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Full text of "Ancient Classic Texts before 400 B.C."

360 BC 
THEAETETUS 
by Plato 
translated by Benjamin Jowett 
THEAETETUS 

PERSONS OF THE DIALOGUE: SOCRATES; THEODORUS; THEAETETUS 
Euclid and Terpsion meet in front of Euclid's house in Megara; they 
enter the house, and the dialogue is read to them by a servant. 

Euclid. Have you only just arrived from the country, Terpsion? 

Terpsion. No, I came some time ago: and I have been in the Agora 
looking for you, and wondering that I could not find you. 

Euc. But I was not in the city. 

Terp. Where then? 

Euc. As I was going down to the harbour, I met Theaetetus-he was 
being carried up to Athens from the army at Corinth. 

Terp. Was he alive or dead? 

Euc. He was scarcely alive, for he has been badly wounded; but he 
was suffering even more from the sickness which has broken out in 
the army. 

Terp. The dysentery, you mean? 

Euc. Yes. 

Terp. Alas! what a loss he will be! 

Euc. Yes, Terpsion, he is a noble fellow; only to-day I heard some 
people highly praising his behaviour in this very battle. 

Terp. No wonder; I should rather be surprised at hearing anything 
else of him. But why did he go on, instead of stopping at Megara? 

Euc. He wanted to get home: although I entreated and advised him 
to remain he would not listen to me; so I set him on his way, and 
turned back, and then I remembered what Socrates had said of him, 
and thought how remarkably this, like all his predictions, had been 
fulfilled. I believe that he had seen him a little before his own 
death, when Theaetetus was a youth, and he had a memorable 
conversation with him, which he repeated to me when I came to 
Athens; he was full of admiration of his genius, and said that he 
would most certainly be a great man, if he lived. 

Terp. The prophecy has certainly been fulfilled; but what was the 
conversation? can you tell me? 

Euc. No, indeed, not offhand; but I took notes of it as soon as I 
got home; these I filled up from memory, writing them out at 
leisure; and whenever I went to Athens, I asked Socrates about any 
point which I had forgotten, and on my return I made corrections; thus 
I have nearly the whole conversation written down. 

Terp. I remember-you told me; and I have always been intending to 
ask you to show me the writing, but have put off doing so; and now, 
why should we not read it through?-having just come from the 
country, I should greatly like to rest. 

Euc. I too shall be very glad of a rest, for I went with 
Theaetetus as far as Erineum. Let us go in, then, and, while we are 
reposing, the servant shall read to us. 

Terp. Very good. 

Euc. Here is the roll, Terpsion; I may observe that I have 
introduced Socrates, not as narrating to me, but as actually 
conversing with the persons whom he mentioned-these were, Theodorus 
the geometrician (of Cyrene) , and Theaetetus. I have omitted, for 
the sake of convenience, the interlocutory words "I said," "I 
remarked, " which he used when he spoke of himself, and again, "he 
agreed, " or "disagreed, " in the answer, lest the repetition of them 
should be troublesome. 

Terp. Quite right, Euclid. 

Euc. And now, boy, you may take the roll and read. 

Euclid's servant reads. 



Socrates. If I cared enough about the Cyrenians, Theodorus, I 
would ask you whether there are any rising geometricians or 
philosophers in that part of the world. But I am more interested in 
our own Athenian youth, and I would rather know who among them are 
likely to do well. I observe them as far as I can myself, and I 
enquire of any one whom they follow, and I see that a great many of 
them follow you, in which they are quite right, considering your 
eminence in geometry and in other ways. Tell me then, if you have 
met with any one who is good for anything. 

Theodorus. Yes, Socrates, I have become acquainted with one very 
remarkable Athenian youth, whom I commend to you as well worthy of 
your attention. If he had been a beauty I should have been afraid to 
praise him, lest you should suppose that I was in love with him; but 
he is no beauty, and you must not be offended if I say that he is very 
like you; for he has a snub nose and projecting eyes, although these 
features are less marked in him than in you. Seeing, then, that he has 
no personal attractions, I may freely say, that in all my 
acquaintance, which is very large, I never knew anyone who was his 
equal in natural gifts: for he has a quickness of apprehension which 
is almost unrivalled, and he is exceedingly gentle, and also the 
most courageous of men; there is a union of qualities in him such as I 
have never seen in any other, and should scarcely have thought 
possible; for those who, like him, have quick and ready and 
retentive wits, have generally also quick tempers; they are ships 
without ballast, and go darting about, and are mad rather than 
courageous; and the steadier sort, when they have to face study, prove 
stupid and cannot remember. Whereas he moves surely and smoothly and 
successfully in the path of knowledge and enquiry; and he is full of 
gentleness, flowing on silently like a river of oil; at his age, it is 
wonderful . 

Soc. That is good news; whose son is he? 

Theod. The name of his father I have forgotten, but the youth 
himself is the middle one of those who are approaching us; he and 
his companions have been anointing themselves in the outer court, 
and now they seem to have finished, and are towards us. Look and see 
whether you know him. 

Soc. I know the youth, but I do not know his name; he is the son 
of Euphronius the Sunian, who was himself an eminent man, and such 
another as his son is, according to your account of him; I believe 
that he left a considerable fortune. 

Theod. Theaetetus, Socrates, is his name; but I rather think that 
the property disappeared in the hands of trustees; notwithstanding 
which he is wonderfully liberal. 

Soc. He must be a fine fellow; tell him to come and sit by me. 

Theod. I will. Come hither, Theaetetus, and sit by Socrates. 

Soc. By all means, Theaetetus, in order that I may see the 
reflection of myself in your face, for Theodorus says that we are 
alike; and yet if each of us held in his hands a lyre, and he said 
that they were, tuned alike, should we at once take his word, or 
should we ask whether he who said so was or was not a musician? 

Theaetetus. We should ask. 

Soc. And if we found that he was, we should take his word; and if 
not, not? 

Theaet. True. 

Soc. And if this supposed, likeness of our faces is a matter of 
any interest to us we should enquire whether he who says that we are 
alike is a painter or not? 

Theaet. Certainly we should. 

Soc. And is Theodorus a painter? 

Theaet. I never heard that he was. 

Soc. Is he a geometrician? 

Theaet. Of course he is, Socrates. 

Soc. And is he an astronomer and calculator and musician, and in 



general an educated man? 

Theaet . I think so. 

Soc. If, then, he remarks on a similarity in our persons, either 
by way of praise or blame, there is no particular reason why we should 
attend to him. 

Theaet. I should say not. 

Soc. But if he praises the virtue or wisdom which are the mental 
endowments of either of us, then he who hears the praises will 
naturally desire to examine him who is praised: and he again should be 
willing to exhibit himself. 

Theaet. Very true, Socrates. 

Soc. Then now is the time, my dear Theaetetus, for me to examine, 
and for you to exhibit; since although Theodorus has praised many a 
citizen and stranger in my hearing, never did I hear him praise any 
one as he has been praising you. 

Theaet. I am glad to hear it, Socrates; but what if he was only in 
jest? 

Soc. Nay, Theodorus is not given to jesting; and I cannot allow 
you to retract your consent on any such pretence as that. If you do, 
he will have to swear to his words; and we are perfectly sure that 
no one will be found to impugn him. Do not be shy then, but stand to 
your word. 

Theaet. I suppose I must, if you wish it. 

Soc. In the first place, I should like to ask what you learn of 
Theodorus: something of geometry, perhaps? 

Theaet. Yes. 

Soc. And astronomy and harmony and calculation? 

Theaet. I do my best. 

Soc. Yes, my boy, and so do I: and my desire is to learn of him, 
or of anybody who seems to understand these things. And I get on 
pretty well in general; but there is a little difficulty which I 
want you and the company to aid me in investigating. Will you answer 
me a question: "Is not learning growing wiser about that which you 
learn?" 

Theaet. Of course. 

Soc. And by wisdom the wise are wise? 

Theaet. Yes. 

Soc. And is that different in any way from knowledge? 

Theaet. What? 

Soc. Wisdom; are not men wise in that which they know? 

Theaet. Certainly they are. 

Soc. Then wisdom and knowledge are the same? 

Theaet. Yes. 

Soc. Herein lies the difficulty which I can never solve to my 
satisf action-What is knowledge? Can we answer that question? What 
say you? which of us will speak first? whoever misses shall sit 
down, as at a game of ball, and shall be donkey, as the boys say; he 
who lasts out his competitors in the game without missing, shall be 
our king, and shall have the right of putting to us any questions 
which he pleases. .. Why is there no reply? I hope, Theodorus, that 
I am not betrayed into rudeness by my love of conversation? I only 
want to make us talk and be friendly and sociable. 

Theod. The reverse of rudeness, Socrates: but I would rather that 
you would ask one of the young fellows; for the truth is, that I am 
unused to your game of question and answer, and I am too old to learn; 
the young will be more suitable, and they will improve more than I 
shall, for youth is always able to improve. And so having made a 
beginning with Theaetetus, I would advise you to go on with him and 
not let him off. 

Soc. Do you hear, Theaetetus, what Theodorus says? The 
philosopher, whom you would not like to disobey, and whose word 
ought to be a command to a young man, bids me interrogate you. Take 
courage, then, and nobly say what you think that knowledge is. 

Theaet. Well, Socrates, I will answer as you and he bid me; and if 



make a mistake, you will doubtless correct me. 

Soc. We will, if we can. 

Theaet . Then, I think that the sciences which I learn from 
Theodorus-geometry, and those which you just now mentioned-are 
knowledge; and I would include the art of the cobbler and other 
craftsmen; these, each and all of, them, are knowledge. 

Soc. Too much, Theaetetus, too much; the nobility and liberality 
of your nature make you give many and diverse things, when I am asking 
for one simple thing. 

Theaet. What do you mean, Socrates? 

Soc. Perhaps nothing. I will endeavour, however, to explain what I 
believe to be my meaning: When you speak of cobbling, you mean the art 
or science of making shoes? 

Theaet. Just so. 

Soc. And when you speak of carpentering, you mean the art of 
making wooden implements? 

Theaet. I do. 

Soc. In both cases you define the subject matter of each of the 
two arts? 

Theaet. True. 

Soc. But that, Theaetetus, was not the point of my question: we 
wanted to know not the subjects, nor yet the number of the arts or 
sciences, for we were not going to count them, but we wanted to know 
the nature of knowledge in the abstract. Am I not right? 

Theaet. Perfectly right. 

Soc. Let me offer an illustration: Suppose that a person were to ask 
about some very trivial and obvious thing-for example, What is clay? 
and we were to reply, that there is a clay of potters, there is a clay 
of oven-makers, there is a clay of brick-makers; would not the 
answer be ridiculous? 

Theaet. Truly. 

Soc. In the first place, there would be an absurdity in assuming 
that he who asked the question would understand from our answer the 
nature of "clay," merely because we added "of the image-makers," or of 
any other workers. How can a man understand the name of anything, when 
he does not know the nature of it? 

Theaet . He cannot . 

Soc. Then he who does not know what science or knowledge is, has 
no knowledge of the art or science of making shoes? 

Theaet . None . 

Soc. Nor of any other science? 

Theaet. No. 

Soc. And when a man is asked what science or knowledge is, to give 
in answer the name of some art or science is ridiculous; for the 
-question is, "What is knowledge?" and he replies, "A knowledge of 
this or that . " 

Theaet. True. 

Soc. Moreover, he might answer shortly and simply, but he makes an 
enormous circuit. For example, when asked about the day, he might have 
said simply, that clay is moistened earth-what sort of clay is not 
to the point. 

Theaet. Yes, Socrates, there is no difficulty as you put the 
question. You mean, if I am not mistaken, something like what occurred 
to me and to my friend here, your namesake Socrates, in a recent 
discussion . 

Soc. What was that, Theaetetus? 

Theaet. Theodorus was writing out for us something about roots, such 
as the roots of three or five, showing that they are incommensurable 
by the unit: he selected other examples up to seventeen-there he 
stopped. Now as there are innumerable roots, the notion occurred to us 
of attempting to include them all under one name or class. 

Soc. And did you find such a class? 

Theaet. I think that we did; but I should like to have your opinion. 

Soc. Let me hear. 



Theaet . We divided all numbers into two classes: those which are 
made up of equal factors multiplying into one another, which we 
compared to square figures and called square or equilateral 
numbers ; -that was one class. 

Soc. Very good. 

Theaet. The intermediate numbers, such as three and five, and 
every other number which is made up of unequal factors, either of a 
greater multiplied by a less, or of a less multiplied by a greater, 
and when regarded as a figure, is contained in unequal sides; -all 
these we compared to oblong figures, and called them oblong numbers. 

Soc. Capital; and what followed? 

