him the proper directives. 

Finally we may note that Mr. von Osten had occa- 
sionally asked the horse to jump or to rear. The com- 
mand in this case was : " Jump ", or the question was : 
" What do the horses do in the circus ? ". Since these 
tests were just as effective when the command was given 
silently, it was an indication that these, too, depended 
upon visual stimuli. What was necessary to cause the 
horse to step backward and then jump forward was to 
step backward oneself, or make a slight movement of the 
hand in that direction. If one wished to make him rear, 
it might be effected by throwing the arm or head slightly 

///. Problems, which Hans solved by approaching the 
objects to be designated. 

The method pursued in these tests was the following: 
From five to eight pieces of colored cloth J^X/4 meters in 
size were arranged in changing series upon the ground, 
the interval between them being equal to the width of 
one piece, or else they were hung upon a string a man's 
height above the ground. This method was also employed 
when placards of like size with written symbols were 
used. The horse stood ten paces away and opposite the 
middle of the series, while Mr. von Osten stood at his 
right. Hans was asked to go and point out the cloth of 
a certain color or the placard with a certain word upon it. 
If the cloth lay upon the ground, Hans picked it up with 


his mouth and carried it to the questioner. If the cloth, 
like the placards, hung from the cord, he approached, 
pointed it out with his nose and then backed up to his 
original position. Before approaching the objects, Hans 
was required to indicate, by tapping, the number of the 
place in the series (counting from left to right), which 
the cloth or placard occupied. Mr. von Osten never 
omitted this requirement. Then the command " Go ! " 
was given, and Hans obeyed. (As a matter of fact, a 
slight directive movement of the head or hand was just 
as effective as the spoken command). 

The following cases, chosen in a haphazard fashion, 
show that the horse's indication of the object's place in 
the series, by means of tapping, was by no means a 
guarantee that he would point it out correctly. Five 
placards hung from the cord. Mr. von Osten asked: 
" What is the position, counting from left to right, of the 
placard which has the word ' aber ' inscribed upon it ? ". 
Hans answered : 3. (It was indeed the middle placard.) 
Then he was commanded : " Go ! ". Thereupon Hans 
went straight to the fourth placard. On another occa- 
sion Hans happened to drop a brown cloth upon a black 
one. His master asked him : " In which place are there 
two cloths ? ". Hans responded correctly, " In the second 
place ". To the question " Which of the two "s the black 
one ? " he also answered rightly : " The lower one ". 
Upon being asked to get it, he brought the white cloth. 

The large number and the irregularities of the errors 
showed that there was no manner of intelligence involved 
in the pointing out process. Thus during the two months 
of our experimentation Hans was asked twenty-five times 
by Mr. von Osten to bring the green cloth. Only six 
times did he succeed in the first attempt, while in five 


instances he selected an orange-colored cloth, four times 
a blue, three times a white one. 

The fact that the errors were equally distributed over 
the tests with the colored cloths and those with the 
placards is strong evidence that the horse's response 
involved no intellectual process, for if that were the case, 
then the responses in the tests with the placards would 
have been very much more difficult, for they would have 
involved the ability to read, whereas the tests with the 
colored cloths demanded only that a few names be 
remembered. Nevertheless, the horse was as unsuccess- 
ful in tests of one kind as he was in those of the other, 
— even when Mr. von Osten acted as questioner. (50% 
failures in 78 placard tests; 46% failures in 103 color 

The fact that commands which were purposely 
enunciated poorly, or else not spoken at all, were executed 
with just as much accuracy as those given aloud, 
strengthened us in our supposition. On one occasion 
I placed a blank placard with the others. When I 
ordered him to approach tabula rasa, he invariably 
went to the right one. The following illustrates how he 
fulfilled quite nonsensical commands. A series of blue 
and green cloths lay upon the ground. Being asked 
where the black, the orange, and the yellow cloths lay, 
Hans shook his head energetically, i. e. they were not 
there. And yet, upon being asked to bring them in the 
order named, he regularly brought one of the blue ones. 

All this goes to show that Hans did not know the 
names of the colors (to say nothing of the symbols on the 
placards). It was plain that here also, as in all the 
other cases, he was controlled by signs made by the 
questioner, the nature of which I soon discovered. Stand- 


ing erect, Mr. von Osten always turned head and trunk 
in the direction of the cloth or placard desired. Hans, 
keeping his eye on his master, would proceed in that 
direction. Even after he had already started out, thanks 
to his large visual field one could control his direction by 
turning slightly more to the right or to the left. If, 
however, he had already arrived at the row of placards or 
cloths, this method ceased to be effective, for then he 
could no longer see the experimenter. It made no dif- 
ference whether the cloths lay on the ground, or were 
suspended, like the placards. 

The following fact justifies the conclusion that the 
bodily attitude of the questioner was the effective signal. 
The more numerous the cloths, or the nearer they were 
placed together, the more difficult one would expect it to 
be for the horse to select the one indicated by the experi- 
menter. Such was indeed the case, for the number of 
errors increased with the number of cloths presented. 

But no matter how many cloths there might be, or how 
closely they might be placed, it was always possible to 
indicate either end of the row, for in that case one had 
merfely to turn to the extreme left or the extreme right, 
and might even turn beyond the row. Hans seldom 
failed in these cases, whereas he made many errors when 
cloths or placards within the series were wanted. 

To turn from the nature and number of Hans's errors, 
to their distribution, — observation proved the hypothesis 
that the nearer two cloths lay together, the greater was 
the chance of their being mistaken one for the other. 
If we designate as " error i " all those cases in which 
Hans went to cloth II instead of to cloth I, cloth III 
instpad of cloth II, to V instead of IV, etc., and as " error 
2". when, he mistook III for I, IV for II, in fine, when- 


ever he went two places too far to the right or left, and as 
" error 3 " whenever he went three places too far to 
either side of the cloth desired, we find the following 
grouping of errors: 

With Mr. von Osten, a total of 63 errors,; 

73% " error i " 

21 ^ :. . " error 2 " 

4% " error 3 " 

1 % " error 4 " 

I % " error 5 " 

With Mr. Pfungst, a total of 64 errors,; 

68 jS " error i " 

20 ^ " error 2 " 

11^ " error 3 " 

I % " error 4 " 

0% " error 5 ". 

The most frequently recurring error, therefore, was the 
one in which the horse, instead of going to the cloth 
desired, approached the one immediately adjacent. On 
page 79 I said that Hans's errors were without system, 
but only in so far as it was impossible to explain them on 
a basis of the colors which seemingly were mistaken one 
for the other. A part of a series in which Mr. von Osten 
acted as questioner may serve as an illustration. The 
order given is that of the experimental series as it 
occurred. Five colored cloths were used. 

Color of the cloth 
asked for : blue, brown, brown, brown, brown, brown, green, green. 

I I I I I I I I 

brought: orange, orange, green, green, yellow, green, blue, orange. 

Place of cloth 

asked for : V 












brought : IV 










The interpretation of this series which it would be hard 
to explain by a reference to the colors which were mis- 
taken, is simply this: Cloths lying near together were 
regularly mistaken on the part of the horse. 

Experimental control of the questioner's movements 
decided the question. If the questioner at first indicated 
the proper direction and then turned about after the 
horse had already started forward, he was as a rule mis- 
led. When the questioner did not face the cloths at all, 
but turned away at right angles, or when he turned his 
back upon them, Hans was completely at sea. If, on 
the other hand, the cloths were arranged, not in a row, 
but in several heaps, so that one might turn to a particular 
heap, but could not indicate a particular cloth, then Hans 
would regularly go to the proper heap, but would always 
bring forth the wrong cloth. After much persuasion Mr. 
von-Osten consented to make a series of these tests him- 
self. Hans's failures were deplorable. He \vould take 
up first one cloth then another, turn again to the first, etc. 
We would mention, however, that this apparent searching 
was not done spontaneously, but in reponse to Mr. von 
Osten's calls, such as "See there!", "The blue!", etc. 
Every time Mr. von Osten called, Hans would drop the 
cloth he was holding in his mouth, or he would turn away 
from the one he was about to grasp, and would then try 
another one. 

In addition to these visual signs, the horse received 
auditory signals in these tests, (as in all others in which 
he was required to bring objects). As soon as the ques- 
tioner noticed that Hans was about to take up the wrong 
cloth, all that was necessary to make him correct his error 
was to give some sort of an. exclamation, such as 
" Wrong! ", " Look, you ! ", " Blue ! ", etc. Hans would 


pass on as long as the calling continued. If he was pick- 
ing up, or about to pick up, a cloth when the exclamation 
was made, he would go on to the next ; but if, at the time 
he was on his way to a certain cloth, he would change his 
direction in response to the call. If he stood before one 
of the pieces at the time, but had not lowered his head, he 
would pass on to the next. In all this he would adhere 
to a certain routine of procedure. If he was approaching 
a series from the right, then a call would cause him to 
turn to the left, if he was coming from the left, he would 
turn to the right. If he had approached the row of 
cloths near the center, he would turn, in response to the 
questioner's calls, to the left, — seldom, very seldom, to the 
right. Mr. von Osten did not seem to be able to control 
the responses of the horse, entirely. As a rule, but not 
always, one call sufficed to make Hans pass on to the next 
cloth. If too many calls were given, he would often go 
too far. Loud exclamations were superfluous. 

These statements are not mere assertions, but are 
founded upon the records of the results. The tests in 
which calls were made show a larger percentage of correct 
responses than do those without calls. Of a total of 103 
tests with colored cloths, which Mr. von Osten performed 
for us, only 37% brought forth successful responses on 
the part of the horse when visual signs were the only 
directives and when there were no directions by means 
of calls, whereas the total percentage of successful re- 
sponses was 54%, if we add to the above those in which 
the vocal exclamations helped to bring about success. 
The corresponding percentages for the total of 78 tests 
with the placards were 23% and 50%. In a total of no 
color tests I myself obtained 31% correct responses under 
the first head, and 56% under the second head. In a 


total of 59 tests with placards I succeeded in getting 31% 
correct responses under the first head and 46% under the 
second head. We must note that without verbal admoni- 
tion only one-third of the tests brought forth correct 
responses, whereas one-half succeeded when those in 
which calls were used, are added. Still, this is a relatively 
poor showing. In the most favorable series that Mr. von 
Osten ever obtained in our presence — and there was only 
one such — 50% of the responses ' without admonition ' 
were correct, and 90% when all the correct reactions, both 
with and without admonition, were taken into account. 

Not all the places in the row required the same amount 
of assistance by means of calls. Those positions which 
needed the most help, were those which it was most 
difficult to indicate to the horse by the visual sign, i. e., 
the attitude of the questioner's body. We noted above 
(page 81) that the cloths at either end of the row were 
less difficult to point out than those nearer the middle. 
If our hypothesis holds true, we would expect that the 
end cloths would involve fewer auditory signals in the 
process of pointing out, and those within the row a 
greater number of such signs. By way of illustration, I 
will cite one series of tests in which Mr. von Osten was 
questioner, chosen not because it is most conformable to ■ 
my hypothesis but because it is the longest (48 consecutive 
tests with five cloths) which I have. In the upper row I 
am placing the successful responses without auditory 
signs, in the lower those involving both auditory and 
visual signs. 

Place of the cloth : I H HI IV V 

No. of sucessful ) visual signs only ; J 2 i 24 

responses. ) visual and auditory signs : S S ^ S S 


We see that without verbal admonition the first and last 
places are most favorable for success, the second and 
fourth far less, and the middle least favorable. These 
differences disappear when admonitions are introduced, 
for all of the places then have the same number of correct 
responses with the exception of the middle, which now has 
even more than the others. 

One more experiment which I made will close the 
discussion. The following colors were placed from right 
to left : orange, blue, red, yellow, black, green. I turned 
my back upon them, and therefore could guide the horse 
by verbal commands only. I asked him to bring the 
orange. Hans approached the yellow. I now called three 
times, allowing a short interval between the calls. At the 
first " Go ! " he passed from the yellow to the red, at the 
second from the red to the blue, and at the third from the 
blue to the orange, which he then proceeded to pick up 
and bring to me. I had noted this same thing in Mr. von 
Osten's tests, although there, there were often other 
factors entering in. By exercising the utmost precision 
in facing the cloths, and by using, in addition, suitable 
oral signs, I succeeded in getting Hans to bring, succes- 
sively, each one of the six cloths in the row, and without 
a single error, — and all this in the presence of Mr. Schil- 
lings who did not have the slightest notion of the secret of 
my success. 

We need hardly say, in passing, that all that was true 
of the tests with colored cloths, was also true of the tests 
in which the placards were used. It was all the same to 
the horse whichever was placed before him. 

We have thus tested all of the horse's supposed achieve- 
ments. None of them stood the critical test. It would 
have been gratifying to have repeated some of the experi- 


ments and to have made Hans the object of further 
psychological investigations, but unfortunately he was no 
longer at my disposal after the publication of the report 
of the December-Commission. Some may say that we 
have had almost enough of a good thing, but we must bear 
in mind that many of the tests which were carried out, — 
such as those in which the method was that of " procedure 
without knowledge ", those in which the ear-muffs were 
used, those in which distractions were introduced, — had 
previously been made by other persons (see pages 41 f, 
45. 63), and with other results, than ours. A more thor- 
ough test, therefore, would have been doubly desirable. 



In the preceding chapter we asked: What is it that 
determines the horse's movements? Independent think- 
ing, or external signs ? — ^We found that it was solely ex- 
ternal signs, which we described as certain postures and 
movements of the questioner. Beyond a doubt these nec- 
essary signs were given involuntarily by all the persons 
involved and without any knowledge on their part that 
they were giving any such signs. This is to be seen 
from their statements, which cannot be cavilled at, as 
well as from the fact that several of them even to-day 
still doubt the correctness of the explanation which we are 
here offering. I myself for some time made these invol- 
untary movements quite unwittingly and even after I had 
discovered the nature of these movements and had thus 
become enabled to call forth at will all the various re- 
sponses on the part of the horse, I still succeeded in 
giving the signs in the earlier naive involuntary manner. 
It is not easy, to be sure, to eHminate at once the influ- 
ence of knowledge and to focus attention with the great- 
est amount of concentration on the number desired, 
rather than upon the movement which leads to a success- 
ful reaction on the part of the horse. To some this may 
appear impossible, but those who are accustomed to do 
work in psychological experimentation, will not deny 
the possibility of such exclusive concentration upon cer- 
tain ideas. 



If we now ask : " What occurred in the mind of the 
questioners, while they were giving the signs ? ", the an- 
swer can be found only by way of the process which in 
psychology is technically called " introspection ", i. e. 
observation of self. In the following we will give the 
most important results of this process of self-observation, 
which took place in the same period in which the observa- 
tions recorded in the preceding chapter were made. 

My first experiments were made while the horse was 
counting or solving arithmetical problems and were as 
follows: Mr. Schillings, who was alone with me in the 
horse's barn, asked me to think of several numbers, main- 
taining that the horse would be able to indicate them cor- 
rectly upon being asked. He stood to the right of the 
horse, I stood erect and at the side of Mr. Schillings. 
There was no one else present. Somewhat skeptical in 
attitude, I concentrated my mind consecutively on five 
small numbers. Hans tapped one of them incorrectly, 
one correctly and three by one unit too many. At the 
time I considered these attempts as unsuccessful and cred- 
ited some curious chance with the answers which were 
correct, or nearly so. This was a mistake, for often 
during the following days, and in the absence of Mr. von 
Osten, the horse would give correct answers. Others, of 
course, would be incorrect, and usually the mistakes 
would be by one unit, — so that I soon saw that even in 
the horse's errors there lay some system. It will be seen 
that Hans responded to me from the very beginning, un- 
doubtedly because I had had the opportunity of watching 
Mr von Osten and Mr. Schillings and had thus patterned 
my behavior after theirs. I was not at first successful in 
getting the horse to respond correctly in the case of large 
numbers. For in order to get complete control over the 


horse, and, what was, as I later discovered, more to the 
point, control of myself, some practice was needed. But 
I was able to work with the horse quite successfully, 
while I was still in the dark as to my own behavior. 

From the very beginning Hans responded as promptly 
to those questions which I articulated merely inwardly, 
as to those which were spoken aloud. That all formula- 
tion of the question was unnecessary, however, was shown 
by the following experiments. If, for example, I did not 
think of any particular number until after the horse had 
begun to tap, and then fixed upon 5, he would tap 5. If, 
however, I told him to count to 6, but gave no further 
thought to the command after he had begun tapping, I 
would get an entirely wrong response. It was easy to 
obtain any answer one wished to a question, simply by 
focussing consciousness, with a great degree of intensity, 
upon the answer desired. Thus Hans answered my ques- 
tion : " How many angles has a hexagon ? ", first by 6, 
then 2, then 27, in accordance with the numbers that came 
into my mind. The animal always followed the ideas 
which were in the questioner's mind, and never his words, 
for it was with the former that the movements upon which 
the horse depended were bound up. 

It was not enough, however, simply to imagine the 
number desired. It was furthermore necessary that the 
questioner be conscious of the moment when the horse 
reached that number. Larger numbers (above 6) were 
therefore, successful only when every single tap was in- 
wardly counted to the end. The manner of counting was 
indifferent. Thus I counted 6 as follows: i, 2, 3, 4, 5, 6, 
and later: 6, 5, 4, 3, 2, i, and then again : 6, 6, 6, 6, 6, 6. 
Finally I used the Greek letters and also nonsense syl- 
lables. And in all cases I obtained six taps, the correct 


response. If, however, I simply counted the taps without 
knowing when the desired number was reached, the re- 
sponses were always incorrect, e. g., I counted 

For No. 10: 10, 10, 10 continuously, Hans tapped 13, 
" " 10: I, 2, 3 to 10 " " 10, 

" " 12: 12, 12, 12 continuously " " 15, 

" " 12: I, 2, 3 to 12 " " 12. 

In the case of smaller numbers, on the other hand, one 
often obtained correct results without counting. In this 
I am borne out by Mr. Schillings. It was merely neces- 
sary to image vividly the number 3, or 4, or even the 
name of a week-day or of a month without the number 
which would indicate it. In the last of these cases the 
number corresponding to the day or the month (e. g. 3 for 
Tuesday, 5 for May, etc.), though not consciously pre- 
sented, still evidently lay at hand in the subconscious. 
To use a popular expression, I usually had a " feeling " 
when Hans had arrived at the right number. 

It was furthermore found that it was not only neces- 
sary to count to, or to think of, the number desired, but 
that this must take place with a high degree of tension of 
expectancy — that is, a strong affective element must 
enter in. The state required for a successful response 
was not the mere passive expectation that the horse would 
tap the number demanded of him nor the wish that he 
might tap it, but rather the determination that he should 
do it. An inward " Thou shalt ", as it were, was spoken 
to the horse. This affective state was registered in con- 
sciousness in terms of sensation of tension in the muscu- 
lature of the head and neck, by intraorganic sensations, 
and finally by a steadily rising feeling of unpleasantness. 
When the final number was reached, the tension would 


suddenly be released, and a curious feeling of relaxation 
would ensue. I have made a series of tests to determine 
the most favorable degree of tension in expectation. It 
was possible to distinguish with certainty, three degrees 
of tension besides the state of utter relaxation, — ^all of 
which I measured by means of the differences in the sen- 
sations of tension. In cases of tension of the first degree 
(greatest concentration) the responses were usually cor- 
rect, a few, however, were lacking by one unit. There 
was therefore in the latter instance a premature release 
of inner tension. In cases of tension of the second de- 
gree all answers were correct except a very few which 
were too great by one unit. In cases of tension of the 
third degree, many answers were wrong, and usually by 
several units too many. I wished to have the horse tap 
ID, with the lowest degree of concentration. He tapped 
13, then in a repetition of the test, 12. I thereupon in- 
creased the tension, Hans then tapped 8. I decreased the 
tension once more, but so that it was somewhat greater 
than at first. Hans tapped 10 correctly. At another time 
I tried to have him tap the number 5, with a low degree 
of tension. He tapped 6. I intensified expectation and 
Hans tapped 4. I again decreased it, and he tapped S, 
comme il faut. Apparently, therefore, the most favorable 
degree of tension was one between the first and second, 
— ^the latter being the least favorable. After some prac- 
tice a lesser degree than was used in the beginning suf- 
ficed to evoke adequate reactions. The flow of nervous 
energy to the motor centers of the brain evidently became 
facilitated through practice. It will be easy to understand 
why the first days of experimentation caused intense 
headaches, which later never occurred. 

Whenever, in the foregoing, we spoke of a certain de- 


gree of concentration which had to be attained, it is not 
to be understood that the same tension had to be main- 
tained throughout the test, from the horse's first tap to 
his last. But rather, that it began with a low degree, and 
gradually increased as the final unit of the count was being 
approached. It may best be represented by a curve whose 
maximum represents that degree of tension which we 
have been discussing. The rise to this maximum which, 
when attained, was followed by a sudden fall, did not 
always occur in the same manner. Three types of curve 
may be distinguished, which were first discovered in 
purely empirical fashion, and later reproduced volun- 
tarily for purposes of experimentation by diagramming 
before each test the intricate curve of the varying degrees 
which the intensity of concentration was to assume. The 
types may be described as follows: 

I. Here the tension curve rises steadily from begin- 
ning to end. This type preponderates in the case of small 
numbers. Thus, when I asked the horse : " How much is 
2 plus 4 ? ", the tension increased slowly with every tap 
from the moment I began counting, until the final tap 
was reached, when it was again relaxed. Externally this 
relaxation is noticeable as a slight jerk. 

II. In this case the curve does not rise at an equal rate, 
but rather more slowly at the beginning and later under- 
goes a sudden increase, or the tension increases immedi- 
ately at the beginning, remains constant for some time 
and then ascends to the maximum. This curve is the 
rule in the case of large numbers and evidently means 
economy of physical energy, for experience soon taught 
that a steady increase in tension from the very beginning 
soon brought it to a level which cannot be long main- 
tained and usually leads to a premature relaxation. In 


the case of very large numbers the alternation of the slight 
and the sudden increase may be repeated several times, 
and at times it may even sink below a level which has al- 
ready been attained, thus making a wave-like curve. 

III. The third type of curve shows a sudden jump be- 
tween two units at a certain point in its course. This 
may occur in the case of both small and large numbers 
but only when the highest or first degree of concentration 
is employed (see page 91). Such a jump frequently 
occurs in the transition from the tap preceding the last to 
the last one which is being eagerly expected. Relax- 
ation — with the upward jerk and raising of the head — 
here occurs at the normal time ; Hans taps to the end with 
his right foot. Oftener still the " jump " described oc- 
curs while passing over to the number just before the 
last. The goal seems within reach and the mental tension 
relaxes, and with it the physical tension, — the head gives 
a slight jerk and Hans makes the back-step. Since, how- 
ever, another tap is still awaited with some degree of 
tenseness and, since complete erection of the head does 
not follow immediately upon the jerk of the head, the 
horse gives another tap with the left foot. Thereupon 
occurs the complete relaxation of attention, and the as- 
sumption of the erect posture on the part of the ques- 
tioner. That this is psychologically the clue which leads 
to the final tap, will readily appear from the following 
remarkable fact : I was able to bring about at will either 
the back-step with the right foot, or the additional extra 
tap with the left foot by concentrating the mind either 
upon the last unit or upon the one just preceding it. In 
either case the movement which served as stimulus to the 
horse followed naturally upon concentration on the num- 
ber. I could of course also control the response by direct 


voluntary control of the movements involved. Hans 
thus solved for me the same ten problems first with the 
back-step, then with the extra final tap. 

Finally we will indicate the one true inner cause of the 
difficulty in getting the number i as a response. It is not 
easy to relax attention immediately after having just 
begun to concentrate. Relaxation, therefore, often oc- 
curs with a certain retardation, and the result is a belated 
jerk of the head. 

Briefly, I would also mention a few of the more inter- 
esting introspective observations which were made in 
situations in which the horse responded with movements 
of the head for answers such as " yes " and " no ", " up " 
and " down ", etc. From the very beginning I put ques- 
tions to Hans which would have to be answered by a 
shake of the head. It often happened that instead of indi- 
cating " o ", Hans would begin tapping some number. 
But the wonder of it was that, in many cases, he re- 
sponded properly. I knew only that I inwardly pro- 
nounced the word "null" (zero), and that I looked ex- 
pectantly at the horse's head. In the case of questions to 
which I expected the answer " yes " or " no ", I imagined 
myself enunciating the answer, i. e., I used motor im- 
agery. The tests failed, the moment I employed only 
visual or auditory imagery, whereas, motor imagery was 
always effective in calling forth correct reactions.* When 

* Thus it is possible to think of the word " no " in three differ- 
ent ways. I may get a visual image of the written or printed word, 
or the auditory image of the word as spoken by another person, or 
finally I might think of it in terms of images of the sensations of move- 
ment which would arise if I myself were to enunciate or write the word. 
And so, in like manner, I could think of any other word in terms of 
either visual or auditory or motor imagery. In all probability the 


the proper response was " up " and " down " I would 
think of those directions in space, and likewise with 
" left " and " right " in which case also I would put my- 
self in the horse's place. 

While I was still ignorant of the nature of the neces- 
sary movements, the tests were successful only when I 
had put the question aloud or in a whisper, but never 
when I failed to enunciate, i. e., when I merely had the 
question in mind ("in idea"). But this also became 
possible after a little practice, although I could not then 
give an explanation for my success. Except in one in- 
stance, we could discern no difference between problems 
spoken and those merely conceived by Mr. von Osten 
who had had the advantage of long practice. But the one 
exception deserves mention. The old gentleman com- 
missioned Hans, presumably without uttering a word, to 
step backward to the left. Hans thereupon responded by 
giving his entire repertoire, as follows: He moved his 
head to the right, then to the left. Then he leaped for- 
ward and repeated the same movement of the head. Here- 
upon he stepped backward and signified a " yes " by a 
movement of the head. He then lowered his head and 
made two leaps forward. After this performance Mr. 
von Osten repeated the same command aloud, and in every 
case Hans responded properly. Again the silent com- 
mand was given and again the horse responded with the 
series of reactions described above, lowering his head 

auditory and motor always occur together,' but still it is possible to make 
the one or the other predominate. 

It appears that the imagery of most persons is a mixture of auditory- 
motor and visual elements, with a predominance of one or the other 
kind. Individuals who utilize almost exclusively the visual (as does the 
author, as a rule), are rare. But rarer still is the pronounced motor type. 


leaping forward, etc. In this experiment, without excep- 
tion, the spoken command evoked adequate reactions, — 
the silent command, an incorrect response. Evidently 
the impulse to movement was not so great with the mere 
conceiving of " right ", " left ", etc., as when the words 
were enunciated. It, therefore, required some practice 
on my part before a sufficiently strong movement-impulse 
became associated with the idea. All this is in no wise 
at variance with the fact that tests involving counting and 
computation were as successful when the problem was 
given in silence, as when it was spoken. The signs for 
tapping, viz. : inclination and erection of the head and 
body, followed the question. The question therefore be- 
came superfluous. On the other hand the signs for head- 
movements on the part of the horse, were given while the 
question was being put. I ask, which way is " upward ", 
and at the same time I look upward. In this case there- 
fore the question itself is not entirely insignificant. — I ex- 
perienced greater difficulty in getting Hans to respond 
with the head-movement to the left. After much prac- 
tice I was able to evoke this movement by means of 
giving the command aloud, but never by means of the 
" silent " command. Accidentally I hit upon a device by 
means of which I attained this end also. I asked the horse 
aloud "Which direction is left?", — whereupon he re- 
acted properly ; then I immediately repeated the question 
silently, and was successful every time. My mental atti- 
tude here was still the same as when I put the question 
aloud. What sort of an attitude this was, I could not, of 
course, have stated explicitly at the time. I could not, 
therefore, awaken it at will, — and if I allowed but a 
minute to elapse between the spoken and the silent ques- 
tion, the vivid after-effect. (the so-called "primary mem- 


ory image ") soon disappeared and the test was wholly 
unsuccessful. Practice, however, soon helped me to over- 
come this last difEculty also. I believe that my inability 
to evoke this specific reaction on the part of the horse, 
lay in the unfavorable position which I assumed, for it 
did not allow the horse to preceive my movements easily. 
For the same reason, Hans would at first indicate " no " 
and " zero " by turning to the right, seldom to the left. 

As in the case of counting, a high degree of concentra- 
tion was also necessary here, but with this difference, 
that here attention was directed to ideas present to the 
mind, ("yes", "no", etc.), whereas in the counting 
process attention was directed toward expected sensory 
impressions (i. e., the taps of the horse). 

All that has been said thus far is readily understood 
psychologically. The following curious fact, however, is 
noteworthy. Hans used the head-movement to indicate 
two such different concepts as " zero " and " no " ; it ap- 
peared therefore that in both cases he was receiving the 
same kind of directive. Observation proved that such 
was the case and the directive in question was none other 
than an imitation in miniature, or rather a movement 
anticipatory of the expected head-movement of the horse. 
Now, whereas the signs for " up ", " down ", " right ", 
and " left " were natural expressive movements which are 
normally associated with the corresponding concepts, this 
cannot be said to be true of " no * and " zero ". My 
laboratory observations (see page 107) lead me to con- 
clude that the movements, by means of which the concepts 
" no " and " zero " are naturally expressed, are quite dif- 
ferent ; and neither of these corresponds to the signs for 
" zero " and " no " which the questioner involuntarily 
gave to Hans. What was the genesis of these unnatural 


forms of expression? If we might assume that the ques- 
tioner always had in mind the movement he awaited on 
the part of the horse, and never thought of " zero " or 
" no ", then the contradiction would solve itself. But I 
must deny decidedly that I ever thought of the movements 
of the horse's head, and Mr. Schillings, whom I ques- 
tioned on this point, agreed with me in this, in so far as his 
own mental processes were concerned. I can see nothing 
for it but that in this instance the expressive movements 
normally connected with the concepts " zero " and " no " 
have been replaced by other forms, without the questioner 
becoming aware of it. That such displacements may 
occur, has been shown by the tests described on pages 107 
to 112. That they did occur in this instance may be 
concluded from the following observation. In respond- 
ing to me, as well as to Mr. Schillings, Hans always 
moved his head first to the left, then to the right, never 
in the opposite order. That this was not a peculiarity of 
the horse, but must be ascribed to the signs which were 
given him, is shown by the possibility of inverting the 
order under experimental control (page 77). Frequently 
Mr. Schillings and I had seen the horse respond to his 
master by means of such head-movements, and the order 
was always, without exception, the one mentioned. It 
must be assumed therefore that the horse's movement, 
which we so often noticed, made such an impression upon 
us, that afterwards it was regularly reproduced on our 
part quite unconsciously, so that Mr. Schillings never, and 
I only after a long time, became aware of the whole 

In closing, just a word as to the discovery of our own 
movements. I soon noticed that every pronounced rais- 
ing of the head or trunk brought about an interruption 


in the horse's response. But only by observing the final 
movement in the case of Mr. von Osten did I discover 
that I, too, performed a slight erection of the head. Ob- 
servation of others was less difficult than the observation 
of one's own movements. As in the case of all other signs 
given to the horse, these movements were so slight that 
they were prone to escape notice even though one's whole 
attention were concentrated upon their detection. I also 
questioned whether in my attempts to disturb the horse by 
means of loud calls, it were really the call or some simul- 
taneous involuntary movement which was the true cause 
of the interruption. The doubt was justified, for when 
I finally learned to cry out vehemently without making 
the slightest move, all my crying was in vain. Also it 
had seemed to me at first as if I were able to induce the 
horse to rear, not only by means of the proper sign or 
movement, but also by a mere command, but I found 
later that in every case there was always some movement, 
were it ever so slight. Finally I tried to simulate volun- 
tarily the oft-mentioned involuntary jerks of the head. 
Although it is not very difficult to execute them at will 
with almost the same minuteness as when they were per- 
formed involuntarily, I still did not succeed in getting a 
series of such jerks of equal fineness throughout. In 
spite of (and partly on account of) the most concentrated 
attention, there would be from time to time a jerk of 
somewhat greater extent and energy. As soon as the 
movement had been executed, I was able to form a good 
judgment as to its relative extent, but I was unable to 
regulate the impulse beforehand. 

With the following comment the chapter will be con- 
cluded. Introspections are necessarily subjective in char- 
acter. If they are to possess general validity, they must 


be borne out by evidence furnished by others — ^and this 
to a greater extent than is necessary for other forms of 
observation. It was hardly possible to get corroboration 
from the other persons who had worked, with Hans, for, 
although some of them were excellent observers of ex- 
ternal natural phenomena, few of them had had the nec- 
essary amount of practice in introspection. The neces- 
sary confirmation, however, was had in laboratory tests, 
which we shall presently describe. 