Theaet. The lines, or sides, which have for their squares the 
equilateral plane numbers, were called by us lengths or magnitudes; 
and the lines which are the roots of (or whose squares are equal to) 
the oblong numbers, were called powers or roots; the reason of this 
latter name being, that they are commensurable with the former 
[i.e., with the so-called lengths or magnitudes] not in linear 
measurement, but in the value of the superficial content of their 
squares; and the same about solids. 

Soc. Excellent, my boys; I think that you fully justify the 
praises of Theodorus, and that he will not be found guilty of false 
witness . 

Theaet. But I am unable, Socrates, to give you a similar answer 
about knowledge, which is what you appear to want; and therefore 
Theodorus is a deceiver after all. 

Soc. Well, but if some one were to praise you for running, and to 
say that he never met your equal among boys, and afterwards you were 
beaten in a race by a grown-up man, who was a great runner-would the 
praise be any the less true? 

Theaet. Certainly not. 

Soc. And is the discovery of the nature of knowledge so small a 
matter, as just now said? Is it not one which would task the powers of 
men perfect in every way? 

Theaet. By heaven, they should be the top of all perfection! 
Soc. Well, then, be of good cheer; do not say that Theodorus was 
mistaken about you, but do your best to ascertain the true nature of 
knowledge, as well as of other things. 

Theaet. I am eager enough, Socrates, if that would bring to light 
the truth. 

Soc. Come, you made a good beginning just now; let your own answer 
about roots be your model, and as you comprehended them all in one 
class, try and bring the many sorts of knowledge under one definition. 

Theaet. I can assure you, Socrates, that I have tried very often, 
when the report of questions asked by you was brought to me; but I can 
neither persuade myself that I have a satisfactory answer to give, nor 
hear of any one who answers as you would have him; and I cannot 
shake off a feeling of anxiety. 

Soc. These are the pangs of labour, my dear Theaetetus; you have 
something within you which you are bringing to the birth. 

Theaet. I do not know, Socrates; I only say what I feel. 

Soc. And have you never heard, simpleton, that I am the son of a 
midwife, brave and burly, whose name was Phaenarete? 

Theaet. Yes, I have. 

Soc. And that I myself practise midwifery? 

Theaet. No, never. 

Soc. Let me tell you that I do though, my friend: but you must not 
reveal the secret, as the world in general have not found me out; 
and therefore they only say of me, that I am the strangest of 
mortals and drive men to their wits' end. Did you ever hear that too? 

Theaet. Yes. 

Soc. Shall I tell you the reason? 

Theaet. By all means. 

Soc. Bear in mind the whole business of the mid-wives, and then 
you will see my meaning better: -No woman, as you are probably aware, 



who is still able to conceive and bear, attends other women, but 
only those who are past bearing. 

Theaet . Yes; I know. 

Soc. The reason of this is said to be that Artemis-the goddess of 
childbirth-is not a mother, and she honours those who are like 
herself; but she could not allow the barren to be mid-wives, because 
human nature cannot know the mystery of an art without experience; and 
therefore she assigned this office to those who are too old to bear. 

Theaet. I dare say. 

Soc. And I dare say too, or rather I am absolutely certain, that the 
mid-wives know better than others who is pregnant and who is not? 

Theaet. Very true. 

Soc. And by the use of potions and incantations they are able to 
arouse the pangs and to soothe them at will; they can make those 
bear who have a difficulty in bearing, and if they think fit they 
can smother the embryo in the womb. 

Theaet . They can . 

Soc. Did you ever remark that they are also most cunning 
matchmakers, and have a thorough knowledge of what unions are likely 
to produce a brave brood? 

Theaet. No, never. 

Soc. Then let me tell you that this is their greatest pride, more 
than cutting the umbilical cord. And if you reflect, you will see that 
the same art which cultivates and gathers in the fruits of the 
earth, will be most likely to know in what soils the several plants or 
seeds should be deposited. 

Theaet. Yes, the same art. 

Soc. And do you suppose that with women the case is otherwise? 

Theaet. I should think not. 

Soc. Certainly not; but mid-wives are respectable women who have a 
character to lose, and they avoid this department of their profession, 
because they are afraid of being called procuresses, which is a name 
given to those who join together man and woman in an unlawful and 
unscientific way; and yet the true midwife is also the true and only 
matchmaker . 

Theaet. Clearly. 

Soc. Such are the mid-wives, whose task is a very important one 
but not so important as mine; for women do not bring into the world at 
one time real children, and at another time counterfeits which are 
with difficulty distinguished from them; if they did, then the, 
discernment of the true and false birth would be the crowning 
achievement of the art of midwif ery-you would think so? 

Theaet. Indeed I should. 

Soc. Well, my art of midwifery is in most respects like theirs; 
but differs, in that I attend men and not women; and look after 
their souls when they are in labour, and not after their bodies: and 
the triumph of my art is in thoroughly examining whether the thought 
which the mind of the young man brings forth is a false idol or a 
noble and true birth. And like the mid-wives, I am barren, and the 
reproach which is often made against me, that I ask questions of 
others and have not the wit to answer them myself, is very just-the 
reason is, that the god compels-me to be a midwife, but does not allow 
me to bring forth. And therefore I am not myself at all wise, nor have 
I anything to show which is the invention or birth of my own soul, but 
those who converse with me profit. Some of them appear dull enough 
at first, but afterwards, as our acquaintance ripens, if the god is 
gracious to them, they all make astonishing progress; and this in 
the opinion of others as well as in their own. It is quite dear that 
they never learned anything from me; the many fine discoveries to 
which they cling are of their own making. But to me and the god they 
owe their delivery. And the proof of my words is, that many of them in 
their ignorance, either in their self-conceit despising me, or falling 
under the influence of others, have gone away too soon; and have not 
only lost the children of whom I had previously delivered them by an 



ill bringing up, but have stifled whatever else they had in them by 
evil communications, being fonder of lies and shams than of the truth; 
and they have at last ended by seeing themselves, as others see 
them, to be great fools. Aristeides, the son of Lysimachus, is one 
of them, and there are many others. The truants often return to me, 
and beg that I would consort with them again-they are ready to go to 
me on their knees and then, if my familiar allows, which is not always 
the case, I receive them, and they begin to grow again. Dire are the 
pangs which my art is able to arouse and to allay in those who consort 
with me, just like the pangs of women in childbirth; night and day 
they are full of perplexity and travail which is even worse than 
that of the women. So much for them. And there are -others, 
Theaetetus, who come to me apparently having nothing in them; and as I 
know that they have no need of my art, I coax them into marrying 
some one, and by the grace of God I can generally tell who is likely 
to do them good. Many of them I have given away to Prodicus, and 
many to other inspired sages. I tell you this long story, friend 
Theaetetus, because I suspect, as indeed you seem to think yourself, 
that you are in labour-great with some conception. Come then to me, 
who am a midwife's son and myself a midwife, and do your best to 
answer the questions which I will ask you. And if I abstract and 
expose your first-born, because I discover upon inspection that the 
conception which you have formed is a vain shadow, do not quarrel with 
me on that account, as the manner of women is when their first 
children are taken from them. For I have actually known some who 
were ready to bite me when I deprived them of a darling folly; they 
did not perceive that I acted from good will, not knowing that no 
god is the enemy of man-that was not within the range of their 
ideas; neither am I their enemy in all this, but it would be wrong for 
me to admit falsehood, or to stifle the truth. Once more, then, 
Theaetetus, I repeat my old question, "What is knowledge? "-and do 
not say that you cannot tell; but quit yourself like a man, and by the 
help of God you will be able to tell. 

Theaet . At any rate, Socrates, after such an exhortation I should be 
ashamed of not trying to do my best. Now he who knows perceives what 
he knows, and, as far as I can see at present, knowledge is 
perception . 

Soc. Bravely said, boy; that is the way in which you should 
express your opinion. And now, let us examine together this conception 
of yours, and see whether it is a true birth or a mere, 
wind-egg : -You say that knowledge is perception? 

Theaet. Yes. 

Soc. Well, you have delivered yourself of a very important 
doctrine about knowledge; it is indeed the opinion of Protagoras, 
who has another way of expressing it, Man, he says, is the measure 
of all things, of the existence of things that are, and of the 
non-existence of things that are not : -You have read him? 

Theaet. yes, again and again. 

Soc. Does he not say that things are to you such as they appear to 
you, and to me such as they appear to me, and that you and I are men? 

Theaet. Yes, he says so. 

Soc. A wise man is not likely to talk nonsense. Let us try to 
understand him: the same wind is blowing, and yet one of us may be 
cold and the other not, or one may be slightly and the other very 
cold? 

Theaet. Quite true. 

Soc. Now is the wind, regarded not in relation to us but absolutely, 
cold or not; or are we to say, with Protagoras, that the wind is 
cold to him who is cold, and not to him who is not? 

Theaet. I suppose the last. 

Soc. Then it must appear so to each of them? 

Theaet. Yes. 

Soc. And "appears to him" means the same as "he perceives." 

Theaet. True. 



Soc. Then appearing and perceiving coincide in the case of hot and 
cold, and in similar instances; for things appear, or may be 
supposed to be, to each one such as he perceives them? 

Theaet. Yes. 

Soc. Then perception is always of existence, and being the same as 
knowledge is unerring? 

Theaet. Clearly. 

Soc. In the name of the Graces, what an almighty wise man Protagoras 
must have been! He spoke these things in a parable to the common herd, 
like you and me, but told the truth, his Truth, in secret to his own 
disciples . 

Theaet. What do you mean, Socrates? 

Soc. I am about to speak of a high argument, in which all things are 
said to be relative; you cannot rightly call anything by any name, 
such as great or small, heavy or light, for the great will be small 
and the heavy light-there is no single thing or quality, but out of 
motion and change and admixture all things are becoming relatively 
to one another, which "becoming" is by us incorrectly called being, 
but is really becoming, for nothing ever is, but all things are 
becoming. Summon all philosophers-Protagoras, Heracleitus, Empedocles, 
and the rest of them, one after another, and with the exception of 
Parmenides they will agree with you in this. Summon the great 
masters of either kind of poetry-Epicharmus, the prince of Comedy, and 
Homer of Tragedy; when the latter sings of 

Ocean whence sprang the gods, and mother Tethys, 

does he not mean that all things are the offspring, of flux and 
motion? 

Theaet. I think so. 

Soc. And who could take up arms against such a great army having 
Homer for its general, and not appear ridiculous? 

Theaet. Who indeed, Socrates? 

Soc. Yes, Theaetetus; and there are plenty of other proofs which 
will show that motion is the source of what is called being and 
becoming, and inactivity of not-being and destruction; for fire and 
warmth, which are supposed to be the parent and guardian of all 
other things, are born of movement and friction, which is a kind of 
motion; -is not this the origin of fire? 

Theaet. It is. 

Soc. And the race of animals is generated in the same way? 

Theaet. Certainly. 

Soc. And is not the bodily habit spoiled by rest and idleness, but 
preserved for a long time by motion and exercise? 

Theaet. True. 

Soc. And what of the mental habit? Is not the soul informed, and 
improved, and preserved by study and attention, which are motions; but 
when at rest, which in the soul only means want of attention and 
study, is uninformed, and speedily forgets whatever she has learned? 

Theaet. True. 

Soc. Then motion is a good, and rest an evil, to the soul as well as 
to the body? 

Theaet. Clearly. 

Soc. I may add, that breathless calm, stillness and the like waste 
and impair, while wind and storm preserve; and the palmary argument of 
all, which I strongly urge, is the golden chain in Homer, by which 
he means the sun, thereby indicating that so long as the sun and the 
heavens go round in their orbits, all things human and divine are 
and are preserved, but if they were chained up and their motions 
ceased, then all things would be destroyed, and, as the saying is, 
turned upside down. 

Theaet. I believe, Socrates, that you have truly explained his 
meaning . 

Soc. Then now apply his doctrine to perception, my good friend, 



and first of all to vision; that which you call white colour is not in 
your eyes, and is not a distinct thing which exists out of them. And 
you must not assign any place to it: for if it had position it would 
be, and be at rest, and there would be no process of becoming. 

Theaet. Then what is colour? 

Soc. Let us carry the principle which has just been affirmed, that 
nothing is self-existent, and then we shall see that white, black, and 
every other colour, arises out of the eye meeting the appropriate 
motion, and that what we call a colour is in each case neither the 
active nor the passive element, but something which passes between 
them, and is peculiar to each percipient; are you quite certain that 
the several colours appear to a dog or to any animal whatever as 
they appear to you? 

Theaet. Far from it. 

Soc. Or that anything appears the same to you as to another man? Are 
you so profoundly convinced of this? Rather would it not be true 
that it never appears exactly the same to you, because you are never 
exactly the same? 