The tests which are to be briefly reported here, were 
begun in November, 1904, and were carried out at the 
Psychological Institute of the University of Berlin. 
The purpose was twofold : first, to discover whether the 
expressive movements noted in Mr. von Osten, Mr. Schil- 
lings, and others, were to be regarded as typical and to 
be found in the majority of individuals, — ^and secondly, 
to ascertain in how far the psychical processes which I 
had noted in my own case and which I believed to lie at 
bottom of these movements, were paralleled in, and con- 
firmed by, the introspections of others. The effort was 
made to make the experimental conditions as nearly as 
possible like those under which the horse had worked. 
The affective atmosphere which colored the situations in 
which the horse took part, could not, of course, be trans- 
ferred, but this was in some respects an advantage. One 
person undertook the role of questioner, another — myself 
— that of the horse. The experiments fall into three 
groups, corresponding to the types of the horse's reac- 
tions: I, tests in counting and computation; 2, tests in 
space reactions ; 3, tests in fetching or designating ob- 

In the experiments in counting and computation, the 
questioner, standing at my right, thought with a high 
degree of concentration of some number (usually be- 
tween I and 10, but sometimes also as high as 100), or 


of some simple problem in addition. Then I would 
begin to tap, — but in human fashion with my right hand, 
rather than with my foot — and continued until I be- 
lieved that I had perceived a final signal. I thus tested, 
all in all, twenty-five persons, of every age and sex (in- 
cluding children of five and six years), differing also in 
nationality and occupation. None of them was aware 
of the purpose of the experiments. It could not escape 
them, to be sure, that they were being watched. It was 
also evident to them that the things noted were certain 
tensions and movements; but none of my subjects dis- 
covered what the particular phenomena were that I was 
looking for. Only in a few isolated instances did they 
report that they were conscious of any movements on 
their part. With the exception of two persons, they all 
made the same involuntary movements which were de- 
scribed in chapter II, the most important of which was 
the sudden slight upward jerk of the head when the final 
number was reached. It was at once evident that the di- 
rection of this jerk depended upon the position which one 
had asked the subject to assume at the beginning of the 
test, the direction changing whenever the position was 
changed. Thus, if the subject stood with head bowed — 
the body either being held erect or likewise bowed, — then 
release of tension would be expressed physically by an 
upward jerk. (Occasionally the entire trunk is slightly 
raised, so that it was possible to observe this physical 
reaction when standing behind the subject). If the sub- 
ject had bent his head backward, the " psychological mo- 
ment " was marked by a forward movement, (although 
under certain conditions the head was, in such a case, 
observed to bend still farther backward). If during the 
tests the head was bent slightly to the right, then the re- 


action was expressed in a movement toward the left, and 
vice versa, if it had been on the left, it was bent to the 
right. If the subject had been bending his head forward 
and to the right, he then raised it upward and to the left, 
etc. In all of these changes of position I noticed an in- 
termediate posture which, to be sure, it was not always an 
easy matter to discover, — viz.: an upright position in 
which there was discernible no manner of head-movement 
or only a slight tremor. If the subject was lying on his 
back with his head supported, then there was noticeable a 
very slight movement to one side. In this same way a 
number of other positions were tested in order to dis- 
cover for each the characteristic movement expressive of 
release of tension. It would therefore appear that the 
raising of the questioner's head, which served as the 
signal for stopping for Mr. von Osten's horse, was but 
one instance of a general law which may perhaps be stated 
thus : The release of muscular tension which occurs with 
the cessation of psychic tension, tends to bring about that 
position of the head (and body) which, at the time, repre- 
sents the slightest amount of muscular strain. — ^These 
movements seldom were pronounced enough to be com- 
pared to motion through a distance of one millimeter, in 
a very few cases only did they attain to the magnitude of 
one or two millimeters. I failed to note them entirely, 
however, in only two individuals, two scientific men whose 
mode of thought was always the most abstract, and one 
of these was, in spite of repeated attempts, unable to elicit 
any response whatever on the part of the horse. 

In the cases of the more suitable subjects I was able 
to indicate not only the number they had in mind, but 
also the divisions in which the number was thought, thus 
12 as 5 and 5 and 2, or the same number as 2 and 5 and 5, 


and I was also able to determine the addends in the 
addition — i. e., whether the problem had been conceived 
as 3+2=5 or as 2+3=5. It frequently happened that 
in the beginning I would sometimes mistake these subdi- 
visions, which were recognizable by the less pronounced 
jerks, for the final number. Thus I would often respond 
with 4 instead of 8, or 3 instead of 9, or with 3 when the 
problem was 3+2, just as Hans had so often done. In 
these tests, too, the difficulty of getting the number i, as 
well as the larger numbers, came to light. Thus three 
times in succession 17 was indicated as 4, as 9, and as 17. 
But after some practice I was able to give numbers as 
high as 58 and 96. The frequency of the errors of one 
unit too many and of one unit too few is also noticeable 
in these tests. 

We also found desirable corroboration, by trustworthy 
subjects, of the introspective observations of the author, 
which were reported in Chapter III, with regard to the 
significance of concentration and the curve of attention. 
It is hardly necessary to mention that no attempts were 
made to influence the subjects in their accounts by asking 
suggestive questions. The most valuable feature about 
these tests was that the mute horse had now been re- 
placed, as it were, by an animal capable of speech, and 
that it was now possible to follow the same process both 
from within and from without. Two illustrations may be 
welcome. The one who took the part of the horse gave 
three taps and made the following entry : " At 3 I saw a 
slight upward jerk of the head on the part of the ques- 
tioner ". The questioner however had thought of 4, and 
made the following note, without knowledge of the other's 
entry : " I was aware of extreme tension, so that it 
was impossible for me to get beyond 3 ". Or again, the 


' horse ', reacting to a movement on the part of the ques- 
tioner, stopped at 3, but the latter, having intended to ob- 
tain 2, made the following entry : " I noted clearly that I 
ceased thinking of the number too late, and did not put 
on the brakes, as it were, until I had arrived at 3 ". We 
see that errors here were entirely the fault of the ques- 
tioner, just as had been the case in the tests with Hans. 
(Seepage I5if.). 

In a second group of experiments I asked a subject to 
fix his mind upon certain concepts, such as " up ", or 
"down", "right" or "left", "yes" or "no", and 
others, in any order he pleased, but with the greatest 
possible degree of concentration. The subject each time 
had the choice of four or six concepts, and he was told 
to think of one of them at the signal " Now ! ". How he 
was to ' think ' the concept was left entirely to him. 
He was also told to interpolate the series with a ' blank ', 
that is, to think of nothing at all. Standing opposite the 
subject, I tried to guess at the mental content of the per- 
son's mind, on the basis of expressive movements. Some- 
times I reacted by shaking or nodding the head, etc., just 
as Hans had done, but as a rule I was content to say 
the word which I thought the subject had in mind. With 
twelve subjects (a total of 350 tests) I made an average 
of 73% correct responses, and in the more favorable cases 
I attained even 90 to 100% correct responses. Very 
slight involuntary movements of the head and eyes, 
which showed but little individual variation, and always 
occurred when the subject began to fix upon the concept, 
were the signs which I used as cues. As in the case of 
the movements expressive of the release of tension, which 
I discussed above, these movements, too, occurred with- 
out the subject being aware of them, (except in those 


rare cases in which they had once or twice been especially 
pronounced). Indeed, it was very difficult and in some 
cases almost impossible for those persons whom I had 
initiated into the secret, to inhibit them voluntarily. 
"Up" and "down", "right" and "left", were ex- 
pressed by movements of head or eye in those directions, 
" forward " by a forward movement of the head, " back " 
by a corresponding movement. " Yes " was accompanied 
by a slight nod of the head ; " no " by two to four rapid 
turnings of the head to either side.* "Zero" was ex- 
pressed by a movement of the head describing an oval in 
the air. Indeed, it was even possible to discover whether 
the subject had conceived of a printed or a written 
zero, for the characteristics of both were revealed in 
the head-movements. I was able later to verify this 
graphically. With Ch. as subject, I made 70% correct 

* It was Charles Darwin ^ who first pointed out that the expressive 
movements (of the coarser sort) to be noted in nearly every race and 
people show a great, though by no means complete, similarity. The 
similarity is most pronounced in the shaking of the head to signify ne- 
gation and nodding to denote affirmation. It will be noted that the 
former is essentially of the nature of a turning toward, and the latter 
a turning away.* These same movements have been reported in the 
case of the blind and deaf Laura Bridgman,' and we have been ex- 
plicitly assured that they were a spontaneous development, and not 
acquired by imitation. For it is by imitation and never before the 
completion of the first year, that our children acquire these move- 
ments. On account of his unreliability, we can put but little stock in 
the statement of Garner," a writer on the speech of monkeys, that 
these same gestures have been observed in the case of those animals. 
My experiments show that the same movements, greatly diminished in 
scope, as a rule accompany the mere thought of " yes," " no," etc. I 
cannot, however, regard the assertion as an established fact that every 
thought process whatsoever is connected with some form of niuscular 
movement, as has been generalized by the French physiologist Fer^.U 
and the American psychologist Wm. James." 


interpretations in a total of 20 tests ; with von A. as sub- 
ject, 72% in a total of 25 tests. And finally I was able 
to interpret the signs without any errors at all. It was 
not absolutely necessary to look directly at the subject's 
face. Even though I focussed a point quite to one side, 
so that the image of the subject's face would fall upon a 
peripheral portion of my retina, I still was able to make 
89% correct interpretations in a total of 20 tests. — This is 
not astonishing after all, when we recall that the periphery 
of the retina possesses a relatively high sensitivity for 
movement impressions, although its chromatic sensi- 
tivity is very low.* 

It was assumed, as indicated on page 99, that in the 
case of Mr. Schillings and myself the movements natur- 
ally expressive of " zero " and " no " had been displaced 

* The productions of mind-readers, so-called, also, are based upon the 
perception of involuntary movements, insofar as they are not based 
upon pre-arranged schemes and trickery. But there we have to do 
principally with tactual perception, since the reader touches the hand of 
the subject and is guided by its tremor. Some of the expert mind- 
readers, however, conduct tests without touching the subject. They 
depend chiefly upon auditory impressions : the sound of footsteps,'* 
involuntary whisperings " and the changes in the subject's respiration " 
and the murmuring of the spectators. To a less degree visual signs also 
are involved : posture and facial expression of the subject, and move- 
ments of eyes and lips.'» Even the heat radiating from the person's 
body is supposed to have some influence.*' And my own experience 
has taught me that surprising results may be obtained by the utilization 
of the movements described in the preceding chapter. 

It may be that these truly microscopic movements also play some 
part in bringing about the success of some of the experiments in telep- 
athy, so-called, (transference of thought from one person to another, 
ostensibly without any mediation of the senses known to us.) In spite 
of the huge mass of " experimental evidence " which has been collected, 
chiefly in England and in America, it appears to me that telepathy is 
nothing but an unproven hypothesis based upon experimental errors. 


— without our being aware of the fact — by others, viz. : 
those which the horse required as directives for his reac- 
tions. Since this was the case, we tried to discover if a 
similar displacement could be brought about experimen- 
tally. The attempt was successful and we discovered that 
under suitable conditions we could cause the subject — 
quite without knowledge on his part, — to establish an 
" association " between any given concept and any given 
expressive movement. The following experimental series 
will serve to illustrate this fact. 

I had one of the subjects (von A.) think of "left" 
and " right " in any order he chose. (The command was 
purposely given only in a general way : " Think of ' right ' 
or ' left ' ".). We had agreed that I was to try to guess 
the mental content of the subject's mind, but I was not 
to utter a word. Instead, I was to indicate " right " in 
every case by an arm movement downward, and " left " 
by a movement upward. To the subject I gave a fictitious 
but plausible reason for all this. The behavior of the sub- 
ject took the following course : In the first three tests he 
moved his eyes to the right when he thought of " right ", 
and to the left when he thought of " left ". This was the 
normal expressive movement. In the fourth test, how- 
ever, the thought " left " was accompanied by an upward 
movement of the eyes. Two further tests again showed 
eye-movements to the right and left. In the seventh test 
with the idea " left " the eyes moved first to the left and 
then immediately upward. In the following ten tests the 
eyes were turned regularly upward at the thought of 
" left ", and downward at the thought of " right ", with 
only one exception which was a normal movement to the 
left. The normal expressive movements, therefore, were 
displaced by the artificial, after the seventh test. 


In the case of another subject (B.) in whom normally 
the thought of " up " was accompanied by a slight rais- 
ing of the head, and " down '' by a downward movement, 
these natural forms of expression disappeared entirely as 
a result of my arm movements to the right to indicate 
that I inferred his having in mind the thought of " up ", 
and to the left when I inferred that he was thinking of 
" down ". Instead, there appeared not merely the de- 
sired movements to the right and left, but rather move- 
ments upward to the right and downward to the left. 
That is, instead of a complete displacement of the old by 
the new, there occurred a combination of the two. 

A third type of result appeared in still another sub- 
ject (Ch.), who normally expressed the concepts " right " 
and " left " by eye or head movements (never both kinds 
at the same time) to the right and left. Here my arm 
movements up and down caused the eye and head move- 
ments to be made simultaneously, so that the thought of 
" right " found expression in an upward movement of 
the head and an eye movement to the right, and the idea 
of " left " in a downward head movement and a move- 
ment of the eye to the left. The subject had no knowl- 
edge of this process, and it took six tests to bring about 
the new reaction. From that point onward the new move- 
ments were so well established that, depending upon 
them for my cue, I was able to make 32 correct infer- 
ences in a total of 40 tests. During the latter part of this 
series I blindfolded the subject, so that I could not see 
the movements of his eyes, and therefore had to base my 
inference entirely upon his head movements. — After re- 
moving the bandage, at the end of the series, I told the 
subject that I would go through another series, in which 
I intended to indicate his thought of " right " by an arm 


movement downward (instead of upward as heretofore), 
and his thought of " left " by a movement upward. 
(This he regarded as an idle whim of mine). It was 
only after the twelfth test that the former " association " 
which I myself had caused to be established, was com- 
pletely displaced by the new. The thought of " right " 
was now accompanied by an eye movement to the right 
and instead of a raising there was a lowering of the head. 
A corresponding change occurred in the head movement 
expressive of the thought of " left ". These responses 
were occasionally varied by some in which only the head 
movement or only the eye movement occurred. But 
these movements were always to the right, or downward 
and to the right, at the thought of " right ", — and to the 
left, or upward and to the left, at the thought of " left ". 
In ten tests I made ten correct inferences. After the new 
association appeared firmly established, I ceased respond- 
ing by means of arm movements, and indicated my 
' guesses ' by word of mouth. At first the newly acquired 
movements continued to appear promptly in the subjects. 
But gradually they tended to become more uncertain and 
finally disappeared, as readily as they had appeared, and 
the normal conditions were once more established. Nor 
was there any tendency to reappear on the following day 
in another series of tests. (Those just described had 
been made on one day in the course of an hour or two). 
But as soon as I again used the earlier method of arm 
movement to indicate my inferences (raising the arm for 
"right", lowering it for "left"), the former artificial 
association was again established, although not until 
some 14 tests had been made, — during which the normal 
movements to the right and left were often inhibited and 
during which the conditions were, on the whole, chaotic. 


The new association, thus re-established, remained con- 
stant during the ten tests of the remainder of the series, 
but has very probably again disappeared long ere this. 
In the case of this subject it appears therefore that the 
new associations were superimposed upon, but in no 
sense displaced, the normal expressive movements. Nor 
did the two coalesce (except in a few exceptional cases), 
but tended as a rule to occur independently of one an- 

I would emphasize once more that none of the subjects 
had any knowledge of the purpose or meaning of the ex- 
periments. Also, I was convinced by questioning the 
subjects afterwards that none of them — and this is the es- 
sential point — had merely conceived of the arm movement 
which they were expecting me to make, instead of con- 
centrating thought upon the idea of " right " or " left ". 
On the contrary, all of them considered my particular 
movements mere vagaries and without purpose, and they 
felt perfectly certain that they were in no wise influenced 
by these movements. Also, none of the subjects was con- 
scious of any movements on their part, except one, who 
was at times aware of her eye movements to the right, 
but never of those to the left, (see page in), nor of the 
head movements which for us constituted the phenomena 
of prime interest. When I asked my subjects what they 
believed to be the cue upon which I based my inferences, 
they invariably responded with probable explanations 
which were always wide of the mark, and those to whom 
I disclosed the cue — (after the experiments were com- 
pleted), were thoroughly astonished. 

In the tests just described we had to do only with such 
ideas or concepts as normally were associated with some 
stereotyped form of expressive movement (see page io6). 


I now chose a group of ideas which are not normally asso- 
ciated with a particular form of motor expression peculi- 
arly characteristic of them, and sought to establish arti- 
ficially such a connection with some arbitrary movement, 
without consciousness of the process on the part of the 
subject. Thus I asked one subject (Miss St.), who had 
no intimation of the aim of the tests, to think of the fol- 
lowing words in any order she might choose : " Ibis " 
(ibis), "Irbis" (panther), " Kiebitz " (plover) and 
" Kiirbis " (pumpkin). I said that I would react to her 
thoughts by means of arm movements forward and back- 
ward to the right and to the left, respectively. 15 out of 
20 tests were successful, without the slightest suspicion 
on the part of the subject (whose whole attention was 
concentrated on the word-content), that she was giving 
me the necessary directives in the form of very minute 
movements of the head and eyes to the right and left, etc. 
She was greatly astonished that I should be able to guess 
words so much alike, — (she did not know that the ele- 
ment of likeness was productive of no difficulty). When, 
during one of the tests, the subject happened to think 
spontaneously of the movement she was expecting me to 
make, she became confused, and as a result the number 
of my sucessful reactions suddenly fell. I never would 
have discovered the cause, had not the subject enlightened 
me without my asking. 

I repeated this series with three other persons, who 
had had some psychological training. I did not use the 
same movement for each word in all three cases, but in- 
dicated the word " Kiebitz ", for instance, by means of an 
upward movement in one case, by turning the head to the 
right in another, etc. In one of the three cases the tests 
were almost wholly unsuccessful. The cause for this 


came to light later, but it would involve too much ex- 
position to discuss it at this point. In the case< of the 
other two persons, the tests were successful beyond ex- 
pectation. I had made my various arm movements only 
a few times when they presently began to raise their 
heads slightly when thinking of " Irbis ", and to move it 
to the right at the thought of " Kiirbis ", etc. In the two 
series of 35 tests I did not have a single error. In a num- 
ber of instances I succeeded in guessing the word upon 
which the subject had decided, even before the test 
proper was entered upon — i. e., before the signal for con- 
centration had been given. Nothing surprised a subject 
more than the remark : " You are intending to think of 
the word ' Kiirbis ' ", or " You had thought of concentra- 
ting your mind upon ' Ibis ' but later decided in favor 
of ' Kiebitz ' ", yet nothing could be more simple. Be- 
fore every test the subject would consider what word he 
would fix upon, and while he was saying to himself " I 
will choose ' Ibis ' ", the proper movement would accom- 
pany his decision, although it was only very slight, be- 
cause attention had not yet attained the degree of con- 
centration which was employed in the test proper. 

In these experiments also, the subjects, whom I know 
to be absolutely trustworthy, declared that they never 
thought of the arm movements which I was to make. 
They regarded them as being quite irrelevant. Also — 
with but one exception — they thought of the objects, in 
so far as they imaged them visually, as being directly 
before them, and not off in the direction indicated by my 
arm movements. Thus they did not image the plover 
(" Kiebitz ") as being on the wing, when I raised my 
arm, or as resting on the ground, when I pointed down- 
ward, etc. One of the subjects had done this occa- 


sionally, but by no means regularly. He was therefore 
asked to localize all objects in the same place, i. e., directly 
in front of him at the level of the eye. He complied with 
this request, but no change, whatever, was observed to 
occur in his expressive movements. 

In order to overcome the difficulty just mentioned, I 
selected another subject (Miss von L.), whose power 
of visualizing was very slight, and requested her to fix 
her mind upon four words which I had selected because 
they were not, necessarily, associated with a particular 
image. The order in which the words were to be thought 
of, was entirely optional on her part. The words were 
"Form", Inhalt", "Mass", and " Zahl", (form, con- 
tent, measure, and number), and each of them I ac- 
companied, with a certain definite arm movement. The 
subject always pronounced the word inwardly as em- 
phatically as possible, but without ever imaging the cor- 
responding arm movement. Often, it must be noted, 
she did not know whether or not the movement which 
I made was the proper one. And yet she, too, soon fell 
into line in the matter of executing unconsciously the 
characteristic head movements. In a total of 50 tests, I 
was able to make 10 correct guesses in the course of the 
first 20 tests, 8 in the next 10 tests, and 19 in the last 20 
tests. Miss von L. noted only a few of her upward head- 
movements, viz. : those that were especially pronounced 
(movements through about 2 millimeters), but of the 
others she knew nothing. The same experiment was re- 
peated with a psychologist, well-trained in introspection, 
as a subject. Success was even greater here. But no 
matter how closely the subject observed himself, he was 
unable to solve the puzzle. 

Variations which were introduced in these tests, I 


will only mention in passing. Thus, instead of making 
an arm movement, I, in some cases, would tap with my 
foot, for " Ibis " once, for " Kiebitz " twice. The sub- 
ject could not see my feet. The involuntary movement- 
expression which became associated with " Ibis " was one 
nod of the head, with " Kiebitz " two nods, etc. Here 
our only concrn was to show that unconscious change 
in natural expressive movements and the acquisition of 
artificial ones are possible in the case of psychically 
normal subjects trained m introspection. 

I was not satisfied with convincing myself subjectively 
of the facts indicated, but sought to fix them objectively, 
by means of a graphic method. For this purpose I used 
the device mentioned by Prof. R. Sommer for the analysis 
of expressive movements.^* The purpose for which 
Prof. Sommer's apparatus had been constructed, was to 
record the involuntary tremor and movement of the 
hand. These movements, of course, take place in the 
three dimensions of space. By means of three levers it 
is possible to record the movements upon the flat surface 
of a smoked paper fastened to the revolving drum of the 
kymograph, the movements in each direction being re- 
corded by a separate lever, in such a way that the three 
curves thus made represent the analysis of a single move- 
ment into its three dimensional components. By making 
slight changes, which tended to complicate the experi- 
ment somewhat, I adapted the apparatus to the measure- 
ment of movements of the head. The method of experi- 
mentation was the following. The subject whose move- 
ments were to be registered, was placed in the device 
in such a way that his trunk and head were bent slightly 
forward, the latter a little more than the former. This, 
it will be remembered, was the usual position of the 


questioner when working with the horse. Three levers 
were attached to his head in such a way that every move- 
ment backward or forward would act upon the first 
lever, every movement to the right or left would move 
the second, and every movement of the head upward or 
downward would be recorded by the third. With regard 
to the sensitivity of the machine, micrometric determina- 
tion showed that when the subject was properly installed, 
movements through so small a distance as xV millimeter 
could be accurately ascertained. The subject was care- 
fully instructed to remain as quiet as possible, but with- 
out constraint. Voluntary movements were thus ob- 
viated. But the question arose : were not the involuntary 
movements thus suffering a loss ? — And it was upon them 
that we were experimenting. The question cannot be 
put aside summarily, but experience taught us that the 
movements in question, nevertheless, did appear quite 
effectually, if one could have the right kind of subjects 
at one's command. We need hardly mention that besides 
the two persons immediately concerned — I, myself, at- 
tended to the apparatus — there was no one else present, 
and that the subject was not allowed to see the curves 
produced on the kymograph. Besides the registration 
of the head-movements, I also undertook to register the 
respiratory-movements of the subject. This was done 
by means of the so-called pneumograph, attached to 
which was a lever recording the thoracic expansion and 
contraction. This was for the purpose of ascertaining 
the relationship, which might eventually be found to 
exist, between the release of psychic tension, on the one 
hand, and respiration, on the other. 

The subject was now told to think of some number, 
which, of course,, was unknown to me. At a given 


moment I was to tap upon one of a series of keys ar- 
ranged like those of a piano, with the middle finger of 
my right hand — corresponding to the right forefoot of 
the horse. The questioner observed my key, I, his head, 
— just what had happened in the experiments with Hans. — 
and as soon as I perceived the involuntary closing signal 
I reacted upon it by releasing, suddenly, another key 
upon the same keyboard, which I had in the meantime 
been pressing down with my second finger, thus marking 
what with Hans had been called the backstep. Each key 
was connected with a separate electro-magnet, and these 
in turn with markers, in such a manner that pressure 
upon the keys closed two electric circuits and, releasing 
the keys, opened them, and both the closing and the 
opening were recorded upon the smoked paper by means 
of the markers. And, finally, in order to ascertain the 
time relations of all these processes, a time-marker in- 
dicated the time in fifth-seconds upon the revolving 
kymograph record. The time-curve was recorded just 
below the other curves. 

Of the curves * thus obtained under the most equable 

* For registering the curves a Hering kymograph was used, with a 
loop 2i metre* long. The kymograph rested on felt. With the aid 
of the Marey model a pneumographic record was taken now of the 
thoracic, now of the abdominal, breathing, never both simultaneously, 
since this was extrinsic to my purpose, and it would have made the 
whole experiment too complex. The time was recorded by means of 
the Jacquet chronograph. For purposes of making more exact measure- 
ments the acoustic current interrupter of Bernstein was used, attuned to 
100 vibrations per second. But this necessitated such rapid revolution 
of the drum of the kymograph that the curves were not compact enough 
for purposes of demonstration. The levers were all fitted with micro- 
meter adjustments. They wrote tangentially and, except the one reg- 
istering the breathing curve, all points lay in one vertical line. The 
error of deflection and that due to the rondure of the writing-surface, 


conditions possible, we publish seven which show the 
great general uniformity of the tests made upon the horse 
with those made in the laboratory. The role of questioner 
was undertaken at different times by Mr. Schillings and 
the students of philosophy, Messrs. von AUesch, Chaym 
and K. Zoege von Manteufifel. To all of them I am 
greatly indebted for their unselfish services in these labor- 
ious tests. The experiments with von Allesch and Chaym, 
who were among the most suitable of my subjects, were 
conducted absolutely without knowledge on their part of 
the nature of the phenomena which I was observing. 
Neither of them knew anything about the expressive 
movements in which they were unconsciously indulging, 
and furthermore, since they kept their heads bowed during 
the entire course of these experiments, they did not per- 
ceive' what it was that I was observing. It is interesting 
to note that Chaym on the occasion of his only visit to 
the horse, immediately received a number of correct 
responses. Without a doubt von Allesch would have 
met with equal success. The other two subjects (von M. 
and Sch.) went through this series of tests, possessing 
some knowledge of the nature of the movements involved. 
Conditions were such that they (and especially Mr. 
Schillings) could not be prevented from obtaining some 

were both very slight on account of the comparative length of the 
levers and the small extent of the excursions, and for that reason syn- 
chronous points lie practically in one perpendicular. Only the breathing 
curve has been moved somewhat to the left, 7.5 millimeters in figures 6 
and 7, 2 millimeters in figure 8, 4.5 millimeters in figure 9. (When the 
breathing was very profound, as occasionally happened, the error of de- 
flection would, of course, have to be taken into account.) The curves 
here used as illustrations have been reproduced in the exact size of the 
originals by the zinco-graphic method, though somewhat compressed 
vertically in order to economize space. 


knowledge of the essentials, at least. However, it would 
be wrong to suppose that for this reason the results were 
more favorable, owing, mayhap, to voluntary efforts on 
the part of the subject. The contrary was true. The two 
subjects who had no knowledge of the character of the 
reactions upon which my responses depended, retained 
their normal habits, unchanged, throughout the series, — 
whereas the last-named two, afraid lest their knowledge 
vitiate the result, lost more and more of their power of 
concentration and within a short time were in a condi- 
tion of tense inhibition, which is all the more conceivable, 
since they had had no psychological training whatever.* 

Their movements, which at first were quite profuse, 
decreased more and more, so that in the case of von 
Manteuffel the percentage of my successful responses 
sank from 73% correct responses in 90 tests to 20% in a 
total of 20 tests, — and in the case of Schillings from 
75-100% to 23% in a series of 35 tests. The curves 
obtained with von Manteuffel as subject, which I am 
here publishing (figures 8 and 15), are, however, true 
to his normal habits. The same is true of the two first 
curves of Schillings (figures 10 and 11), whereas the 
third (figure 12) shows distinctly the traces of the state 
of inhibition into which he fell, and represents the same 
condition as when Mr. Schillings, while preoccupied, tried 
to work with Hans. All the finer details of the pheno- 
mena in question, were likewise unknown to these two 

For purposes of a clearer understanding of the various 

* My own expressive movements, on the other hand, are as pronounced 
as ever. I still find the attempt to suppress them as difficult now 
as when I was working with the horse (page 57). I could not, o£ 
course, procure a curve of these movements of my own. 



curves, figure 5 is inserted to give the general scheme 

of their arrangement. 




\[ -t 









f down 


Fig. 5. 

All curves are to be read like script from left to right. 
Jhe first is the breathing curve of the questioner, the 
second, third and fourth curves represent his head move- 


ments, — all translated through the workings of the levers 
into up-and-down movements. The objective direction of 
these head movements is indicated by the arrows. It will 
be noted that (because the lever in question was one 
with two arms, and therefore reverses all movements 
made) each lowering of the head of indicated by a rise in 
the fourth curve, and each raising is the head is recorded 
by a sinking in the same curve. The records of the head 
movements forward and backward and to the left and 
right (curves 2 and 3) are two and one-half times the 
size of the actual movements; while the curve of the 
movements up and down (curve 4) — which is of especial 
interest to us — is five times its actual size. The fifth 
and sixth curves, which record my own responses, 
represent the taps of the horse, — the fifth indicating the 
number of taps and the sixth the back-step, which was 
Hans's reaction when he noted the head- jerk of the 
questioner. The seventh, the lowest line, indicates the 
time in fifth-seconds. Since the rate at which the drum 
revolved was not uniform for all the tests, the fifth- 
second marks do not appear the same distance apart in 
all the records, but are farther apart the greater the 
rapidity with which the drum revolved. For the experi- 
ment itself this is quite immaterial. Figures 6 to 9 cor- 
respond in detail with the diagram just described. 
Figures 10 to 12 differ only in that the breathing and 
back-step curves (the first and sixth in the diagram) are 
lacking. In these there is no response on my part to 
the head-jerk of the subject, but tapping was continued 
ad libitum (in the case of the illustrations here given I 
tapped to 5). When these latter curves were taken the 
ordering and the technique of the experiments had not 
yet been perfected. When this was finally done, Mr. 


Schillings, who acted as subject in those tests, had to be 
eliminated from the ranks of appropriate subjects on 
account of the increasing inhibitions, which' gradually 
developed as described on page 120. 

Analysis of such curves is rather difficult, and those 
of different subjects cannot be directly compared. It is 
necessary to make a study of the normal curve of each 
subject taken when his affective state could be described 
as " indifferent ". The influences of the purely physi- 
ological processes, such as pulse * and respiration, must 
also be determined. And even so, an interpretation of 
the curve becomes possible only when a large mass of 
material is at hand, and when the introspections of the 
subject are taken into consideration. The following 
remarks, therefore, are not based solely upon the illus- 
trations given, but upon the mass total of my results. 

In beginning our analysis, let us take first the breathing 
curve. Our results here were quite in accord with the 
view taken by Zoneff and Meumann,^" who believe that 
in the respiration is to be found a good index of the 
affective tone of the subject's mental state. In the 
greater number of cases it was possible to conclude as to 

* Slight head movements accompanying the pulse-beat were until re- 
cently regarded as the symptom of certain diseases of the vascular 
system (the so-called symptom of Nusset), but H. Frenkel has now 
shown them to exist also in normal individuals.^' I myself discovered 
such movements (lateral as well as sagittal) more or less pronounced in 
all the curves obtained from my subjects. The most striking case was 
that of a young physician whose circulatory system was perfectly healthy. 
In most instances I was able to note these oscillatory movements 
directly and to count them without much difficulty. For purposes of 
control the radial pulse was always determined at the same time. The 
observation of the phenomenon appears to be especially easy in the 
case of somewhat full-blooded individuals. 


the degree of concentration of attention, — ^and when this 
was very great, it was even possible to get a clue as to 
the number thought of. Since the high degree of ten- 
sion, under which a subject labored during a test, would 
be accompanied by strong affective coloring, we cannot 
regard as normal any of the curves here reproduced 
(with the exception of the two high points in figure 9). 
Although breathing was always deep and regular before 
and after a test, during the test it was less deep and ir- 
regular. Very often it was suspended altogether (figures 
7, 8 and 9). In ordinary life we often notice that highly 
concentrated attention is usually accompanied by non- 
voluntary inhibition of movements in the musculature 
which, for the moment, is not directly involved ; the man 
lost in thought slackens his pace and finally stands still, 
the intent listener or looker-on holds his breath. 
— N,Of the three curves registering the movements of the 
head, we find that nothing peculiarly characteristic is 
revealed by the two upper ones, giving the movements 
up and down, and to the right and left, respectively. 
They are the ordinary tremor-like movements and in- 
dicate nothing beyond the fact that the subject is unable 
to hold his head absolutely quiet for even one second. 
It is the third line that is of interest to us, for it is here 
that the oft-mentioned head-jerk (which indicates arrival 
— in the counting — at the number expected) registers 
itself. The moment of the head-jerk corresponds, almost 
without exception, with the moment of the first deep 
inhalation, — just as one would be led to expect from 
common experience. But we are not to regard the head- 
jerk as a result of the inhalation, for it also occurs when 
the subject complies with the request that he hold his 
breath during the test. The actual height of the jerks 


recorded in figures 6 to 12 was }i to i}4 millimeters and 
tlie average height obtained from the forty curves of 
these four subjects was i millimeter. There is great 
individual variation: the greatest height that was ob- 
tained from the records was 2^ millimeters, the lowest 
^ millimeter. The variations within the records of 
the several individuals are comparatively slight and 
are evidently dependent, in the main, upon the degree 
of concentration of attention. Thus in the case of von 
AUesch, where in 75 tests the average height of the jerk 
is I millimeter, the mean variation is ^ millimeter. If, 
in order to obtain some idea of the size of Mr. von Osten's 
movements,* we compared the values gained in the 
laboratory with those which would probably obtain in 
his case, we would say that his head movements were 
more minute than almost any of those of which we 
obtained records. At the most they could not have been 
more than }i millimeter (when measured in terms of 
the distance through which the brim of his broad hat 
moved, they would appear to be about Ij4 times as large. 
See page 49.) The movements of Mr. Schillings, on 
the other hand, were certainly four or five times as great 
as those of Mr. von Osten, and occasionally even greater 
than that. When we turn to consider the time-interval 
elapsing between the subject's final head-jerk and my 
reaction (as recorded in the sixth curve), we find that 

* In a special series of experiments a subject was instructed to exe- 
cute rapid head movements as minute and as evenly as possible. 
These were registered objectively and at the same time I made judg- 
ments concerning them. The results showed that my judgments were 
most exact in the case of the most minute jerks. The thing that made 
it especially easy to judge the movements of Mr. von Osten under nor- 
mal conditions, (page 220), was their extraordinary evenness, such as I 
have not met with in any other individual. 


the reaction-time averages ^ seconds, a value which 
agrees very favorably with that estimated for the horse 

Fig. 6. Fig. 7. 

(page 56). Thus it appears that man and beast have 
the same reaction-time — though we must bear in mind 


that I worked under some difficulty, since I had to care 
for the apparatus. 

Let us now turn to a discussion of the several figures. 

Figure 6 (von Allesch) gives a typical view of the 
great, and at the same time economic concentration of 
attention characteristic of the subject. Respiration (first 
curve) is not so profound as usual, yet is changed very 
little. The head-jerk (fourth curve) is of medium height. 
It occurs just at the proper moment, — the subject had 
thought of 2, and had directed his attention economic- 
ally. This attention was of the kind described as type I. 
on page 93. The lowering of the head, (recorded in the 
figure by a rise in the curve), immediately following upon 
the head-jerk upward, is irrelevant. 

In figure 7 (Chaym) we have a record of a different 
nature. Respiration was inhibited throughout the test, — 
(the small waves are due to the pulsating of the heart) ; 
immediately after the test deep breathing takes place. 
Tension steadily increased till 3, the number expected, 
was reached. The head, accordingly, gradually sank a 
little forward. The head-jerk ensued during an interval 
beginning just before the reaching of the goal and ended 
immediately after. The movement was predominantly 
backward, its upward direction being only through a 
distance of J4 millimeter. (This subject was not so 
strongly motor as the preceding one.) The reaction 
followed promptly as seen in curve 6. It was the decided 
raising of the head which follows the head-jerk, that 
prevented the usual back-step with the left foot, when 
the subject was working with Hans. 

Figure 8 (von Manteuffel) is typical of strong and 
at the same time economical concentration. Respiration, 
normally deep and very regular, is for a time completely 


inhibited. Tension rises steadily and the head gradually 
inclines forward. In the interval between the number 

Fig. 8. Fig. 9. 

before the final one and the final one the subject makes a 
sudden bend forward and immediately upon reaching the 



final number gives a violent jerk of the head, upward. 
The attention here would be characterized as being of type 
III, described on page 94. (Owing to lack of space it is 
impossible to give an example of type II, which is only 
to be found in the case of very large numbers.) 

Figure 9 (von Allesch) is expressive of great, but — 
according to the subject's introspection — not economical 
concentration. Respiration, which before and after the 
test was quite regular, during the test itself shows a 

Fig. 10. 

pause. (The tiny waves are due to the heart-beat.) The 
subject had thought of 5, and this number is accompanied 
by a decided head-jerk. But we note that even before 
the final jerk a number of less pronounced jerks occur — 
the result of poorly regulated psychic tension. 

Figure 10 (Schillings) depicts a very high degree of 
uneconomical concentration. There was sudden concen- 
tration at the beginning of the test, and a steady increase 
throughout its course. Accordingly Mr. Schillings bent 


forward at the start, and inclined still farther forward 
at the second — and just before the third — tap. But 
at 3 there is a sudden upward jerk. The number 
thought of had been 4, tension therefore had exploded, as 
it were, too soon. 

Figure 11 (again of Schillings) gives indications, on 
the other hand, of a niedium and economic concentration 
of attention, which is more normal in character. The 
number thought of was 4. 

Fig. II. 

Figure 12 (Schillings again) is indicative of a low 
degree of psychic tension. With the very first tap the 
head begins to rise and continues to do so throughout 
the test. A true final jerk does not occur, we note rather 
in all three curves registering the head movements, slight 
time-marking movements, especially in the second curve. 
In the third curve they are at first minute, but increase 
steadily in size until the fourth tap, after which they 
suddenly disappear. The subject had, as a matter of fact, 


thought of the number 4, but it is hardly probable that 
Hans would have reacted properly upon these stimuli. 
Mr. Schillings had thought of the same number in all 
three tests given in figures 10, 11 and 12. The prob- 
abilities are that if he had been working with the horse 
at the time, in the first case Hans would have reacted 
with three taps with the right foot and a final tap with the 
left, as a result of the questioner's bending forward again 
after the premature head- jerk at 3. In the second in- 

FlG. 12. 

Stance the horse would probably have given four taps 
with the right foot, and in the third, the chances are that 
he would have continued to tap beyond the 4. 

These curves give, on the v^hole, a fair idea of the in- 
tensity and of the course of attention of the various 

Let us now consider a number of records which illus- 
trate the expressive movements involved in the process 
of thinking of such concepts as " up ", " down ", etc. 


Their arrangement is identical with the scheme given in 
figure 5, with the exception that the tapping curves (the 
sixth and seventh) do not appear. The subject was asked 
to think of any of the words " up ", " down ", " right ", 
" left ", " yes ", " no ", etc. He was to begin to conceive 

Fig. 13. 

them vividly when the command " Now ! " was given. 
This moment is recorded in figures 13 to 15 on the fifth 
curve. What has been said on page 123 with regard to 
respiration, holds also/ in these instances : only the first 
rise recorded in figu/e 14 can be regarded as normal. 


The magnitude of these movements varies between J4 
and 3 millimeters. The records of the subject whose 
movements were most extensive, show an average of i^^ 
millimeter (based on 50 tests), with a mean variation of 
^ millimeter. Lack of space precludes the reproduction 
of more than three records. 

Figure 13 (von Allesch) shows the movement accom- 
panying the thought of " up ", a slight raise of the head, 
recorded in the fourth curve. (The thought of " down " 
is accompanied by a corresponding downward move- 

Figures 14 (von Allesch) and 15 (von Manteuffel) 
illustrate the nod which is associated with the thought 
of " yes " in the case of two subjects. It is essentially 
the same in both: the head is lowered and then raised. 
The first of the two subjects is more decidedly motor, 
and his movements therefore were somewhat the more 
extensive. In the case of the second subject the nod 
proper is followed by another which is somewhat less 

A number of other experiments were carried out which 
corresponded with the color-selecting tests made upon 
Hans. (Page 78.) Five sheets of white paper, J4 
meter long and J4 meter wide, were arranged in a series 
upon the floor, 34 meter apart. A dot marked the middle 
of each. The experimenter stood at a distance of 7j4 
meters and. directly opposite the middle' sheet. At about 
Yi meter to the right or left of him stood the subject who 
took the part of the " horse ". The problem of the ex- 
perimenter was to indicate to the " horse " a certain one 
of the five sheets, but without the use of word or gesture. 
I at first undertook the role of " horse ", whereas the 
others consecutively played the part of questioner. All 


of them looked fixedly at the sheet which they had in 
mind. Besides, it usually happened that they would turn 
at least their heads, and often their bodies, more or less 

Fig. 14. Fig. ij. 

in the direction of the particular sheet — and this without 
purpose or knowledge on their part, but purely as a 
result of concentration upon the sheet they wished me 
to point out. One of the experimenters remarked, quite 


casually, that he had noted that I always made a better 
judgment, the more intently he thought of the sheet. 
Others often admitted that, when I had made an error, 
they had not imagined the sheet vividly, or had been 
debating whether or not to decide to think of the neigh- 
boring sheet — the one I had designated. This indecision 
could be noticed by the direction of the eyes. But the 
following table shows how uniform, on the whole, was 
the behavior of the various persons when under the 
guidance of the same impulse. The number of tests was 
200 in each case. All errors were of the same character. 
Neighboring sheets were mistaken for each other, and 
the errors were never of more than one position to either 
side. Their number can easily be obtained by subtracting 
the percentage of correct inferences from the total, 

Experimenter : v. A. B. C. Mrs. v. H. K. Miss v. L. 

Correct inferences : 88^ 88^ 77^ 81^ 77^ 8z;? 

It will be seen that the number of correct interpretations 
is quite high and in none of the cases does it deviate far 
from the mean average of 82%. 

I based my judgment as to the direction of the subject's 
eyes, upon an imaginary line perpendicular to the center 
of the cornea. (This perpendicular does not always 
coincide with the subject's line of vision, which was the 
thing I was after, but this cannot be directly obtained. 
This, of course, was what made the judgment a rather 
difficult matter.) My judgment as to the direction of 
the head I based largely on the direction of the nose, 
(to express it more accurately : upon the direction of the 
median plane.) I purposely noted only the position of 
the experimenter and not the movement which led up to 


to it. When I tried to do the latter, the results were not 
always satisfactory, because the head and eyes of the 
person would frequently, in the process of adjustment, 
move beyond the goal and thus lead me into error. An 
attempt was made to make each judgment as independent 
as possible of the preceding one. But usually, ,^fter a 
few tests, an unintentional association became established 
between certain attitudes and the different places in the 
series of papers. Often all that was necessary was to 
observe the experimenter in order to know which of the 
places he had in mind, it was not necessary to look at 
the papers at all. Every change in the position of the 
person would, of course, make the association thus' es- 
tablished, useless. 

Later, the subjects and I changed roles, I took the 
part of the experimenter and they the part of the 
" horse ". The number of tests in each case was 200 
as before. Here, too, errors were, with but one excep- 
tion, never more than of one place to either side. 
Whether the error was one place to the right or one place 
to the left appeared to depend upon the position of the 
person making the judgment, i. e., it depended on whether 
he stood at my right or at my left. The following results 
were obtained: 

Subject ("horse"): v. A. B. C. Mrs. v. H. K. Miss v. L. 
Correct inferences : 76^ 79^ 75^ 8i^ 77^ 74^ 

A certain agreement can be seen in these results. The 
average of correct inferences is somewhat lower than 
that which was obtained by me (page 135), Tjjo as over 
against 82%. This is probably due to the fact that the 
subjects had had so little practice compared with me. 
' With one of these subjects, Mr. Koffka, a student of 


philosophy, I carried these tests somewhat further, vary- 
ing them partly by increasing the number of sheets of 
paper, partly by decreasing the distance between them. 
The increase in the number of sheets made only a slight 
difference in the results. With 200 tests in each case I 
obtained the following results : 

No. of sheets : 







Correct inferences : 







With but few exceptions, the errors were, as a rule, of 
one place. The series with an odd number of sheets (5, 
7. 9) gave better results than those with an even number 
(6, 8, 10). In the tests with the odd number of sheets 
the experimenter (K.) stood in front of the middle sheet, 
so that it was at the apex of a right angle made by the 
series of papers and the median plane of the subject's 
body; whereas in the case of the even number of papers 
the subject stood opposite the space between the two 
middle sheets, thus making the position of the sheets less 

In the preceding tests the distance between the centers 
of the neighboring sheets was always 50 centimeters, so 
that the angle through which the median plane of the ex- 
perimenter's body would have to turn in order to pass 
from one sheet to the next, was about zVa degrees. In 
the following tests these distances were gradually 
decreased. The sheets, always five in number, were 
replaced by ever narrower white strips of paper mounted 
on dark cardboard and illumined by a Nernst lamp. 
The following table shows the decrease in correct infer- 
ences running parallel with the decrease of the angle 
through which the subject would have to turn in order 
to be in line with the several pieces of a series succes- 


sively. The percentage in each case is based upon at 
least lOO tests. 

Angle: JJ" 3° ^i" 2° l^ 1° 

Distance between the 
centres of two neigh- 
boring papers: . 50cm 39cm. 33cm. 26cm. 20cni. 13cm. 

No. of correct inferen- 
ces : . . . y7% 72% 71% 6&% 66% 6i!{ 

A curious and unexpected change was here noted in 
the subject, Mr. Kofifka, who, while concentrating his 
attention to the uttermost, began unawares to develop 
a new system of expressive movements of the head. 
When the distance between the sheets was relatively 
great, he had been in the habit of turning his head and 
eyes in the direction of the sheet intended, and as the 
distances became less he had reacted only by a turning 
of the eyes. But now, as the distances were still further 
decreased, he began again to react by means of head 
movements, and these were of exaggerated magnitude, 
for which he would compensate, as it were, by an eye- 
movement in the opposite direction. Although the head 
movements decreased in scope as the distances between 
the sheets were steadily decreased, they still were always 
decidedly greater than the eye movements, which I was 
now normally led to expect and which could be judged 
without much difficulty. This form of reaction was much 
more satisfactory as a cue, and therefore it came to pass 
that, whereas in the preceding series I had made only 60% 
correct inferences when the angle was i degree, I now 
found that — the angle remaining the same — 80% of my 
inferences were correct. (My final judgment I continued 
to base, as before, upon the position, and not upon the 


movement, of head and eye). The number of correct 
inferences continued relatively high, even after the dis- 
tance between the papers was decreased tenfold, — as 
will be seen from the following table: 

Angle: ... 1° 30' 13' 9' 7' 6' 5' 3' 2' 

Distance between the 
centres of two neigh- 
boring papers : . . 131 65 33 20 15 13 II 6} 4mm. 

Percentage of correct 
inferences : . .. 80 79 78 81 84 80 77 68 68^ 

Beginning with an angle of i' (distance between the 
centers of two neighboring papers = 2 mm.), the sub- 
ject was unable to focus, with sufficient steadiness of 
vision, upon one paper alone, and the movements, for that 
reason, ceased to manifest themselves. Comparing the 
results obtained in the case of this subject with those 
obtained from two others, whose reactions had remained 
normal, B. and Miss St., we find that with them there 
were only 53% correct inferences in both cases (based 
each upon 200 tests), when the angle was 5'. In my 
errors, too, I often shot wider of the mark. In another 
series of 200 tests, in which Miss St. " merely thought 
of the places ", I had a percentage of 56% correct infer- 
ences, and my errors did not become any coarser. Miss 
St. believed this a case of true telepathy, but I had been 
guided in my judgments entirely by her unwittingly 
made movements — or rather the direction — of her eyes. 
The magnitude of these movements bore a constant rela- 
tionship to the distance between papers as it was con- 
ceived by the subject. 

Reviewing the experiments discussed in this chapter, 
we find that the same kind of movements and postures, 


which had beph noted in persons experimenting with the 
horse, tended to redur in the laboratory, in so far as the 
mental attitude of the subjects, given in their introspec- 
tive accounts, corresponded with that of the questioners 
of the hoBser 



The author having described the observations made 
upon the horse, and having discussed the activities of the 
questioner upon the basis of observations made object- 
ively and upon his own introspections, and having veri- 
fied the results thus obtained, by means of laboratory 
tests, — we are now in a position to solve satisfactorily all 
the problems which this interesting case has presented. 

That which is least difficult to understand is the 
hors e's se eming knowledge of language and particularly 

TTirability to^answer questions, no matter by whom, or in 
what dialect, they were put. As a matter of fact, it made 
no difference who desired an answer, for the only person 
upon whom the experiment depended was the questioner, 
that is, the one who asked the horse to tap. We have 
everywhere designated this person as the experimenter 
or questioner. It was he who gave the directions, and 
since all, that were. J^nvoTvBd were _vis.ual signs, the drama 
in which Hans appeared as the hero, was nothing but a 

-pantomime. All speech was superfluous and, except 
in so far as the tone of voice in which it was spoken 
was soothing or reprimanding, it was quite unintel- 
ligible to the horse. 

From the foregoing, the reader understands without 
further explanation Hans's ability to count and to make 
computations. If the number of taps had depended 
solely upon the length of time and the angle at which 



the questioner bent forward, the horse would have been 
able to tap any number desired. Since, however, only 
the right foot was employed, the left one being used at 
most for making a final tap, the number of taps had an 
upper limit which was due to the fatigue of the animal. 
This limit was about loo. That it was possible to ask 
such questions as : " How many times is 100,000 con- 
tained in 654321 ? ", and thus to give problems involving 
millions, is perfectly clear. 

All wonderful feats of counting and computation which 
were accomplished while thus experimenting with the 
horse are to be accredited, not to the horse, but to 
the questioner. If such is the case, they certainly cannot 
be considered astonishing. Thus, when to the question, 
" How many of the gentlemen present are wearing straw 
hats ? " the horse answers correctly in accordance with 
the wording of the question and omits the straw hat of 
a lady, then Mr. von Osten is the guide. It is no wonder 
that Hans never showed the slightest excitement when 
confronted with difficult problems, nor that it apparently 
took no time whatever to solve them. 

Hans, however, was also a faithful mirror of all the 
errors of the questioner. Aside from mistakes due to 
occasional interruptions on the part of visitors, these 
errors had two sources: faulty computation and ina^ 
quate concentratiprij^i. e., aside from arithmetical errors 
~oir the part of the questioner, were his premature or be- 
lated movements. Since both of these factors might be 
operative, the following three possibilities arise. 

(a) The questioner computes correctly but does not 
move at the proper moment. Nearly all the errors which 
had been accredited to the horse, were of this kind. 

A part of these errors had the appearance of being 


significant, that is, they might be interpreted as a mis- 
_j22£ghg5^Q" "^ .thej[uestion. If, for instance, instead 
of a sum only one of the quantities was given, or, if in- 
stead of a product only one of the factors was given, it 
might be interpreted that the horse simply wished to re- 
peat the problem. Thus, Mr. von Osten in response to the 
question : " How much is 3 times 5 ? ", twice in succession 
received the answer, " 3 ", and upon my question, " How 
much is 3 plus 4?" he answered, "3", and to "How 
much is 2 times 6 ? " he tapped 6, and to " What is one- 
fourth of 36?" 4. In part (certainly in the second and 
third example cited) an individual quantity or factor 
had been emphasized in the consciousness of the ques- 
tioner (cf. page 105) and in part the reactions were due 
to chance. Thus, when Mr. Hahn asked the question: 
"What is one-half of 10?", he received the following 
responses: 2 and 10, and then 17 and 3. To this class 
belong also, the tests made by the Commission of Sep- 
tember and reported in Supplement III. (See page 255). 
Other errors, even though they may not have appeared 
to be significant, might yet have been characterized as 
mistakes du^ to speed ; as when, e. g., Hans made an error 
of one unit — and sometimes, though less frequently, of 
two units — too much or too little in his response. One 
might be led to believe that Hans had not made an error 
of calculation but merely of counting in the process of 
giving his result, which always had to be done by the 
cumbersome method of tapping. As a matter of fact, 
the trouble lay in the wrong degree of concentration on 
the part of the questioner: In errors of + i, tension was 
too slight, in those of — i, it was too great (see pagegi). 
This comes out clearly in a comparison of the two more 
extensive series which I took in the case of Mr. Schil- 


lings. During the first series, he was well disposed, and 
was able to concentrate effectively, while during the 
second, he was nervous and easily diverted. This dif- 
ference in intensity of concentration in the case of the 
two series is attested, not only subjectively by Mr. Schil- 
lings's introspective statement, but may be measured 
objectively by means of the number of final taps which 
the horse gave with his left foot during these two series. 
We saw (page 94) that these final taps were always a 
sign of intense concentration and, as a matter of fact, 
one-half of the horse's responses to Mr. Schillings during 
the first series were made in this way; whereas, in the 
second series, only one-third were of this sort. (I, my- 
self, was never able to get, without conscious control, a 
greater number of this type of response.) We may 
therefore say that, in the first series we had a high degree 
of tension, or concentration, whereas, in the second 
series, we had a low degree. The errors distribute them- 
selves over the two series as follows : 

+ r +2 —1 —2 
Series I (31 tests) 

Correct responses : 87% 

Incorrect " : 0% 0% 13^ 0% 

Series II (40 tests) 

Correct responses : 40^. 

Incorrect " 40^ Z% z.%,% 0% (and< 

other liinds of errors.) 

We find in Series I no " + i " errors, but only " — i " 
errors; in series II, on the other hand, the errors are 
almost exclusively of the " + i " category, equaling the 
number of correct responses, and there is only one 
" — I " error. A series obtained in the case of Mr. von 
Osten is almost as satisfactory an illustration. When he 


first began to take part in tests in which the procedure 
was the one we characterized as " without knowledge " 
and had to note their complete failure, he was thrown 
into such confusion that the responses in the case of 
procedure with knowledge were also incorrect. The 
errors there were always + i, (whereas those in the case 
of procedure with knowledge, which were due to quite 
different causes, were very great and inconstant.) The 
number of -)- i errors obtained on this occasion com- 
prises one-fourth of all the plus errors which were evei- 
obtained in the case of Mr. von Ost«n during the entire 
course of these experiments. Finally, I would mention 
two examples of my own. In the course of my very first 
attempts with Hans I obtained, as I said on page 89, 
three responses in a total of five which exceeded the cor- 
rect result by i. This I would explain by the fact that 
although I employed a high degree of concentration, I 
nevertheless was somewhat skeptical. The result was a 
certain deficiency in the degree of concentration. A 
second example which I would cite is taken from the 
period in which I had already discovered the cue to 
Hans's reactions and goes to show that I was then still 
able to eliminate the influence of this knowledge and to 
work ingenuously. To the question, " How much is 9 
less I ? " I, momentarily indisposed, received the answer 
10, and then six times in succession the answer " 9 ", and 
finally the correct response, " 8 ". 

Errors of another kind — the not infrequent offenses 
against the very elements of counting and the funda- 
mental arithmetical processes — were regarded in part 
as intentional jokes and by an authority in pedagogy as 
a " sign of independence and stubbornness which might 
also be called humor ". Hans emphatically asserted that 


2+2 was 3 or he would answer questions given in imme- 
diate succession as follows : " How many eyes have 
you ? — 2. " How many ears ? " — <z. " How many tails ? " 
— 2. These errors, as a matter of fact, evince neither 
wit nor humor, but prove incontrovertibly that Hans had 
not even mastered the fundamentals. 

Many of the errors baffle every charitable attempt at 
interpretation. These gave the horse the reputation of 
capriciousness and unreliability. If Hans designated the 
tone " e " as the seventeenth, or " g " as the eleventh, or 
when he called Friday the 35th day of the week or 
believed 50 pfennige to be worth only 48, the cause for 
these responses lay either in the insufficient degree of 
tension on the part of the questioner (as in the first 
three examples) or in the extravagant expenditure of the 
same (as in the last case). If, therefore, the horse 
at times would " hopelessly flounder " which would seem 
to be indicated by tapping now with the right and now 
with the left foot, then as a matter of fact, this form of 
reaction came about as was described on page 61, with 
this difference that there we had to do with voluntary 
controlled movements on the part of the questioner, 
whereas here, they are the result of an unsuitable degree 
of tension which expressed itself in frequent and dis- 
concerting jerks. Besides the answer 3, this so-called 
floundering was the only reaction the average person 
could obtain from the horse in the absence of Mr. von 
Osten and Mr. Schillings. It would however occur 
also in the case of these gentlemen and would be re- 
ceived by them with resentment when in truth it was 
Hans's greatest feat, for he showed his extremely keen 
reaction upon every movement of the questioner. To 
this group belong also the errors in the case of higher 


numbers, the sole cause of which lay in the difficulty with 
which tension could be maintained and the body kept 
motionless for so long a period. These errors occurred 
in accordance with a certain law. If, for instance, a cer- 
tain test repeatedly evoked incorrect responses, the 
questioner would gradually increase the duration of 
tension and would thus come a little nearer to the desired 
goal with every test. In this way, Mr. von Osten desiring 
30 as an answer obtained consecutively the responses, 
25, 28, 30 ; and I, myself, for the answer 20, received con- 
secutively the responses 10, 18, 20 (see also the laboratory 
tests, page 105). Sometimes too, the questioner would 
flag in his efforts/before the goal was reached. Thus in 
one of my first tests, I received for the answer 11 the 
following responses: i, 4, 5, 7, 4. I was unable to get 
beyond 7. In other instances, the horse responded first 
with too few and then with too many taps. The correct 
response therefore could only be obtained after an ap- 
preciable amount of gauging of tension, as in target 
practice there must be a gauging of distance. (See 
page 92). In this way Mr. von Osten obtained for 10 
the responses 8, 8, 11, 10, and Mr. Schillings for 17, 
received 9, 16, 19, 18, 18, 14, 9, 9, and finally, after some 
efforts, 17 taps. Thus there was a rise from 9 to 19, 
then a fall back to 9 and after eight tests the correct 
response. As long as we attempt to explain this fact 
as error on the part of the horse, so long will it remain 
inexplicable, but the moment we regard it from the point 
of view of the psychology of the tension of expectation, 
it becomes perfectly plain. 

The same holds true for the curious predilection which 
Hans appeared to have for the numbers from 2 to 4, 
especially for 3 (see page 68). As a matter of fact the 


cause of this lies in nothing other than the inadequate con- 
centration of attention on the part of the questioner and 
less often in an extravagant expenditure of concentration, 
which explodes immediately after the first tap on the 
part of Hans (as in the case of my first tests) ; but usu- 
ally the cause lay in a complete lack of concentration, 
though the same result may be produced by various 
causes. It is usually after 2 to 4 taps of the horse's foot 
that the questioner, who does not concentrate, makes his 
first move which naturally puts an end to the tapping 
on the part of the horse. As a rule this jerk follows im- 
mediately upon the second tap. (On the other hand, re- 
laxation of attention is very difficult upon the first tap. 
See page 95). The questioner, however, would expect 
further tapping and therefore would not bring his body 
back to a completely erect position and the result would 
be a 3, the last unit of which would be given by the 
final tap with the left foot. Here we also obtained light 
as to the answers which Hans gave in those tests in 
which the method was that of " procedure without 
knowledge". These responses had nothing to do with 
the problem, for neither the horse nor any one else knew 
the solution. But in the horse's responses the degree of 
tension of the questioner's concentration was faithfully 
mirrored. An experimenter who was as skillful in con- 
centrating as Mr. von Osten, obtained — almost without 
exception — very high numbers, whereas one whose con- 
centration was slight would receive in response to nearly 
all questions the answers 2, 3 or 4. Thus, the Count zu 
Castell received in response to seventeen questions the an- 
swer 2, three times, the answer 3, six times, and the 
answer 4, four times, two answers being accidentally cor- 


Another group of errors was characterized as-At ub- 
bornn ess on the pajrt, of Jians, such as his persistence in 
repeating an incorrect response, or his repetition of a 
former correct answer in response to later questions 
where it was perfectly senseless. During a demonstration 
before a large number of persons, I held a slate with the 
number 13 upon it within the horse's view and also 
within view of the spectators. I, myself, did not know 
what number was written on the slate. Having been 
asked to tap the number, Hans responded by tapping 
5. The grand-stand shouted " Wrong ! " I asked Hans 
to try again. Four times in succession he answered 5. 
At another time Mr. von Osten and I each whispered a 
number (7 and i, respectively,) into the horse's ear and 
asked him to add the two. Three times in succession he 
tapped II. After the test had been repeated in accord- 
ance with " procedure with knowledge " and a correct 
response had been received, we tried once more a test of 
" procedure without knowledge ". Again, he responded 
with an 11. On a third occasion, I asked Hans to tap 5. 
He responded with a 4 and then, correctly, with a 5. 
Thereupon, I asked him to tap 6. Again, he responded 
with a 4. Then I asked him to tap 7. Once more he re- 
sponded with a 4, and only when I proceeded to count 
aloud did he tap 7 correctly. I had him repeat the 7 and 
then went over to 9. Promptly he responded with an- 
other 7. In these cases, which by-the-way were not very 
frequent, we have to do, not with stubbornness on the 
part of Hans, but with the persistence of that number 
in the consciousness of the questioner. Modern psy- 
chology has recognized this tendency of ideas, which 
have once been in consciousness, to reappear on other 
occasions even though they are wholly inappropriate. 


It has been termed " perseverative tendency." (Persever- 
ationstendenz ").^^ 

While the errors thus far discussed appeared sporadi- 
cally in long series of correct responses, there still might 
be observed at times a massing of errors, usually at the 
beginning of a day of experimentation or at the begin- 
ning of a new series. We were regularly told that Hans 
always had to have time to adjust himself to new cir- 
cumstances. The records often showed comments such 
as these : " After a number of practice tests the horse 
appears particularly well disposed ", or " Hans, at first 
inattentive, does not respond. Suddenly he gets the hang 
of things ". Different questioners who worked with the 
horse required different lengths of time to obtain proper 
responses. Some needed a quarter of an hour, others 
scarcely half a minute. I, myself, found that in the 
degree in which I learned to control my attention, in that 
degree did this phenomenon tend to disappear, but would 
reappear the moment I became indisposed. From this 
we see that, instead of attributing all sorts of mental 
characteristics, such as stubbornness, etc., to the horse, 
we should lay them to the account of the questioner. As 
a matter of fact we find that this " getting into the sweep 
of things ", i. e. the overcoming of psycho-physical 
inertia, has, long been known in the case of man and has 
been experimentally determined and called " Anregung " 
(excitation) by the psychiatrist, Kraepelin,^^ and his 
pupil, Amberg.=' A massing of errors toward the end 
of a long series occurred only when the questioner was 
fatigued. There was nothing which had to be interpreted 
as fatigue or as indisposition on the part of the horse, 
(except in the few cases of very large numbers, of. 
page 67). To be sure, Mr. von Osten always offered 


these two excuses. That they were without warrant is 
shown by the fact that Hans, after appearing indisposed 
or fatigued while working with one questioner, would 
nevertheless react promptly and correctly a moment later 
for some other experimenter, and furthermore, when 
working with me, the number of his correct responses 
would rise or fall with my own mental disposition. __—- ' 

Finally, I would here note a rather interesting obser- 
vation for which I am indebted to Mr. Schillings and the 
Count zu Castell. They had noticed, independently of 
each other, that the horse would often fail to react 
when for any length of time he was given problems deal- 
ing _with abstract nu mber s^ even though they were of the 
simplest kind; but that he would immediately improve 
whenever the questions had to do withconcrete jjbject^,^.. 
They believed that Hans found applied mathematics more 
interesting, and that abstract problems, or those which 
were altogether too elementary, bored him. The Count 
zu Castell furthermore noticed that the responses tended 
to be more correct as soon as he had the horse count 
oij.eGts- which he, himself, (Castell) could see during the 
test. Quite in "accord witK This is the statement to be 
found in the report of the September-Commission, in 
which we find this note in a discussion of the arithmetical 
problems (not involving visible objects), which the gen- 
tlemen already mentioned had given the horse. " The 
horse responded with less and less attentiveness and ap- 
peared to play with the questioner." Here again, that 
was looked for in the animal which should have been 
sought in the man. Mr. Schillings^ was capable of in- 
tense, but not continued Concentration and it was he who 
was bored, and not the horse^" And it was the Count zu 
Castell and not the horse that found it necessary to in- 


voke the aid of perceptual objects to bring his attention 
to the proper height of concentration. 

The reader will see that thus far I have supposed the 
horse to be a never-failing mechanism and that I have 
placed all errors to the account of the questioner. The 
horse never failed to note the signal for. stopping and 
therefore never was the immediate cause of an error. It 
is not to be denied that now and then he would cease 
tapping spontaneously and in this way would become 
the cause of an error. We have no data on this point, but 
undoubtedly the horse's share in the total number of 
errors was very slight. 

(&.) Another source of error was faulty computation 
on the part of the questioner. The questioner made the 
signal for stopping when the expected number of taps 
had been reached. The horse faithfully mirrored the 
miscalculation of the questioner. I have knowledge of 
only one such case. The journals report that once Mr. 
von Osten, when someone called to his attention that Hans 
had indicated the wrong day of the week, replied : " Yes, 
you are right, it was not Thursday, but Friday," where- 
upon Hans being asked again, promptly responded cor- 
rectly. This appeared to the reporter in question as proof 
of the subjective influence of Mr. von Osten upon the 

f — (c.) When errors in calculation and failures in proper 
concentration combine, i. e. when the questioner makes a 
mistake in calculation because he is excited or inatten- 
tive and for the same reason does not make the move- 
ment, which is the signal for stopping, in accordance 
with the number which he deems to be the correct an- 
swer, then the result is usually wrong, but it may be cor- 
rect in the few cases in which the two errors exactly 
compensate each other. Nothing has been so effective 


in establishing Hans's reputation, nothing has brought 
him so many followers, as these cases in which he, rather^ 
than his mentor, has been in the right. Compared with 
the mass of cases in which Hans was wrong these latter 
cases are diminishingly few in number, yet these few 
made such an impression upon the observers that their 
number tended to be overestimated. As a matter of fact, 
I have been able to discover records of only seven 
such cases. Two of these were reported by the Count 
zu Castell. On the 8th of September, he entered the 
horse's stall, alone, and believing it to be the seventh 
day of the month, he asked Hans the date. The horse 
responded correctly with 8 taps. At another time he 
held up before Hans a slate on which were written the 
numbers 5, 8 and 3 and asked the horse to indicate their 
sum which in the momentary excitement, vaguely ap- 
peared to Castell to be 10. To his chagrin he noticed 
that Hans continued to tap. Thereupon he intentionally 
remained motionless until the horse had stopped tapping 
spontaneously — as he thought — at 16. (The newspapers 
reported that the numbers to be added had been 5, 3, and 
2; that the questioner had expected the answer 11, but 
that Hans had in three tests always ceased tapping at 
10.) In both cases the questioner regarded the answers 
of the horse as wrong and recognized his mistake when 
his attention was called to it. I, myself, had the same 
experience. One time I received in response to the ques- 
tion, " What day of the week is Monday ? ", the answer 
2, although I had expected the answer i ; at another time 
I asked, "How much is 16 less 9?", and the horse re- 
sponded with 7 taps, although I had erroneously expected 
S- I noticed my mistake only when my attention was 
called to it by one of those present. Another example is 


related by Mr. Schillings. A row of colored cloths lay 
before Hans. Beside them stood an army officer. Point- 
ing to the latter's red coat Mr. Schillings asked the horse 
to indicate, by means of tapping, the place in the row 
where a piece of the same color lay. Hans tapped eight 
times, but Mr. Schillings reprimanded him because the 
red piece was, as a matter of fact, second in the row. 
Upon a repetition of the test, Hans again tapped 8. (By 
some, the facts are recounted as having been the other 
way round; viz.: Hans tapped 2 instead of 8. This of 
course would call for a different explanation.) It was 
noticed that at the place which would be indicated by 
eight taps there was not a red piece but a carmine colored 
piece of cloth. A newspaper reports, somewhat vaguely, 
a sixth case as follows : Hans was asked to spell the name 
"Donhoff" and began correctly: "Do". Mr. von 
Osten, who somehow began to think of another name, 
" Dohna ", interrupted him and wished to correct him by 
suggesting o instead of 6 (i. e., 2 taps instead of 3). 
Hans, however, " continued to spell the entire word with 
the greatest equanimity. He had not erred. A similar 
experience is reported by Mr. H. von Tepper-Laski, the 
well known hippologist. Although the details have 
slipped from his memory, he reports that in the case in 
question the correct answer was thrice refused by the 
questioner who thought that the horse's answer was in- 
correct. Hans, upon being severely reprimanded in a 
loud and harsh tone of voice, turned about as if disgusted 
with the injustice of the man and made straight for his 
stall. — It is clear that in the cases described we are not 
dealing with accidentally correct responses, for in nearly 
every case the test was repeated a number of times and 
the same responses were received each time. As a mat- 


ter of fact, my own introspection convinced me that the 
third and fourth cases were surely, and the first and 
sixth were very probably, due to insufficient concentra- 
tion on the part of the questioner. Accordingly there is 
everywhere in these cases a difference of + i or -|- 2 be- 
tween the number thought of and the number tapped 
(see page 92 f.). The data in the second and fifth 
and still more in the seventh case were too meager to 
warrant an attempt at explanation, for it is not even 
known whether Hans responded with more or fewer taps 
than was expected by the questioner. It is unfortunate 
that a more complete record was not made. 