Theaet. The latter. 

Soc. And if that with which I compare myself in size, or which I 
apprehend by touch, were great or white or hot, it could not become 
different by mere contact with another unless it actually changed; nor 
again, if the comparing or apprehending subject were great or white or 
hot, could this, when unchanged from within become changed by any 
approximation or affection of any other thing. The fact is that in our 
ordinary way of speaking we allow ourselves to be driven into most 
ridiculous and wonderful contradictions, as Protagoras and all who 
take his line of argument would remark. 

Theaet. How? and of what sort do you mean? 

Soc. A little instance will sufficiently explain my meaning: Here 
are six dice, which are more by a half when compared with four, and 
fewer by a half than twelve-they are more and also fewer. How can 
you or any one maintain the contrary? 

Theaet. Very true. 

Soc. Well, then, suppose that Protagoras or some one asks whether 
anything can become greater or more if not by increasing, how would 
you answer him, Theaetetus? 

Theaet. I should say "No," Socrates, if I were to speak my mind in 
reference to this last question, and if I were not afraid of 
contradicting my former answer. 

Soc. Capital excellent! spoken like an oracle, my boy! And if you 
reply "Yes," there will be a case for Euripides; for our tongue will 
be unconvinced, but not our mind. 

Theaet. Very true. 

Soc. The thoroughbred Sophists, who know all that can be known about 
the mind, and argue only out of the superfluity of their wits, would 
have had a regular sparring-match over this, and would -have knocked 
their arguments together finely. But you and I, who have no 
professional aims, only desire to see what is the mutual relation of 
these principles-whether they are consistent with each or not. 

Theaet. Yes, that would be my desire. 

Soc. And mine too. But since this is our feeling, and there is 
plenty of time, why should we not calmly and patiently review our 
own thoughts, and thoroughly examine and see what these appearances in 
us really are? If I am not mistaken, they will be described by us as 
f ollows : -first, that nothing can become greater or less, either in 
number or magnitude, while remaining equal to itself-you would agree? 

Theaet. Yes. 

Soc. Secondly, that without addition or subtraction there is no 
increase or diminution of anything, but only equality. 

Theaet. Quite true. 

Soc. Thirdly, that what was not before cannot be afterwards, without 
becoming and having become. 

Theaet. Yes, truly. 



Soc. These three axioms, if I am not mistaken, are fighting with one 
another in our minds in the case of the dice, or, again, in such a 
case as this-if I were to say that I, who am of a certain height and 
taller than you, may within a year, without gaining or losing in 
height, be not so tail-not that I should have lost, but that you would 
have increased. In such a case, I am afterwards what I once was not, 
and yet I have not become; for I could not have become without 
becoming, neither could I have become less without losing somewhat 
of my height; and I could give you ten thousand examples of similar 
contradictions, if we admit them at all. I believe that you follow me, 
Theaetetus; for I suspect that you have thought of these questions 
before now. 

Theaet . Yes, Socrates, and I am amazed when I think of them; by 
the Gods I am! and I want to know what on earth they mean; and there 
are times when my head quite swims with the contemplation of them. 

Soc. I see, my dear Theaetetus, that Theodorus had a true insight 
into your nature when he said that you were a philosopher, for 
wonder is the feeling of a philosopher, and philosophy begins in 
wonder. He was not a bad genealogist who said that Iris (the messenger 
of heaven) is the child of Thaumas (wonder) . But do you begin to see 
what is the explanation of this perplexity on the hypothesis which 
we attribute to Protagoras? 

Theaet. Not as yet. 

Soc. Then you will be obliged to me if I help you to unearth the 
hidden "truth" of a famous man or school. 

Theaet. To be sure, I shall be very much obliged. 

Soc. Take a look round, then, and see that none of the uninitiated 
are listening. Now by the uninitiated I mean: the people who believe 
in nothing but what they can grasp in their hands, and who will not 
allow that action or generation or anything invisible can have real 
existence . 

Theaet. Yes, indeed, Socrates, they are very hard and impenetrable 
mortals . 

Soc. Yes, my boy, outer barbarians. Far more ingenious are the 
brethren whose mysteries I am about to reveal to you. Their first 
principle is, that all is motion, and upon this all the affections 
of which we were just now speaking, are supposed to depend: there is 
nothing but motion, which has two forms, one active and the other 
passive, both in endless number; and out of the union and friction 
of them there is generated a progeny endless in number, having two 
forms, sense and the object of sense, which are ever breaking forth 
and coming to the birth at the same moment. The senses are variously 
named hearing, seeing, smelling; there is the sense of heat, cold, 
pleasure, pain, desire, fear, and many more which have names, as 
well as innumerable others which are without them; each has its 
kindred object each variety of colour has a corresponding variety of 
sight, and so with sound and hearing, and with the rest of the 
senses and the objects akin to them. Do you see, Theaetetus, the 
bearings of this tale on the preceding argument? 

Theaet. Indeed I do not. 

Soc. Then attend, and I will try to finish the story. The purport is 
that all these things are in motion, as I was saying, and that this 
motion is of two kinds, a slower and a quicker; and the slower 
elements have their motions in the same place and with reference to 
things near them, and so they beget; but what is begotten is 
swifter, for it is carried to fro, and moves from place to place. 
Apply this to sense: -When the eye and the appropriate object meet 
together and give birth to whiteness and the sensation connatural with 
it, which could not have been given by either of them going elsewhere, 
then, while the sight: is flowing from the eye, whiteness proceeds 
from the object which combines in producing the colour; and so the eye 
is fulfilled with sight, and really sees, and becomes, not sight, 
but a seeing eye; and the object which combined to form the colour 
is fulfilled with whiteness, and becomes not whiteness but a white 



thing, whether wood or stone or whatever the object may be which 
happens to be colour, ed white. And this is true of all sensible 
objects, hard, warm, and the like, which are similarly to be regarded, 
as I was saying before, not as having any absolute existence, but as 
being all of them of whatever kind, generated by motion in their 
intercourse with one another; for of the agent and patient, as 
existing in separation, no trustworthy conception, as they say, can be 
formed, for the agent has no existence until united; with the patient, 
and the patient has no existence until united with the agent; and that 
which by uniting with something becomes an agent, by meeting with some 
other thing is converted into a patient. And from all these 
considerations, as I said at first, there arises a general reflection, 
that there is no one self-existent thing, but everything is becoming 
and in relation; and being must be altogether abolished, although from 
habit and ignorance we are compelled even in this discussion to retain 
the use of the term. But great philosophers tell us that we are not to 
allow either the word "something," or "belonging to something," or "to 
me," or "this," or "that," or any other detaining name to be used, 
in the language of nature all things are being created and 
destroyed, coming into being and passing into new forms; nor can any 
name fix or detain them; he who attempts to fix them is easily 
refuted. And this should be the way of speaking, not only of 
particulars but of aggregates such aggregates as are expressed in 
the word "man," or "stone," or any name of animal or of a class. 
Theaetetus, are not these speculations sweet as honey? And do you 
not like the taste of them in the mouth? 

Theaet . I do not know what to say, Socrates, for, indeed, I cannot 
make out whether you are giving your own opinion or only wanting to 
draw me out . 

Soc. You forget, my friend, that I neither know, nor profess to 
know, anything of! these matters; you are the person who is in labour, 
I am the barren midwife; and this is why I soothe you, and offer you 
one good thing after another, that you may taste them. And I hope that 
I may at last help to bring your own opinion into the light of day: 
when this has been accomplished, then we will determine whether what 
you have brought forth is only a wind-egg or a real and genuine birth. 
Therefore, keep up your spirits, and answer like a man what you think. 

Theaet. Ask me. 

Soc. Then once more: Is it your opinion that nothing is but what 
becomes? the good and the noble, as well; as all the other things 
which we were just now mentioning? 

Theaet. When I hear you discoursing in this style, I think that 
there is a great deal in what you say, and I am very ready to 
assent. Soc. Let us not leave the argument unfinished, then; for there 
still remains to be considered an objection which may be raised 
about dreams and diseases, in particular about madness, and the 
various illusions of hearing and sight, or of other senses. For you 
know that in all these cases the esse-percipi theory appears to be 
unmistakably refuted, since in dreams and illusions we certainly 
have false perceptions; and far from saying that everything is which 
appears, we should rather say that nothing is which appears. 

Theaet. Very true, Socrates. 

Soc. But then, my boy, how can any one contend that knowledge is 
perception, or that to every man what appears is? 

Theaet. I am afraid to say, Socrates, that I have nothing to answer, 
because you rebuked me just now for making this excuse; but I 
certainly cannot undertake to argue that madmen or dreamers think 
truly, when they imagine, some of them that they are gods, and 
others that they can fly, and are flying in their sleep. 

Soc. Do you see another question which can be raised about these 
phenomena, notably about dreaming and waking? 

Theaet. What question? 

Soc. A question which I think that you must often have heard persons 
ask: -How can you determine whether at this moment we are sleeping, and 



all our thoughts are a dream; or whether we are awake, and talking 
to one another in the waking state? 

Theaet . Indeed, Socrates, I do not know how to prove the one any 
more than the other, for in both cases the facts precisely 
correspond; -and there is no difficulty in supposing that during all 
this discussion we have been talking to one another in a dream; and 
when in a dream we seem to be narrating dreams, the resemblance of the 
two states is quite astonishing. 

Soc. You see, then, that a doubt about the reality of sense is 
easily raised, since there may even be a doubt whether we are awake or 
in a dream. And as our time is equally divided between sleeping and 
waking, in either sphere of existence the soul contends that the 
thoughts which are present to our minds at the time are true; and 
during one half of our lives we affirm the truth of the one, and, 
during the other half, of the other; and are equally confident of 
both . 

Theaet. Most true. 

Soc. And may not the same be said of madness and other disorders? 
the difference is only that the times are not equal. 

Theaet. Certainly. 

Soc. And is truth or falsehood to be determined by duration of time? 

Theaet. That would be in many ways ridiculous. 

Soc. But can you certainly determine: by any other means which of 
these opinions is true? 

Theaet. I do not think that I can. 

Soc. Listen, then to a statement of the other side of the 
argument, which is made by the champions of appearance. They would 
say, as I imagine-can that which is wholly other than something, 
have the same quality as that from which it differs? and observe, 
-Theaetetus, that the word "other" means not "partially," but 
"wholly other." 

Theaet. Certainly, putting the question as you do, that which is 
wholly other cannot either potentially or in any other way be the 
same . 

Soc. And must therefore be admitted to be unlike? 

Theaet. True. 

Soc. If, then, anything happens to become like or unlike itself or 
another, when it becomes like we call it the same-when unlike, other? 

Theaet. Certainly. 

Soc. Were we not saying that there, are agents many and infinite, 
and patients many and infinite? 

Theaet. Yes. 

Soc. And also that different combinations will produce results which 
are not the same, but different? 

Theaet. Certainly. 

Soc. Let us take you and me, or anything as an example : -There is 
Socrates in health, and Socrates sick-Are they like or unlike? 

Theaet. You mean to, compare Socrates in health as a whole, and 
Socrates in sickness as a whole? 

Soc. Exactly; that is my meaning. 

Theaet. I answer, they are unlike. 

Soc. And if unlike, they are other? 

Theaet. Certainly. 

Soc. And would you not say the same of Socrates sleeping and waking, 
or in any of the states which we were mentioning? 

Theaet. I should. 

Soc. All agents have a different patient in Socrates, accordingly as 
he is well or ill. 

Theaet. Of course. 

Soc. And I who am the patient, and that which is the agent, will 
produce something different in each of the two cases? 

Theaet. Certainly. 

Soc. The wine which I drink when I am in health, appears sweet and 
pleasant to me? 



Theaet. True. 

Soc. For, as has been already acknowledged, the patient and agent 
meet together and produce sweetness and a perception of sweetness, 
which are in simultaneous motion, and the perception which comes 
from the patient makes the tongue percipient, and the quality of 
sweetness which arises out of and is moving about the wine, makes 
the wine, both to be and to appear sweet to the healthy tongue. 

Theaet. Certainly; that has been already acknowledged. 

Soc. But when I am sick, the wine really acts upon another and a 
different person? 

Theaet. Yes. 

Soc. The combination of the draught of wine, and the Socrates who is 
sick, produces quite another result; which is the sensation of 
bitterness in the tongue, and the, motion and creation of bitterness 
in and about the wine, which becomes not bitterness but something 
bitter; as I myself become not but percipient? 

Theaet. True. 

Soc. There is no, other object of which I shall ever have the same 
perception, for another object would give another perception, and 
would make the perception other and different; nor can that object 
which affects me, meeting another, subject, produce, the same, or 
become similar, for that too would produce another result from another 
subject, and become different. 