The frequent and intentional attempts of Mr. von . 
Osten to induce the horse to give an incorrect response, 
— which, by-the-way, were regularly unsuccessful — ^be- 
long only apparently to this group. Thus he asked, e. g., 
" 2 times 2 is 5, is it not? " " 3 times 3 is 8? ", etc., but 
Hans refused to be misled, and responded correctly. 
This was from the very beginning one of the main argu- 
ments for independent thinking on the part of the horse. 
The actual procedure was as follows, even though the 
questioner had said " 2 times 2 is 5 '', there still was pres- 
ent in his consciousness the number 4. I, myself, would 
think either of the first member of the equation, i. e., 2 
times 2, in which case Hans would respond with 4 taps or 
I would have in mind the second member, i. e., 5, in 
which case he would respond with 5 taps. Never did I 
succeed ii? thinking of both at the same time. The associ- 
ation between the thought " 2 times 2 " and the concept 
"4" is so close and supported by so many other associ- 
ations that the attempt to form a new one, that is at com- 
plete variance with all these, is futile. One may say 
" 2 times 2 equals 5 " but it is impossible to conceive it. 


Let us turn now, from the tests in counting and compu- 
tation to those in reading. We have seen that Hans 
manifested his seeming knowledge of language symbols 
in a threefold manner: (he might approach a. slate on 
which was written the symbol asked for,fpr he would 
indicate its location in a series of slates by means of tap- 
ping, oi^finally by means of so-called spelling of the 
word which was written upon a slate or placard. The 
r responses by means of approaching a placard were very 
\ often unsuccessful, while indications by means of tapping 
\ were scarcely ever unsuccessful. If it were true that 
higher intellectual proceesses * were here involved, then 
the converse would have been expected, for tapping re- 
quired not only the ability to read, but also the ability to 
count. If, on the other hand, we assume that the horse 
simply followed the directions given by the questioner's 
movements, this seeming difficulty resolves itself, for it 
would be more difficult for Hans to perceive the signs 
which he receives while moving than those which he re- 
ceives while tapping. When we recall that it was easier 

* Professor Shaler ^, a well-known American savant, mentions a 
three-year old pig belonging to a Virginian farmer, that was able to read 
and had some understanding of language. From numerals which were 
written upon cards and spread out before it, this pig could compose 
dates. It could also select from among certain cards one upon which 
was written a given name, asked for by the master. Supposedly no 
signs of any kind were given. (Shalerthought to exclude effectively the 
sense of smell, which is so highly developed in the pig, in that he, Shaler, 
himself smelled at the cards, since he also " possessed an acute olfactory 
sense I ") Since we are told that the farmer in question made a business 
of supplying trained pigs for exhibition purposes, the case appears sus- 
picious. We hear of a pig exhibited in London, that was able to read 
and spell, and could also tell the time by the watch ^. We cannot 
tell, however, whether the two pigs, which beyond a doubt were mechan- 
ically trained to respond to signals, are identical or not. 


to direct the horse to a placard near the end of a row 
than one nearer the center (see page 81), we can 
readily understand how it was that during the experimen- 
tation carried on by the September-Commission (Supple- 
ment III ; page 255), Hans was able to point out immedi-"~-? 
ately the placards on which were written the names " Cas- \ 
tell " and " Stumpf ", for they were at the two extreme 
ends, but was unsuccessful in locating the one on which 
was written the name " Miessner " which was not a bit 
more difficult to read, but was located at the fourth place 
in the row. He first approached the fifth card, then upon 
repetition of the test he pointed out the other neighboring 
tablet, viz., the third. 

In spelling, Hans was quite indifferent whether his 
table with the eighty-four number signs upon it stood 
before him, for he had no knowledge of letters. Neither 
Mr. von Osten nor Mr. Schillings required it, for the 
former knew the table by heart and Mr. Schillings told 
me that before every test he made a note of the 
numbers which were necessary to indicate the required 
letters, trusting in this way to control the responses 
of the horse and never guessing that by so doing 
he was making it possible for the horse to answer cor- 
rectly. The newspaper reports aroused much interest at 
the time by stating that Hans was able to spell such 
proper names as " Pliiskow " and " Bethmann-HoUweg ", 
even to putting in the difficult " w " and " th ". The 
friends of Mr. von Osten at the same time called attention 
to the exquisite auditory acuteness of the horse which 
enabled him to perceive the aspirated " w " and to dis- 
criminate between the "th" and "t", (the "th" is 
softer than the "t" in German. — Translator). This ex- 


planation, of course, must have appeared somewhat 
daring even at that time. 

Hans was quite guiltless of the many limitations im- 
puted to him concerning his knowledge of symbols. That 
he was unable to read capitals or Latin script was merely 
a vagary of the master, like the belief that it was neces- 
sary to confine one's self in one's questions to a certain 
vocabulary and to a certain form. Mr. von Osten's ap- 
fparent failure to elicit responses from the horse on topics 
'of which it was ignorant is a beautiful illustration of the 
I power of imagination. Mr. von Osten was convinced 
from the very first that Hans could not answer such ques- 
tions. When the belief in success was lacking, of course 
there was not the requisite amount of concentration 
which, alone, leads to perceptible expressive movements 
and thus elicits a successful reaction on the part of the 

"~~" Mr. Schillings, owing to his great impressionability, 
remained long under the spell of Mr. von Osten's point 
of view. Thus I find in the record of the September- 
Commission that the question " How much is 3 plus 2 ? " 
was answered incorrectly by Hans, but he responded cor- 
rectly the moment Mr. Schillings replaced the word 
" plus " which was " tabooed ", by the word " and ". For 
a long time also he could receive no response to ques- 
tions put in French until one day he made the discovery 
that, curiously enough, the animal never responded ade- 
quately unless he himself firmly believed in the possi- 
bility of success. It is noteworthy that the Count zu 
Castell, independently of Mr. Schillings, made the same 
discovery. Mr. Schillings made his curious discovery— 
which he was unable to interpret, but which aroused some 
suspicion— on the following occasion. One day — whether 


accidentally or because his prejudice was temporarily 
overcome — he commanded ; " Dis deux ! ". Hans re- 
sponded promptly with 2 taps. He was greatly sur- 
prised and believed that Hans had gotten hold of the 
French by hearing it spoken in his environment. Possi- 
bly he understood also " trois " and " quatre " ? He put 
the questions and received correct responses. He asked 
again, " dix ", " vingt ", and so on to " soixante ". At 
" soixante — six " he became doubtful. Indeed, Hans 
failed him. At " quatre-vingt ", the game began again. 
" Cent ", again, succeeded. The old saying that " Faith 
will move mountains " was verified once more.* 

* It has been scientifically proven that a number of supposed mys- 
tical phenomena, table-moving, table-rapping, and divination by means 
of the rod, all are the result of involuntary movements made unawares 
by those concerned, just as in the case of this work with Hans. (We 
must of course except those not infrequent instances in which the phe- 
nomena in question are purposely and fraudulently simulated.) There 
is this difference, however, that there the thing affected is a lifeless ob- 
ject, — the table or the rod, — here it is a living organism, the horse; hence 
there the immediate effect of the movement is physical work in the form 
of energy expended in moving the table, here the movement becomes a 
visual stimulus. A number of observations which I find in the relevant 
literature, and which I shall introduce into this chapter, may serve to 
show how close is the similarity between the two cases, how much 
depends upon the questioner, and how little really upon the Instrument 
— whether table or horse — which is acted upon. 

Two examples will sufiice to illustrate the significance of belief and 
of the concentrated attention that results from it. The first is taken 
from the letters of Father P. Lebrun on the divining rod ^, which ap- 
peared in 1696. An old woman once told a treasure-seeker that she had 
always heard that a treasure was buried at a certain place in the fields. 
The man, who was known as an expert in the art of using the divining 
rod, immediately set out to locate the gold. Lo, and behold, the moment 
he set foot on the spot described by the old woman, the branch turns 
downward, and from Its movements the man gathers that twelve feet 
below ground there lies buried some copper, silver and gold. He calls 


Hans's seeming knowledge of the value of coins and 
cards, of the calendar and the time of day, as well as his 
ability to recognize persons or their photographs, can 
now be readily understood. In all of these cases, we had 
to deal, in so far as knowledge is concerned, only with 
that of the questioner, — the horse simply tapped the 
number the questioner had in mind. The meaning which 
was supposed to be expressed by the tapping never 
existed as far as Hans was concerned ; it was only in the 
mind of the questioner that the concepts: ace, gold, 
Sunday, January, were associated with " i ", etc. The 
same was true with regard to all other wonderful feats 
of memory. The sentence : " Briicke und Weg sind vom 

a peasant to dig a pit eleven feet deep, then he sends him away so that 
no other should get into the secret. He himself digs a foot deeper, but 
all in vain, for he finds nothing. Standing in the pit, he again takes up 
the branch. Again it moves, but this time it points upward, as if to 
indicate that the treasure had disappeared from the earth. Dismayed, 
he climbs out of the pit and questions the branch a third time. This 
time it points downward once more. He climbs back into the pit. 
Presently he feels the prick of conscience (for in the 17th century many 
regarded the dipping of the divining rod as the work of the Devil). 
Terrified, he exclaims : " O God, if the thing I am doing here is wrong, 
then I renounce the Evil One and his rod (s'il y adu mal, je renonceau 
demon et k la baguette "). Having spoken, he once more takes the rod 
in hand to test it. It does not move. Horrified, for now there was no 
longer any doubt that Satan was the cause of its movements, the man 
makes the sign of the cross and runs away. But he had hardly gone 
more than two or three hundred paces when the thought strikes him : 
Is it really true that the branch will no longer move for him .' He 
throws a coin to the ground, cuts a branch from a bush nearby, and is 
overjoyed when he notes how it dips down toward the money. 

Another example is to be found in a report of the well-known physi- 
cist, Ritter ", of Munich, which appeared during the early part of 
the 19th century. Ritter, a man with a bent for natural philosophy and 
metaphysics, describes an instrument which was to replace the divining 
rod, and which he called " balancier." It was simple enough, consisting 


Feinde besetzt ", (The road and the bridge are held 
by the enemy), which was given to the horse one day and 
correctly repeated by him on the following day, was not 
an answer elicited from the horse by means of a question, 
but rather a system of automatic reactions which were 
induced by certain involuntary movements of the ques- 
tioner as stimuli. Far from showing a wonderful 
memory in these feats — as is claimed for him by the 
very non-critical compiler, Zell ^' — Hans, on the contrary, 
has at his service a remarkably small number of asso- 
ciations. For, besides possessing the powers of any 
ordinary horse, he recognizes only a few meager visual 
signs. To be sure, we find in the literature a horse that 

of a metal strip that was balanced horizontally upon a pivot, and was 
supposed to be put into motion in the presence of metals. Ritter used 
this instrument in his numerous experiments with the Italian Campetti, 
a man who had achieved a measure of fame in Europe for his ability to 
discover springs and metals by the use of the divining rod. Carrying 
the "balancier" on the tip of the middle finger of his left hand, Cam- 
petti — whose integrity one cannot cavil at — had to touch repeatedly a 
plate of zinc or pewter, and had to count aloud the number of touches 
he made. The following curious law was found to obtain (that was 
probably suggested to the subject by Ritter without his being aware of 
it) : with the first contact the " balancier " turns to the left, with the 
second to the right, and with the third it remains at rest. At 4 it turns 
once more to the left, at 5 to the right, at 6 it remains at rest, etc. It 
remained immovable only at the so-called trigonal numbers (3, 6, 
9, 15, 21, etc.). Ritter tells us that when Campetti did not really count 
or did not think of the number, then it would not have any influence 
whatever upon the action of the instrument. This Ritter ascribes to 
the agency of electricity (which in the i8th and 19th centuries was made 
to play very much the same role that Satan had played in the i6th and 
17th centuries). 

The similarity of these two cases and that of Mr. Schillings is evident. 
When the questioner of the horse and the bearers of the " balancier " 
and of the divining rod are confident of success, they succeed. When 
they do not expect success, they fail. 


was said to have recognized 1500 signals/^ but all proof 
is lacking and the report is so meager that we cannot 
discover whether these signs were auditory or visual.* 
Having thus disposed of all questions concerning the 
horse's apparent feats of reason and memory, let us turn 
to those in the field of sensation. We shall begin with 
vision. That Hans was unable to sel ect colore d pieces 
of cloth merely upon the basis~of color quality, without 
reference to their order, was shown in Chapter II. It 
would, however, be somewhat hasty to infer color-blind- 
ness from this fact, as did Romanes ^^ on the basis of 
similar unsucessful responses on the part of a chim- 
panzee (" Sally" of the London Zoological Garden). It 
is much easier to explain the failure of the horse than 
that of the monkey on the basis of intellectual poverty, 
a poverty of associative activity. It presumably can 
_discriminate between . the various colors, but it cannot 
asociate with these their names. The existence of 
chromatic vision in the lower forms is by no means as 
unquestionable as is assumed by popular thought. Even 
teleological considerations which are often brought for- 
ward (especially that of the ornamental and protective 
coloring of so many animals) can never do more than 
establish a certain probability. For definite proof, we 
need data given by observation (we have none in this 
case), or experimental evidence. Such evidence we 
have, but it is insufficient in quantity and unfortunately 
most of it was obtained under inadequate experimental 

* The French investigators Vaschide and Rousseau make a reference 
to this case, and mistakenly state the number of signals as 1500 instead 
of 115 '". Ettlinger ^' taks over this wrong figure and makes the 
additional mistake of assuming that the reference is to an original inves- 
tigation made by the two Frenchmen. 


conditions* We know nothing regarding chromatic 
vision in the horse, though we have often had trained 
horses which apparently possessed color discrimination. 
The earliest report of this kind I find in a work published 
in the year 1573.^" Here we read that a number of 
Germans exhibited two horses in Rome which could, 
upon request of their masters, point out those persons 
among the spectators who were wearing stockings of 
any designated color. The passage, " conoscevano i 
colori ", (they recognized the colors,) proves nothing and 
no one has ever heard, even in modern times, of a horse 
that actually knew colors. 

Nor did Hans possess anything like that high degree 
of visual acuity which had been attributed to him. He 
was supposed to be able to read easily at a distance small, 
almost illegible script, which we ourselves could decipher 
only with the greatest difficulty close at hand. It was 
also supposed that he could distinguish ten- and fifty- 

* All told, there are hardly more than half dozen experimental inves- 
tigations of the color-sense in mammals, — to speak only of these. 
■ Three of them deserve especial mention. One, the work of the Amer- 
ican, Kinnaman, " on two Rhesus monkeys. Then a brief but careful 
piece of work by Himstedt and Nagel.'* These two investigators were 
able to determine that their trained poodle could distinguish red of any 
tone or shade from the other colors, and from Professor Nagel I learned 
that later the tests were extended and the same was shown to be true 
concerning the blue and the green. And finally there is an investiga- 
tion which hitherto has been known only from a reference which Pro- 
fessor Dahl,25 the investigator, himself makes. The work is on a mon- 
key, Cercopithecus (Chlorocebus) griseoviridis Desm. (Professor 
Dahl has kindly allowed me to look over the records of the experi- 
ments. He intends to publish the monograph at an early date.) 

All of these investigators arrive at the conclusion that the animals 
tested by them possess color-sense. The monkey last-mentioned shows 
one peculiarity : it was unable to distinguish a saturated blue from the 
black. It will require further tests to clear this up. 


pfennig pieces whose faces had become worn beyond 
recognition for us. None of these accomplishrnents have 
stood the test. We haveTRT reason- tcTBelTeve that Hans 
can see the objects about him more clearly than other 
horses, regarding whom one usually assumes that they 
receive only vague visual impressions. Horses do not 
as a rule seem to be near-sighted as_ is often.._assert.ed by 
the layman, but rather somewhat far-sighted, or if we 
Tiiay believe Riegel,^' who tested some six hundred 

linrspg fhpv prphably havp pnrmal viann. But we are 

told that many horses — and according to some authors all 
— have an innate imperfection which detracts con- 
siderably from the clarity of vision. This imperfection 

•consists in an irregular formation of the sclerotic coat 
and of the lens of the eye.^' The two organs do not have 

\-h,e same refraction in all parts. As a result, objective 
points~afe not imaged as points upon the retina. (Hence 
the name : astigmatism, i. e., " without points ", for this 
disorder.) The retinal image of the object is not only 
vague, but also distorted.* 

Many will doubt whether with such imperfect images 
an animal can react to directives so minute, as we have 
asserted to be true in the case of Hans. In considering 
this question we must distinguish between the directives 
for pointing out colors and the directives for tapping and 
for head movements on the part of the horse. In point- 

* There is no justification for the wide-spread belief that the horse 
which on account of the greater size of his eye (more correctly, on 
account of the greater focal distance) receives larger retinal images of 
objects than does the human eye, for that reason also sees objects, 
larger than we do. Horses' shying is often explained in this way. But 
the conclusion just mentioned is erroneous. The retinal image is not 
the perceptual image. It undergoes many transformations within the 
nervous system itself. 


ing out and bringing forth pieces of colored cloth there 
is involved the perception of an object at rest, viz.: 
the direction of the questioner who is standing quietly;^ 
whereas in the case of responses by means of tapping the 
stimulus is the horse's perception of the questioner's 
movements. Now, the construction of the horse's eye, 
as described above, is not favorable for the perception 
of objects (so-called acuity of vision). This may partly 
account for the slight success of the horse in those tests i 
in which he was required to select a piece of cloth of a! 
designated color, in so far as these commands were not ' 
accompanied by calls or exhortations. Where human 
observers averaged eighty per cent correct responses 
(page 135), Hans, under similar conditions was suc- 
cessful in only one-third of the tests'. In his errors he 
was also wider of the mark than were the human obser- 
vers (page 82). The object perceived, to be sure, is 
a large one, viz. : the questioner, and he at close range. 
We must therefore consider more specifically what are 
the determining factors that make for success or failure 
of the response. 1 First of all, the innocent questioner 
very often did not designate thT'difection with sufficient 
cleaiuess. Furthermore, ^Hans presumably was not 
able to discriminate sufficiently between the direction of 
the experimenter's eye and that of his head, which two 
directions did not always coincide. "^ Finally the horse's 
attention was often diverted, while he was running toward 
the piece indicated, by the other pieces lying to the right 
and to the left, and for this reason the addition of a single 
piece to the otherwise unchanged row of five pieces 
tended to decrease greatly the chances of success. 

The case is different with the perception of the direct- 
ive signs for tapping, for nodding and shaking the head. 


etc., all of which require the perception of movements. 
This is not necessarily more difficult on account of the 
imperfect constitution of the tissues that serve for the 
refraction of light. Some authors even aver that this 
facilitates the perception of moving objects. This view 
was first advanced by the excellent ophthalmologist, R. 
Berlin ''^ of Stuttgart. In arriving at this view he was 
guided by the following considerations. The peculiar 
form of astigmatism of the lens of the horse's eye, which 
Berlin has described as " butzenscheibenformig ",* be- 
cause it appears in the form of a series of glossy concentric 
circles around the lens nucleus, has the property of en- 
larging the pathway (and with it the rapidity) of moving 
retinal images. If we take a speculum by means of which 
a view may be had of the interior of the eye, and fixate 
a definite point on the retina of the horse, and then 
make a slight movement of the head horizontally, we 
find that the point fixated moves — apparently at least — 
toward the border of the pupil. In a normally con- 
structed eye this seeming movement will be in a straight 
line, while in the eye of the horse, (according to Berlin), 
its path is curved, and therefore longer. Berlin believes 
that the same thing which here occurs in the case of this 
merely apparent movement, must also happen when an 
external moving object is imaged on the horse's retina. 
Its pathway, too, will be curved, and therefore longer, so 
that if the head of Mr. von Osten moves past the animal's 
eye, then the image on the horse's retina will take a 
longer, more circuitous route than it would if the eye 

* " Butzenscheiben " are the small circular panes of green glass, used 
in leaded windows in early days. They are high in the middle (hence 
the name : " Butze," a protuberance) with a number of concentric circles 
around the central elevation. — Translator. 


were not astigmatic. We cannot, however, immediately 
conclude from the fact that an objective movement is 
imaged as being greater in extent on the retina, that it 
will therefore be more readily perceived by much less 
that it will appear greater to, the horse, than would 
be the case if the lens were normally constructed. The 
visual percept is not immediately dependent upon the 
retinal processes, for between the two are interpolated 
complex, inaccessible nervous processes. Still, Berlin 
believes that he is justified in drawing this conclusion 
from a number of relevant considerations. Accepting 
it, he believes that it would be possible for the horse to 
perceive movements, that for the human eye. which is 
not subject to this form of astigmatism, would lie below 
the threshold. 

This theory, the simplicity of which certainly must 
make a strong appeal, has been adopted by a number of 
well-known investigators (Schleich*", Konigshofer *^). 
If we also could accept it, then Hans's phenomenal power 
of perceiving the movements of objects would be ex- 
plained. But doubts arise which restrain us. Even if 
we were to accept Berlin's view in general, we should 
still come upon the following difficulties. \ In the first 
place, it is questionable whether the peculiar form of 
astigmatism mentioned is indeed as common as he sup- 
poses.* The references in the literature are exceedingly 

* Since no opportunity was given us to examine Hans's eyes we do 
not know wliat their condition is in this respect. Though it would have 
been interesting to know, it would hardly make any difference in the 
views presented. If Hans should prove to be either far or near-sighted, 
then, if we are to make any supposition at all, it would be that the defect 
could not be very great, since near sightedness exceeding 2 or 3 diopters 
and far-sightedness exceeding one diopter is seldom found in the case of 
the horse. According to Mr. von Osten, Hans at one time manifested 


meager on this point. In order to make a few tests at 
least, I undertook to examine nine horses with the aid of 
Dr. R. Simon, oculist, to whom I am greatly beholden 
for the assistance given in these and other tests to be 
mentioned presently. In not one of the nine cases did 
we discover anything like the curved deflection which is 
supposed to be the sign of the form of astigmatism in 
question. But in order to test objectively whether Ber- 
lin's assumption were justified, we examined in the 
laboratory fresh specimens taken from two horses. The 
eyes were fastened in a frame in what corresponded to 
their normal position. Their posterior spherical wall 
(i. e., their respective retinal surface) was replaced by a 
piece of ground glass. On a spherical surface linear 
movements of a point of light are always imaged as 
curves, no matter what the shape of the lens forming 
the image may be. (For a more detailed statement see 
page 170, at close of note.) Since, however, our inves- 
tigation had to do only with those curves which were 
due to the qualities peculiar to the lens, we had to replace 
the spherical by a plane projection surface. In front of 
the eye thus modified a strong light was placed at such 
a distance that the image of it, produced on the im- 
provised back of the eye by the cornea and the lens, 
was a sharply defined point of light. Now, when the 
source of light was moved, the point of light would also 
move on the glass plate. Sitting at some distance behind 
the eye, we observed the movements of this point through 
a telescope. Thus we became witnesses of what happens 
upon the horse's retina when a moving object passes in 

a tendency to shy easily. Be this as it may, for little could be concluded 
from it, since in many extremely shy horses, no kind of visual imper- 
fection can be discovered. 


front of his eye. Although we saw the point of light 
move through relatively long distances both horizon- 
tally and vertically, no sort of deflection in its pathway 
could be noted. Berlin's exposition does not hold true 
for the eyes of the horses, either living or dead, which 
were examined by us. 

But in the case of some of the horses in whom Berlin 
had seen the phenomenon for which we sought in vain, 
he himself tells us, the deflection was very slight. In 
that case, it would appear, no great advantage would 
be gained along the lines indicated. But even assuming 
the degree of deflection to be very great, his theory goes 
to pieces on the very point it was supposed to explain. 
A concrete example will make this clear. If Mr. von 
Osten, standing two feet away from the horse, raised 
his head }i millimeter (which figure by no means rep- 
resents the extreme values that were obtained), then in 
the horse's retinal image every point of the man's head 
would move through a distance of 0.0025 millimeter — 
assuming the horse's eye to be free from astigmatism 
and assuming its focal distance to be 25.5 millimeters. 
If, however, other conditions remaining the same, we 
presuppose an extreme form of astigmatism, one in which 
the path of the retinal image is not a straight line, but 
is deflected into a semicircle, then each point would pass 
through a distance of nearly 0.004 millimeter. If the 
sensitive retinal elements have a diameter of 0.002 milli- 
meter (as Berlin, somewhat inexactly, states), then from 
two to four elements would be stimulated in case there 
were no astigmatic deflection. But in case the deflection 
did take place, it would not necessarily involve more 
elements, as can be seen by making a simple graph ; in- 
deed we can imagine cases in which the circuitous path 


would involve even fewer elements than the straight 
one. And finally, when the movement which the horse is 
to perceive, does not occur in a straight line but in the 
form of a curve, (which will generally be the rule), 
then the astigmatism will tend in many cases to decrease 
the curvature of the image's path on the retina, and 
sometimes even obviate it entirely. In all these cases, 
on Berlin's own theory, the perception of the movements 
would be hindered rather than aided.* 

* For the benefit of specialists I would say the following in addition 
to the more general remarks just made. For the most part, the deter- 
minations of refraction made on the eye of the horse are still rather 
unreliable. In sciascopy there is a dispute among investigators con- 
cerning ambiguous shadows, and in the use of the refraction-ophthal- 
moscope no definite region of the eye's background has been adhered 
to by the various investigators. It appears that Riegel, whose diligent 
researches mentioned on page 164 were published in 1904, knew nothing 
concerning the round area in the horse's eye, discovered by I. Ziim " in 
1902. Also, if so great a degree of astigmatism is really the rule as is 
emphasized especially by Hirschberg*^ and Berlin,'^* then the simple 
refractive index usually given — sometimes within a half diopter- 
would be meaningless. Berlin *5 and Bayer *' believe the vagueness of 
the retinal image resulting from the astigmatism, is offset by this : that 
the oval pupil functions as a stenopaic slit. In view of the width of the 
horse's pupil this appears to me to be rather hypothetical. 

Concerning Berlin's theory of deflecting astigmatism I would say the 
following : Of the two ophthalmoscopic signs mentioned as being 
characteristic of this form of astigmatism, — the concentric circles and 
the arcuate deflection of the pathway of the fixated points, — when there 
is a movement of the eye of the observer (or of the eye observed), ac- 
cording to Berlin the former is not so constant as the latter. So far as 
I know, the concentric ring formation is mentioned only by Bayer*' and 
Riegel,*' and is said to occur principally in horses with myopic vision— 
and hence, relatively, in a minority of cases. Judging from the particu- 
lars, we are inclined to believe that a case of " Butzenscheiben "—lens 
reported by Schwendimann *8o jg ;„ reality a case of senile sclerosis. 
Berlin repeatedly warns us against mistaking the one for the other."' 
The arcuate deflection, on the other hand, has not been mentioned else- 


But to come now to the most pertinent objection. We 
saw that Berlin's whole train of thought rested upon the 

where as a personal observation. In Berlin's calculation ♦' of the in- 
crease in the extent of the retinal pathway an ambiguity has crept in. 
He says that " in the astigmatic eye there are stimulated 207 times as 
many nervous elements as would be stimulated in the ideally normal 
eye." It ought to read " 207 more " instead of " 207 times as many." 
And this number holds only for the one case computed by Berlin, and 
under the specific assumption that exactly ^ times the normal number 
of elements were stimulated (571 instead of 364). Therefore the gen- 
eral statement which Bayer ^^ makes in his text-book, that according to 
Berlin's evaluation " 207 times more nervous elements " are stimulated 
in the astigmatic eye than in the non-astigmatic one, does not hold true. 
Closing this note, a few remarks concerning the experiments made 
by Dr. Simon and myself. AU of the nine horses were tested for the 
vertical image by means of the ophthalmoscope. In most cases Wolff's 

electric speculum was used. Atropine was not employed. For the 

laboratory tests the adipose and the muscular tissues were removed 
from the eye-ball and the rear part of the bulb cut away. The front 
part, containing the cornea and the lens, was fastened over one opening 
of a metal cylinder which was closed at the other end by means of a 
disc of ground glass. The whole, approximately as long as a horse's 
eye, was filled with a normal salt solution whose refractive index (1.336) 
corresponds quite closely with that of the vitreous humor of the horse's 
eye. The pressure from within was regulated so that on the one hand 
it was not dimmed and yet on the other there were no wrinkles in the 

cornea. The source of light the filament of a Nernst lamp was 

moved about in a plane 120 cm. distant from the eye and perpendicular 
to the optic axis. It was moved through the point of intersection as 
well as at various distances from it. Movement in horizontal and verti- 
cal directions was in each case along lines 150 centimeters in length, 
which would correspond to an angle of vision of not less than 64°. The 
pathway of the imaged point was controlled by means of the cross-hairs 
of the telescope. If in the same way we observe through the sclerotic 
of an intact eye-bulb a point of light falling upon the retina and shining 
through the sclerotic and choroid (which is not difficult when we use an 
intense light), then to the observer its pathway will, of course, appear to be 
deflected convexly toward the periphery, — and the deflection will appear 
the greater, the farther the point of light is removed from the optic axis. 


assertion that it made no difference whether we regarded 
by means o£ -the speculum the seeming movement of a 
fixed retinal point, or whether the image of an external 
moving object is passing over the horse's retina. As a 
matter of fact, however, these two processes are very 
different from one another. In moving the mirror, with 
its small opening we are looking through ever changing 
portions of the horse's lens, — testing it out, as it were. 
The horse, on the other hand, sees with all parts of the 
lens simultaneously, in so far as the lens is not covered 
by the iris. The arcuate deflection, which is nothing but 
a registration of the difference in the indices of refraction 
of the different parts of the lens used consecutively, 
might thus be formed for the observer using the mirror, 
but never for the horse. For these reasons we cannot 
conclude that the kind of astigmatism described can 
really increase the horse's acuity in the perception of 

Since the light-refracting apparatus of the horse's eye 
does not offer a satisfactory explanation for the extraor- 
dinary keenness of visual perception possessed by the 
Osten horse, we must go a step further and ask whether 
it may not perhaps be found in the part immediately 
sensitive to light, the retina. That portion really would 
seem to be adapted to the perception of movements of 
minimal extent, and for this reason : it is more than three 
times as great in extent as the human retina, and the 
horse's retinal images are likewise larger owing to the 
position of the nodal point. The cells of the retina that 
are sensitive to light, the rods and cones, might therefore 
be correspondingly larger than those of the human eye, 
without thereby making the whole organ less efficient 
than the human eye. But the most recent measure- 


merits °^ have shown that the rods and cones of the horse's 
eye are more minute than ours. Assuming that, in the 
case of the horse, as is presumably the case in human 
vision, the transition of a stimulus from one retinal cell 
to the next already in itself induces a sensation of move- 
ment, then the horse ought indeed be extraordinarily keen 
in the perception of moving objects (provided that the 
horse's more minute cells are packed just as closely as in 
the human retina). And besides, there are two specially 
adapted areas within the retina of the horse. The 
"band" (streifenformige Area") which was discovered 
fifteen years ago by Chievitz,^'' is a strip of i to 1J/2 mil- 
limeters in width, traversing the entire retina horizontally, 
and is noteworthy on account of its structure and prob- 
ably, too, on account of its greater efficiency. It may 
have something to do with the accomplishments of the 
Osten horse; but in how far it would be hard to say. 
The other noteworthy portion of the horse's retina is the 
"round area " discovered some four years ago, located 
at the rear outer end of the " band ", and it is the best- 
equipped part of the horse's retina and corresponds to the 
area of clearest vision, the yellow spot, in the human eye. 
But this round area need not come in for consideration 
by us, for its location would indicate that it is used in 
binocular vision, that is, seeing with both eyes.°^ But in 
all our experiments the Osten horse observed only with 
one eye. That does not mean, however, that under other 
circumstances the round area may not be of very great 

In the present state of our knowledge, all attempts at 
explanation are, of course, of the nature of hypotheses. 
If further investigations should disclose this explanation 
to be untenable, then we would either have to suppose 


some unknown power in the eye of the horse,* or else 
seek a cause in the animal's brain. Further experiments 
on other horses would be necessary in order to discover 
whether the species as a whole possesses this ability or 
whether only certain ones are thus endowed. The 
former is of course more probable. In this particular 
case conditions were unusually favorable for the develop- 

* Konigshofer, who as we have already said, seconds the explanation 
given by the ophthalmologist Berlin (and who confounds " Butzen- 
scheiben " astigmatism with the common, so-called regular form), be- 
lieves " that not only astigmatism but also the shape of the blind-spot of 
the eye must be taken into consideration. This portion of the retina, 
where the fibres of the optic nerve enter the eye (and called " blind-spot " 
because there are no cells there that are sensitive to light) is very nearly 
circular in man, but differs in shape in the different species of animals. 
Konigshofer thought he had discovered that a relatively elongated blind 
spot was favorable to keenness of vision. If we place the mammalia 
in series on the basis of their relative keenness of vision, he says, we 
would find that this series is identical with the one in which they are 
grouped with reference to the form of the blind-spot from the circular 
up to the most elongated. (In such a series the marmot takes the place 
of honor.) > 

This exposition is not very satisfactury, however. We cannot be sure 
what he means by " keenness of vision " (" scharfaugigkeit "). Is it 
visual acuity in the usual sense of the term (as is said in one of his pas- 
sages), or keenness in the perception of the movements of objects, (this 
would appear to be his real meaning), or both at the same time. But 
whatever the significance he may put into the term, any such attempt 
at grouping the lower forms must prove unsatisfactory from the very 
start on account of the scant data which we possess on visual perception 
in animals. The experiences of the hunt upon which Konigshofer 
partly bases his view, are entirely inadequate for such a purpose. This 
much is certain, that the Osten horse, in spite of a blind-spot which, 
thought somewhat oval, is by no means very elongated, possesses an 
extraordinary acuity in the perception of movements. Even if the par- 
allelism' mentioned by Konigshofer were really shown to exist, it would 
not explain the matter until it were also shown in what way keenness of 
vision is dependent upon the shape of the blind-spot, — a portion of the 
eye which is not immediately operative in the visual sensation at all. 


ment of this ability. We must bear in mind that in all 
probability Mr. von Osten's movements -very gradually 
became as minute as they are now, and that therefore 
Hans at first learned to react to such as were relatively 
coarse. Furthermore, his practice extended throughout 
four years and during this time it was his sole occupation. 
Without specific predisposition, however, all this practice 
would have been utterly futile. We can also readily 
appreciate how indispensable in the struggle for existence 
a well-developed power of perceiving moving objects 
must be to horses (and most other animals) living in 
their natural condition and habitat, in order to be aware 
of the approach of enemies, or, in the case of carnivora, 
the presence of prey. In view of all these considerations 
we can readily see how it was possible that the horse, 
perhaps in spite of rather defective vision, could react 
with precision to movement-stimuli which escaped ob- 
servation by human eyes. 