Theaet. True. 

Soc. Neither can by myself, have this sensation, nor the object by 
itself, this quality. 

Theaet. Certainly not. 

Soc. When I perceive I must become percipient of something-there can 
be no such thing as perceiving and perceiving nothing; the object, 
whether it become sweet, bitter, or of any other quality, must have 
relation to a percipient; nothing can become sweet which is sweet to 
no one . 

Theaet. Certainly not. 

Soc. Then the inference is, that we [the agent and patient] are or 
become in relation to one another; there is a law which binds us one 
to the other, but not to any other existence, nor each of us to 
himself; and therefore we can only be bound to one another; so that 
whether a person says that a thing is or becomes, he must say that 
it is or becomes to or of or in relation to something else; but he 
must not say or allow any one else to say that anything is or 
becomes absolutely: -such is our conclusion. 

Theaet. Very true, Socrates. 

Soc. Then, if that which acts upon me has relation to me and to no 
other, I and no other am the percipient of it? 

Theaet. Of course. 

Soc. Then my perception is true to me, being inseparable from my own 
being; and, as Protagoras says, to myself I am judge of what is 
and-what is not to me. 

Theaet. I suppose so. 

Soc. How then, if I never err, and if my mind never trips in the 
conception of being or becoming, can I fail of knowing that which I 
perceive? 

Theaet . You cannot . 

Soc. Then you were quite right in affirming that knowledge is only 
perception; and the meaning turns out to be the same, whether with 
Homer and Heracleitus, and all that company, you say that all is 
motion and flux, or with the great sage Protagoras, that man is the 
measure of all things; or with Theaetetus, that, given these premises, 
perception is knowledge. Am I not right, Theaetetus, and is not this 
your newborn child, of which I have delivered you? What say you? 

Theaet. I cannot but agree, Socrates. 

Soc. Then this is the child, however he may turn out, which you 
and I have with difficulty brought into the world. And now that he 
is born, we must run round the hearth with him, and see whether he 



is worth rearing, or is only a wind-egg and a sham. Is he to be reared 
in any case, and not exposed? or will you bear to see him rejected, 
and not get into a passion if I take away your first-born? 

Theod. Theaetetus will not be angry, for he is very good-natured. 
But tell me, Socrates, in heaven's name, is this, after all, not the 
truth? 

Soc. You, Theodorus, are a lover of theories, and now you innocently 
fancy that I am a bag full of them, and can easily pull one out 
which will overthrow its predecessor. But you do not see that in 
reality none of these theories come from me; they all come from him 
who talks with me. I only know just enough to extract them from the 
wisdom of another, and to receive them in a spirit of fairness. And 
now I shall say nothing myself, but shall endeavour to elicit 
something from our young friend. 

Theod. Do as you say, Socrates; you are quite right. 

Soc. Shall I tell you, Theodorus, what amazes me in your 
acquaintance Protagoras? 

Theod. What is it? 

Soc. I am charmed with his doctrine, that what appears is to each 
one, but I wonder that he did not begin his book on Truth with a 
declaration that a pig or a dog-faced baboon, or some other yet 
stranger monster which has sensation, is the measure of all things; 
then he might have shown a magnificent contempt for our opinion of him 
by informing us at the outset that while we were reverencing him 
like a God for his wisdom he was no better than a tadpole, not to 
speak of his fellow-men-would not this have produced an 
over-powering effect? For if truth is only sensation, and no man can 
discern another's feelings better than he, or has any superior right 
to determine whether his opinion is true or false, but each, as we 
have several times repeated, is to himself the sole judge, and 
everything that he judges is true and right, why, my friend, should 
Protagoras be preferred to the place of wisdom and instruction, and 
deserve to be well paid, and we poor ignoramuses have to go to him, if 
each one is the measure of his own wisdom? Must he not be talking ad 
captandum in all this? I say nothing of the ridiculous predicament 
in which my own midwifery and the whole art of dialectic is placed; 
for the attempt to supervise or refute the notions or opinions of 
others would be a tedious and enormous piece of folly, if to each 
man his own are right; and this must be the case if Protagoras Truth 
is the real truth, and the philosopher is not merely amusing himself 
by giving oracles out of the shrine of his book. 

Theod. He was a friend of mine, Socrates, as you were saying, and 
therefore I cannot have him refuted by my lips, nor can I oppose you 
when I agree with you; please, then, to take Theaetetus again; he 
seemed to answer very nicely. 

Soc. If you were to go into a Lacedaemonian palestra, Theodorus, 
would you have a right to look on at the naked wrestlers, some of them 
making a poor figure, if you did not strip and give them an 
opportunity of judging of your own person? 

Theod. Why not, Socrates, if they would allow me, as I think you 
will in consideration of my age and stiffness; let some more supple 
youth try a fall with you, and do not drag me into the gymnasium. 

Soc. Your will is my will, Theodorus, as the proverbial philosophers 
say, and therefore I will return to the sage Theaetetus: Tell me, 
Theaetetus, in reference to what I was saying, are you not lost in 
wonder, like myself, when you find that all of a sudden you are raised 
to the level of the wisest of men, or indeed of the gods?-for you 
would assume the measure of Protagoras to apply to the gods as well as 
men? 

Theaet . Certainly I should, and I confess to you that I am lost in 
wonder. At first hearing, I was quite satisfied with the doctrine, 
that whatever appears is to each one, but now the face of things has 
changed. 

Soc. Why, my dear boy, you are young, and therefore your ear is 



quickly caught and your mind influenced by popular arguments. 
Protagoras, or some one speaking on his behalf, will doubtless say 
in reply, good people, young and old, you meet and harangue, and bring 
in the gods, whose existence of non-existence I banish from writing 
and speech, or you talk about the reason of man being degraded to 
the level of the brutes, which is a telling argument with the 
multitude, but not one word of proof or demonstration do you offer. 
All is probability with you, and yet surely you and Theodorus had 
better reflect whether you are disposed to admit of probability and 
figures of speech in matters of such importance. He or any other 
mathematician who argued from probabilities and likelihoods in 
geometry, would not be worth an ace. 

Theaet . But neither you nor we, Socrates, would be satisfied with 
such arguments . 

Soc. Then you and Theodorus mean to say that we must look at the 
matter in some other way? 

Theaet. Yes, in quite another way. 

Soc. And the way will be to ask whether perception is or is not 
the same as knowledge; for this was the real point of our argument, 
and with a view to this we raised (did we not?) those many strange 
questions . 

Theaet. Certainly. 

Soc. Shall we say that we know every thing which we see and hear? 
for example, shall we say that not having learned, we do not hear 
the language of foreigners when they speak to us? or shall we say that 
we not only hear, but know what they are saying? Or again, if we see 
letters which we do not understand, shall we say that we do not see 
them? or shall we aver that, seeing them, we must know them? 

Theaet. We shall say, Socrates, that we know what we actually see 
and hear of them-that is to say, we see and know the figure and colour 
of the letters, and we hear and know the elevation or depression of 
the sound of them; but we do not perceive by sight and hearing, or 
know, that which grammarians and interpreters teach about them. 

Soc. Capital, Theaetetus; and about this there shall be no 
dispute, because I want you to grow; but there is another difficulty 
coming, which you will also have to repulse. 

Theaet. What is it? 

Soc. Some one will say, Can a man who has ever known anything, and 
still has and preserves a memory of that which he knows, not know that 
which he remembers at the time when he remembers? I have, I fear, a 
tedious way of putting a simple question, which is only, whether a man 
who has learned, and remembers, can fail to know? 

Theaet. Impossible, Socrates; the supposition is monstrous. 

Soc. Am I talking nonsense, then? Think: is not seeing perceiving, 
and is not sight perception? 

Theaet. True. 

Soc. And if our recent definition holds, every man knows that 
which he has seen? 

Theaet. Yes. 

Soc. And you would admit that there is such a thing as memory? 

Theaet. Yes. 

Soc. And is memory of something or of nothing? 

Theaet. Of something, surely. 

Soc. Of things learned and perceived, that is? 

Theaet. Certainly. 

Soc. Often a man remembers that which he has seen? 

Theaet. True. 

Soc. And if he closed his eyes, would he forget? 

Theaet. Who, Socrates, would dare to say so? 

Soc. But we must say so, if the previous argument is to be 
maintained. 

Theaet. What do you mean? I am not quite sure that I understand you, 
though I have a strong suspicion that you are right. 

Soc. As thus: he who sees knows, as we say, that which he sees; 



for perception and sight and knowledge are admitted to be the same. 

Theaet . Certainly. 

Soc. But he who saw, and has knowledge of that which he saw, 
remembers, when he closes his eyes, that which he no longer sees. 

Theaet. True. 

Soc. And seeing is knowing, and therefore not-seeing is not-knowing? 

Theaet. Very true. 

Soc. Then the inference is, that a man may have attained the 
knowledge, of something, which he may remember and yet not know, 
because he does not see; and this has been affirmed by us to be a 
monstrous supposition. 

Theaet. Most true. 

Soc. Thus, then, the assertion that knowledge and perception are 
one, involves a manifest impossibility? 

Theaet. Yes. 

Soc. Then they must be distinguished? 

Theaet. I suppose that they must. 

Soc. Once more we shall have to begin, and ask "What is 
knowledge?" and yet, Theaetetus, what are we going to do? 

Theaet. About what? 

Soc. Like a good-for-nothing cock, without having won the victory, 
we walk away from the argument and crow. 

Theaet. How do you mean? 

Soc. After the manner of disputers, we were satisfied with mere 
verbal consistency, and were well pleased if in this way we could gain 
an advantage. Although professing not to be mere Eristics, but 
philosophers, I suspect that we have unconsciously fallen into the 
error of that ingenious class of persons. 

Theaet. I do not as yet understand you. 

Soc. Then I will try to explain myself: just now we asked the 
question, whether a man who had learned and remembered could fail to 
know, and we showed that a person who had seen might remember when 
he had his eyes shut and could not see, and then he would at the 
same time remember and not know. But this was an impossibility. And so 
the Protagorean fable came to nought, and yours also, who maintained 
that knowledge is the same as perception. 

Theaet. True. 

Soc. And yet, my friend, I rather suspect that the result would have 
been different if Protagoras, who was the father of the first of the 
two-brats, had been alive; he would have had a great deal to say on 
their behalf. But he is dead, and we insult over his orphan child; and 
even the guardians whom he left, and of whom our friend Theodorus is 
one, are unwilling to give any help, and therefore I suppose that must 
take up his cause myself, and see justice done? 

Theod. Not I, Socrates, but rather Callias, the son of Hipponicus, 
is guardian of his orphans. I was too soon diverted from the 
abstractions of dialectic to geometry. Nevertheless, I shall be 
grateful to you if you assist him. 

Soc. Very good, Theodorus; you shall see how I will come to the 
rescue. If a person does not attend to the meaning of terms as they 
are commonly used in argument, he may be involved even in greater 
paradoxes than these. Shall I explain this matter to you or to 
Theaetetus? 

Theod. To both of us, and let the younger answer; he will incur less 
disgrace if he is discomfited. 

Soc. Then now let me ask the awful question, which is this: -Can a 
man know and also not know that which he knows? 

Theod. How shall we answer, Theaetetus? 

Theaet. He cannot, I should say. 

Soc. He can, if you maintain that seeing is knowing. When you are 
imprisoned in a well, as the saying is, and the self-assured adversary 
closes one of your eyes with his hand, and asks whether you can see 
his cloak with the eye which he has closed, how will you answer the 
inevitable man? 



Theaet . I should answer, "Not with that eye but with the other." 

Soc. Then you see and do not see the same thing at the same time. 

Theaet. Yes, in a certain sense. 

Soc. None of that, he will reply; I do not ask or bid you answer 
in what sense you know, but only whether you know that which you do 
not know. You have been proved to see that which you do not see; and 
you have already admitted that seeing is knowing, and that 
not-seeing is not-knowing: I leave you to draw the inference. 

Theaet. Yes, the inference is the contradictory of my assertion. 

Soc. Yes, my marvel, and there might have been yet worse things in 
store for you, if an opponent had gone on to ask whether you can 
have a sharp and also a dull knowledge, and whether you can know near, 
but not at a distance, or know the same thing with more or less 
intensity, and so on without end. Such questions might have been put 
to you by a light-armed mercenary, who argued for pay. He would have 
lain in wait for you, and when you took up the position, that sense is 
knowledge, he would have made an assault upon hearing, smelling, and 
the other senses; -he would have shown you no mercy; and while you were 
lost in envy and admiration of his wisdom, he would have got you 
into his net, out of which you would not have escaped until you had 
come to an understanding about the sum to be paid for your release. 
Well, you ask, and how will Protagoras reinforce his position? Shall I 
answer for him? 

Theaet. By all means. 

Soc. He will repeat all those things which we have been urging on 
his behalf, and then he will close with us in disdain, and say:-The 
worthy Socrates asked a little boy, whether the same man could 
remember and not know the same thing, and the boy said No, because 
he was frightened, and could not see what was coming, and then 
Socrates made fun of poor me. The truth is, slatternly Socrates, 
that when you ask questions about any assertion of mine, and the 
person asked is found tripping, if he has answered as I should have 
answered, then I am refuted, but if he answers something else, then he 
is refuted and not I . For do you really suppose that any one would 
admit the memory which a man has of an impression which has passed 
away to be the same with that which he experienced at the time? 
Assuredly not. Or would he hesitate to acknowledge that the same man 
may know and not know the same thing? Or, if he is afraid of making 
this admission, would he ever grant that one who has become unlike 
is the same as before he became unlike? Or would he admit that a man 
is one at all, and not rather many and infinite as the changes which 
take place in him? I speak by the card in order to avoid entanglements 
of words. But, my good sir, he would say, come to the argument in 
a more generous spirit; and either show, if you can, that our 
sensations are not relative and individual, or, if you admit them to 
be so, prove that this does not involve the consequence that the 
appearance becomes, or, if you will have the word, is, to the 
individual only. As to your talk about pigs and baboons, you are 
yourself behaving like a pig, and you teach your hearers to make sport 
of my writings in the same ignorant manner; but this is not to your 
credit. For I declare that the truth is as I have written, and that 
each of us is a measure of existence and of non-existence. Yet one man 
may be a thousand times better than another in proportion as different 
things are and appear to him. 

And I am far from saying that wisdom and the wise man have no 
existence; but I say that the wise man is he who makes the evils which 
appear and are to a man, into goods which are and appear to him. And I 
would beg you not to my words in the letter, but to take the meaning 
of them as I will explain them. Remember what has been already 
said, -that to the sick man his food appears to be and is bitter, and 
to the man in health the opposite of bitter. Now I cannot conceive 
that one of these men can be or ought to be made wiser than the other: 
nor can you assert that the sick man because he has one impression 
is foolish, and the healthy man because he has another is wise; but 



the one state requires to be changed into the other, the worse into 
the better. As in education, a change of state has to be effected, and 
the sophist accomplishes by words the change which the physician works 
by the aid of drugs. Not that any one ever made another think truly, 
who previously thought falsely. For no one can think what is not, or 
think anything different from that which he feels; and this is 
always true. But as the inferior habit of mind has thoughts of kindred 
nature, so I conceive that a good mind causes men to have good 
thoughts; and these which the inexperienced call true, I maintain to 
be only better, and not truer than others. And, my dear Socrates, 
I do not call wise men tadpoles: far from it; I say that they are 
the physicians of the human body, and the husbandmen of plants-for the 
husbandmen also take away the evil and disordered sensations of 
plants, and infuse into them good and healthy sensations-aye and 
true ones; and the wise and good rhetoricians make the good instead of 
the evil to seem just to states; for whatever appears to a state to be 
just and fair, so long as it is regarded as such, is just and fair 
to it; but the teacher of wisdom causes the good to take the place 
of the evil, both in appearance and in reality. And in like manner the 
Sophist who is able to train his pupils in this spirit is a wise 
man, and deserves to be well paid by them. And so one man is wiser 
than another; and no one thinks falsely, and you, whether you will 
or not, must endure to be a measure. On these foundations the argument 
stands firm, which you, Socrates, may, if you please, overthrow by 
an opposite argument, or if you like you may put questions to me-a 
method to which no intelligent person will object, quite the 
reverse. But I must beg you to put fair questions: for there is 
great inconsistency in saying that you have a zeal for virtue, and 
then always behaving unfairly in argument. The unfairness of which I 
complain is that you do not distinguish between mere disputation and 
dialectic: the disputer may trip up his opponent as often as he likes, 
and make fun; but the dialectician will be in earnest, and only 
correct his adversary when necessary, telling him the errors into 
which he has fallen through his own fault, or that of the company 
which he has previously kept. If you do so, your adversary will lay 
the blame of his own confusion and perplexity on himself, and not on 
you; will follow and love you, and will hate himself, and escape 
from himself into philosophy, in order that he may become different 
from what he was. But the other mode of arguing, which is practised by 
the many, will have just the opposite effect upon him; and as he grows 
older, instead of turning philosopher, he will come to hate 
philosophy. I would recommend you, therefore, as I said before, not to 
encourage yourself in this polemical and controversial temper, but 
to find out, in a friendly and congenial spirit, what we really mean 
when we say that all things are in motion, and that to every 
individual and state what appears, is. In this manner you will 
consider whether knowledge and sensation are the same or different, 
but you will not argue, as you were just now doing, from the customary 
use of names and words, which the vulgar pervert in all sorts of ways, 
causing infinite perplexity to one another. Such, Theodorus, is the 
very slight help which I am able to offer to your old friend; had he 
been living, he would have helped himself in a far more gloriose 
style . 

Theod. You are jesting, Socrates; indeed, your defence of him has 
been most valorous . 

Soc. Thank you, friend; and I hope that you observed Protagoras 
bidding us be serious, as the text, "Man is the measure of all 
things," was a solemn one; and he reproached us with making a boy 
the medium of discourse, and said that the boy's timidity was made 
to tell against his argument; he also declared that we made a joke 
of him. 

Theod. How could I fail to observe all that, Socrates? 

Soc. Well, and shall we do as he says? 

Theod. By all means. 



Soc. But if his wishes are to be regarded, you and I must take up 
the argument, and in all seriousness, and ask and answer one 
another, for you see that the rest of us are nothing but boys. In no 
other way can we escape the imputation, that in our fresh analysis 
of his thesis we are making fun with boys. 

Theod. Well, but is not Theaetetus better able to follow a 
philosophical enquiry than a great many men who have long beards? 

Soc. Yes, Theodorus, but not better than you; and therefore please 
not to imagine that I am to defend by every means in my power your 
departed friend; and that you are to defend nothing and nobody. At any 
rate, my good man, do not sheer off until we know whether you are a 
true measure of diagrams, or whether all men are equally measures 
and sufficient for themselves in astronomy and geometry, and the other 
branches of knowledge in which you are supposed to excel them. 

Theod. He who is sitting by you, Socrates, will not easily avoid 
being drawn into an argument; and when I said just now that you 
would excuse me, and not, like the Lacedaemonians, compel me to 
strip and fight, I was talking nonsense-I should rather compare you to 
Scirrhon, who threw travellers from the rocks; for the Lacedaemonian 
rule is "strip or depart," but you seem to go about your work more 
after the fashion of Antaeus: you will not allow any one who 
approaches you to depart until you have stripped him, and he has 
been compelled to try a fall with you in argument. 

Soc. There, Theodorus, you have hit off precisely the nature of my 
complaint; but I am even more pugnacious than the giants of old, for I 
have met with no end of heroes; many a Heracles, many a Theseus, 
mighty in words, has broken my head; nevertheless I am always at 
this rough exercise, which inspires me like a passion. Please, then, 
to try a fall with me, whereby you will do yourself good as well as 
me . 

Theod. I consent; lead me whither you will, for I know that you 
are like destiny; no man can escape from any argument which you may 
weave for him. But I am not disposed to go further than you suggest. 

Soc. Once will be enough; and now take particular care that we do 
not again unwittingly expose ourselves to the reproach of talking 
childishly . 

Theod. I will do my best to avoid that error. 

Soc. In the first place, let us return to our old objection, and see 
whether we were right in blaming and taking offence at Protagoras on 
the ground that he assumed all to be equal and sufficient in wisdom; 
although he admitted that there was a better and worse, and that in 
respect of this, some who as he said were the wise excelled others. 

Theod. Very true. 

Soc. Had Protagoras been living and answered for himself, instead of 
our answering for him, there would have been no need of our 
reviewing or reinforcing the argument. But as he is not here, and some 
one may accuse us of speaking without authority on his behalf, had 
we not better come to a clearer agreement about his meaning, for a 
great deal may be at stake? 

Theod. True. 

Soc. Then let us obtain, not through any third person, but from 
his own statement and in the fewest words possible, the basis of 
agreement . 

Theod. In what way? 

Soc. In this way: -His words are, "What seems to a man, is to him." 

Theod. Yes, so he says. 

Soc. And are not we, Protagoras, uttering the opinion of man, or 
rather of all mankind, when we say that every one thinks himself wiser 
than other men in some things, and their inferior in others? In the 
hour of danger, when they are in perils of war, or of the sea, or of 
sickness, do they not look up to their commanders as if they were 
gods, and expect salvation from them, only because they excel them 
in knowledge? Is not the world full of men in their several 
employments, who are looking for teachers and rulers of themselves and 



of the animals? and there are plenty who think that they are able to 
teach and able to rule. Now, in all this is implied that ignorance and 
wisdom exist among them, least in their own opinion. 

Theod. Certainly. 

Soc. And wisdom is assumed by them to be true thought, and ignorance 
to be false opinion. 

Theod. Exactly. 

Soc. How then, Protagoras, would you have us treat the argument? 
Shall we say that the opinions of men are always true, or sometimes 
true and sometimes false? In either case, the result is the same, 
and their opinions are not always true, but sometimes true and 
sometimes false. For tell me, Theodorus, do you suppose that you 
yourself, or any other follower of Protagoras, would contend that no 
one deems another ignorant or mistaken in his opinion? 

Theod. The thing is incredible, Socrates. 

Soc. And yet that absurdity is necessarily involved in the thesis 
which declares man to be the measure of all things. 

Theod. How so? 

Soc. Why, suppose that you determine in your own mind something to 
be true, and declare your opinion to me; let us assume, as he 
argues, that this is true to you. Now, if so, you must either say that 
the rest of us are not the judges of this opinion or judgment of 
yours, or that we judge you always to have a true opinion: But are 
there not thousands upon thousands who, whenever you form a 
judgment, take up arms against you and are of an opposite judgment and 
opinion, deeming that you judge falsely? 

Theod. Yes, indeed, Socrates, thousands and tens of thousands, as 
Homer says, who give me a world of trouble. 

Soc. Well, but are we to assert that what you think is true to you 
and false to the ten thousand others? 

Theod. No other inference seems to be possible. 

Soc. And how about Protagoras himself? If neither he nor the 
multitude thought, as indeed they do not think, that man is the 
measure of all things, must it not follow that the truth of which 
Protagoras wrote would be true to no one? But if you suppose that he 
himself thought this, and that the multitude does not agree with 
him, you must begin by allowing that in whatever proportion the many 
are more than one, in that proportion his truth is more untrue than 
true . 

Theod. That would follow if the truth is supposed to vary with 
individual opinion. 

Soc. And the best of the joke is, that he acknowledges the truth 
of their opinion who believe his own opinion to be false; for he 
admits that the opinions of all men are true. 

Theod. Certainly. 

Soc. And does he not allow that his own opinion is false, if he 
admits that the opinion of those who think him false is true? 

Theod. Of course. 

Soc. Whereas the other side do not admit that they speak falsely? 

Theod. They do not. 

Soc. And he, as may be inferred from his writings, agrees that 
this opinion is also true. 

Theod. Clearly. 

Soc. Then all mankind, beginning with Protagoras, will contend, or 
rather, I should say that he will allow, when he concedes that his 
adversary has a true opinion-Protagoras, I say, will himself allow 
that neither a dog nor any ordinary man is the measure of anything 
which he has not learned-am I not right? 

Theod. Yes. 

Soc. And the truth of Protagoras being doubted by all, will be 
true neither to himself to any one else? 

Theod. I think, Socrates, that we are running my old friend too 
hard . 

Soc. But do not know that we are going beyond the truth. 



Doubtless, as he is older, he may be expected to be wiser than we are. 
And if he could only just get his head out of the world below, he 
would have overthrown both of us again and again, me for talking 
nonsense and you for assenting to me, and have been off and 
underground in a trice. But as he is not within call, we must make the 
best use of our own faculties, such as they are, and speak out what 
appears to us to be true. And one thing which no one will deny is, 
that there are great differences in the understandings of men. 

Theod. In that opinion I quite agree. 

Soc. And is there not most likely to be firm ground in the 
distinction which we were indicating on behalf of Protagoras, viz., 
that most things, and all immediate sensations, such as hot, dry, 
sweet, are only such as they appear; if however difference of 
opinion is to be allowed at all, surely we must allow it in respect of 
health or disease? for every woman, child, or living creature has 
not such a knowledge of what conduces to health as to enable them to 
cure themselves . 