We can understand also the horse's never-flagging 
attentiveness when we recall that self-preservation 
prompts eternal vigilance over against all that is going 
on in the animal's environment. (In the case of Hans, 
hunger was at first the motive ; later, habit did the work.) 
Furthermore, the lower form is not hindered in giving 
itself over to its sense-impressions by the play of ab- 
stract thought which tends so strongly to direct inward 
our psychic energy, — at least, in the case of the cultured. 

Nevertheless, Hans still remains a phenomenon not 
only in excelling all his critics in the power of observa- 
tion, but also in that he is the first of his species, in fact 
the first animal, in which this extraordinary perceptual 
power has been proven experimentally to be present. It 
has long been known °^ that horses could be trained to 


respond to cues in the form of slight movements, which 
remained unnoticed by the layman, and this fact has 
been made use of by circus trainers to its fullest extent. 
But such signs, I have discovered, are without excep- 
tion, of a far coarser sort than thosgs^^we have here de- 
scribed, and they can be instantly detected by the prac- 
tised observer. Nor was it known to professional trainers 
that it was possible for the master to direct a horse to 
any point of the compass simply by means of the quiet 
posture of the body. For this reason it was believed 
that no signs could possibly be involved in the color- 
selecting-tests (cf. Supplement IH, page 255). In this 
we have the support of some of our experts, as is wit- 
nessed by the following extract from a letter of his Ex- 
cellency Count G. Lehndorff, one of our best hippological 
authorities, who at one time carefully examined the Osten 
horse. (The letter was addressed to Mr. Schillings, and 
I have permission of both gentlemen to use it). In it he 
says : " If the author's statements, in which you also have 
concurred, are correct, and if, as a matter of fact, the 
horse really does react to such minute movements as are 
absolutely imperceptible to the human observer, then we 
have indeed something quite new, for hitherto no one 
would have believed that horses can perceive movements 
which man cannot. But I am even more surprised by the 
explanation of the color-selecting feats. — This too, is 
something absolutely new. One would not have deemed 
it possible that a horse could do anything of the kind 
simply by Using the posture of a man's body as a cue to 
which it could react with such precision." 

And yet, even though both facts were new concerning 
the horse and had not hitherto been proven experiment- 
ally regarding any other species, nevertheless something 


of this sort has been known concerning the dog for some 
time. His ability to single out an object upon which his" 
master had intently fixed his gaze, was made the basis of 
a special form of training, called " eye-training," ^'^ nearly 
one hundred yf^^'s ago. The dog was taught to focus 
constantly upoti his master's eyes and then upon com- 
mand to select the object which he, the master, had been 
fixating. Such a dog has been described by the natural- 
ists A. and K. Mtiller.°^ But the master of the dog, unlike 
Mr. von Osten, would not permit anyone else to work 
with the animal, and the two brothers, recognizing the 
trick, were justified in adding that " the whole afifair 
aimed at deceiving the public, and the dog's reputation 
was but a means of making money ". The success of 
such exhibitions appeared furthermore, to depend upon 
the close proximity of the trainer and the dog, whereas 
the direction of the head (and even of the body) could 
very probably be perceived at greater distances also. 
At least we learn from a reputable source that in the 
hunt, dogs can perceive from the mere posture of their 
master, what direction he intends to take.'* 

But a still more curious fact is this, that dogs, too, learn 
— evidently spontaneously — to react to the minimal in- 
voluntary expressive movements of their master. The 
first example mentioned in the literature on the subject 
is that of an English bull-dog called Kepler, belonging 
to the English astrophysicist. Sir William Huggins.^' 
We are told that this dog seemingly could solve the most 
difficult problems, such as extracting square roots and 
the like. The numbers were indicated by barking, — 
thus one bark was for one, two barks for two, etc. Every 
correct solution was rewarded with a piece of cake. 
Huggins states explicitly that he gave no signals volun- 


tarily, but that he was convinced that the dog could see 
from the questioner's face, when he must cease barking, 
for he would never for an instant divert his gaze during 
the process. Huggins was unable, however, to discover 
the nature of the effective signs. This satisfactory, 
though still unproven, explanation has been accepted by 
specialists, among them Sir John Lubbock.'" I, too, 
regard this dog as a predecessor of our Hans. 

A similar case is reported by Mr. Hugo Kretschmer, 
a writer of Breslau, in the " Schlesische Zeitung " of 
August 21, 1904. To him I am beholden for a detailed 
written statement, which he has kindly permitted me to 
use in this connection. The gentleman named, first 
trained his dog to ring the table-bell, and this, by press- 
ing the dog's paw upon the bell-button. When the dog 
had learned to do this independently, his master tried to 
teach him the rudiments of numbers, in such a way that 
the animal was to give one ring of the bell for the num- 
ber I, two for 2, etc. But these attempts failed utterly 
and had to be abandoned. But Mr. Kretschmer had 
noticed that he was able to get the dog to ring any num- 
ber which he, Mr. Kretchmer, might decide upon. 
(Success was always rewarded by a bit of bread and 
butter.) At first Mr. Kretschmer tried to imagine vividly 
only the final number, but failed thereby to elicit correct 
responses from the dog. But he did succeed when he tried 
making a series of separate volitions. Thus for the num- 
ber 5, he would " will " each separate push of the button 
on the part of the dog. Even so, however, he never got 
beyond 9, for then the dog would become impatient and 
would ring the bell continuously. Anything that diverted 
the dog's attention, such as noises, etc., also entailed 
failure. In these tests master and dog had faced each 


other, each gazing steadfastly at the other. Mr. Kretch- 
mer was convinced, however, that the dog was not 
guided by any sort of sign, but rather by suggestion. 
He based his belief on the following two observations. 
After some practice, he says, the tests were also success- 
ful when he did not look at the dog, but stood back to 
back with it, or when he screened himself from the dog's 
view by stepping to one side behind a curtain. The 
tests were unsuccessful, on the other hand, whenever he 
was mentally fatigued or had taken some alcoholic drink. . 
The arguments do not appear to me to be adequate. If 
he turned his back upon the dog and no other observer 
was present, he had no means of knowing whether the 
dog did not, after all, peer around to get a peep at him. 
If others who knew the desired number, were present, 
the dog might have gotten his cues from them. And 
there may be some doubt whether the curtain adequately 
served the purpose for which it was intended. At any 
rate, it was added that all attempts to influence the dog 
from an adjoining room — which would thus exclude 
effectively all visual signs — were utter failures. I am 
also strengthened rather than weakened in my belief, by 
the second argument which Mr. Kretschmer makes, viz. ; 
that mental fatigue or the use of alcohol on the part of 
the questioner tends to make the result unsatisfactory. 
We noted a similar effect in the case of the horse (page 
150), where a disturbance of the " rapport " between the 
questioner and the horse was invoked by some by way of 
explantion. The facts were explained by us much more 
simply. We attributed the result to the close correlation 
between the type of mental concentration and the nature 
of the expressive movements — ^ correlation which we 
have shown experimentally to exist. I cannot, therefore. 


subscribe to the view that this dog did not require either 
visual or other sensory signs. The tests which were 
made for the purpose of strengthening that view, are on 
a par, I believe, with those mentioned on page 45. 
And since auditory, olfactory, and other stimuli, though 
not impossible, still are improbable, I believe that out 
Hans, Huggins's dog, and the one belonging to Mr. 
Kretschmer, differ from one another only in this, that 
the first taps, the second barks, and the third presses a 

And finally I have access to a letter from the Rhine 
Province in which there is a brief account of a dog that 
would promptly obey any cornmand that was given with- 
out a sound and supposedly without the accompaniment 
of the slightest kind of gesture. It is specially mentioned 
that the animal steadily watched its master during these 
tests. The perception of the slightest involuntary ex- 
pressive movements is in all probability the secret in this 
case also. Here, too, suggestion has been invoked by 
way of explanation, but there was not the slightest at- 
tempt made to find for it a more specific foundation, and 
we cannot suppress an objection based on the matter of 
principle. It is incumbent upon anyone who uses a term 
so ambiguous, to define what content he desires to have 
put into it. If he does not do this, he is giving us, in^ 
stead of a concept, a bare word, instead of bread, a 

While we must reject the explanation based on sug- 
gestion,* we believe, on the other hand, that we have 

* I can find examples of supposed suggestion in the case of animals 
given only by Rouhet." He says that by means of'suggestion he taught 
a half-year old half-blooded mare-colt which he had raised himself, to 
fetch and carry, and this in a very short time. In order to indicate to 


here again, evidence of the presence of visual signs, 
given unwittingly and involuntarily, just as I am sure 
that they were involved in the two preceding cases, and 
similarly in the case of the Huggins dog. Since the ef- 
fective signs were discoverable in none of these canine 
predecessors of Hans, an investigation would be desir- 
able, based upon the insight gained as a result of these 
experiments upon Mr. von Osten's horse. Unfortunately 
this is impossible, since the dogs in question are dead. 
But others like them undoubtedly exist in many places. 
We might mention that when Hans first came under the 
limelight of public attention, there was also frequent 
reference to the Huggins dog, but he soon dropped out 

the colt what was wanted, Rouhet would concentrate with his whole 
mind upon the object intended (a watch), and at the same time he would 
bend forward slightly. In the third test, that is at the end of fifteen 
minutes, he had accomplished his purpose, and in the tenth lesson, no 
more mistakes occurred. The colt would fail to respond, however, as 
soon as he refrained from making any gestures, or was in a laissez faire 
frame of mind, or when he thought of other things. He therefore be- 
lieves that there must have been some kind of immediate, though in- 
explicable, connection between the brain of the trainer and that of the 
horse. I think the explanation is evident : the connection was not as 
he thought, an immediate one, but arising through the mediation of the 
man's attitude (" attitude un peu baissee "), and of his movements 
(" gestes "), both resulting from his intense concentration (" tension de 
la pensee "). 

In general we may say that, no matter what content we may wish to 
put into the term " suggestion," not a single fact has since come to 
light which would justify, and much less demand, the application of the 
term to lower forms, unless we would expand the definition of the term 
to the extent of comprising every kind of command, every arousal of 
ideas, whatsoever. But it would then be nothing but a new name for 
old knowledge 62 and would lose all explanatory value. (Hypnotism, 
so-called, in the case of horses, I shall discuss elsewhere in another' 
connection.) «« 


of the discussion again.** And this for two reasons. 
The dog never took his gaze from his master and ap- 
peared to be entirely dependent upon him in his reac- 
tions. Hans, on the other hand, seemed to give evidence 
of a high degree of independence and never appeared to 
look at the questioner. But we know now that, though 
he was never dependent upon the will of his master, he, 
^too, abjectly hung upon the man's involuntary movements 
and never for a moment lost him from view. But since 
the horse is able to observe with one eye alone, and 
needed to direct only it and not the entire head toward 
the questioner, in order to focus comfortably, one could 
not conclude as to his line of vision from the direction of 
the head. Since, furthermore, in the horse the pupil is 
hardly distinguishable from the darkly pigmented iris 
and since the white sclerotic is hidden by the eyelids, 
except when the eye is turned very much, it is difficult to 
determine what direction the eye is taking. I once pur- 
posely stepped backward to the horse's flank, so that he 
had to turn his eye far back and thus the outer border 
of the iris and the white sclerotic coat became visible 
and all doubt concerning the line of vision was removed. 
This doubt could never, arise in the case of the dog, the 
median plane of whose head is always directed toward 
the object fixated, and Zborzill is justified in saying, as 
he does, in his discussion of training of the kind men- 
tioned on page 177, " But any careful observer can im- 
mediately guess the mariner in which such a dog has 
been trained." °* If Hans had chanced to possess so- 
called " glass-eyes " — in which the dark pigment is 
wholly or partly lacking, so that the black pupil is clearly 
defined against the lighter background, — then no doubt 
could ever have arisen concerning the direction of the 


eye, and Hans never would have come to be regarded as 
the " clever " Hans. 

After the publication of the December report, Hans 
acquired a reputation for excellence in thought-reading 
and thus the discussion of thought-reading among 
animals in general became once more the order of the 
day. That is to say that many of our domestic animals 
are — like the human mind-reader (a la Cumberland), 
— supposed to have the ability to infer the thoughts of 
their masters from slight involuntary movements. They 
are thus aware when the feeding hour approaches, when 
they may go out in the open, etc. They also appear to 
be aware that their welfare lies in our hands, and there- 
fore would seem to have a vital interest in divining our 
intentions and our wishes. Not only our spoken words, 
but also numberless movements — usually without our 
knowing it and often contrary to our desire — speak a 
clear language. As is well said by the American neuro- 
pathologist, Beard, °° (who first explained the phenom- 
enon of thought-reading, on the basis of the perception 
of very minute muscular jerks, and therefore called it 
"muscle-reading" or "body-reading"): "Every horse 
that is good for anything is a muscle-reader; he reads 
the mind of his driver through the pressure on the bit, — 
though not a word of command is uttered." We know 
that in the case of perfectly trained horses the rider's 
mere thought of the movement which he expects the 
horse to make, is seemingly sufficient to cause the animal 
to execute it.* Such cases are of course very much like 

* An aiustration is given by Babinet ^* concerning the horse of an 
English lord. Mr. Burkhardt-Foottit, also, that excellent trainer, who 
has been master for more than forty of the most highly-trained horses, 
tells us that while sitting on a well-managed horse it sometimes hap- 

l84 the horse of MR. VON OSTEN 

that of our Hans, excepting that instead of visual signs 
they involve aids of a mechanical nature, which, however, 
does not alter the general principle, since both of them are 
of the nature of sensory stimulation. But we must not 
overlook the essential difference between this so-called 
thought-reading on the part of animals and that which is 
done by man. The human thought-reader can interpret 
movements, for he is familiar with the ideas which are 
their source. Thus when at the second tap, I notice a 
very slight jerk of the subject's head, and a stronger one 
at the fifth tap, I infer that he thought of the problem 
2 -f- 3 = 5- While the experimenter thus cannot be said 
to read thoughts, he still infers them. The animal, on the 
other hand, we may be reasonably sure, draws no such 
inferences. In its conscious life it remains ever on the 
sensory level. If we could ask Hans about it, he would 

pened that he had merely thought of making a certain turn, when the 
horse immediately executed it, before he, the rider, had to his knowl- 
edge given any sign or aid. An observation belonging under this head 
is also made in Tolstoi's " Anna Karenina " '■', this perfect mine of 
acute psychological observation. In the famous description of the race 
we are told concerning Count Wronskij riding his Frou-Frou just behind 
Machotin mounted upon Gladiator, who was leading the race : " At the 
very moment when Wronskij thought that it was time to overtake 
Machotin, Frou-Frou, divining her master's thought, increased her pace 
considerably and this without any incitement on his part. She began 
to come nearer to Gladiator from the more favorable, the near side. 
But Machotin would not give it up. Wronskij was just considering 
that he might get past by making the larger circuit on the off-side, 
when Frou-Frou was already changing direction and began to pass 
Gladiator on that side." Similar experiences might be gathered else- 
where. Not infrequently the reflection of the rider that his horse had 
not for a long time indulged in some trick peculiar to him, will imme- 
diately call it forth ; or doubts on the part of the rider concerning the 
possibility of crossing some barrier, are often the cause of the horse's 
fall or of his refusal to leap and of his running away. 


probably answer : " As soon as my master stoops forward, 
I begin to tap ; as soon as he moves, I stop. The thing 
which induces me to act thus is the carrot which is given 
me ; what it is that induces my master to make his move- 
ments, I do not know." — It is therefore erroneous to 
believe that animals require the power of abstract think- 
ing in order to utilize the signs which are consciously 
or unconsciously given them, as is argued by Goldbeck °' 
when he says with reference to the training for visual 
signs, which we have already mentioned before : 
" There the dog has consciously interpreted the visual 
impression in terms of the conclusion that he is expected 
to bring forth the leaf indicated." Nor was there any 
justification for the critic who thought he could put the 
essence of the report of December, given in Supplement 
IV, into the following words: " He (Hans) showed that 
he has the power of attention, can draw logical conclu- 
sions, and can communicate the result of his thinking, — 
and all this independently." Yet none of this had been 
asserted. The whole thing may be explained satisfactorily 
by means of a process of simple association established 
between the signs observed in the master and certain re- 
actions on the part of the horse. The fact that the move- 
ments made were so exquisitely minute does not change 
the matter in the least. Such signs call for a high degree 
of sensory keenness and great concentration of attention, 
but by no means an " extremely high intelligence." 

Let us turn now from the consideration of visual per- 
ception to th at of auditory perceptio n in the horse. We 
saw that the "Tact that Hans was able to respond to com- 
mands which were only inwardly enunciated, that is, 
commands which were merely thought of but not spoken, 
was not proof of great acuity of hearing, but rather that 


hearing was not at all involved. If Hans had been deaf 
he would, none the less, hav^promptly obeyed the com- 
mands. Blind and near-sighted horses try to overcome 
their deficiency by means of the sense of hearing, and 
hence show a pronounced play of ears. In the case of 
j the Osten horse, however, attention has been diverted from 
auditory stimuli in the process of habituation to visual 
signs, and as a result ear-movements are almost com- 
pletely wanting. One is not of course permitted to deny 
a priori that perhaps some associations might have 
been formed between objects and the vocal signs belong- 
ing to them, e. g., between the colored cloths and the 
names of the colors if both had been presented together 
oftener than was the case. 

But there is a dearth of reliable observation as to how 
far auditory associations of this sort may be established 
in horses. Usually the following is cited. Horses learn 
to start ofif, to stop, and to turn about in response to calls. 
They are able to distinguish properly between the ex- 
pressions " right " and " left ", or equivalent terms. 
Upon command they will start to walk, to trot or to run. 
And they also know the name by which they are usually 
called. All authors agree that cavalry horses understand 
the common military commands ; one writer even avers 
that they excel the recruits in this respect.®^ Some be- 
lieve that in riding schools the horses pay closer heed to 
the calls of the riding-master than to the control of un- 
practised riders, even when the two are at variance with 
one another.'"* My experience with the Osten horse and 
a number of other pertinent observations aroused in 
me the suspicion that much that is called or spoken in 
the process of managing a horse may possibly be just so 
much labor lost. In consequence I made a series of 


relevant experiments. I have thus far tested twenty-five 
horses of different kinds, from the imported Arabian 
and English full-blood, down to the heavy draft-horse. 
The experiments were made partly in the courtyard of 
military barracks, partly in the circus, and partly in a 
riding-school or in private stalls. I am specially indebted 
for kind assistance to Messrs. von Lucanus, Busch, and 
to H. H. Burkhardt -Foottit and E. Schumann, the two 
excellent trainers connected with the Busch Circus. 
During these tests, the horses were always amid circum- 
stances familiar to them, whether free or bridled, under 
a rider or hitched to a wagon. All aids or signals, except 
the calls, were eliminated in so far as it was possible. ^^ 

The results of those tests were in substance as follows : 
Many horses react to a smack of the lips by a rather fast 
trot. Many stop on the cry " Hola " or " Brr ". This / 
last was nicely illustrated in the case of two carriage j 
horses supplied with large blinders and held with a loose ; 
rein, and hitched to a landau. One of them regularly 
stopped when the " brr " was given by the driver, i 
whereas the other, which had not been habituated to this i 
signal, kept serenely on the trot, so that the vehicle i 
regularly veered off the track — a sure sign that no un- 
intentional aid was being given by means of the reins. 
Other horses, again, were accustomed to halt in response 
to a long-drawn-out " hola ", but it was the cadence of 
melody rather than the word that was effective, since 
any other word, or even a series of inarticulate sounds, 
would produce the same result, provided they were given 
with the proper inflection. When this was changed, then 
the response would fail. v, _, 

The result was not so apparent when it came to con- 
trolling the kinds of gait. One riding-school horse, when 


lunged and in a gallop, could be induced by a friendly 
call — ^the word again was a matter of inconsequence — to 
slacken his pace into a trot and from a trot into a walk. 
But this reaction was by no means very precise. Another 
a full-blood, contrary to the trainer's expectation and to 
his great astonishment, failed to respond to any kind of 
spoken command as soon as the one who carried the 
reins refrained from making any movements which might 
indicate what was wanted. (To refrain from all ex- 
pressive movements of this kind is by no means an easy 
matter). The slightest move, apart from any help by 
means of the reins or the whip-handle, was sufficient to 
evoke a response. The results in the case of the military 
horses, differed in many particulars. Thanks to the 
courtesy of Captain von Lucanus I had the opportunity 
of testing three cavalry horses, two geldings and one 
mare, aged nine, thirteen, and nineteen years respectively, 
and all of them in the regiment ever since their fourth 
year. They had been selected as the " most intelligent " 
in the squadron, and we were assured that they would 
obey punctiliously all the usual commands. They were 
ranged behind one another, with the customary distance 
of two horses' lengths between, and were ridden each by 
his accustomed rider. Both starting and stopping upon 
command were tested. The horses were held by the 
reins, but the riders were cautioned to refrain from giving 
any aid that might cause the horse to start when starting 
was to be tested, or that might restrain him when stop- 
ping in response to the spoken command was to be tested. 
If a suspicion arose — a thing which happened only twice, 
however — ^that a rider had actively aided in his horse's 
reaction, then an officer would mount into the saddle. 
If it appeared that one of the horses was simply imitat- 


ing the others, then the others were purposely restrained 
by their respective riders. The commands were given 
by the corporal who usually had charge of the horses. In 
a few cases the sergeant of the squadron gave the com- 
mands, but this made no difference in the success of the 
experiment. Now as to the results. Whenever the 
horses were trotting or walking, all commands, without 
exception, were in vain. They effected neither an in- 
crease nor a decrease in the pace. A result was obtained 
only when the horses were standing when the test began ; 
and this result was simple enough, — upon certain calls 
the animals would respond by b^ginnmg_to„walk. This 
was the only reaction that was obtained. The most effec- 
tive of the~xarnmands appeare3~To~Ge " Squadron, — 
march ! " But the command " Squadron ! " or 
" March ! " alone, were quite as effective ; yet none of 
these commands was obeyed without exception. Reac- 
tions were occasionally obtained in response to "trot ! ", 
" gallop ! " " retreat ! ", (the usual introductory " squad- 
ron " was purposely omitted here, because it alone suf- 
ficed to start the horses). But the reactions were always 
the same, viz., to start on a walk. Another series of 
commands (such as those which are addressed to the 
rider alone, e.g., "Lances down!") had no effect what- 
ever; a certain amount of selection therefore did seem 
to take place. In all these tests the order of the horses 
with reference to each other's position was repeatedly 
changed. One of the horses, the youngest, and reputed 
to be the most " intelligent ", (he was as a matter of fact 
the most spirited), gave evidence of,j_grggarious_ instinct, 
intensified by habit, which, if it had been overlooked, 
might have become a source of serious error. Not being 
accustomed to go at the head^^adiea-se-pla^d it started 


properly in only i8% of all such cases. When, however, 
(other conditions remaining the same,) he was put in 
second or third place, he started properly in 67% of the 
tests, and if we take into account only those cases in 
which the three most effective commands were used 
(" Squadron ! ", " March ! ", and " Squadron— march !") 
he reacted correctly in 91% of the cases. (The number 
of tests was 17, 36 and 22 respectively for the three 
groups mentioned.) The horse, therefore, almost always 
began to step properly when he stood behind one of his 
companions, but seldom when he stood at the head. And 
when he stood at the head and began to walk at the 
proper moment, it was plain that it was a case of imita- 
tion and not initiative, for the horse was still able to see 
the others, owing to the extent of his field of vision back- 
ward, and he was always the last to move, whereas other- 
wise he was always the first to move, and always difficult 
to restrain. So when the horses to the rear were re- 
strained or when the intervening distance of two horses' 
lengths was lessened, so that this gelding could not see 
the one in the rear, he failed completely to respond. Ac- 
cordingly these three horses did little to justify the faith 
which their squadron had placed in them. 

/~ Now a few words on the manner in which horses react 
upon the call of their names. We are not concerned 

' with those that are seldom or never called by name 
(such as those in the cavalry). I have not discovered 
one horse that constantly and unequivocally reacted upon 
the mention of its name (though I would not assert that 
there are none that would do so.) I was nearly always 
able to convince the owners or grooms, who at first had 
maintained a contrary opinion, that any inarticulate sound 
was capable of producing the same effect as the calling 


of the name. What the significance of inflection may be, 
I am not at all certain. When a certain one of a number 
of horses standing in the same stable was called, all of 
them responded by pricking their ears, raising their 
heads, or else turning about. For this reason the reac- 
tion of the horse specifically called lost all significance. 
Likewise the call which is ordinarily used in. lunging 
when the man in the center of the circle wishes the horse 
to change its gait, or to advance toward him, also proved 
jneffectuaj. as soon as the man inhibited every sort of 
_rnoyement. A slight nod, on the other hand, was always 
effective. Several times I have tried to call horses to me, 
when they were free and running about in the arena, but 
was unsuccessful. After I had given them some sugar, 
however, they would always come to me — whether I had 
called or not — and would then refuse to leave my side. 
But this is a matter of common observation. 

I would, however, regard all of these tests as merely 
provisional. In spite of the greatest effort, it was not 
always possible to control all the conditions of the ex- 
periment, and furthermore, the number of tests would 
have to be materially increased in order to yield an 
appreciation of the difference due to race, age, and the 
individual variation and training of horses. But we 
may, even now, be sure of one thing. Over against the 
certainty with which horses react to visual stimuli (in 
the form of movements perceived), it does not appear 
that the formation of auditory associations is greatly 
favored^_by_ nature ^n these animals, — indeed, auditory 
associations- -are far less common than is generally sup^_ 
posed.* Horses compare very unfavorably with dogs Jn 

* All the authors who have given practical suggestions for the train- 
ing of horses, whether free or with lunging reins, have great faith in 


this respect. The latter easily learn to react with a high 
degree of precision to auditory signs, — as I learned from 
a series of experiments which I was enabled to perform. 
The Osten horse, therefore, does not stand alone among 
his kind in his inferior auditory equipment, as one might 
be tempted to believe at first blush. 

the efficacy of calls, but usually recommend a mingling of calls and 
movements in the way of signs, (thus Loiset," Baucher,'^ von Amim"). 
It therefore cannot be stated just in how far the calls really effect any- 
thing. In other cases I am inclined to doubt outright the influence 
which is ascribed to the auditory signs. Meehan '* gives an account of 
a horse that was exhibited in London in the early go's of the last cen- 
tury. Pawing with his hoof, this horse apparently was able to count 
and answer questions in arithmetic, and among other accomplishments 
he was supposed also to be able to understand something of language. 
In reality, however, he merely responded to cues which were disclosed 
to the reporter by the trainer. In pawing, the horse was guided by 
movements of the trainer, and in nodding or shaking the head he repu- 
tedly got his cue from the inflections of the man's voice. Is it not prob- 
able that in this latter case it was the movements which accompanied 
speech that were alone effective in inducing the nod or the shake of the 
head, so that the exhibiter was deceiving not merely the public, but also 
himself ? Perhaps we may also doubt the exposition made by the well- 
known hippologist. Colonel Spohr.™ He tells us that it is easy to train 
horses to raise the left foot or the right foot in response to the com- 
mands " Left— foot ! " or " Right— foot ! " and that it will be the fore 
foot when one is standing in front of the horse, and the hind foot if one 
stands near the rear. It cannot be so very difiicult, he thinks, even to 
get the horse to understand the commands " Left (or right) — fore foot! " 
and " Left (or right) — hind foot 1 " — and all without any other aids 
but the spoken words. Should this really be possible without even 

the slightest kind of designating movement ? The following case, 

again, I believe is undoubtedly based upon a, misinterpretation. Red- 
ding ™ relates concerning his nineteen-year old horse that he himself had 

owned for thirteen years, and had always kept in single harness, 

that this horse not only understood the meaning of a long list of words, 
such as : bureau, post-office, school, churchyard, apple, grass, etc., 
but he also knew a number of persons by name, as well as their 
places of residence. If he were told in advance to halt at a certain resi. 


It is easy to explain the musical accomplishments. The 
tones which were played for the horse, were known to 
Mr. von Osten, since he himself played the harmonica, 
or when someone else played it, he, Mr. von Osten, 
could see the stoppers. He then thought of the number 

dence, he would do it without any further aid from the driver. For 
this reason the happy owner felt certain that the animal possessed a 
high order of intelligence and " that this horse does reason." What 
sources of error were here operative, whether signs were given by means 
of reins, or head or arm movements, could be determined only by a 
careful examination of the case. 

And finally we would exercise some reserve in entertaining the sug- 
gestions for the acoustic education of horses which have come from 
various sources. Colonel Spohr '^ whom we have just been mention- 
ing, thinks that it would not be a. difficult matter to get a horse 
to respond with a walk to one smack of the lips, with a trot to two 
smacks, and with a galop to three, and then he could be made to 
slacken his pace once more into a trot in response to one long-drawn 
" Pst ! " and to stop in response to two. Others have gone even further. 
Decroix," at one time leader in veterinary affairs in France, conceived the 
idea of working out a universal language as regards the commands that 
are given to horses, in the humane purpose of sparing them the whip. 
He called it " Volapiik hippique." For the commands " go," " right," 
"left," and "halt," he suggests these: "Hi I" "Hal" " He I " 
and " Ho ! " respectively. From these it was possible to make 
eight combinations, such as " Hi ! Hi ! " for " Trot ! " " He ! He ! " for 
" Left about " (while the single " He " was to mean " Forward, to the 
left ! ") " Ho ! Ho ! " for " Back ! " etc. Decroix thought that the 
whole system could be inculcated in a very few lessons. He even had 
a medal struck which was to be awarded to the driver or rider who 
should first exhibit a horse, thus instructed, to the Societe Nationale 
d'Acclimatation de France (of which Decroix was president). Eight 
years have elapsed since then, but we have heard of no one who has 
earned the medal mentioned. In the future greater care will probably 
be exercised in the putting forth of such suggestions, and two sources 
of error may be guarded against, viz. : involuntary movements on the 
part of the rider or driver, and imitation of the horses amongst them- 
selves. (One horse, guarded by an experienced rider, may serve as 
copy for ten others with inexperienced men in the saddle.) 


which indicated the tone in question, and Hans would 
tap it. Thus arose the tale of the horse's absolute tonal 
memory. This tale gained much support at the time, 
from an experience which has been recounted to me by 
the well-known composer, Professor Max Schillings. 
It shows more clearly than any other report how very 
confused were the threads that had been spun in the whole 
matter. In order to test the horse's musical ability Prof. 
Schillings played, let us say, three tones upon the accus- 
tomed instrument. Complying with Mr. von Osten's 
wish. Prof. Schillings always indicated which three he 
was about to play. The horse always tapped them cor- 
rectly. In order to make a decisive test, Prof. Schillings 
then played, without anyone's knowledge, a note that was 
in reality a third below the one he had indicated to Mr. 
von Osten. Curiously enough, Hans tapped, as a matter 
of fact, the number indicating the note that was actually 
struck, and it was only in the third repetition and after 
many exhortations on the part of the master " to have 
a care ", that the horse finally tapped the number in- 
dicating the note Mr. von Osten had in mind and which 
in truth was the wrong one. This curious experiment 
seemed to those to whom Professor Schillings commu- 
nicated it, to yield conclusive evidence of the horse's 
absolute hearing. As a matter of fact, however. Prof. 
Schillings had unwittingly, and, contrary to any inten- 
tion on his part, inspired the horse. Standing, as he did, 
just behind the right shoulder of the horse, he was able 
to interrupt Hans (who had begun to tap in response to 
a move on the part of Mr. von Osten,) by means of an 
involuntary movement which did the work of a closing 
signal. At the same time Mr. von Osten, likewise stand- 
ing to the right of the horse and expecting more taps. 


remained perfectly quiet. (This is as it was in the tests, 
mentioned on page 71, in which, of two experimen- 
ters, one started the horse tapping, and the other stopped 
him.~i Mr. von Osten very probably lost patience after 
Hans had seemingly given the wrong response twice, 
and thereupon came nearer to the horse and thus by 
monopolizing its attention — so as to exclude Prof. Schil- 
lings — he was able to get the respanse so ardently 
'desired,* When, in tests such as theSe, two stoppers 

* General Noizet ™ has left us a story of the middle of the last century, 
which in essential detail corresponds closely with the one just given. 
The scene is a French chateau and the hero is — a rapping table, highly 
prized on account of the intelligent answers it could give. Seated about 
it were a number of ladies and at the other end of the room sat a French 
savant, a member of the Academy. The ladies requested him to put a 
simple mathematical question to the table, and complying with their 
request, he asked for the cube root of 4. None of the ladies who sat 
about the table knew the solution ; the table unhesitatingly gave 6 raps. 
This answer was refused as incorrect. The table was asked to try again, 
and again it wrapped 6. For this it was bitterly reproached. Hereupon 
the questioner, who during the whole time had remained in his place at 
the other end of the room, came forward with the confession that the 
table was innocent, that he had made a mistake. He had asked for the 
cube root of 4, but had really meant to ask for the cube of that number, 
viz., 64, and the table had as a matter of fact given the first numeral of 
that number. 

One is immediately struck by the analogy between this case and that 
of Professor Schillings. In both cases those immediately concerned 
(the women in the one, Mr. von Osten in the other) believe that a wrong 
answer is being given repeatedly. The cause of the error lies in a per- 
son who seemingly is not concerned with the response. (The French- 
man asked the question, but did not sit at the table. Professor Schillings 
sounded the notes, but it was Mr. von Osten who got the horse to tap.) 
In both instances the questioner asks one thing, but had something else 
in mind. (With the Frenchman it was a slip of the tongue ; Mr. Schil- 
lings did it purposely.) And finally, in both cases the response cor- 
responds not to the question that has been asked, but to that which has 
been thought, so that, though seemingly wrong, the responses of both 


were opened and thus two notes sounded, Mr. von Osten 
would count the number of stoppers intervening between 
the two, and Hans would tap the number. And so arose 
the tale of Hans's knowledge of musical intervals. 
Whenever the two notes were sung or whistled, in which 
case there would be no stoppers that could be counted, 
then Mr. von Osten, who was quite destitute of musical 
knowledge, was at a loss, and also Hans. If, however, 
the intervening notes were sung, then everything went 
smoothly once more. Major and minor chords were 
regularly characterized as " beautiful ", all others as 
"bad", (but even here errors occurred). A musician 
had taught Mr. von Osten these distinctions. The old 
man also knew the melodies that were played on the 
hand-organ. Each one had a number assigned to it, and 
Hans was required to tap the number of the melody in 
token of recognition. — Hans was as ignorant of musical 
time, as he was of melody ,and all attempts to get him to 
march in regular step were utterly futile. A number of 
musical tests were made in the absence of Mr. von Osten. 
In these Mr. Hahn undertook the questioner's role, and 

table and horse were really correct. By way of explanation, Noizet 
believes that he has a case of true thought-transference or " telepathy " 
(page io8). The questioner watched with utmost attentiveness the rap- 
ping of the table, and the women in turn regarded the man. And thus, 
Noizet believes, the man's thought was transferred to the minds of the 
others without the mediation of eye or ear, etc., and hence unvitiated by 
the words that had been spoken. I myself prefer another explanation. 
At that moment in which the rapping arrived at the expected number, 
the Frenchman executed a movement characteristic of release of tension 
and to this the women of the circle reacted. It was not necessary that 
they should be able to account for this afterward, (just as sometimes 
occurs in the case of thought-readers '"). It is very probable, too, that 
they were not of a very reflective turn of mind anyway. We are war. 
ranted, I think, in regarding the two cases as Identical in kind. 


since he had had musical training, he was aware of what 
the numbers should be, even when he could not see the 
stoppers of the harmonica, and, therefore, we readily un- 
derstand why it was that the horse responded so wonder- 
fully in his case. 

The so-called musical ability of horses appears, from 
all that is known, to be confined within very narrow 
bounds. Only one fact is universally accepted, viz., 
horses of the military are believed to possess a knowl- 
edge of the significance of trumpet signals, and are often 
_said to interpret them more readily than the recruits.^^ 
Since no experiments had been made along these lines, I 
undertook to make a brief test of the cavalry horses men- 
tioned on page 188. As in the preceding tests, the three 
animals were arranged behind one another with the cus- 
tomary distance of two horses' lengths between, and each 
was ridden by hia accustomed -rider. _ They were held by 
the reins, but received no aid of any kind, either to start 
them or to restrain them. A bugle then sounded the vari- 
ous signals at the other end of the barrack's courtyard. 
We had been previously assured that the horses would 
certainly react without fail. But, as a matter of fact, the 
result was quite the contrary. Two of the horses did not 
move at all, and the third, a thirteen-year old gelding, was 
startled nearly every time and would tear off in a gallop — 
even though a trot had been sounded. I would not, 
however, venture to draw any conclusions from results 
such as these. Many more tests would have to be made, 
and some of them upon the whole squadron, before a 
judgment could be given.* 

* Frofessor Fliigel,"' basing his statements on an article appearing in 
" Schorer's Familienblatt " (Beriin, 1890, No. 8, p. 128), gives an account 
of similar experiments which were supposed to have been conducted by 


I shaljL.now_ turn_to peculiarities o f character , highly 
humanized, which have been attributed to Hans. His 
" sympathies " and " antipathies ", so-called, were noth- 
ing but erroneous appellations for the success or failure 
on the part of the respective individuals to elicit responses. 
He who could procure answers frequently, apparently 
stood high in the horse's favor. That Hans shook his 
head violently when asked by Mr. von Osten : " Do you 
like Mr. Stumpf ? ", and answered in the affirmative the 
further question: "Do you like Mr. Busch?", was noth- 
ing but a confession — unwilling, to be sure — on the part 
of the master himself. In the first case the master 
thought " no ", in the second instance, " yes ", and the 

the Zoological Society for Westphalia and Lippe, and presumably 
showed that " the horses of the military do not understand the bugle 
calls." No matter how well trained a horse may have been, it would 
not respond to a signal. This report, however, is due to a mistake. 
Such experiments have never been made by the society mentioned, so I 
am told by its director, Dr. Reeker. Nor do I know of any one else 
who has made experiments of this kind. However, Professor Landois," 
the eminent zoologist, now deceased (founder of the scientific society 
mentioned), tested four circus-horses for their musical ability and spe- 
cifically for their sense of musical time. He arrives at the conclusion that 
horses "have no feeling for time, whatsoever." With but few ex- 
ceptions,^'*' all experts to-day are of the same opinion. Horse-trainers, 
especially, are universally agreed on this point. It is easy to see in any 
circus performance that it is not the horses that accommodate them- 
selves to the music, but that the music accommodates itself to them, 
and that the trained horses*' are induced to do their artistic stepping 
only by the aids given by their riders. Furthermore, all these horses are 

trained without the use of music. It would therefore appear that 

the time had arrived when the tales of the dancing horses of the Sybarites 
ought no longer to gain credence. Two Greek writers, Athenaeus*' 
and iElian,*' tell us that the inhabitants of Sybaris, far-famed for their 
luxurious habits, had trained their horses to dance to the music of flutes 
during their banquets. Kuilding upon this, the men of Crotona, in one 
of their campaigns against the Sybarites, ordered the flute-players to 


two thoughts were accompanied by the corresponding 
head movements, to which Hans responded mechanically. 
Hans appeared to be well-disposed toward me, but evi- 
dently because I always rewarded him liberally when he 
answered correctly, and I did not scold him when his 
responses were wrong, as did Mr. von Osten and Mr. 
Schillings, who instead of seeking the cause within them- 
selves, were always ready to rebuke Hans for his con- 
trariety and fickleness. The horse did not show, in so 
far as can be judged^t all, any real affection for his 
master. On the other hand it would be Imwaf ranted to 
say that, in spite of all rewards, he developed a grudge 
against all those who bothered him with instruction and 
examination. Shortly after the close of our experimenta- 

play the tunes familiar to the Sybarite horses. Immediately the well- 
trained steeds began to dance, thus throwing the whole Sybarite army 
into confusion, and the men of Crotona won the day. (The same story 
is told in more detail concerning the horses of the inhabitants of Cardia. 
Both accounts, somewhat mixed, are to be found in Julius Africanus," 
a writer of the third century of the Christian era.) — In recent years a 
French veterinary surgeon, Guenon,'" experimented on the effect of 
music upon the horses of the military. He entered their stalls, playing 
upon a flute, and noted their behavior. Four-fifths of the animals, he 
says, were deeply moved, yes, delighted, even, ("charmes." One inter- 
preter °l calls it a case of hypnosis !). This emotional excitement was 
expressed — somewhat unaesthetically — by the dropping of excrementa. 
Guenon characterizes the feeling-state of these animals as being a mix- 
ture of pleasure and astonishment, of satisfaction and excitement 
(" melange de plaisir et d'etonnement, de satisfaction et de trouble.") 
He also asserts that the horse's musical taste is similar to our own. But 
I can find nothing in his whole exposition which might prove this. In- 
deed there is nothing that could be interpreted as anything other than 
a purely sensuous effect upon the horses. I may go a step farther and 
say that thus far the sense of music, i. e., understanding of melody, 
harmony and rhythm, has not been shown to exist in any animal. Some 
animals may, however, be susceptible to the sensuous pleasantness of 
the tones themselves. 


tion it happened that Hans severely injured his groom by 
a blow in the face. Yet this man had always been very 
gentle with the horse and had been forbidden by Mr. von 
Osten to make Hans solve any problems for him. Ex- 
perts assure me that we have here to deal, not with a 
case of " moral insanity ", but with a very common ex- 
perience, — although this view will probably be cavilled 
at by enthusiastic lovers of horses. The work of so 
excellent an expert as Fillis,"^ for instance, bears us out 
in this respect. 

The horse's supposed fickleness was nothing but a 
token of the fact that even those who were accustomed to 
working with him, did not have him completely in hand. 
(They simply did not understand how to obtain correct 
responses from the horse.) It often happened that in the 
evening, when it had become so dark that the movements 
of Mr. von Osten could no longer be seen, Hans had to 
suffer bitter reproaches because he made so many errors. 
That, in truth, he never was stubborn and that the cause 
of failure really lay in the questioner, is shown by the 
fact that the mood, for which he was reproved, would dis- 
appear the moment the questioner voluntarily controlled 
the signals. We may add that there was no basis for the 
assumption that " he had an uncommon, finely constituted 
nervous system " or was possessed of a " high degree of 
nervousness ". Both these phrases were often mentioned 
by way of explanation. Hans was restive, as horses usu- 
ally are. And besides, he lived a life so secluded (he 
was never allowed to leave the courtyard) that as a result 
he was easily disturbed by strange sights and sounds. 
There was not the slightest trace of the clinical symptoms 
of neurasthenia — on the contrary he gave the impression 


of perfect health, — which was curious enough when we 
remember his rather unnatural mode of life. 

Hans's stubbornness was,.a myth. He was suspected of 
it whenever the sameerror occurred a number of times 
in succession, i. e., when the questioner did not properly 
regulate his attention (page 146) or when he was being 
controlled by " perseverative tendency ", mentioned on 
page 149. Mr. Schillings, who has provided me with 
material here as elsewhere, relates the following episode 
which occurred on one such occasion. To one and the 
same question put alternately by Mr. von Osten and Mr. 
Schillings, Hans responded correctly, with two taps, to 
the former, and just as persistently incorrectly, with three 
taps, to the latter. After Mr. Schillings had sufiEered this 
to occur three times he accosted the horse peremptorily : 
" And now are you going to answer correctly ? ". Here- 
upon Hans promptly shook his head, to the great merri- 
ment of all those present. (Mr. Schillings had, with no 
accounted reason, expected a "no".) Hans was called 
willful whenever the same question was successively an- 
swered by different responses, as frequently happened 
with the increasing tension that characterized the high 
numbers (page 145). He was also regarded as stubborn 
when no reply at all was forthcoming, as in the tests with 
the blinders;___ 

Hans's supposed distrust of the questioner, when the 
latter did not know the answer to the problem, is noth- 
ing but a poor attempt to account for the failure of those 
tests. Hans's distrust of the correctness of his own re- 
sponses was supposed to be evident from his tendency to 
begin to tap once more if, after the completion of a task, 
the questioner did not immediately give expression to 


some form of approval or disapproval — ^^just as a school- 
boy begins to doubt his answer if the teacher remains 
silent for a short time. In terms of the results of our 
experimentation this would mean that whenever the ques- 
tioner did not resume the erect posture, after Hans had 
given the final tap with the left foot, then the horse would 
immediately begin once more to tap with the other foot 
(page 6i). 

— As the evil characteristics, so, too, the good. Thus, his 
precipitancy, which was'supposedly evidenced by his be- 
ginning to tap before the questioner had enunciated the 
question, was nothing but a reflection of the questioner's 
own precipitancy in bending forward (page 57). Never 
did Hans evince the slightest trace of spontaneity. He 
never spelled, of his own accord, anything like " Hans is 
hungry," for instance. He was rather like a machine 
that must be started and kept going by a certain amount 
of fuel (in the form of bread and carrots). The desire 
for food did not have to be operative in every case. The 
tapping might ensue mechanically as a matter of habit — 
for horses are to a large extent creatures of habit. This 
lack of spontaneity could hardly be reconciled with the 
horse's reputation for cleverness. It would not be neces- 
sary to touch upon the signs that were supposed to be- 
token genius: the intelligent eye, the high forehead, the 
carriage of the head, which clearly showed that " a real 
thought process was going on inside ", — all these, we 
said, would not need mentioning, if they had not been 
taken seriously by sober-minded folk. If there is a report 
that Hans turned appreciatively toward visitors who 
made some remark in praise of his accomplishments, — it 
is evidence qnly of the observer's imaginativeness. 

Turning from a consideration of the horse to that of 


the persons experimenting with him,* the first and most 
important question that arises is this : How was it pos- 
sible that so many persons (there were about forty) were 

* I cannot enter upon a discussion of the latest psychological prob- 
lems, here involved, partly because that vfould take us beyond the pur- 
pose of this monograph, and partly because they are still moot questions 
and hence not suited to popular treatment. Briefly though, they are 
these ; What is the nature of the relationship between cognitive and 
affective states on the one hand and involuntary, (so-called expressive) 
movements on the other ? Is this connection an external thing, as it 
were, an association arising as a habit formation, or does every idea 
partake essentially of a motor character ? Do purely cognitive states 
give rise to such movements, or does the movement impulse depend 
more particularly upon the affective consciousness accompanying the 
cognitive states ? And in how far do given kinds of expressive move- 
ments depend upon certain ideational types (c.f. page 95) ? Thus, 
what is the influence of the visual image upon the gestures for " up," 
" down," etc. .' And then, are these involuntary movements, when not 

noted, truly unconscious, or merely not attended to, in other words, 

are they beyond the pale of consciousness or merely " at the fringe ? " 
The various writers speak almost without exception of unconscious 
movements in the strict sense of the term. My own introspections, how- 
ever, have led me to doubt whether they are quite unconscious. Since 
I have attained some practice I am able to describe in detail (under 
conditions of objective control) my involuntary movements, no matter 
how slight, even down to mere muscular tensions. None of my sub- 
jects, however, has as yet succeeded in this. It is no very easy matter 
to be on the lookout for some unknown movements which might even- 
tually occur, while attempting to concentrate attention to the utmost 
upon a certain definite ideational content, for this very dividing of 
attention effects a decrease in the force of the movement, and thus 
makes it all the more difiicult to discover. From my own experience, 
however, I am inclined to believe that these movements are not uncon- 
scious, but merely unattended to, in other words, we have a narrowing 
down of the apperceived content within certain limits, but not a narrow- 
ing down of consciousness, (much less a " splitting " of consciousness 
or of personality as the thing unfortunately has sometimes been called). 
In order, however, not to be guilty of premature judgment, I have 
avoided the terms " unconscious " and " unattended to," and chose ex- 
pressions which leave these finer distinctions untouched. 


able to receive responses from the horse, and many of 
them on the very first occasion ? The answer is not hard 
to find. All of these persons came to the horse in very 
much the same frame of mind — which found a similar 
expression in all, in both posture and movements. And 
it was these motor expressions of the questioner (aside 
from the signs for " yes " and " no ", which I believe I 
have adequately explained on page 98), that the horse 
needed as stimuli for his activity. 

The next question that arises is: why did only a few 
persons receive responses regularly from Hans, whereas 
the greater number were favored only occasionally? 
What was the selective principle involved? The answer 
is, that the successful person had to belong to a certain 
type, which embodied the following essential character- 

1. A certain measure of ability and tact in dealing with 
the horse. As in the case of dealing with wild animals, 
such as the lion, etc., Hans must not be made uneasy by 
timidity in the questioner, but must be approached with 
an air of quiet authority. 

2. The power of intense concentration, whether in ex- 
pectation of a certain sensory impression (the final tap), 
or in fixing attention upon some idea-content (" yes ", 
" no ", etc.). It is only when expectancy and volition are 
very forceful, that a sufficient release of tension can en- 
sue. This release of tension is accompanied by a change 
in innervation and results in a perceptible movement. 
And it was only when the thought of " yes ", or " up ", 
etc., was very vivid, that the nervous energy would spread 
to the motor areas and thence to the efferent fibers, and 
thus result in the head-movement of the questioner. 


From infancy we are trained to keep all of our volun- 
tary muscles under a certain measure of control. During 
the state of concentration just described, this control is 
relaxed, and our whole musculature becomes the instru- 
ment for the play of non-voluntary impulses. The 
stronger the customary control, the stronger must the 
stimuli be which can overcome it. The steady unremit- 
ting fixation, which resulted in the horse's selection of 
the cloths, also involves a high degree of concentration. 

3. Facility of motor discharge. Great concentration 
was necessary of course, but not sufficient. Persons in 
whom the flow of nervous energy tended to drain off 
over the nerves leading to the glands and the vascular 
system might betray great tension, not so much by move- 
ments as by a flow of perspiration (we have many excel- 
lent examples of this given by Manouvrier) '' or by a 
violent beating of the heart, blushing and the like, — in 
short, by secretory and vasomotor effects. Or it is not 
inconceivable that long dealing with very abstract 
thoughts might have weakened the tendency of overflow 
to other parts of the brain, and that therefore the entire 
discharge is used up in those portions of the brain which 
are the basis of the intellectual processes. But if expres- 
sive movements occur, the motor pathways must be par- 
ticularly unresisting in order to take up the overflow of 
psychophysic energy. This is the necessary condition 
for obtaining the tapping and the head movements on the 
part of the horse, although for the tapping there is still 
one other circumstance necessary: viz., 

4. The power to distribute tension economically — i. e., 
the ability to sustain it long enough, and to release it at 
the right moment (after the manner of the curves de- 


scribed on page 93), and to control properly the un- 
avoidable variations which will occur.* 

• The mental state just described is probably essentially the same as 
that of the spiritualistic " mediums " when they are occupied with table- 
rapping and table-moving. In both'cases concentration is very intense, 

in other words, the field of attention is limited. We saw that this state 
not only favors the tendency toward involuntary movement, but on ac- 
count of the absorption of the individual's attention by a certain limited 
content, the person will be unaware of the voluntary movements as 
they occur. And we are not necessarily here dealing with neurasthenic, 
hysteric, or other diseased nervous conditions. In the case of table- 
rapping there are movements of the hands, in our case there are those 
of the head. Our head, balanced as it is upon the cervical vertebral 
column, is continually in a state of unstable equilibrium and therefore 
peculiarly susceptible to movement-impulses of every kind. But I could 
induce not only movements of the head, but also of the arms and legs, 
and this by having the subject assume a posture which enabled him to 
hold arms or legs in as unstable a position as possible. He might 
stretch out his legs horizontally before him, or he could raise them ver- 
tically upward as in the hand-stand in gymnastic work. An extract 
from a treatise by Count A. de Gasparin,''' which appeared about the 
middle of the last century, may serve to show how close the corres- 
pondence between the two processes, that of getting the table to rap 
and that of causing Hans to respond, really is. The report of this 
writer, based upon the detailed record of his tests in table-moving and 
table-rapping, closely parallels in many minute detail the observations 
which were made in the course of our experimentation with Hans. The 
case is all the more remarkable when we bear in mind that this writer 
did not seek the cause of the phenomena, as we did, in involuntary move- 
ments, but thrusting aside this explanation, he posited the cause in the 
agency of some mysterious fluid. It may not be amiss to say that this 
as well as most other references were consulted after the present experi- 
ments and introspections had been completed. Of the page references 
preceding the following citations, the first always refers to the page in 
the French original, and the other, enclosed in brackets, to the parallel 
passage in the present monograph. 

P. 49 [31]. Some questioners are especially suitable (" experimenta- 
teurs hors ligne "), but in their absence, other persons may also operate 
successfully ("lesucces, quoique moins brillant alors, n'est pas impos- 


The experience of a number of practical men, who 
have had much to do with horses and yet achieved but 

P. 25 [229]. But even the most suitable questioners do not always 
succeed equally well (" les plus surs d'eux-memes ne r^ussissaient pas 
egalement tous les jours.") 

P. 42 [151]. When the questioner is in any way indisposed, the 
measure of success is also less. 

P. 91 & 87 [150]. The Questioner must first get into the sweep of 
things (" en train "), and once he has done so, all interruption what- 
soever must be avoided. 

P- 9' [93]- Unless there is sufficient tension on the part of the ques- 
tioner, the test will fall. (" La volonte est-elle absente, rien ne bouge.") 

P. 210 [93]. When there is too low a degree of tension, then too 
great a number will be tapped (" si votre volonte ne les [les tables] ar- 
r^te pas au moment ou se termine le chiffre pense, elles continueront 

P- 3' [93]- l^"t too great concentration of attention will also produce 

failure ("s'il n'arrivait de desirer trop fortemeut le succes et de 

m'impatienter en cas de retard, je n'avais plus aucune action sur la 

P. 36 [151]. If the proper mood (" entrain habituel ") is wanting and 
the tests are unsuccessful, it is best not to attempt some new and diffi- 
cult experiment, but to turn to some that are simpler and more enter- 
taining (" La table obeissait mal ; les coups etaient frappes moUement et 

comme a regret Alors nous avons pris un parti dont nous nous 

sommes bien trouves ; nous avons persevere, et persevere gaiement ; . . . . 
nous avons ecarte la pensee des tentatives nouvelles, et insiste sur les 
operations aisees et arausantes. Apres un certain temps les disposi- 
tions etaient changees, la table bondissait et attendait a peine nos com- 

P. 199 [41, 90]. It is not necessary to enunciate the questions aloud 
(" On est convenu que celui qui commanderait ne prononcerait pas a 
haute voix le nombre de coups, mais se con tente rait de lespenser, apres 
les avoir communiques a I'oreille de son voisin. Eh bien ! la table a 
obei. U n'y a jamais eu la moindre erreur.") 

P. 199 [64 ff.]. The large numbers are tapped more rapidly than the 
small ones ("la table a indique notre age tel qu'il etait dans notre es- 
prit, se hatant meme de la maniere la plus comique lorsque le nombre 
des coups a frapper etait un pe>i considerable.") 

P. 210 [35 ff.]. Tests in which " procedure was without knowledge " 


very modest success with Hans, goes to show that it is 
not always the lack of sufficient authoritativeness, men- 
tioned under heading i that is the sole cause of failure, 
as has been claimed so often. That the horse was, to a 
certain degree, influenced by this element of authority is 
shown, however, by the following incident. A certain 
gentleman, when alone in the courtyard with Hans, re- 
ceived responses only so long as I (concealed in the barn) 
kept the barn-door open just a little, so that my presence 
could be known to the horse. As soon as I closed the 
door, Hans refused to respond to the gentleman. Those 
who possessed sufficient power of concentration and the 
requisite motor tendency — the two characteristics men- 
tioned under i and 2 above, — were able to obtain re- 
sponses from the horse without any previous practice. 
Practice merely effected a more economic distribution of 
attention, so that the larger numbers especially were 
more successful as a result (pages 68 and 89). Those 
who were lacking in either of the characteristics men- 
tioned under 2 and 3 would not be aided even by the 
greatest amount of practice, as is shown by the case men- 
failed completely (" Les tables ne revelent pas ce qui n'est pas dans la 
pensee et dans la volonte de I'experimentateur ; quand on veut les 
charger d'autre chose que d'obeir comme des membres, on arrive a des 
erreurs continuelles.") 

P. 28, 29, 217 [72]. When of two experimenters each tries to get 
the horse to tap a different number, then that one who is the better able 
to compel the animal's attention, will be the successful one. (" L'un veut 
faire prevaloire un chiffre pense plus considerable, I'autre un chiftre 

pense moins considerable Eh bien : I'operateur le plus puissant 

I'emporte." " Ainsl A est charge secretement de faire frapper 25 
coups, B est charge secretement de I'arrSter k 18 ; A I'emporte, et les 

25 coups s'ach^vent On fait maintenant I'inverse : Best charge 

secretement de faire frapper 13 coups; A est charg^ secretement de 
I'arrStei i 7 ; A I'emporte encore et le chiffre 7 ne peut etre depasse.") 


tioned in Supplement III (page 255). — That many in- 
dividuals were at first successful but were later unable 
to get any successful responses, is to be accounted for by 
the fact that the power of concentration, at first present, 
later rapidly disappeared; ' "This "temporary increase in 
the power of doing mental work was first investigated 
experimentally by Rivers and Kraepelin,'^ and was called 
by them " Antrieb " and aptly likened to the first pull of 
a team of horses in starting off. This, too, explains an 
experience which befell a number of the horse's visitors, 
who later described it to me. Wishing to utilize a mo- 
mentary absence of Mr. von Osten, they excitedly put a 
hasty question to Hans, and with amazing regularity 
received correct responses. — Besides Mr. von Osten, Mr. 
Schillings and myself, not many were always able to in- 
duce Hans to bring the colored cloths or to execute the 
head movements. It was easy, on the other hand, to get 
him to nod. Therefore there was some truth m Mr. von 
Ostens' assertion, that Hans would be unable to answer 
a difficult question if he had not previously indicated by 
means of a nod that he had grasped its import. Those 
who were not concentrating sufficiently, would not look 
into Hans's face, when he was expected to nod, and 
would not bend over, when Hans ought to begin tapping — 
such persons could not, therefore, since they did not in- 
duce Hans to nod, elicit the tapping. I, myself saw the 
" no " successfully elicited only in the case of Mr. von 
Osten, Mr. Schillings and Mr. Hahn ; the " right " and 
" left " only in the case of the former two. It must re- 
main uncertain whether this failure on the part of other- 
wise suitable persons to elicit the responses for " right " 
and " left " was due to their accompanying these ideas by 
movements of the eyes instead of by movements of the 


head, (pageio6). For unfortunately it was not possible 
to make special tests to discover whether Hans reacted to 
isolated eye movements. There is, however, more than 
one reason why I would doubt this. Taken all in all, 
there were but few persons who were entirely represent- 
ative of the type described (c. f. page 31) — they were 
those who are commonly characterized as being of a lively 
temperament and strongly impulsive. Thus Hans 
acquired a reputation for " Einkennigkeit ", that is, he 
would accustom himself only to certain persons. Such 
a reputation was hard to reconcile with his much praised 

In closing, just a word on the influence of the public 
that was present. As was shown on page 69, the public 
in general did not influence the horse jn his reactions. 
The effec t upon the questioner, however, was unmistak- 
able, and worked in a twofold manner. / On the one hand 
the questioner's zeal was increased and with it the ten- 
sion of concentration. 20n the other hand, it introduced 
an element of diversion, and attention was divided be- 
tween the horse and the spectators, and thus concentra- 
tion suffered. If the disturbing effect was slight, as in 
the case of Mr. von Osten, then the favorable influence 
exercised by the presence of the public outweighed the 
unfavorable. Mr. von Osten was, for that reason, often 
particularly successful when working in the presence of 
a large body of spectators. This was noted by many and 
was ascribed to the ambition of the horse. When, how- 
ever, a person was easily diverted, as was Mr. Schillings, 
then the presence of the public had a less fortunate effect. 

This, then, completes my explanation of the facts 
gleaned from observation and experimentation. It ac- 
complishes all, I hope, that may be expected of an ex- 


planation. All the known achievements of the horse, all 
the successes and failures of the questioner, have been re- 
duced^ ts^^^^^ggle principle ;, no secondary hypothesis has 
been invoked, and but slight place has been given to the 
element of chance. Nevertheless, it may not be out of 
place to forestall two objections which might possibly be 
raised. |[ First, some may assert that it was through our 
experimentation that the horse became mechanized and 
incapacitated as regards conceptual thinking; that form- 
erly he really could solve arithmetical problems, and only 
later developed the very bad habit of depending upon the 
signs which I gave him. This objection is to be refuted 
in that I did not originate these signs, but first noted them 
in Mr. von Osten, himself, and in that Hans still works 
as faithfully as ever for Mr. von Osten. I have learned 
from many trustworthy witnesses that the horse still con- 
tinues to give brilliant exhibitions of his " ability ". If, 
on the other hand^nyone should assert that it was only 
with us that HansVeacted to movements, but that with 
his master he really thought and still thinks, then I must 
ask for proof. This latter argument is hy no means very 
original. When Faraday in 1853 proved experimentally 
that "table-rapping" is the result of involuntary move- 
ments on the part of the participants standing about the 
table, the spiritualists asserted that his experiments had 
nothing in common with their own proceedings, because 
his subjects (who by the way, had been up to that time 
firm believers in table-rapping) probably did move the 
table, they said, while they (the spiritualists) do no such 


In the preceding discussion we have regarded the 
achievements of the horse as well as Mr. von Osten's 
explanation of them, as matters of fact. Let us now con- 
sider the question: How did the horse come by these 
achievements, and how did its master arrive at his curi- 
ous theory in explanation of them? Did he indeed seek 
to instill in the horse's mind the rudiments of human 
culture through long years of painstaking instruction in 
accordance with the method described in Supplement I 
(page 245) ? If that is the case, then, of course his hoped- 
for success was only seeming, not real. Or did he, as so 
many critics aver, systematically train the horse to re- 
spond automatically to certain cues, and propound his 
theory merely for the purpose of misleading the public? 
There might possibly be another alternative, viz.: was 
there a mixture of instruction and of training to respond 
to cues? 

The production of the horse's achievements would not 
require a great deal of explanation, if it were a case of 
mere training for the purpose of establishing certain re- 
sponses to certain cues. It might be desirable, however, 
before deciding in favor of one of these possibilities, to 
indicate briefly the process of development, as it might 
occur, if the point of view is taken that bona fide instruc- 
tion was given. 



This development would probably be as follows : — Mr. 
von Osten, as the result of theoretical speculation or of a 
misinterpretation of the facts of experience, having ar- 
rived at the conclusion that the horse possessed extraor- 
dinary capacity, finally undertook to instruct a certain 
horse for a period covering three years. This one hav- 
ing died, he, nothing daunted, undertook the education of 
another one. What it was that influenced this old 
teacher of mathematics to deprive humankind of the bene- 
fit of his extraordinary pedagogical ability and love of 
teaching, we do not know. It may be that he had had 
bitter experience in that line, or again, mayhap the new- 
ness and tremendousness of this other task stimulated 
him. His first problem must have been to arouse the in- 
terest of the animal in this process of education. It was 
hardly to be believed that Hans would eagerly cooperate 
in a process which promised to yield him no immediate 
benefit. The teacher sought to overcome this lack of im- 
mediate interest by the means of rewards. To Hans the 
sweet carrot was as toothsome a bite as candy is to the 
child. And since the horse was furthermore kept on low 
rations on account of the relatively low amount of physi- 
cal exercise he took, the anticipation of the carrots was 
doubly enticing. 

The first thing that Mr. von Osten sought to teach the 
horse, according to his own statement, was the significance . 
of the names of colors and of the spatial directions such | 
as " up ", " down ", etc. In the case of children there 
is a simple test by means of which we may discover if 
they have put any content into these words. The test is : 
Do they, themselves, use them correctly? Do they call 
the blue, blue, and the red, red? Since the horse could 
not speak, his instructor had to give him some means by 


which he could make himself understood. He taught 
Hans to approach the colors and select the cloth of the 
color wanted. He also taught him to make those move- 
ments of the head or body which correspond with the 
expressions : " up ", " down ", etc. 

First of all, Hans had to be taught to bring the cloths. 
Then began the pointing out of the different colors, ac- 
companied each time by their proper names. It is very 
probable that at first Hans had to be led each time to each 
separate colored cloth and taught to raise it or to touch 
it with his nose. Later, Mr. von Osten, after having pro- 
nounced the name of the color, remained at his place, 
with his head and body directed to the cloth in question 
and gazing intently at it, in order to see whether or not 
the horse was pointing out the right one. Naturally 
Hans would, at first^jgiLa liaadred-times-where he would 
succeed but once, buf since the horse would receive the 
anticipated reward in case of success, he gradually be- 
came conscious^ that this reward was attached to execu- 
tions which had some special mark. This special mark 
would be expressed in human speech by the statement 
that the horse would go in the direction indicated by the 
position of the instructor's body. For Hans, of course, 
this would not take the form of an abstract statement, 
but simply of a definite way of seeing and of going and a 
cofrelation of the two in a certain definite manner, — ^the 
whole being a process, the elements of which remained 
unanalyzed and unaccounted for by Hans. Owing to the 
position of the eye, it was possible for him to keep his 
master within his field of vision, while he was approach- 
ing the cloths. And only when he had correlated his ap- 
proach in a certain definite manner with his visual per- 
ception of the master, i. e., only when he had felt his way. 


as it were, along the latter's line of vision, did he receive 
his reward. A su fficient number of repetitions was all 
that was necessary to establish an association~In~the 
psychological sense of the term. In the same manner, 
dogs will learn, as was indicated on page 177, to bring an 
obj.ect upon which the master has fixed his gaze, it mat- 
tering little whether or not the name of the object be 
enunciated. There is only this difference, that, in the 
case of the dog it is not ^possible to keep the image of the 
master within the field of vision; but neither is it neces- 
sary, for he has recognized— the- object before he has 
started for it. We must remember, however, that it does 
not simplify an attempt at explanation to assume that Mr. 
von Osten consciously trained the animal to respond to 
certain bodily positions of the questioner. For, even in 
this case, it would be necessary to explain how it was pos- 
sible for him to train the horse to heed the cues. — In the- 
course of time, the instructor may have noticed that when- 
ever he moved during the course of a test the horse in- 
variably failed. But he may have regarded this merely as 
an incidental distraction and afterward was careful to re- 
main quiet. As soon as he increased the number of cloths 
upon the floor, it was no longer possible for him to give 
the horse such accurate directive signs, and the number 
of errors consequently increased. Ascribing them to the 
inattentiveness of his pupil, he sought to encourage him 
by such calls as " look out ", " look there ", " see there ", 
believing that, thus, he was directing the horse's attention 
to the desired color. Without understanding the mean- 
ing of the calls, Hans learned, however, to keep moving 
just as long as the calling continued, for if he did this he 
was regularly rewarded. An association was established 
between the call and the impulse to move on. And with 


these two associations established, Hans gave the impres- 
sion of having grasped the meaning of the color terms. 

The origin of the proper movements in response to the 
jterms " up " and " down " may be explained by the fact 
that the movements themselves were practised in a 
purely external fashion. Thus, whenever the word 
" left " was pronounced, the horse's head was pulled to 
the left by means of the bridle or the reward was held off 
to that side. Later, Mr. von Osten, who looked expect- 
pectantly at the horse's head, whenever he pronounced the 
word would unconsciously move his own head in the di- 
rection in which he desired the horse to turn. This is 
quite in accord with the words of Darwin to the effect that 
whenever we wish an object tq move in a certain direc- 
tion it is well-nigh impossible for us to inhibit an uncon- 
scious, involuntary movement in that direction. Proof for 
-this -may- be found on all sides, in daily experience.''' 
Imagine, for instance, the strain sensations of the bowler 
or billiard player as he follows the moving ball. It is im- 
possible to decide whether Mr. von Osten, consciously 
continued to image the head movements which he ex- 
pected the horse to make or whether these anticipatory 
images later remained below the threshold as was always 
the case with Mr. Schillings and myself (see page loo). 
But this question is of little significance, for even assum- 
ing that he always thought of the movement he expected 
on the part of the horse, this by no means implies that he 
was conscious of the movements on his part, which were 
associated with the thought process. 