Theod. I quite agree. 

Soc. Or again, in politics, while affirming that just and unjust, 
honourable and disgraceful, holy and unholy, are in reality to each 
state such as the state thinks and makes lawful, and that in 
determining these matters no individual or state is wiser than 
another, still the followers of Protagoras will not deny that in 
determining what is or is not expedient for the community one state is 
wiser and one counsellor better that another-they will scarcely 
venture to maintain, that what a city enacts in the belief that it 
is expedient will always be really expedient. But in the other case, I 
mean when they speak of justice and injustice, piety and impiety, they 
are confident that in nature these have no existence or essence of 
their own-the truth is that which is agreed on at the time of the 
agreement, and as long as the agreement lasts; and this is the 
philosophy of many who do not altogether go along with Protagoras. 
Here arises a new question, Theodorus, which threatens to be more 
serious than the last. 

Theod. Well, Socrates, we have plenty of leisure. 

Soc. That is true, and your remark recalls to my mind an observation 
which I have often made, that those who have passed their days in 
the pursuit of philosophy are ridiculously at fault when they have 
to appear and speak in court. How natural is this! 

Theod. What do you mean? 

Soc. I mean to say, that those who have been trained in philosophy 
and liberal pursuits are as unlike those who from their youth 
upwards have been knocking about in the courts and such places, as a 
freeman is in breeding unlike a slave. 

Theod. In what is the difference seen? 

Soc. In the leisure spoken of by you, which a freeman can always 
command: he has his talk, out in peace, and, like ourselves, he 
wanders at will from one subject to another, and from a second to a 
third, -if the fancy takes him he begins again, as we are doing now, 
caring not whether his words are many or few; his only aim is to 
attain the truth. But the lawyer is always in a hurry; there is the 
water of the clepsydra driving him on, and not allowing him to 
expatiate at will: and there is his adversary standing over him, 
enforcing his rights; the indictment, which in their phraseology is 
termed the affidavit, is recited at the time: and from this he must 
not deviate. He is a servant, and is continually disputing about a 
fellow servant before his master, who is seated, and has the cause 
in his hands; the trial is never about some indifferent matter, but 
always concerns himself; and often the race is for his life. The 
consequence has been, that he has become keen and shrewd; he has 
learned how to flatter his master in word and indulge him in deed; but 
his soul is small and unrighteous. His condition, which has been 
that of a slave from his youth upwards, has deprived him of growth and 
uprightness and independence; dangers and fears, which were too much 



for his truth and honesty, came upon him in early years, when the 
tenderness of youth was unequal to them, and he has been driven into 
crooked ways; from the first he has practised deception and 
retaliation, and has become stunted and warped. And so he has passed 
out of youth into manhood, having no soundness in him; and is now, 
as he thinks, a master in wisdom. Such is the lawyer, Theodorus . 
Will you have the companion picture of the philosopher, who is of 
our brotherhood; or shall we return to the argument? Do not let us 
abuse the freedom of digression which we claim. 

Theod. Nay, Socrates, not until we have finished what we are 
about; for you truly said that we belong to a brotherhood which is 
free, and are not the servants of the argument; but the argument is 
our servant, and must wait our leisure. Who is our judge? Or where 
is the spectator having any right to censure or control us, as he 
might the poets? 

Soc. Then, as this is your wish, I will describe the leaders; for 
there is no use in talking about the inferior sort. In the first 
place, the lords of philosophy have never, from their youth upwards, 
known their way to the Agora, or the dicastery, or the council, or any 
other political assembly; they neither see nor hear the laws or 
decrees, as they are called, of the state written or recited; the 
eagerness of political societies in the attainment of office-clubs, 
and banquets, and revels, and singing-maidens, -do not enter even 
into their dreams. Whether any event has turned out well or ill in the 
city, what disgrace may have descended to any one from his 
ancestors, male or female, are matters of which the philosopher no 
more knows than he can tell, as they say, how many pints are contained 
in the ocean. Neither is he conscious of his ignorance. For he does 
not hold aloof in order; that he may gain a reputation; but the 
truth is, that the outer form of him only is in the city: his mind, 
disdaining the littlenesses and nothingnesses of human things, is 
"flying all abroad" as Pindar says, measuring earth and heaven and the 
things which are under and on the earth and above the heaven, 
interrogating the whole nature of each and all in their entirety, 
but not condescending to anything which is within reach. 

Theod. What do you mean, Socrates? 

Soc. I will illustrate my meaning, Theodorus, by the jest which 
the clever witty Thracian handmaid is said to have made about 
Thales, when he fell into a well as he was looking up at the stars. 
She said, that he was so eager to know what was going on in heaven, 
that he could not see what was before his feet. This is a jest which 
is equally applicable to all philosophers. For the philosopher is 
wholly unacquainted with his next-door neighbour; he is ignorant, 
not only of what he is doing, but he hardly knows whether he is a 
man or an animal; he is searching into the essence of man, and busy in 
enquiring what belongs to such a nature to do or suffer different from 
any other; -I think that you understand me, Theodorus? 

Theod. I do, and what you say is true. 

Soc. And thus, my friend, on every occasion, private as well as 
public, as I said at first, when he appears in a law-court, or in 
any place in which he has to speak of things which are at his feet and 
before his eyes, he is the jest, not only of Thracian handmaids but of 
the general herd, tumbling into wells and every sort of disaster 
through his inexperience. His awkwardness is fearful, and gives the 
impression of imbecility. When he is reviled, he has nothing 
personal to say in answer to the civilities of his adversaries, for he 
knows no scandals of any one, and they do not interest him; and 
therefore he is laughed at for his sheepishness; and when others are 
being praised and glorified, in the simplicity of his heart he 
cannot help going into fits of laughter, so that he seems to be a 
downright idiot. When he hears a tyrant or king eulogized, he 
fancies that he is listening to the praises of some keeper of cattle-a 
swineherd, or shepherd, or perhaps a cowherd, who is congratulated 
on the quantity of milk which he squeezes from them; and he remarks 



that the creature whom they tend, and out of whom they squeeze the 
wealth, is of a less traitable and more insidious nature. Then, again, 
he observes that the great man is of necessity as ill-mannered and 
uneducated as any shepherd-for he has no leisure, and he is surrounded 
by a wall, which is his mountain-pen. Hearing of enormous landed 
proprietors of ten thousand acres and more, our philosopher deems this 
to be a trifle, because he has been accustomed to think of the whole 
earth; and when they sing the, praises of family, and say that someone 
is a gentleman because he can show seven generations of wealthy 
ancestors, he thinks that their sentiments only betray a dull and 
narrow vision in those who utter them, and who are not educated enough 
to look at the whole, nor to consider that every man has had thousands 
and ten thousands of progenitors, and among them have been rich and 
poor, kings and slaves, Hellenes and barbarians, innumerable. And when 
people pride themselves on having a pedigree of twenty-five ancestors, 
which goes back to Heracles, the son of Amphitryon, he cannot 
understand their poverty of ideas. Why are they unable to calculate 
that Amphitryon had a twenty-fifth ancestor, who might have been 
anybody, and was such as fortune made him and he had a fiftieth, and 
so on? He amuses himself with the notion that they cannot count, and 
thinks that a little arithmetic would have got rid of their 
senseless vanity. Now, in all these cases our philosopher is derided 
by the vulgar, partly because he is thought to despise them, and 
also because he is ignorant of what is before him, and always at a 
loss . 

Theod. That is very true, Socrates. 

Soc. But, my friend, when he draws the other into upper air, and 
gets him out of his pleas and rejoinders into the contemplation of 
justice and injustice in their own nature and in their difference from 
one another and from all other things; or from the commonplaces 
about the happiness of a king or of a rich man to the consideration of 
government, and of human happiness and misery in general-what they 
are, and how a man is to attain the one and avoid the other-when 
that narrow, keen, little legal mind is called to account about all 
this, he gives the philosopher his revenge; for dizzied by the 
height at which he is hanging, whence he looks down into space, 
which is a strange experience to him, he being dismayed, and lost, and 
stammering broken words, is laughed at, not by Thracian handmaidens or 
any other uneducated persons, for they have no eye for the 
situation, but by every man who has not been brought up a slave. 
Such are the two characters, Theodorus : the one of the freeman, who 
has becomes trained in liberty and leisure, whom you call the 
philosopher-him we cannot blame because he appears simple and of no 
account when he has to perform some menial task, such as packing up 
bed-clothes, or flavouring a sauce or fawning speech; the other 
character is that of the man who is able to do all this kind of 
service smartly and neatly, but knows not how to wear his cloak like a 
gentleman; still less with the music of discourse can he hymn the true 
life aright which is lived by immortals or men blessed of heaven. 

Theod. If you could only persuade everybody, Socrates, as you do me, 
of the truth of your words, there would be more peace and fewer 
evils among men. 

Soc. Evils, Theodorus, can never pass away; for there must always 
remain something which is antagonistic to good. Having no place 
among the gods in heaven, of necessity they hover around the mortal 
nature, and this earthly sphere. Wherefore we ought to fly away from 
earth to heaven as quickly as we can; and to fly away is to become 
like God, as far as this is possible; and to become like him, is to 
become holy, just, and wise. But, my friend, you cannot easily 
convince mankind that they should pursue virtue or avoid vice, not 
merely in order that a man may seem to be good, which is the reason 
given by the world, and in my judgment is only a repetition of an 
old wives fable. Whereas, the truth is that God is never in any way 
unrighteous-he is perfect righteousness; and he of us who is the 



most righteous is most like him. Herein is seen the true cleverness of 
a man, and also his nothingness and want of manhood. For to know 
this is true wisdom and virtue, and ignorance of this is manifest 
folly and vice. All other kinds of wisdom or cleverness, which seem 
only, such as the wisdom of politicians, or the wisdom of the arts, 
are coarse and vulgar. The unrighteous man, or the sayer and doer of 
unholy things, had far better not be encouraged in the illusion that 
his roguery is clever; for men glory in their shame -they fancy that 
they hear others saying of them, "These are not mere good-for 
nothing persons, mere burdens of the earth, but such as men should 
be who mean to dwell safely in a state." Let us tell them that they 
are all the more truly what they do not think they are because they do 
not know it; for they do not know the penalty of injustice, which 
above all things they ought to know-not stripes and death, as they 
suppose, which evil-doers often escape, but a penalty which cannot 
be escaped. 

Theod. What is that? 

Soc. There are two patterns eternally set before them; the one 
blessed and divine, the other godless and wretched: but they do not 
see them, or perceive that in their utter folly and infatuation they 
are growing like the one and unlike the other, by reason of their evil 
deeds; and the penalty is, that they lead a life answering to the 
pattern which they are growing like. And if we tell them, that 
unless they depart from their cunning, the place of innocence will not 
receive them after death; and that here on earth, they will live 
ever in the likeness of their own evil selves, and with evil 
friends-when they hear this they in their superior cunning will seem 
to be listening to the talk of idiots. 

Theod. Very true, Socrates. 

Soc. Too true, my friend, as I well know; there is, however, one 
peculiarity in their case: when they begin to reason in private 
about their dislike of philosophy, if they have the courage to hear 
the argument out and do not run away, they grow at last strangely 
discontented with themselves; their rhetoric fades away, and they 
become helpless as children. These however are digressions from 
which we must now desist, or they will overflow, and drown the 
original argument; to which, if you please, we will now return. 

Theod. For my part, Socrates, I would rather have the digressions, 
for at my age I find them easier to follow; but if you wish, let us go 
back to the argument. 

Soc. Had we not reached the point at which the partisans of the 
perpetual flux, who say that things are as they seem to each one, were 
confidently maintaining that the ordinances which the state 
commanded 2nd thought just, were just to the state which imposed them, 
while they were in force; this was especially asserted of justice; but 
as to the good, no one had any longer the hardihood to contend of 
any ordinances which the state thought and enacted to be good that 
these, while they were in force, were really good; -he who said so 
would be playing with the name "good, " and would, not touch the real 
question-it would be a mockery, would it not? 

Theod. Certainly it would. 

Soc. He ought not to speak of the name, but of the thing which is 
contemplated under the name. 

Theod. Right. 

Soc. Whatever be the term used, the good or expedient is the aim 
of legislation, and as far as she has an opinion, the state imposes 
all laws with a view to the greatest expediency; can legislation 
have any other aim? 

Theod. Certainly not. 

Soc. But is the aim attained always? do not mistakes often happen? 

Theod. Yes, I think that there are mistakes. 

Soc. The possibility of error will be more distinctly recognized, if 
we put the question in reference to the whole class under which the 
good or expedient fall That whole class has to do with the future, and 



laws are passed under the idea that they will be useful in after-time; 
which, in other words, is the future. 

Theod. Very true. 

Soc. Suppose now, that we ask Protagoras, or one of his disciples, a 
question :-0, Protagoras, we will say to him, Man is, as you declare, 
the measure of all things-white, heavy, light: of all such things he 
is the judge; for he has the criterion of them in himself, and when he 
thinks that things are such as he experiences them to be, he thinks 
what is and is true to himself. Is it not so? 

Theod. Yes. 

Soc. And do you extend your doctrine, Protagoras (as we shall 
further say), to the future as well as to the present; and has he 
the criterion not only of what in his opinion is but of what will 
be, and do things always happen to him as he expected? For example, 
take the case of heat : -When an ordinary man thinks that he is going to 
have a fever, and that this kind of heat is coming on, and another 
person, who is a physician, thinks the contrary, whose opinion is 
likely to prove right? Or are they both right?-he will have a heat and 
fever in his own judgment, and not have a fever in the physician's 
judgment? 

Theod. How ludicrous! 

Soc. And the vinegrower, if I am not mistaken, is a better judge 
of the sweetness or dryness of the vintage which is not yet gathered 
than the harp-player? 

Theod. Certainly. 

Soc. And in musical composition-the musician will know better than 
the training master what the training master himself will hereafter 
think harmonious or the reverse? 

Theod. Of course. 

Soc. And the cook will be a better judge than the guest, who is 
not a cook, of the pleasure to be derived from the dinner which is 
in preparation; for of present or past pleasure we are not as yet 
arguing; but can we say that every one will be to himself the best 
judge of the pleasure which will seem to be and will be to him in 
the future?-nay, would not you, Protagoras, better guess which 
arguments in a court would convince any one of us than the ordinary 
man? 

Theod. Certainly, Socrates, he used to profess in the strongest 
manner that he was the superior of all men in this respect. 

Soc. To be sure, friend: who would have paid a large sum for the 
privilege of talking to him, if he had really persuaded his visitors 
that neither a prophet nor any other man was better able to judge what 
will be and seem to be in the future than every one could for himself? 

Theod. Who indeed? 

Soc. And legislation and expediency are all concerned with the 
future; and every one will admit that states, in passing laws, must 
often fail of their highest interests? 

Theod. Quite true. 

Soc. Then we may fairly argue against your master, that he must 
admit one man to be wiser than another, and that the wiser is a 
measure: but I, who know nothing, am not at all obliged to accept 
the honour which the advocate of Protagoras was just now forcing 
upon me, whether I would or not, of being a measure of anything. 

Theod. That is the best refutation of him, Socrates; although he 
is also caught when he ascribes truth to the opinions of others, who 
give the lie direct to his own opinion. 

Soc. There are many ways, Theodorus, in which the doctrine that 
every opinion of: every man is true may be refuted; but there is 
more difficulty, in proving that states of feeling, which are 
present to a man, and out of which arise sensations and opinions in 
accordance with them, are also untrue. And very likely I have been 
talking nonsense about them; for they may be unassailable, and those 
who say that there is clear evidence of them, and that they are 
matters of knowledge, may probably be right; in which case our 



friend Theaetetus was not so far from the mark when he identified 
perception and knowledge. And therefore let us draw nearer, as the 
advocate of Protagoras desires; and the truth of the universal flux 
a ring: is the theory sound or not? at any rate, no small war is 
raging about it, and there are combination not a few. 

Theod. No small, war, indeed, for in most the sect makes rapid 
strides, the disciples of Heracleitus are most energetic, upholders of 
the doctrine. 

Soc. Then we are the more bound, my dear Theodorus, to examine the 
question from the foundation as it is set forth by themselves. 

Theod. Certainly we are. About these speculations of Heracleitus, 
which, as you say, are as old as Homer, or even older still, the 
Ephesians themselves, who profess to know them, are downright mad, and 
you cannot talk with them on the subject. For, in accordance with 
their text-books, they are always in motion; but as for dwelling 
upon an argument or a question, and quietly asking and answering in 
turn, they can no more do so than they can fly; or rather, the 
determination of these fellows not to have a particle of rest in 
them is more than the utmost powers of negation can express. If you 
ask any of them a question, he will produce, as from a quiver, sayings 
brief and dark, and shoot them at you; and if you inquire the reason 
of what he has said, you will be hit by some other newfangled word, 
and will make no way with any of them, nor they with one another; 
their great care is, not to allow of any settled principle either in 
their arguments or in their minds, conceiving, as I imagine, that 
any such principle would be stationary; for they are at war with the 
stationary, and do what they can to drive it out everywhere. 

Soc. I suppose, Theodorus, that you have only seen them when they 
were fighting, and have never stayed with them in time of peace, for 
they are no friends of yours; and their peace doctrines are only 
communicated by them at leisure, as I imagine, to those disciples of 
theirs whom they want to make like themselves. 

Theod. Disciples! my good sir, they have none; men of their sort are 
not one another's disciples, but they grow up at their own sweet will, 
and get their inspiration anywhere, each of them saying of his 
neighbour that he knows nothing. Fro these men, then, as I was going 
to remark, you will never get a reason, whether with their will or 
without their will; we must take the question out of their hands, 
and make the analysis ourselves, as if we were doing geometrical 
problem . 

Soc. Quite right too; but as touching the aforesaid problem, have we 
not heard from the ancients, who concealed their wisdom from the 
many in poetical figures, that Oceanus and Tethys, the origin of all 
things, are streams, and that nothing is at rest? And now the moderns, 
in their superior wisdom, have declared the same openly, that the 
cobbler too may hear and learn of them, and no longer foolishly 
imagine that some things are at rest and others in motion-having 
learned that all is motion, he will duly honour his teachers. I had 
almost forgotten the opposite doctrine, Theodorus, 

Alone Being remains unmoved, which is the name for the all. 

This is the language of Parmenides, Melissus, and their followers, who 
stoutly maintain that all being is one and self-contained, and has 
no place which to move. What shall we do, friend, with all these 
people; for, advancing step by step, we have imperceptibly got between 
the combatants, and, unless we can protect our retreat, we shall pay 
the penalty of our rashness-like the players in the palaestra who 
are caught upon the line, and are dragged different ways by the two 
parties. Therefore I think that we had better begin by considering 
those whom we first accosted, "the river-gods," and, if we find any 
truth in them, we will help them to pull us over, and try to get 
away from the others. But if the partisans of "the whole" appear to 
speak more truly, we will fly off from the party which would move 



the immovable, to them. And if I find that neither of them have 
anything reasonable to say, we shall be in a ridiculous position, 
having so great a conceit of our own poor opinion and rejecting that 
of ancient and famous men. Theodorus, do you think that there is any 
use in proceeding when the danger is so great? 

Theod. Nay, Socrates, not to examine thoroughly what the two parties 
have to say would be quite intolerable. 

Soc. Then examine we must, since you, who were so reluctant, to 
begin, are so eager to proceed. The nature of motion appears to be the 
question with which we begin. What do they mean when they say that all 
things are in motion? Is there only one kind of motion, or, as I 
rather incline to think, two? should like to have your opinion upon 
this point in addition to my own, that I may err, if I must err, in 
your company; tell me, then, when a thing changes from one place to 
another, or goes round in the same place, is not that what is called 
motion? 

Theod. Yes. 

Soc. Here then we have one kind of motion. But when a thing, 
remaining on the same spot, grows old, or becomes black from being 
white, or hard from being soft, or undergoes any other change, may not 
this be properly called motion of another kind? 

Theod. I think so. 

Soc. Say rather that it must be so. Of motion then there are these 
two kinds, "change," and "motion in place." 

Theod. You are right. 

Soc. And now, having made this distinction, let us address ourselves 
to those who say that all is motion, and ask them whether all things 
according to them have the two kinds of motion, and are changed as 
well as move in place, or is one thing moved in both ways, and another 
in one only? 

Theod. Indeed, I do not know what to answer; but I think they 
would say that all things are moved in both ways. 

Soc. Yes, comrade; for, if not, they would have to say that the same 
things are in motion and at rest, and there would be no more truth 
in saying that all things are in motion, than that all things are at 
rest . 

Theod. To be sure. 

Soc. And if they are to be in motion, and nothing is to be devoid of 
motion, all things must always have every sort of motion? 

Theod. Most true. 

Soc. Consider a further point: did we not understand them to explain 
the generation of heat, whiteness, or anything else, in some such 
manner as the following : -were they not saying that each of them is 
moving between the agent and the patient, together with a 
perception, and that the patient ceases to be a perceiving power and 
becomes a percipient, and the agent a quale instead of a quality? I 
suspect that quality may appear a strange and uncouth term to you, and 
that you do not understand the abstract expression. Then I will take 
concrete instances : I mean to say that the producing power or agent 
becomes neither heat nor whiteness but hot and white, and the like 
of other things. For I must repeat what I said before, that neither 
the agent nor patient have any absolute existence, but when they 
come together and generate sensations and their objects, the one 
becomes a thing a certain quality, and the other a percipient. You 
remember? 

Theod. Of course. 

Soc. We may leave the details of their theory unexamined, but we 
must not forget to ask them the only question with which we are 
concerned: Are all things in motion and flux? 

Theod. Yes, they will reply. 

Soc. And they are moved in both those ways which we distinguished, 
that is to Way, they move in place and are also changed? 

Theod. Of course, if the motion is to be perfect. 

Soc. If they only moved in place and were not changed, we should 



be able to say what is the nature of the things which are in motion 
and flux. 

Theod. Exactly. 

Soc. But now, since not even white continues to flow white, and 
whiteness itself is a flux or change which is passing into another 
colour, and is never to be caught standing still, can the name of 
any colour be rightly used at all? 

Theod. How is that possible, Socrates, either in the case of this or 
of any other quality-if while we are using the word the object is 
escaping in the flux? 

Soc. And what would you say of perceptions, such as sight and 
hearing, or any other kind of perception? Is there any stopping in the 
act of seeing and hearing? 

Theod. Certainly not, if all things are in motion. 

Soc. Then we must not speak of seeing any more than of not-seeing, 
nor of any other perception more than of any non-perception, if all 
things partake of every kind of motion? 

Theod. Certainly not. 

Soc. Yet perception is knowledge: so at least Theaetetus and I 
were saying. 

Theod. Very true. 

Soc. Then when we were asked what is knowledge, we no more 
answered what is knowledge than what is not knowledge? 

Theod. I suppose not. 

Soc. Here, then, is a fine result: we corrected our first answer 
in our eagerness to prove that nothing is at rest. But if nothing is 
at rest, every answer upon whatever subject is equally right: you 
may say that a thing is or is not thus; or, if you prefer, "becomes" 
thus; and if we say "becomes," we shall not then hamper them with 
words expressive of rest. 

Theod. Quite true. 

Soc. Yes, Theodorus, except in saying "thus" and "not thus." But you 
ought not to use the word "thus," for there is no motion in "thus" 
or in "not thus." The maintainers of the doctrine have as yet no words 
in which to express themselves, and must get a new language. I know of 
no word that will suit them, except perhaps "no how, " which is 
perfectly indefinite. 

Theod. Yes, that is a manner of speaking in which they will be quite 
at home . 

Soc. And so, Theodorus, we have got rid of your friend without 
assenting to his doctrine, that every man is the measure of all 
things-a wise man only is a measure; neither can we allow that 
knowledge is perception, certainly not on the hypothesis of a 
perpetual flux, unless perchance our friend Theaetetus is able to 
convince us that it is. 

Theod. Very good, Socrates; and now that the argument about the 
doctrine of Protagoras has been completed, I am absolved from 
answering; for this was the agreement. 

Theaet . Not, Theodorus, until you and Socrates have discussed the 
doctrine of those who say that all things are at rest, as you were 
proposing . 

Theod. You, Theaetetus, who are a young rogue, must not instigate 
your elders to a breach of faith, but should prepare to answer 
Socrates in the remainder of the argument. 

Theaet. Yes, if he wishes; but I would rather have heard about the 
doctrine of rest. 

Theod. Invite Socrates to an argument-invite horsemen to the open 
plain; do but ask him, and he will answer. 

Soc. Nevertheless, Theodorus, I am afraid that I shall not be able 
to comply with the request of Theaetetus. 

Theod. Not comply! for what reason? 