Everything up to this point might be explained as the 
working of simple memory association, but when we 
come to problems in counting and arithmetical calcula- 
tion, we are in the field of conceptual thought. Here, 


again, it was necessary for Mr. von Osten to invent a 
suitable means of expression for the horse, and once more 
this had to be borrowed from the treasury of gesture- 
language. Tapping with the hoof was naturally hit upon 
as one of the normal, expressive movements of the horse. 
This has long been used by trainers, in preparing horses 
for show purposes. The method used in training the 
horse to make this response is of no import, whether it 
was by touching his foot with the hand, or tapping his 
leg, or by any other means. 

It is possible that many will declare, as being non- 
sensical, any attempt to introduce number-concepts * into 
an animal's mind, because the necessary motor basis is 
lacking. We will not, just at this point, stop to discuss 
whether or not it was not possible to develop number- 
concepts from purely auditory or visual representations. 
It is evident, however, that Mr. von Osten believed that 
a motor basis of some sort was essential. In the case of 
man this basis is found in the enunciation of the number 
names (or in the manipulation of the fingers). Mr. von 
Osten seemed to think that he was justified in assuming 
that, even in the case of the horse, some form of inner 
articulation of the word-sounds was possible ; — at the 
same time, in so doing, he did not blink at the psycho- 
logical difficulty of this hypothesis. The tapping of the 
foot was to be regarded merely as the expression of the 
process of inner counting, but not as the motor basis of 
the process. For this latter purpose tapping would be 
quite inadequate, for the number complexes which arise 
in the summation process of counting, could not be dif- 

*The author intends to take up the problem of counting, so-called, on 
the part of animals and of the principle involved, in another work soon 
to be forthcoming. 


ferentiated by mere tapping with the foot, any more than 
a child could learn to count by employing only one finger. 
Mr. von Osten evidently imagined the process was some- 
what like this : Whenever Hans was about to count 5, he 
would enunciate inwardly the numbers from i to 5, and 
would accompany each word with a tap of the foot. 
Since, furthermore, wooden pins and balls could be used — 
as in the case of children — for giving visual content in 
learning the significance of the number-terms, it seemed 
as if all the conditions necessary for the formation of 
number-concepts were supphed. However, the most es- 
sential thing had to be presupposed, viz. : that the horse 
virtually possessed the general power of forming con- 
cepts,* and that all that had been lacking was the suitable 
conditions for its development. Mr. von Osten held 
tenaciously to this conviction, and it was this conviction 
that was the basis for the infinite patience with which the 
tests had been pursued. 

To come now to the learning process itself; — we may 
assume that, at first, whenever the horse began to tap in 
response to commands, he would receive a reward for this 
purely mechanical feat. Wooden pins were then planted 
on the ground and designated as : one, one two, etc., and 

* There are some who believe they are warranted in concluding the 
opposite from the structure of the animal's brain alone. We may say 
that the brain of the horse, compared with that of the ape, or even that 
of the dog, represents a relatively low type of development. But owing 
to the rapid changes in the views, often contradictory, concerning the 
nature of the nervous structures and processes underlying the thought 
process, any conclusion based on such views would be premature. For 
this reason we cannot agree with the French physiologist who was 
dissecting the brain of a horse and, struck by its smallness of size, ex- 
claimed : " When I saw your proud look and beautiful neck, I hesitated 
a moment before mounting upon your back. But now that I have seen 
how small is your brain, I no longer have any qualm about using you."" 


each time someone would raise the horse's foot as many 
times as the count demanded (see Supplement I). Then 
Mr. von Osten would take his stand at the horse's side 
and would command him, let us say, to tap 3. Hans 
noting merely (from his master's position) that he was 
expected to tap, would begin. The instructor, who had 
bent forward in order to watch the horse tapping,* would 
involuntarily straighten up again at the third tap, without 
being conscious of it and quite unaware that he was thus 
giving a signal. The horse would be startled, and some- ; 
times he would immediately cease tapping and sometim^ 
not. But it was only in the first case that he would re- 
ceive a reward. Thus, unknown to the instructor, an 
association became established between the sight of the 
upward jerk of the instructor and the act of ceasing to 
tap. To be sure, the animal would receive sundry visual"" 
impressions from the wooden pins set up before him and 
the auditory stimulations of the spoken number names, on 
the basis of which, the concepts were to be formed in his 
mind. But in this chaos of visual impressions (at times 
there were two wooden pins, then three, then four, some- 
times there were the pins, at others, the balls of the count- 
ing-machine) — and in the babel of word-sounds — which 
evidently meant nothing but noise to him — amidst all this 
there was but one constant element: the final movement 
of the instructor's body. The moment the horse reacted 
to this, he would receive the tidbit at the hands of his 
overjoyed master, and thus he became more and more ac- . 
customed to attend to this jerk, even after it had grad- 

* This natural and close connection between the process of attention 
and the movement toward the object attended to is clearly expressed in 
our English and French terras, derived from the Latin " tendere ad — ," 
to reach toward—. 


ually decreased in scope. And the reason again, why this 
jerk tended to become less pronounced was that the tests 
were gradually becoming more and more successful. For, 
corresponding to the degree in which the horse began to 
react properly, the instructor's tenseness and excitement 
tended to decrease, and with this decrease of the emo- 
tional element in the man's consciousness, the accompany- 
ing non-voluntary, expressive movement gradually be- 
came less pronounced until it attained that extraordinary 
refinement which it possesses to-day. We noticed also, 
that whenever the horse, for any reason, had to be trained 
anew, Mr. von Osten's movements would, on the whole, 
become somewhat more gross, as for instance after the 
tests with the blinders. There is not a shadow of a 
doubt that this increase in the movement's extent was en- 
tirely unintentional, since the horse could not see his mas- 
ter at all on account of the blinders which had been 
attached to the trappings. 

In the same way it is possible to explain the details. 
Mr. von Osten himself said that at first Hans had tapped 
at times with his left foot, at times with his right, just 
as he pleased. But later his master taught him to tap 
only with the right. Whenever he began with the left, 
Mr. von Osten would immediately interrupt him, and he 
was allowed to add only a final tap with his left foot. 
Thus, this additional tap which was sometimes made with 
the left foot was but the vestige of an earlier rudimentary 
habit. The signal for it was the stooping posture in which 
the master remained after the head-jerk had been made. 
Whenever Mr. von Osten had given Hans a small number 
to tap, he would bend forward only a little. But when 
he expected a larger number he would bend forward 
somewhat more, owing to the desire to observe the tap- 


ping more carefully. From the slight inclination of the 
master's body the horse would get the cue that he was ex- 
pected to tap for a short time only, by the greater de- 
gree of inclination he would know that he was to tap for 
a longer period. In the second case he tapped rapidly 
and did not raise his foot as high from the ground — 
evincing a regard for the saving of energy, which may 
well be attributed to a horse. And thus arose the con- 
nection between the degree of inclination of the in- 
structor's body and the horse's rate of tapping. 

So, now that the ability to count and solve problems 
had become fixed — as the old gentleman thought — ^he be- 
gan to instruct the horse in other branches. Since every- 
thing had been translated into terms which were to be 
expressed by means of tapping with the foot, and thus 
really put into terms of number — which was perhaps 
natural for an old teacher of mathematics — the same 
mechanism was involved in these accomplishments as in 
those of counting, etc. Mr. von Osten saw the animal's 
intelligence steadily increase, without having the slightest 
notion that between his words and the responsive move- 
ments of the horse, there were interpolated his own un- 
conscious movements — and that thus instead of the much 
desired intellectual feats on the part of the horse, there 
was merely a motor reaction to a purely sensory stimulus. 
It has been a common custom of man to posit some ex- 
traneous cause for movements resulting from certain in- 
voluntary motions of his own, of which he is not aware, 
(witness the divining-rod).* And furthermore, when 

* G. Franzius," privy counselor of the admiralty, master of the dry- 
dock at Kiel, is responsible for the undeserved revival of the ancient 
belief, long buried by science, that the divining branch is put into motion 
solely as the result of the influence of hidden springs or treasures, and 


these results appear to be rational, the tendency is to 
seek their cause in some extraneous intelligence, not his 
own. Just as the spiritualists ascribe the " messages " 
which are revealed to them through table-rapping, to cer- 
tain rational spirits, so Mr. von Osten credited the intelll- 1 
gence of the horse with the result produced by his own/ 
involuntary signs — i. e., with the proper solution of prob-/ 

Two other phenomena may have tended to strengthen 
Mr. Ton"Osten's belief in Hans's intelligenceJ^'One was 
the misleading similarity with which the horse'^s supposed 

without any agency in the person who is holding it. The untenability of 
this theory comes home to us most forcibly when we recall how various 
are the kinds of things which have been discovered by means of the 
branch. First there is gold and water, which are the only ones men- 
tioned by Mr. Franzius. The water can be thus discovered only when 
it flows below ground, say that which is passing through the mains of a 
city, whereas the water of the Rhine or the Elbe would have no effect 
on the branch. Besides gold, every other kind of metal has been sup- 
posedly located by the branch, — as well as coal, gypsum, ochre, red-chalk 
sulphur and petroleum, — according to the desire of the one searching. 
Thus, the very same branch that just a moment ago was influenced by 
the least bit of underground water, may remain unaffected by the presence 
of a large body of water, if in the meantime I have changed my plan 
and decide to search for coal or for gold. But that is not all. The 
branch will point out a murderer or the place where a murder has been 
committed, it will discover the thief or his trail, as well as the things 
stolen or merely touched by him. It will indicate where the boundary- 
stone that has been moved, ought to stand. The branch further dis- 
closes the sins of the persons concerning whom it is consulted, as well 
as their talents and abilities, the journeys they have made and the wounds 
they have received. It will indicate whether or not a person has money 
and how much. It can announce what absent persons are doing and 
what apparel they are wearing, and of what color it is. It will give in- 
formation on theological, medical, zoological, and botanical questions. 
In fine, no matter what the question, it will never fail of an answer."", '"1 
The impossibility of explaining the phenomena in a purely physical 
way was recognized at a very early date. For a long time the activity 


errors in computation and the poorly adjusted concentra- 
tion of the questioner, were expressed. We recall the 
difficulty in the case of very high numbers. This might 
easily be considered as being due to the horse's ability to 
work more readily with small, rather than with large 
numbers, whereas, as a matter of fact, it was due solely 
to the difficulty of the questioner to keep his attention 
concentrated upon the number for so long a time. We 
recall also the frequency of errors of one unit too few 
and one unit too many. These were easily interpreted as 
miscounts on the part of Hans, but in truth were the re- 

of the users of the divining rod seems to have been restricted to the 
search for metals. The first (or one of the first) to raise his voice 
against it was the learned G. Agricola 1"^ (15^6), and after him there 
were many who all wrote more or less independently of one another. 
Aside from swindle and chance, it was usually believed that sorcery of 
the agency of Beelzebub was involved, and for that reason the Church 
has repeatedly forbidden the use of the divining-rod. But even in the 
17th century we find some who believed that it was imagination alone 
that moved the person's hand, and with it the rod, '"', i"* (" fortassis 
etiam phantasia manum in motum concitante ") ; and that points out 
the essentials of the solution of the phenomenon, and we will not go 
into the matter here in detail. A number of complex psychological 
problems arising in connection with it are still waiting to be solved, but 
this much appears certain ; the staff or branch plays no other part in the 
whole process than that which is served by the three levers in the tests 
described in Chapter IV (pages 116 ff.), — they simply magnify the ex- 
pressive movements of the diviner. And so we can understand why 
the instruments serving as rod might be so varied. Hay-forks, pickets, 
clock-springs and pendulums, scissors and pliers have been used. A 
knife and fork or two pipes, fastened together, an open book, and even 
a sausage, grasped at both ends and thus bent together somewhat, — 
all have served the purpose equally well. We can understand, too, how 
some adepts are able to achieve the same degree of success-r-for they 
do succeed beyond a doubt — ^without any rod whatever, but simply by 
placing the index fingers end to end and bending them somewhat, and 
even by merely groping about with hands outstretched or folded before 


suit of the poorly concentrated attention of the questioner. 

i^^dded to this was the seeming independence and self- 
sufficiency of the horse. Often the number given by him 
was other than that desired by his master. Usually Hans 
was in the wrong in such cases, but sometimes, too, he 
was right. At any rate, this served to give the impression 
of independence of thought which his master so thor- 
oughly believed he possessed, and which was the goal 
of his endeavors — though as a matter of fact he was 
farther removed than ever from that goal. 

Some may ask : Does not this whole process partake of 
the essentials of all training, (though cumbersome and 
misunderstood, to be sure), and is there any need of in- 
vestigating whether or not the actual development was 
of the sort here outlined, or whether it actually took the 
course common to all training? 

In order to answer this question we must determine 
more specifically what we mean by the term " training ". 
Usually we take it to mean the establishment in the ani- 
mal, of definite habits of motor reaction in response to 
certain stimuli purposely selected by the trainer, and with- 
out involving any process of animal consciousness other 

^^;th5n_assQ.ciationj Such a conception may be applied also 
to man, if we assume that the higher thought processes 
can be eliminated. If that were the case, the above defini- 
tion would not have to be changed, not even with regard 
to the word " animal ", for we must take it in the antique 
sense of " zoon ", a signification readopted by modern 
zoology. The concept may be widened, however, by 
omitting the differentia of " purpose ", or even more, by 
including the habitual association of ideas or images 
(instead of movements) with certain sensory stimuli. 
But in so doing, we must bear in mind that we are going 


beyond the usual content which in everyday practice is 
put into the term " training ". Especially, when we cease 
to regard the presence of purpose in the trainer's mind 
(both in giving the stimulus as well as in the habituation 
of the animal to them) as essential. When this is done, 
the conception of training really resolves itself into the 
much wider conception of habit-building, and the whole 
discussion becomes merely a quarrel over words. In 
order to obviate this, let us bear in mind that in the fol- 
lowing, the word " training " is always taken in the usual 
and narrower sense. The term then is still ambiguous 
only in so far as it has not merely its original significance 
of the act of purposely habituating (a person or an ani- 
.mal) to perform certain definite movements, but by trans- 
ference is also used to denote the effect, i. e., the occur- 
' rence of the movements in question. But this does not 
really detract from the clearness of the concept itself. 
Having cleared up the question of definition, let us re- 
turn to our original problem: Does the hypothetical ac- , 
count of the probable development of the horse's reac- ! 
tions, which is given on pages 213 to 220, represent a j 
case of training? This must be denied decidedly with ; 
regard to the tapping of numbers and the solution of/ 
arithmetical problems. For here the sensory stimuli which 
were purposely given, i. e., the wooden pins, the balls, 
and the spoken words, were intended to subserve the 
function of arousing not movement, but thought proc- 
esses in the horse; whereas the function of the horse's 
movements was to give expression to these thought 
processes. Of the really effective stimuli — the slight 
movements on his part — the master was never conscious, 
much less were they purposely made. The same holds 
true for the " up " and " down ", " yes " and " no ", etc., 


for here also Mr. von Osten counted upon the rise of the 
corresponding concepts, and not merely upon a purely ex- 
ternal, mechanical association of meaningless sounds with 
certain movement-responses on the part of the horse. 
This might also explain the genesis of Mr. von Osten's 
belief that Hans was able mentally to put himself in the 
place of the questioner, (page 19). At any rate it is 
very improbable that he, Mr. von Osten himself, clearly 
distinguished between the concept : " up " and the sound 
of the word " up ". When we come to consider the 
horse's selection of the colored cloths, and even more his 
leaping and rearing, we find that the distinction between 
" training " and " instruction " vanishes. If we had to 
deal only with this class of achievements, we might per- 
haps say, without fear of going very far wrong, that the 
only difference between this and the ordinary form of 
training was that Mr. von Osten had intended to train 
the horse to respond to auditory signs (words), but had 
unintentionally trained him to respond to visual signs in- 
stead. But it is not this type of performance that has be- 
come the bone of contention. Just as it would be mislead- 
ing to maintain that Mr. von Osten's effort was nothing 
other than a case of training, so it also would be unjustifi- 
able to designate the results of his effort by that name, 
since the really effective stimuli were not, as has been 
pointed out just now, given intentionally. 

As far as the horse is concerned, it is a matter of in- 
difference whether or not really effective stimuli were 
given intentionally by the questioner. The animal knows 
nothing of human purposes and if he were transferred to 
a circus, he would find nothing new in the method em- 
ployed there, except the use of the whip. We, however, 
define our concepts from the human and not from the 


horse's point of view. We may definitely say, tlierefore, 
that the method described cannot be regarded as that of 
training, neither in its application nor in the effect pro- 
duced, though in the latter it closely simulates the effects 
of the training method. 

Having thus differentiated between the methods of in- 
struction and training, let us now attempt to decide on 
the basis of such indications as we may possess, which of 
the two was actually represented by the development of 
the horse's attainments. Surveying the facts which we 
have at hand, we may say that there are hosts of reasons 
why we cannotj^ssurne-Jiiat it _ffias a case ^of. training. 
Everything that we know from our own observation and 
from the well-attested statements of others, with regard 
to the actuaL process of instruction, weighs against the 
assumption. "il/Vnother evidence of this is the long period 
of time which Mr. von Osten required (both in the case 
of Hans, as well as with his predecessor), whereas the 
same end would have been much-jnore speedily attained 
if it had been a case of training. i>X further argument is 
the fact that a large horse was selected for the purpose, 
whereas a small mare would have been far more suit- 
able, (c. f., " Clever Rosa", page 7). -'"Again, the whip, 
that sorcerer's rod of all professional trainers, was here 
absent. i^ And finally, many traits of character of Mr. von 
Osten, as well as his conduct during the whole course of 
events, militate against such an assumption. He gener- 
ously turned the horse over to us, as he had given it over 
to Count zu Castell, Count Matuschka and Mr. Schillings. 
He eagerly besought a scientific investigation. He had 
made several reports to different ministries. All of these 
acts could only hasten the denouement. What could have 
been his motive? Some thought they detected an effort 


at pecuniary speculation, and an advertisement of June, 
1902, in the " Militarwochenblatt ", in which Hans was 
offered for sale, seemed to confirm the conjecture. Mr. 
von Osten says that this occurred at a time when he him- 
self was sick and had become tired of the job. And why 
should he not be willing to sell even a thinking horse, 
since he had become convinced that any other could be 
instructed in the same way? Besides, I have it on good 
authority that after the publication of the September re- 
port he received several exorbitant offers; to mention 
only one of them : a local vaudeville company was ready 
to pay him 30,000 to 60,000 marks per month. He re- 
fused every one of these offers. Some may say that per- 
haps he wanted still more. But if he knew that the day of 
judgment was close at hand, he also knew that before 
then, if ever, was the sunshiny day on which to make his 
hay. A more auspicious time he could never hope to see 
again. — Let us add, once more, that he never charged 
admission to any of Hans's performances, although there 
were many who were anxious to see the horse, and many 
enthusiasts had come from a great distance. And finally, 
he was an old man, unmarried and entirely alone, a prop- 
erty owner, but a man whose wants were few and very 
simple — and his Hans was almost his sole companion. 
Is it possible that such a man, one who had all the pride 
of gentle birth, would become a trickster in his old age, 
all for the love of money? 

The unreliability of Mr. von Osten's signs is good 
proof of their involuntary nature. Anyone who had seen 
him work with the horse could not have helped noticing 
that he certainly did not have complete control over the 
animal, and was not able, at a given moment, to make 
Hans perform a certain feat, as would have been the case 


if the process had been one of " training ". Again and 
again Hans failed to make the right count. Before a 
large audience, one time, it took four tests to get him to 
tap properly up to 20, and in all four I could note clearly 
that it was Mr. von Osten who, by his involuntary pre- 
mature movements, was the innocent cause of the failure. 
On another occasion, after Hans had done some beauti- 
ful work in fractions, in the presence of a large number 
of spectators, the master asked him the simple question: 
" Where is the numerator in a fraction ? " — The answer 
was first : " to the left ", and then, after a severe repri- 
mand: "down" (below), and finally: "up" (above). 
He often made just such incorrect movements of the head. 
In the color-selecting tests the average of error was quite 
unpredictable. With an equal number of tests, on one 
day, half would be successful, on another, four fifths, on 
a third, one-tenth. Often Hans appeared to be " indis- 
posed" for days at a time. The color tests would often 
end in expressions of rage on the part of Mr. von Osten 
and in consequence Hans would become startled and 
would then storm about the courtyard so that it was dan- 
gerous to try to approach him. Some may object that all 
this was mere comedy and that possibly Mr. von Osten 
prevented some of the tests from turning out successfully. 
But this objection is to be met by the statement that very 
often failure would occur just when it was particularly 
desirable to have the tests appear in a favorable light 
before a large and enthusiastic assemblage of visitors. 
After such failures he would be downcast on account of 
Hans's contrariness. It is also significant that Mr. von 
Osten's percentage of error, corresponds very closely 
with my percentage of error in the " non-voluntary " 
tests, (page 84f.), whereas he never was able to obtain 


the errorless results which I obtained in my " voluntary " 

But we must be careful not to confuse non-voluntary 
movement and lack of knowledge of the movement. And 
again we must distinguish between knowledge of the 
grosser and the finer signals. Mr. von Osten was aware 
of the grosser movements, and talked quite freely con- 
cerning them, but in so doing, showed that he was quite 
unaware of their true function. He undertook to show 
us what we already knew — that, when he remained stand- 
ing perfectly erect, he could elicit no sort of response 
from Hans. Furthermore, that whenever he continued to 
bend forward, Hans would always respond incorrectly 
and with very high numbers. He knew, also, that Hans 
was distracted in his operations every time the questioner 
resumed the erect posture while the tapping was in prog- 
ress. This he demonstrated to us on one occasion in the 
following manner. He said to Hans : " You are to count 
to 7 ; I will stand erect at 5 ". He repeated the test five 
times, and each time Hans stopped tapping when the mas- 
ter raised his body. Several such tests resulted in the 
same way. Mr. von Osten, however, believed this to be a 
caprice of the horse and at first declared that he would 
yet be able to eliminate it, but later became resigned to it 
as an irremediable evil. Mr. von Osten was also aware 
that the questioner ought not move while the horse was 
approaching a colored cloth, and cautioned me in regard 
to it, though I had already noted as much. And finally, he 
also knew what influence his calls had while the horse 
was selecting the cloth, and he told me that it was of great 
assistance to Hans to be admonished frequently, since 
thus his attention was brought to bear upon the proper 
cloth. Yet, when we requested Mr. von Osten to desist 


calling, since he was thereby influencing the horse in the 
choice of the cloth, he answered : " Why that's just what 
I wish to do ! " — But though the statement that he was 
aware of the nature of these grosser signs is thus seen 
to be true, it by no means necessarily implies that he had 
purposely trained the animal to respond to them. In 
these observations of his he had builded better than he 
knew — he evidently had no notion of their scientific sig- 
nificance. But the same thing might happen to those 
who were suppossed to be somewhat less naive, as is 
shown by the experience of Mr. Schillings, who quite un- 
consciously, for many months had been giving not only 
the finer, but also the grosser signs, and never guessed 
the true nature of affairs until I explained it to him. Nor 
was it an easy matter for me to get at the facts involved 
in the process, although it now all appears so very simple. 

On the other hand, it is also true that Mr. von Osten - 
knew nothing whatever of the finer, more minute signals, 
such as the final jerk, the head-movement upward, down- 
ward, etc., and it is difficult to conceive how he might 
have gained any knowledge of them. We might per- 
haps conceive of four possible sources, i He might have/ 
come upon them by chance. But it is extremely im- 
probable that in the million of possible forms of sig- 
naling he should have hit upon those that at the 
same time represent the natural expressive movements. 
'=^0r he might have derived a knowledge of them through 
a study of the pertinent literature. I have searched 
diligently for such a source, in both the old and the 
modern literature, but in vain. From the sixteenth 
century on, there is a series of accounts of horses that 
were able to spell and to solve problems in arithmetic, 
and the reports on learned dogs go back even to the time 


of Justinian, in the middle of the sixth century.'"' AH 
of these animals were kept for purpose of speculation and 
were exhibited for pecuniary reasons only. Nor does one 
read that any person could work with these animals off- 
hand, which was the characteristic feature of the Osten 
horse.* In many cases we find mention made of the 

* There is only one, and I believe it is only a seeming exception 
to be found in the literature on the subject. We are told that 
about the year 1840 a French revenue official named Leonard had two 
hunting dogs that, besides other things, were able to play at dominoes, 
and this not only with their master, but with anyone and without the 
master's assistance. The owner had educated them simply for the fun 
of it, and not for pecuniary gain. This statement is made by both 
writers who, apparently independently of one another, have discussed 
the case, Youatt '"^ and de Tarade."" De Tarade himself played 
with them, and gives directions how to teach dogs to play the game. 
But his exposition is so naive, and even ridiculous, for those who know 
anything about the subject, that we do not believe it necessary to at- 
tempt a detailed refutation. Youatt never saw the animals. But he 
tells us that not only the dog's partner, but also the master, sat at the 
game. Youatt's assertion, however, that "not the slightest intimation 
could have been given by Mr. Leonard to the dog," but that the animal 
carried on the game by means of its own observation and calculation, 
appears to me a rather bold statement. After my own experience with 
dogs, I firmly believe this to have been impossible. Hachet-Souplet,"" 
who shares my conviction, explains the matter as follows : the dog 
would simply place a domino having the number of eyes named by his 
partner, thus the 6 adjacent to the 6, the 3 to the 3, etc. But even so 
a great deal would have to be attributed to the dog, (although in that 
case real counting would by no means be absolutely necessary, for an 
association between the number term and the total picture of the cor- 
responding group of eyes would suffice.) But we must note that neither 
of the writers mentions that the numbers were always called aloud by 
the partner. After the failure of the experiments of Sir John Lub- 
bock,'" we must doubt very much if a dog is able to match one domino 
with another having the same number of eyes. We are therefore in- 
clined to believe that this dog continually received signs from its master. 
These signs probably were visual, perhaps also auditory, and they were 
by no means involuntary. For in a book on the training of animals, 


signs to which the animals reacted. Thus for the begin- 
ning or stopping of the animal's scraping or tapping, the 
signals were respectively raising and lowering of the eyes 
on the part of the trainer,"^ lowering and raising of the 
whip"* or of the arm, stepping forward and back- 
ward,"° and as a closing signal a slight bending for- 
ward."" The signals for beginning and ceasing to bark 
in the case of dogs, were the trainer's commands to 
" speak ", and, at the same time, his looking at the dog, 
and then looking away for a closing sign ; ^" or a mouth- 
movement on the part of the trainer and then a withdraw- 
ing of the left hand which had been resting on the hip."' 
Among the signals for nodding and shaking the head we 
find the following mentioned: raising and lowering the 
hand or arm "° or the whip ; "° a movement of the hand 
toward the horse's nose, as a signal for nodding, and an 
arm-movement as a signal for shaking the head.^^^ For 
this last, we find recommended also a slight breathing 
upon the animal,'^^ and — in the case of dogs — a mouth- 
movement simulating blowing, or a turn of the fingers.^^^ 
(We will not dwell upon the many signals for selecting 
objects, which are mentioned, since we have already dis- 
cussed this point on page 23of). In all these instances it 
is plain that we have to do with purely voluntary and 

which Leonard, the owner of the dogs, has published, and in which he 
describes minutely the method by which they had been trained in their 
various accomplishments, he does not mention with so much as a syl- 
lable the game of dominoes, a thing which he certainly would have 
dwelt upon, if he had believed in the animals' power of independent 
thought. He would not have remained silent concerning this greatest 
— though only apparent — achievement of his educational endeavors. 
But his whole book is evidence that he was too wise to have thus de- 
ceived himself, and our only alternative is to believe that he was play- 
ing a joke on his credulous admirers. 


" artificial " signals. The only example of involuntary 
s^gns which. Mr. von Osten could have found in literature, 
was that of Huggins's dog, which need not be considered 
here, since, as was said on page 177, the really effective 
signs in that case were not discovered^iA third means by 
which Mr. von Osten might have gamed a knowledge of 
the involuntary, natural expressive signs, would have 
been by observing others. If he had had opportunity of 
observing another von Osten and another Hans, he might 
have gotten at the secret. But since this was not the 
case, this possibility vanishes.M-A fourth possibility is 
self-observation. We would then have to assume that 
Mr. von Osten at first really tried to educate the horse 
to think, but soon recognized the fruitlessness of such an 
attempt. At the same time, he then would have noticed 
his own involuntary movements and their effect upon the 
horse, and having noted them, voluntarily reduced their 
extent and utilized them in the training process. But 
here also there is much that militates against this assump- 
tion when we consider how great is the difficulty of con- 
sciously refining movements which at first were rather 
coarse, unless it be by the adjustment of the proper de- 
gree of concentration of attention, a subtlety of method 
of which we could hardly believed Mr. von Osten capable. 
We must remember, also, that in the first publication re- 
garding Hans which, by the way, marks the beginning 
of his career, (" Das lesende und rechnende Pferd," by 
Major-General E. Zobel, in the " Weltspiegel " of July 7, 
1904), we may read the following: " He (Mr. von Osten) 
is always willing to have the horse undergo an examina- 
tion on the part of a stranger, and promises that after 
Hans has become fairly well acquainted he will display 
the same degree of efficiency as he displays with the mas- 


ter, himself. This occurred at a time when Mr. Schil- 
lings, the man who was destined to prove the truth of 
the statement, had not yet appeared on the scene. How 
was Mr. von Osten to know beforehand that every ques- 
tioner, who might appear, would execute the same move- 
ments that he himself had used?- We would recall also 
that not one in the great multitude of persons who worked 
successfully with the horse in the absence of Mr. von 
Osten, had noticed, even in the slightest measure, any of 
these movements in themselves. The position and repute 
of these persons vouches for their veracity, — among them 
were the writer of the article just mentioned, the Count 
zu Castell, Count Matuschka, Count von Eickstedt- 
Peterswaldt, General Koring, Dr. Sander, Mr. H. Suer- 
mondt and Mr. H. von Tepper-Laski. Some of these 
gentlemen were quite unwilling to believe that they exe- 
cuted such movements.. This happened in the case of Mr. 
von Tepper-Laski, who had visited Hans ten times and 
who had, during the course of these visits, frequently 
worked alone with the horse and had received correct re- 
sponses. Count Eickstedt, too, although he was one of 
those who had been made acquainted with the nature of 
the movements involved before being allowed to visit the 
horse, was unable to note them either in his observation 
of Mr. von Osten, or of himself, when, in compliance with 
his own wish, he was left alone with Hans. Nor did any 
of the laboratory subjects, some of whom were well trained 
in introspection, discover the true nature of affairs. 
They were thoroughly astonished when the facts of the 
case were explained to them. And I, also, as was men- 
tioned on page 100, did not become aware of my own 
movements, until I had noted those of Mr. von Osten. 
In fine, everything would indicate that we have here not 


an intention to deceive the public, but a case of pure self- 

This self-deception is easily understood when we con- 
sider the two predominent characteristics of the man : the 
pedantry of the pedagogue, and his^groneness to be pos- 
"sessed by a single ideaj which is a peculiarity "of those of 
an inventive turn of mind. Adhering closely to a pre- 
formed plan, he carefully and narrowly circumscribed 
the scope and order of instruction. He would not go on 
to the number 5 if he were not thoroughly convinced that 
the 4 had been completely mastered, nor would he go on 
to a more difficult problem in multiplication, until he felt 
certain that Hans was entirely proficient in the problems 
of the simpler sort. If he had ever put a question to 
Hans before its regular order, he would have discovered, 
to his amazement, that there really existed no difficulties 
for Hans, and also that the horse really required no ap- 
preciable time to acquire new material. Mr. von Osten 
would have had a like experience if he had asked Hans 
concerning the value of Chinese coins or the logarithm 
of 1000. However, he never did anything of the kind, 
but always adhered closely to his plan. He required the 
questioner to say : " 2 and 2 ", and never " 2 plus 2 ". 
Nor were capitals or Latin script to be used in the writ- 
ten material. And if upon request he did so, he did it, 
without faith in the result, and hence there was failure. 

* P. Wasmann, S. J. in the third edition of his book, " Instinkt und 
Intelligenz im Tierreich " (Freiburg, Herder, 1905), discusses the case 
of Hans and quotes from a letter I wrote him concerning the matter. 
In the quotation an error has crept in, wljich I -would here correct. 
The statement is ascribed to me that " Hans differs from other horses 
only in his extraordinary power of observation, an unintentional by- 
product of intentional training," whereas in my letter I said : " uninten- 
tional by-product of intentional education.'' 


And so he declared that " if you use Latin script Hans 
becomes confused and will be out of sorts for several 
weeks thereafter." Mr. von Osten is, and ever will re- 
main, the schoolmaster, and will never become the psy- 
chologist, the " soul-vivisectionist ". Who would work a 
child with such puzzling questions ? and Hans was to him 
like a child. Thus the old man believed himself to be a 
witness of a continuous, organic development of the 
animal soul — a development which in reality had no other 
existence than in his own imagination. 

Added to this pedantry was an extraordinary un- 
critical attitude of mind, induced by his obsession by one 
favorite idea, which blinded him to all objections. He met 
objectionable observations on the part of others in one of 
two ways. One method was by attributing to Hans certain 
remarkable qualities, such as an extraordinary keenness of 
hearing and a wonderful power of memory, or again, cer- 
tain defects, such as moodiness and stubbornness, — which 
as a matter of fact, were only so many back-doors by 
which he might escape from the necessity of ofifering ade- 
quate explanations. When Hans was able to give off-hand 
a gentleman's name which he had heard years before, it 
was called a case of extraordinary memory. When the 
horse insisted that 2 times 2 was 5, he maintained that 
it was an example of animal stubbornness. There was 
still a simpler method of overcoming inconvenient objec- 
tions and that was by ignoring them altogether. The 
number i, the simplest and most fundamental in the 
system of numbers, was one of the most difficult for Hans. 
(Page 671). Mr. von Osten was aware of this, but 
thought little of it. During the very first visit of Pro- 
fessor Stumpf, Mr. von Osten asked the horse: "By 
how much must you increase the numerator of the frac- 


tion }i, in order to get a whole number?" Hans re- 
peatedly answered incorrectly and always tapped num- 
bers that were too great. The same question was then 
asked concerning the fraction ^, and immediately there 
was a correct response, (the favorite number 3). Mr. 
von Osten said very naively : " In the case of the differ- 
ence of I, he always goes wrong. It was just what I 
expected." Mr. von Osten still relates that the distinc- 
tion between right and left created far greater difficulty 
for Hans than all of the work in fractions, and that even 
to-day it is not thoroughly established; also, that the se- 
lection of colored cloths is often a failure still, although 
it was one of the first things in which he was given in- 
struction. It appears never to have dawned upon Mr. 
von Osten that the arts in which Hans seemed to excel, 
also formed the standing repertoire of so many trained 
horses, regarding whom it was well-known that they 
owed all of their cleverness to the training given them 
by their masters. This fact alone should have induced 
him to make some form of critical investigation. 

When Hans suddenly became a celebrity, and he, him- 
self, the object of an enthusiastic following, the whole 
affair evidently took Mr. von Osten off his feet. Stran- 
gers took the further instruction of the horse in charge, 
and the rate and degree of Hans's progress became dis- 
concerting. One day it came to pass that the horse even 
understood French, and the old gentleman, whose aposto- 
lic exterior had always exerted a high degree of sugges- 
tion upon his admirers, in turn fell captive to the spell of 
retroactive mass-suggestion. He no longer was uneasy 
concerning the most glaring kinds of failure. On one 
occasion he even insisted upon the completion of a series 
of tests in which procedure was " without knowledge ", 


which promised no results whatever. " The animal's stub- 
bornness must be broken," he commented. On the other 
hand, he regarded every criticism as a form of personal 
insult. And once he showed a member of the committee 
of the Society for the Protection of Animals the door, be- 
cause the man, without having looked at his watch, wanted 
to show it to Hans and ask him the time. Many other 
critics had similar experiences. 

Summarizing the remarks of this chapter, our judg- 
mpnt must be as follows : It is in the highest degree im- 
probable that Mr. von Osten purposely trained the horse 
to respond to certain cues. It is also improbable that he 
knew that in every test he was giving signals, (although 
I can form no judgment concerning what happened after 
the publication of the latest report). To assume the 
contrary would land us in the midst of insoluble contra- 
dictions of the many ascertained facts in the case. The 
explanation here essayed, however, should prevent that. 
To be sure, we, must then reckon with curious inner 
contradictions in Mr. von Osten's character. But such 
contradictions are to be found, upon earnest analysis, in 
nearly every human character. And Mr. von Osten may 
say with the poet : " Ich bin kein ausgekliigelt Buch. 
Ich bin ein Mensch mit seinem Widerspruch." 


If we would make a brief summary of the status of Mr. 
von Osten's horse in the light of these investigations and 
try to understand what is the beating upon the question 
of animal psychology in general, we may make the follow- 
ing statements. 

Hans's accomplishments are founded first upon a one- 
sided development of the power of perceiving the slight- 
est movements of the questioner, secondly upon the in- 
tense and continued, but equally one-sided, power of at- 
tention, and lastly upon a rather limited memory, by 
means of which the animal is able to associate perceptions 
of movement with a small number of movements of its 
own which have become thoroughly habitual. 

The horse's ability to perceive movements greatly ex- 
ceeds that of the average man. This superiority is prob- 
ably due to a different constitution of the retina, and per- 
haps also of the brain. 

Only a diminshingly small number of auditory stimuli 
are involved. 

All conclusions with regard to the presence of emo- 
tional reactions, such as stubbornness, etc., have been 
shown to be without warrant. With regard to the emo- 
tional life we are justified in concluding from the be- 
havior of the horse, that the desire for food is the only 
effective spring to action. 

The gradual formation of the associations mentioned 
above, between the perception of movement and the 
movements of the horse himself, is in all probability not 



to be regarded as the result of a training-process, but as 
an unintentional by-product of an unsuccessful attempt 
at real education, which, though in no sense a training- 
process, still produced results equivalent to those of such 
a process. 

All higher psychic processes which find expression in 
the horse's behavior, are those of the questioner. His 
relationship to the horse is brought about almost wholly 
by involuntary movements of the most minute kind. The 
interrelation existing between ideas having a high de- 
gree of affective coloring and the musculature of the 
body, (which is brought to light in this process), is by 
no means a novel fact for us. Nevertheless, it is possible 
that this case may be of no small value, on account of the 
great difficulties which are usually met in the attempt to 
establish experimentally the more delicate details in this 

And, returning to the considerations of the first chap- 
ter, if we ask what contributions does this case make 
toward a solution of the problem of animal consciousness, 
we may state the following: The proof which was ex- 
pected by so many, that animals possess the power of 
thought, was not furnished by Hans. He has served to 
weaken, rather than strengthen, the position of these en- 
thusiasts. But we must generalize this negative conclu- 
sion of ours with care, — for Hans cannot without fur- 
ther qualification be regarded as normal. Hans is a do- 
mesticated animal. It is possible (though the opposite is 
usually assumed), that our animals have suffered in the 
development of their mental life, as a result of the proc- 
ess of domestication. To be sure, in some respects they 
have become more specialized than their wild kin, (e. g., 
our hunting dogs), and in their habits they have become 


adapted largely to suit our needs. This latter is shown 
by all the anecdotes concerning " clever " dogs, horses, 
etc. But with the loss of their freedom they have also 
gradually been deprived of the urgent need of self-preser- 
vation and of the preservation of their species, and thus 
lack one of the greatest forces that make for psychic 
development. And often their artificial selection and 
culture has been with a view to the development of muscle 
and sinew, fat and wool, all at the expense of brain de- 
velopment.* Our horses are, as a rule, sentenced to an 
especially dull mode of life. Chained in stalls (and usu- 
ally dark stalls at that,) during three- fourths of their 
lives, and more than any other domestic animal, enslaved 
for thousands of years by reins and whip, they have 
become estranged from their natural impulses, and owing 
to continued confinement they may perhaps have suffered 
even in their sensory life. A gregarious animal, yet kept 
constantly in isolation, intended by nature to range over 
vast areas, yet confined to his narrow courtyard, and de- 
prived of opportunity for sexual activity, — he has been 
forced by a process of education to develop along lines 
quite opposite to his native characteristics. Neverthe- 
less, I believe that it is very doubtful if it would have 
been possible by other methods, even, to call forth in the 
horse the ability to think. Presumably, however, it 
might be possible, under conditions and with methods of 
instruction more in accord with the life-needs of the 
horse, to awaken in a fuller measure those mental activi- 
ties which would be called into play to meet those needs. 

* BufIon,i24 the great naturalist, expresses himself not less pessimis- 
tically in his own brilliant manner : " Un animal domestique est un 
esclave dont on s'amuse, dont on se sert, dont on abuse, qu'on alt^re, 
qu'on depaise et que I'on denature." 



Though our investigations do not give support to the 
fantastic acounts of animal intelligence given by Brehms, 
they by no means warrant a return to Descartes and his 
theory of the animal-machine (as is advocated by a num- 
ber of over-critical investigators). We cannot deny the 
validity of conclusions from analogy without denying at 
the same time the possibility of an animal psychology — 
indeed of all psychology. And all such conclusions indi- 
cate that the lower forms possess the power of sense- 
perception, that they, like us, presumably have at their 
disposal certain images, and that their psychic life is to a 
large extent also constituted of mere image-associations, 
and that they too, learn by experience. Also that they 
are susceptible to feelings of pleasure and of pain and 
also to emotions, as jealousy, fear, etc., though these 
may be only of the kind which have a direct relation to 
their life-needs. We are in no position to deny a priori 
the possibility of traces of conceptual thought in those 
forms nearest man in the scale — whether living in their 
natural manner or under artificial conditions. And even 
less so since the final word has not yet been spoken re- 
garding the nature of conceptual thinking itself. All that 
is certain is that nothing of the kind has been proven to 
occur in the lower forms, and that as yet not even a 
suitable method of discovering its existence has been 
suggested. But the community of those elementary 
processes of mental life which we have mentioned above 
is in itself enough to connect the life of the lower forms 
with ours, and imposes upon us the duty of regarding 
them not as objects for exploitation and mistreatment, 
but as worthy of rational care and affection. 




[By C. Stumpf] 

The following is a report of the account, which Mr. 
von Osten gave Professor Schumann and me, of the 
method which he had used in the instruction of the horse, 
and which was illustrated by actual demonstrations. I 
cannot testify, of course, that Mr. von Osten really did 
adhere to this method throughout the four years in which 
he tutored the horse, but I will say that I have several 
good reasons for believing that it was impossible for him 
to have trumped up this make-believe scheme afterward, 
merely to mislead us. Among the reasons are the fol- 
lowing: He was always ready to give a detailed expla- 
nation of any question which we might interpose; the 
written statements of Major von Keller, who has known 
Mr. von Osten for a period of fifteen years; the testi- 
mony of General Zobel, who became acquainted with the 
whole process fully a year before any public exhibi- 
tions were given; the accounts given by the tenants in 
Mr. von Osten's house, who for years saw the process of 
instruction going on in the courtyard of the apartment 
building, — according to their account his intercourse with 



the horse was hke that with a child at school, — ^he made 
much use of the apparatus and never did they notice any- 
thing Hke an habituation to respond to certain signals; 
and finally the appearance of the apparatus itself— some 
of which could not be bought at second hand — was most 

The apparatus used for the work in arithmetic consisted 
mainly of a set of large wooden pins, a set of smaller 
ones (such as are to be had in toy-shops), a counting- 
machine, such as is commonly used in the schools, a chart 
upon which were pasted the numbers from i to loo, and 
finally the digits, cut large and in brass and suspended 
from a string. For the work in reading Mr. von Osten 
used the chart shown in the frontispiece of this book. 
Here we have the letters of the alphabet in small German 
script with numbers written below which serve to indi- 
cate the row, and what place in that row, the letters 
occupy. For tones, a small, child's organ was used with 
the diatonic scale C^ to C^, and for instruction in colors, 
a number of colored cloths were used. 

The work in arithmetic began by placing a single 
wooden pin in front of Hans and then commanding him : 
" Raise the foot ! — One ! " Here we must assume that 
the horse had learned to respond to the command to raise 
the foot during the preceding period, when tapping in 
general had been taught. In order to get the horse to 
learn that he was to give only one tap, Mr. von Osten 
tried to control the tapping by means of holding the ani- 
mal's foot, just as a" teacher tries to aid a pupil in learning 
to write by guiding his hand. He repeated this exercise 
so often that finally the single tap was made. And al- 
ways the right foot was insisted upon. Bread and carrots 
were the constant rewards. 


Two of the pins were now set up and the command 
given : " Raise the foot ! — One, two ! " Mr. von Osten 
again aided the establishment of the proper association by 
using his hand as before. At the same time the two pins 
were pointed out, and the order was always without ex- 
ception from left to right. Gradually it became unneces- 
sary to touch the foot or to point to the pins, and instead 
the question was introduced : " How many are there ? ", in 
order that the horse should become accustomed to these 
words as an invitation to give the taps when he saw the 
wooden pins before him. 

Then three pins were taken and the words " one, two, 
three " were spoken, and so on. In naming a number 
the preceding ones were always named along with it, in 
order that the normal order might thus be learned at the 
same time. Later the number alone, without the preced- 
ing ones, sufficed to elicit the proper number of taps. 
The last word of the series thus becomes characteristic 
of the series as a whole. It differs from all the others, 
and thus becomes the sign for the whole series of num- 
bers thus named, each of which arises as a memory image 
at the proper place in the series and is accompanied by a 
tap of the foot. Thus, Mr. von Osten at any rate had 
accounted to himself for his success. 

But Hans was not to acquire merely this relatively me- 
chanical process of counting (hardly to be called count- 
ing), but he was to acquire also some meaning content 
for the number terms. For this purpose everything de- 
pended upon the concept " and ". Only he who can grasp 
its meaning will be able to understand a number. 2 is 
I and I, 3 is 2 and i. Mr. von Osten had someone hold 
a large cloth before the horse, where the wooden pins 
usually were placed. He then had the cloth taken uo and 


he would pronounce emphatically the word "and". 
After this had been done a number of times, he put up two 
of the pins and obscured them by the cloth. The cloth 
was again raised'^nd the word " and " pronounced. Then 
Hans, as a result of his previous instruction (so Mr. von 
Osten thought) would give two taps at sight of the pins. 
The thing was repeated with three pins, then with one, 
and so on, and the horse would always execute the proper 
number of taps. 

Now, five pins were set up, the three to the right being 
covered by the cloth. The horse tapped twice and Mr. 
von Osten said " two ". Then the cloth was raised, Hans 
gave three further taps, and Mr. von Osten said " and 
three " with emphasis. 

In this simple manner he tried to get the horse to un- 
derstand that the three belongs to the two, and that both 
together make five. The image of the five pins as it was 
known from previous experience, was to be associated 
with the combined groups of two and three, and con- 
versely, it was to be reproduced when these groups were 
presented. Later the cloth and pins were omitted and the 
question was asked: "How much is two and three?". 
The horse tapped five times. It had learned how to add. 
Still this could be regarded only as a mechanical process, 
if the horse were able to add only those numbers which 
had been presented together one or more times in the 
manner just described. And so long as we remained 
within the first decade, we could get twenty-five binary 
combinations whose sum does not exceed lo (counting 
inverted orders we would have forty-five binary permu- 
tations), — all of which might have been practised sepa- 
rately. But as a matter of fact, Mr. von Osten did not 
take this course, for as he himself says, he allowed Hans 


to discover a great deal for himself. " Hans had to de- 
velop the multiplication table for himself." — With larger 
numbers and more addends, the number of combinations 
becomes so great that there can be no doubt they were 
not practised separately. 

Since, after all this preliminary instruction, Hans 
really began to give solutions of new problems, the master 
believed that this was proof that he had succeeded in in- 
culcating the inner meaning of the number concepts, and 
not merely an external association of memory images 
with certain movement responses. But he always re- 
mained within the sphere of the ideas thus developed, 
and adhered closely to the customary vocabulary and its 
usage. Every new concept, each additional word was 
explained anew. 

It would not be legitimate to condemn the whole pro- 
cedure from the very beginning on the ground of the 
horse's lack of knowledge of language or of its use. It 
was Mr. von Osten's aim to convey to the horse an un- 
derstanding of the language, by means of sense-presenta- 
tions, adequate to give rise to the proper sense-percep- 
tions. Helen Keller and other blind deaf-mutes have 
been educated to an understanding of the language with- 
out the aid of vision and hearing. They have come to it 
through the sense of touch alone. Everything depends 
upon whether or not the predisposition for it is present. 
And it was quite rational that Mr. von Osten should 
have chosen counting and arithmetical calculation as the 
processes by which to make his attack upon the animal 
mind, for as a matter of fact, nowhere else is it so easy 
to bridge the gap between perception and conception and 
nowhere else can the sign of success or failure be per- 
ceived so readily as in the handling of numbers. It is 


unfortunate, however, that he did not utilize these same 
signs for purposes of counter-testing also, as, for in- 
stance, by inquiring for the cube root of 729. But he was 
prevented from doing this by his close adherence to his 
pedagogical principle and by his unquestioning faith in 
the soundness of the entire procedure. 

In teaching multiplication the counting machine was 
used. Two of the ten balls on one of the rods were 
pushed far to the left, thus : 00. " How many are 
there ? " Two taps. " Very well. That is once two." 
Another group of two was pushed to the left, at a short 
interval from the first group, thus : 00 00. " How many 
times two balls are there ? " was asked, with a decided 
movement of the hand toward the two groups. Two 
taps. "How many, therefore, are two times two?" 
Four taps. 

The horse was supposed to learn the meaning of the 
word " times " by means of the spatial separation of the 
groups; he was to be taught to notice and to count the 
groups, and also the number of units in a single group. 
Three times two then meant three groups with two units 
in each group. The horse was supposedly aided by the 
following factors: the relative nearness of the units be- 
longing to one group, as over against the space interval 
between the groups themselves; also that the groups 
were pointed out as wholes in connection with the em- 
phatic enunciation of the words ' once , ' twice , etc. ; 
and finally the touching and raising of the horse's foot 
by means of the hand until all the desired associations of 
the ideas with one another and with the corresponding 
tapping movements were quite perfect. 

Subtraction was taught in the following manner. Five 
pins were set up ; the horse tapped five times. Mr. von 


Osten then removed two of them and said emphatically : 
" I take away, — minus. " How many are still stand- 
ing?" The horse tapped three times. Here, too, there 
was at first some assistance by means of the hand to get 
the tapping. 

In division four balls were first pushed to the left end 
of the rod, thus : 0000. " How many balls are there to 
the left ? " Four taps. They were now divided into two 
pairs, thus : 00 00. Pointing to the units of one group, 
the teacher asks : " There are always how many in the 
group?" Two taps. Three groups were formed, thus: 
00 00 00. " There are now how many balls to the left ? " 
Six taps. "And there are always how many in each 
group?", (pointing at them). Two taps. "And how 
often is two contained in six ? ", (pointing to the groups 
consecutively). Three taps, etc. 

The ideas of ' part ', of ' whole ', and of ' being con- 
tained ' were illustrated by means of a chalk line which 
was interrupted in one or more places by erasure. 

In all these operations Mr. von Osten adhered strictly 
to the rule, and required others to do so too, that the num- 
ber upon which the operation was performed, must be 
mentioned first. Thus, one was not to say, " take 3 away 
from 7 ", but " from 7 take away 3." Otherwise, he be- 
lieved, Hans would become easily confused. Also one 
was not allowed to say " to multiply ", but to " take " a 
certain number so many " times ". He, himself, never 
departed from this practice. 

We will not go into the details of the method by which 
Hans was taught the meaning of the number signs, of the 
signs of operation, of the numbers above 10, or the signifi- 
cance of " digits " " tens ", etc. Only this, — when in 
problems in addition the sum was greater than 10, the 10 


was first tapped and then the remainder of the number 
added to the lo. Thus : " You are to add 9 and 5. How 
much must you add to the 9 to have 10?" One tap. 
" But now, you were to add not merely i, but 5 ; how 
much have you still to add to the 10? " — Four taps. In 
like manner, whenever the addends were below 20 or 30 
and the sum above 20 or 30, Mr. von Osten would ask 
for the 20 or 30 taps first. He thought that he was thus 
giving his pupil an ever firmer grasp upon the principle 
of the structure of our number system, in which all higher 
numbers are constituted of tens and digits. For the 
same reason he used at first, instead of the words ' eleven ' 
and 'twelve' ('elf and ' zwolf ' in the German), ex- 
pressions which in English might be rendered as ' one- 
teen ' and ' two- teen ' (' einzehn ' and ' zweizehn ' in the 
German) ; and only later, after the animal had seemingly 
mastered the meaning in question, did Mr. von Osten re- 
place them by the usual forms. 

All this was beautifully conceived and might perhaps 
form the basis for the instruction of primitive races. 
But it is of immediate interest for us only because it 
enables us to better understand the origin of the con- 
viction under which Mr. von Osten and his followers 



"The undersigned came together for the purpose of 
investigating the question whether or not there is in- 
volved in the feats of the horse of Mr. von Osten any- 
thing of the nature of tricks, that is, intentional influ- 
ence or aid, on the part of the questioner. After a care- 
ful investigation they are unanimously agreed that such 
signs are out of the question under the conditions which 
were maintained during this investigation. This decision 
in no wise takes into account the character of the men 
exhibiting the horse, and who are known to most of the 
undersigned. In spite of the most attentive observation, 
nothing in the way of movements or other forms of ex- 
pression which might have served as a sign, could be dis- 
covered. In order to obviate involuntary movements on 
the part of those present, one series of tests was made 
with only Mr. Busch present. Among these tests were 
some in which, according to his professional judgment, 
the possibility of tricks of the sort commonly used in 
training, was excluded. Another series of tests was made 
in such a way that the correct answers to the questions 
which Mr. von Osten put to the horse, were unknown to 
the questioner. From previous observation the greater 
number of the undersigned also know of a large number 
of cases in which, during the absence of Mr. von Osten 
and Mr. Schillings, other persons were likewise able to 
obtain correct responses from the horse. Among these 



were some cases in which the questioner did not know 
the correct solution of the problem or was mistaken about 
it. And lastly, several of the undersigned have become 
acquainted with the method which Mr. von Osten used, 
which has little in common with methods of training, and 
is patterned after the instruction given in the elementary 
schools. As a result of these observations the under- 
signed are of the opinion that unintentional signs of the 
kind which are at present familiar, are likewise excluded. 
They are unanimously agreed that this much is certain: 
This is a case which appears in principle to dififer from 
any hitherto discovered, and has nothing in common with 
training, in the usual sense of that word, and therefore 
is worthy of a serious and incisive investigation. 
Bbrwn, September 12, 1904. 

Faui, Suscb, Circus-manager. 

OTTO, Count zu Castki,i.-Rudenhausbn. 

Dr. a. Grabow, member of the schoolboard, retired. 

Robert Hahn, Teacher, Municipal schools. 

Dr. Ludwig Heck, Director of the Zoological Garden. 

Dr. Oscar Heinroth, Assistant in the Berlin Zoo- 
logical Garden. 

Dr. Richard Kandt. 

Major F. W. von Keller, retired. 

Major-Generai, Th. Koring, retired. 

Dr. Miessner, Assistant in the Royal Veterinary 

Prof. Nagei,, Head of the department of sense-physi- 
ology in the Physiological Institute of the Univer- 
sity of Berlin. 

Prof. C. Stumpf, Director of the Psychological In- 
stitute, Member of the Academy of Sciences. 

Henry Suermondt." 



The important meetings occurred on the nth and 
I2th of September and both of them extended over four 
hours. The greatest difficulty was occasioned by the con- 
dition laid down by Mr. von Osten : that we were to work 
without him from the very beginning. In a certain sense 
this condition had been met once before when Mr. 
Schillings appeared upon the scene, a man whose fair- 
ness ought to be doubted by none. He came utterly 
skeptical, and yet in the course of a week he learned 
to handle the horse and received responses regularly. 
However, since the public had begun to doubt Mr. 
Schillings also, another person had to attempt the role 
of questioner. Count zu Castell tried to do this and 
practised for some days before the meetings, but his 
success — ^although of no small moment — was not great 
enough to be convincing. 

In apprising Mr. von Osten of this fact we caused a 
veritable catastrophe. He declared in a most decisive 
manner that he would have to insist upon the condition 

* A few days after the I2th of September I made the present abstract 
from the original records af the Commission, which T have here ab- 
breviated somewhat. (See page 8). Referring once more to the misun- 
derstanding mentioned on page 3, I would say that the closing sentence 
of the report is here reygiven literally as it then appeared. C. St. 



he had imposed, since the public demanded it, and he 
could never assist in any tests, until he had been cleared 
of the suspicion of having descended to the use of tricks. 
If it should take weeks to accustom the horse to a new 
questioner, there would be no alternative but to wait 
that length of time. 

A happy circumstance helped us out of our difficulty. 
We had chanced in our discussion to mention the ex- 
perience of Dr. Miessner, a member of the commission, 
who on the day before had gone to witness an exhibition 
of the mare " Qever Rosa ", and who believed that 
he had succeeded in discovering the tricks involved. 
There was a sudden change in Mr. von Osten's attitude. 
He expressed his willingness to undergo the most strin- 
gent examination and agreed to anything in the way of 
conditions of control, challenging even the proven ability 
of Dr. Miessner. " I have neither whip nor rod, as had 
the man in the exhibition, and agree to any precautionary 
measures you may care to take." 

After he had gone, the commission decided to ask him 
to have the horse perform one of the more common, 
simple, feats. They were going to watch him very 
closely. Different members were assigned the task of 
attending to different parts of his body (head, eyes, right 
hand, left hand, etc.) while Mr. Busch, since he was the 
most proficient in the detection of tricks, was to regard 
the total behavior of the man. 

The exhibitions included the indication of the day of 
the week by means of taps, the day just past, the day 
ahead, its date, arithmetical problems, and the counting 
of rings strung upon a rod. Messrs. Grabow and Hahn 
interpolated a few tests themselves, in which they did the 
questioning. All tests were successful. 


Mr. von Osten withdrew, and in comparison of notes 
which followed, Mr. Busch, as well as all the others, 
declared that they had discovered nothing of the nature 
of a visible sign. Mr. Busch said that he had also kept 
an eye on the spectators and had noticed nothing there. 
Nevertheless, he desired to see Mr. von Osten go through 
one series with no one else but himself (Busch) present. 

This was done, and on this occasion a number of tests 
were made in the recognition of colored cloths. The 
horse was required to indicate, by tapping, the place in 
the series which the cloth occupied and was then asked 
to bring the green or the red, as the case might be, in 
his mouth. Furthermore, he was asked to approach that 
one of the five gentlemen standing at a distance, whose 
photograph had been shown him. Then he was requested 
to spell the words " Rat " and " Busch " according to the 
method which he had been taught. Nearly all of these 
tests were likewise successful. 

In the conference which followed, Mr. Busch again 
declared that he had noticed no trace of a sign ; he main- 
tained that, in the selecting of colored cloths (especially 
when they were placed so closely together) and in the 
approach toward a person, there was no possibility what- 
ever that some trick was being used. 

During the session of September 12th, Mr. von Osten 
agreed to two sets of experiments. 

I. Another man was to put the question to the horse. 
Mr. von Osten himself was to stand, back to back to the 
questioner and to bend forward, so that he was effectually 
hidden from the horse's view, yet could, by means of 
occasional calls, make his presence known to the animal. 
The assumption was that it would be conducive to suc- 
cess if the horse knew that the master was present and 


was awaiting the answer, and yet at the same time the 
possibility of receiving a sign was obviated. 

2. Another man in Mr. von Osten's absence was to 
ask the horse to tap a certain number. Then the ques- 
tioner was to leave, and Mr. von Osten, returning, was 
to ask the horse to perform some arithmetical process 
with the number which was thus unknown to the master. 
Mr. von Osten said that he thought that this method was 
somewhat risky, since the horse would be aware that he, 
Mr. von Osten, did not know the number, and might 
therefore be in a humor to play some prank. 

The questions of the first sort were answered with 
but very few errors. Mr. Hahn and Count zu Castell 
asked simple questions in arithmetic. When Mr. von 
Osten withdrew into the stable, the count put several 
other problems, among them the counting of persons 
and of windows, all of which were solved correctly. 

Between the first and second series of tests the follow- 
ing experiments were interpolated. The names of six 
members of the commission were written upon six slates 
respectively, which were then suspended from a string. 
Mr. von Osten pointed to one of the men and asked: 
" On which of the slates is this gentleman's name to be 
found ? ". The correct number was tapped in every case. 
The command to approach the slate in question was also 
obeyed as a rule, although this was not as uniformly suc- 
cessful as tapping. 

In the conference which followed, Mr. Busch declared 
that the feats appeared inconceivable to him; and again 
none of the men had noted anything in the way of signs. 

Now followed the second series of tests mentioned 
above. In order to be sure to get the correct responses, 
Mr. Schillings, who up to this point had not been present 


at any of the experiments, was asked to put the questions 
to the horse. Mr. von Osten went into the house, accom- 
panied by a member of the commission. And again, Mr. 
Schillings would go out before the second part of the 
test, without having met Mr. von Osten. 

Five tests were made in this way. They were not 
attended by such amazing success as were the preceding 
ones, but nevertheless the results were surprising. The 
horse nearly always repeated the number itself, instead 
of performing the operation required. Since, however, 
Mr. Schillings, owing to a misunderstanding, had, in the 
first two cases, said to the horse : " You are to repeat 
this number for Mr. von Osten ", the errors might appear 
to be a result of this request. 

At the final discussion, the result of which was the 
unanimous declaration which was given for publication, 
not only the data obtained during these two sessions, but 
also the earlier experiences of some of the members of 
the commission were taken into consideration. None of 
the tests witnessed could be referred to chance or to the 
use of tricks. Count zu Castell pointed out that in the 
course of eight days he had elicited forty correct 
responses from the horse, among them some in regard 
to which he himself had been momentarily in error. 
Other members recalled the many instances in previous 
exhibitions, during which both Mr. Schillings and Mr. 
von Osten were absent, when questions were put to the 
horse by others. The commission also had access to a 
detailed account written by Professor Stumpf on Mr. 
von Osten's method of instruction, based on the ex- 
planations and demonstrations which Mr. von Osten 
had himself given. As a result of these considerations 
the commission felt under obligations to give public 


expression to its conviction. In the report it limited 
itself, however, to the purely negative side — ^principally 
in denying the use of tricks, — and expressed no opinion 
with regard to the actual genesis of the horse's accom- 
plishments, since it believed that there was great possibil- 
ity that other factors were involved which ought to be 
carefully investigated. 


Together with Dr. E. von Hornbostel and Mr. O. 
Pfungst, I have tried during the past few weeks to find 
an explanation of the accomplishments of the horse 
' Hans ' by the experimental method. We had access 
to the horse in the absence of the master and groom. 
The results are as follows : 

The horse failed in his responses whenever the solution 
of the problem that was given him was unknown to any 
of those present. For instance, when a written number 
or the objects to be counted were placed before the 
horse, but were invisible to everyone else, and especially 
to the questioner, he failed to respond properly. There- 
fore he can neither count, nor read, nor solve problems 
in arithmetic. 

The horse failed again whenever he was prevented by 
means of sufficiently large blinders from seeing the per- 
sons, and especially the questioner, to whom the solution 
was known. He therefore required some sort of visual 

These aids need not, however,— and this is the peculi- 
arly interesting feature in the case, — be given inten- 
tionally. The proof for this is found in the fact that in 
the absence of Mr. von Osten the horse gave correct 
replies to a large number of persons; and to be more 
specific, Mr. Schillings and later Mr. Pfungst, atter 



working with the horse for a short time, regularly re- 
ceived correct answers, without their being in any way 
conscious of having given any kind of signal. 

So far as I can see, the following explanation is the 
only one that will comport with these facts. The horse 
must have learned, in the course of the long period of 
problem-solving, to attend ever more closely, while 
tapping, to the slight changes in bodily posture with 
which the master unconsciously accompanied the steps 
in his own thought-processes, and to use these as closing 
signals. The motive for this direction and straining of 
attention was the regular reward in the form of carrots 
and bread, which attended it. This unexpected kind of 
independent activity and the certainty and precision of 
the perception of minimal movements thus attained, are 
astounding in the highest degree. 

The movements which call forth the horse's reaction, 
are so extremely slight in the case of Mr. von Osten, that 
it is easily comprehensible how it was possible that they 
should escape the notice even of practised observers. 
Mr. Pfungst, however, whose previous laboratory ex- 
perience had made him keen in the perception of visual 
stimuli of slightest duration and extent, succeeded in 
recognizing in Mr. von Osten the different kinds of 
movements which were the basis of the various accom- 
plishments of the horse. Furthermore, he succeeded in 
controlling his own movements, (of which he had 
hitherto been unconscious), in the presence of the horse, 
and finally became so proficient that he could replace 
these unintentional movements by intentional oneS; He 
can now call forth at will all the various reactions 
of the horse by - making the proper kind of . voluntary 
movements, without asking the relevant question or 

REPORT OF DECEMBER qth, 1904 263 

giving any sort of command. But Mr. Pfungst meets 
with the same success when he does not attend to 
the movements to be made, but rather focuses, as 
intently as possible, upon the number desired, since 
in that case the necessary movement occurs whether he 
wills it or not. In the near future he will give a special 
detailed report of his observations, which gives promise 
of becoming a valuable contribution to the study of in- 
voluntary movements. Also he will give an account of 
our tests and of the mechanism of the various accomplish- 
ments of the horse. We must also defer, till then, the 
disproof of certain seemingly relevant arguments in favor 
of the horse's power of independent thought. 

Some defenders of the view which maintains the 
horse's rationality may urge that it was only through 
our experiments that the animal became trained and 
spoiled in so far as the ability to think is concerned. 
They are refuted in this, however, by the fact that the 
horse still continues to solve problems involving decimal 
fractions and to determine calendar dates for Mr. von 
Osten, as brilliantly as ever, as is shown by his recent 
demonstration before a large group of spectators. That 
these results are now being achieved in a manner essen- 
tially different from formerly is nothing but a bare asser- 

On the other hand, now that the possibility has been 
established that these wonderful results may be obtained 
in all their complexity by means of intentional signs, 
many will question whether Mr. Von Osten did not 
himself train the horse from the very beginning to 
respond to these signs. No one has the right, how- 
ever, to charge an old man, who has never had a blemish 
on his reputation, with having invented a most refined 


network of lies, if the facts can be explained in a satis- 
factory manner in some other rational way. And this 
can be done in this case. For we have seen that there 
is another alternative, other than the theory that the 
horse can think or the assumption that tricks have been 

And now, aside from the specific results obtained, 
what is the scientific and philosophic import of the whole 
affair ? — For one' thing, the revolution in our conception 
of the animal mind, which had been hoped for by some, 
and feared by others, has not taken place. But a con- 
clusion of an opposite character is justified. If such un- 
exampled patience and high pedagogical excellence as 
was daily brought to bear by Mr. von Osten during the 
course of four long years, could not bring to light the 
slightest trace of conceptual thinking, then the old asser- 
tion of the philosophers that the lower forms are incapable 
of such thinking, finds corroboration in the results of 
these experiments so far as the animal scale up to and in- 
cluding the ungulates is concerned. For this reason the 
tremendous effort put forth by Mr. von Osten, is not, 
in spite of the self-deception under which he labors, lost 
to science. If anyone has the courage to try the experi- 
ment with the dog or the ape, the insight which we have 
now gained will enable him to beware of one source of 
error which hitherto has not been noticed. 

In the face of much misapprehension which has arisen, 
I wish once more to say emphatically that the committee 
of September 12th in no wise declared itself to be con- 
vinced that the horse had the power of rational thinking. 
The committee restricted itself entirely to the question 
whether or not tricks were involved, and, intentionally 
and rightly referred the positive investigation to a purely 

REPORT OF DECEMBER qth, 1904 265 

scientific court. I would also report that for some time 
Mr. Schillings has been convinced, by his own observa- 
tions, of the horse's lack of reason, and when he was 
apprised of our conclusion in the matter, he embraced it 
without wavering. I have no intention of taking part 
in any discussion which may arise in the press as a result 
of the present report. Unless they wish to confine them- 
selves to mere guesswork, the defenders of other views 
will not shrink from the task of basing their criticism 
upon careful methodical experimentation, and they will 
keep a detailed record of their results day by day; for 
statements based solely upon memory, without specific 
report of experimental conditions, prove nothing. 

Prof. Carl Stumpf. 
December 9th, 1904. 


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