Soc. My reason is that I have a kind of reverence; not so much for 
Melissus and the others, who say that "All is one and at rest," as for 
the great leader himself, Parmenides, venerable and awful, as in 



Homeric language he may be called; -him I should be ashamed to approach 
in a spirit unworthy of him. I met him when he was an old man, and I 
was a mere youth, and he appeared to me to have a glorious depth of 
mind. And I am afraid that we may not understand his words, and may be 
still further from understanding his meaning; above all I fear that 
the nature of knowledge, which is the main subject of our 
discussion, may be thrust out of sight by the unbidden guests who will 
come pouring in upon our feast of discourse, if we let them 
in-besides, the question which is now stirring is of immense extent, 
and will be treated unfairly if only considered by the way; or if 
treated adequately and at length, will put into the shade the other 
question of knowledge. Neither the one nor the other can be allowed; 
but I must try by my art of midwifery to deliver Theaetetus of his 
conceptions about knowledge. 

Theaet . Very well; do so if you will. 

Soc. Then now, Theaetetus, take another view of the subject: you 
answered that knowledge is perception? 

Theaet. I did. 

Soc. And if any one were to ask you: With what does a man see 
black and white colours? and with what does he hear high and low 
sounds?-you would say, if I am not mistaken, "With the eyes and with 
the ears . " 

Theaet. I should. 

Soc. The free use of words and phrases, rather than minute 
precision, is generally characteristic of a liberal education, and the 
opposite is pedantic; but sometimes precision, is necessary, and I 
believe that the answer which you have just given is open to the 
charge of incorrectness; for which is more correct, to say that we see 
or hear with the eyes and with the ears, or through the eyes and 
through the ears . 

Theaet. I should say "through," Socrates, rather than "with." 

Soc. Yes, my boy, for no one can suppose that in each of us, as in a 
sort of Trojan horse, there are perched a number of unconnected 
senses, which do not all meet in some one nature, the mind, or 
whatever we please to call it, of which they are the instruments, 
and with which through them we perceive objects of sense. 

Theaet. I agree with you in that opinion. 

Soc. The reason why I am thus precise is, because I want to know 
whether, when we perceive black and white through the eyes, and again, 
other qualities through other organs, we do not perceive them with one 
and the same part of ourselves, and, if you were asked, you might 
refer all such perceptions to the body. Perhaps, however, I had better 
allow you to answer for yourself and not interfere; Tell me, then, are 
not the organs through which you perceive warm and hard and light 
and sweet, organs of the body? 

Theaet. Of the body, certainly. 

Soc. And you would admit that what you perceive through one 
faculty you cannot perceive through another; the objects of hearing, 
for example, cannot be perceived through sight, or the objects of 
sight through hearing? 

Theaet. Of course not. 

Soc. If you have any thought about both of them, this common 
perception cannot come to you, either through the one or the other 
organ? 

Theaet. It cannot. 

Soc. How about sounds and colours: in the first place you would 
admit that they both exist? 

Theaet. Yes. 

Soc. And that either of them is different from the other, and the 
same with itself? 

Theaet. Certainly. 

Soc. And that both are two and each of them one? 

Theaet. Yes. 

Soc. You can further observe whether they are like or unlike one 



another? 

Theaet . I dare say. 

Soc. But through what do you perceive all this about them? for 
neither through hearing nor yet through seeing can you apprehend 
that which they have in common. Let me give you an illustration of the 
point at issue: -If there were any meaning in asking whether sounds and 
colours are saline or not, you would be able to tell me what faculty 
would consider the question. It would not be sight or hearing, but 
some other. 

Theaet. Certainly; the faculty of taste. 

Soc. Very good; and now tell me what is the power which discerns, 
not only in sensible objects, but in all things, universal notions, 
such as those which are called being and not-being, and those others 
about which we were just asking-what organs will you assign for the 
perception of these notions? 

Theaet. You are thinking of being and not being, likeness and 
unlikeness, sameness and difference, and also of unity and other 
numbers which are applied to objects of sense; and you mean to ask, 
through what bodily organ the soul perceives odd and even numbers 
and other arithmetical conceptions. 

Soc. You follow me excellently, Theaetetus; that is precisely what I 
am asking. 

Theaet. Indeed, Socrates, I cannot answer; my only notion is, that 
these, unlike objects of sense, have no separate organ, but that the 
mind, by a power of her own, contemplates the universals in all 
things . 

Soc. You are a beauty, Theaetetus, and not ugly, as Theodorus was 
saying; for he who utters the beautiful is himself beautiful and good. 
And besides being beautiful, you have done me a kindness in 
releasing me from a very long discussion, if you are clear that the 
soul views some things by herself and others through the bodily 
organs. For that was my own opinion, and I wanted you to agree with 
me . 

Theaet. I am quite clear. 

Soc. And to which class would you refer being or essence; for 
this, of all our notions, is the most universal? 

Theaet. I should say, to that class which the soul aspires to know 
of herself. 

Soc. And would you say this also of like and unlike, same and other? 

Theaet. Yes. 

Soc. And would you say the same of the noble and base, and of good 
and evil? 

Theaet. These I conceive to be notions which are essentially 
relative, and which the soul also perceives by comparing in herself 
things past and present with the future. 

Soc. And does she not perceive the hardness of that which is hard by 
the touch, and the softness of that which is soft equally by the 
touch? 

Theaet. Yes. 

Soc. But their essence and what they are, and their opposition to 
one another, and the essential nature of this opposition, the soul 
herself endeavours to decide for us by the review and comparison of 
them? 

Theaet. Certainly. 

Soc. The simple sensations which reach the soul through the body are 
given at birth to men and animals by nature, but their reflections 
on the being and use of them are slowly and hardly gained, if they are 
ever gained, by education and long experience. 

Theaet. Assuredly. 

Soc. And can a man attain truth who fails of attaining being? 

Theaet. Impossible. 

Soc. And can he who misses the truth of anything, have a knowledge 
of that thing? 

Theaet. He cannot. 



Soc. Then knowledge does not consist in impressions of sense, but in 
reasoning about them; in that only, and not in the mere impression, 
truth and being can be attained? 

Theaet. Clearly. 

Soc. And would you call the two processes by the same name, when 
there is so great difference between them? 

Theaet. That would certainly not be right. 

Soc. And what name would you give to seeing, hearing, smelling, 
being cold and being hot? 

Theaet. I should call all of them perceiving-what other name could 
be given to them? 

Soc. Perception would be the collective name of them? 

Theaet. Certainly. 

Soc. Which, as we say, has no part in the attainment of truth any 
more of being? 

Theaet. Certainly not. 

Soc. And therefore not in. science or knowledge? 

Theaet. No. 

Soc. Then perception, Theaetetus, can never be the same as knowledge 
or science? 

Theaet. Clearly not, Socrates; and knowledge has now been most 
distinctly proved to be different from perception. 

Soc. But the original aim of our discussion was to find out rather 
what knowledge is than what it is not; at the same time we have made 
some progress, for we no longer seek for knowledge, in perception at 
all, but in that other process, however called, in which the mind is 
alone and engaged with being. 

Theaet. You mean, Socrates, if I am not mistaken, what is called 
thinking or opining. 

Soc. You conceive truly. And now, my friend, Please to begin again 
at this point; and having wiped out of your memory all that has 
preceded, see if you have arrived at any clearer view, and once more 
say what is knowledge. 

Theaet. I cannot say, Socrates, that all opinion is knowledge, 
because there may be a false opinion; but I will venture to assert, 
that knowledge is true opinion: let this then be my reply; and if this 
is hereafter disproved, I must try to find another. 

Soc. That is the way in which you ought to answer, Theaetetus, and 
not in your former hesitating strain, for if we are bold we shall gain 
one of two advantages; either we shall find what we seek, or we 
shall be less likely to think that we know what we do not know-in 
either case we shall be richly rewarded. And now, what are you 
saying?-Are there two sorts of opinion, one true and the other 
false; and do you define knowledge to be the true? 

Theaet. Yes, according to my present view. 

Soc. Is it still worth our while to resume the discussion touching 
opinion? 

Theaet. To what are you alluding? 

Soc. There is a point which often troubles me, and is a great 
perplexity to me, both in regard to myself and others. I cannot make 
out the nature or origin of the mental experience to which I refer. 

Theaet. Pray what is it? 

Soc. How there can be-false opinion-that difficulty still troubles 
the eye of my mind; and I am uncertain whether I shall leave the 
question, or over again in a new way. 

Theaet. Begin again, Socrates, -at least if you think that there is 
the slightest necessity for doing so. Were not you and Theodorus 
just now remarking very truly, that in discussions of this kind we may 
take our own time? 

Soc. You are quite right, and perhaps there will be no harm in 
retracing our steps and beginning again. Better a little which is well 
done, than a great deal imperfectly. 

Theaet. Certainly. 

Soc. Well, and what is the difficulty? Do we not speak of false 



opinion, and say that one man holds a false and another a true 
opinion, as though there were some natural distinction between them? 

Theaet . We certainly say so. 

Soc. All things and everything are either known or not known. I 
leave out of view the intermediate conceptions of learning and 
forgetting, because they have nothing to do with our present question. 

Theaet. There can be no doubt, Socrates, if you exclude these, 
that there is no other alternative but knowing or not knowing a thing. 

Soc. That point being now determined, must we not say that he who 
has an opinion, must have an opinion about something which he knows or 
does not know? 

Theaet. He must. 

Soc. He who knows, cannot but know; and he who does not know, cannot 
know? 

Theaet. Of course. 

Soc. What shall we say then? When a man has a false opinion does 
he think that which he knows to be some other thing which he knows, 
and knowing both, is he at the same time ignorant of both? 

Theaet. That, Socrates, is impossible. 

Soc. But perhaps he thinks of something which he does not know as 
some other thing which he does not know; for example, he knows neither 
Theaetetus nor Socrates, and yet he fancies that Theaetetus is 
Socrates, or Socrates Theaetetus? 

Theaet. How can he? 

Soc. But surely he cannot suppose what he knows to be what he does 
not know, or what he does not know to be what he knows? 

Theaet. That would be monstrous. 

Soc. Where, then, is false opinion? For if all things are either 
known or unknown, there can be no opinion which is not comprehended 
under this alternative, and so false opinion is excluded. 

Theaes . Most true. 

Soc. Suppose that we remove the question out of the sphere of 
knowing or not knowing, into that of being and not-being. 

Theaet. What do you mean? 

Soc. May we not suspect the simple truth to be that he who thinks 
about anything, that which, is not, will necessarily think what is 
false, whatever in other respects may be the state of his mind? 

Theaet. That, again, is not unlikely, Socrates. 

Soc. Then suppose some one to say to us, Theaetetus : -Is it 
possible for any man to think that which is not, either as a 
self-existent substance or as a predicate of something else? And 
suppose that we answer, "Yes, he can, when he thinks what is not 
true. "-That will be our answer? 

Theaet. Yes. 

Soc. But is there any parallel to this? 

Theaet. What do you mean? 

Soc. Can a man see something and yet see nothing? 

Theaet. Impossible. 

Soc. But if he sees any one thing, he sees something that exists. Do 
you suppose that what is one is ever to be found among nonexisting 
things? 

Theaet . I do not . 

Soc. He then who sees some one thing, sees something which is? 

Theaet. Clearly. 

Soc. And he who hears anything, hears some one thing, and hears that 
which is? 

Theaet. Yes. 

Soc. And he who touches anything, touches something which is one and 
therefore is? 

Theaet. That again is true. 

Soc. And does not he who thinks, think some one thing? 

Theaet. Certainly. 

Soc. And does not he who thinks some one thing, think something 
which is? 



Theaet . I agree. 

Soc. Then he who thinks of that which is not, thinks of nothing? 

Theaet. Clearly. 

Soc. And he who thinks of nothing, does not think at all? 

Theaet. Obviously. 

Soc. Then no one can think that which is not, either as a 
self-existent substance or as a predicate of something else? 

Theaet. Clearly not. 

Soc. Then to think falsely is different from thinking that which 
is not? 

Theaet. It would seem so. 

Soc. Then false opinion has no existence in us, either in the sphere 
of being or of knowledge? 

Theaet. Certainly not. 

Soc. But may not the following be the description of what we express 
by this name? 

Theaet. What? 

Soc. May we not suppose that false opinion or thought is a sort of 
heterodoxy; a person may make an exchange in his mind, and say that 
one real object is another real object. For thus he always thinks that 
which is, but he puts one thing in place of another; and missing the 
aim of his thoughts, he may be truly said to have false opinion. 

Theaet. Now you appear to me to have spoken the exact truth: when 
a man puts the base in the place of the noble, or the noble in the 
place of the base, then he has truly false opinion. 

Soc. I see, Theaetetus, that your fear has disappeared, and that you 
are beginning to despise me. 

Theaet. What makes you say so? 

Soc. You think, if I am not mistaken, that your "truly false" is 
safe from censure, and that I shall never ask whether there can be a 
swift which is slow, or a heavy which is light, or any other 
self-contradictory thing, which works, not according to its own 
nature, but according to that of its opposite. But I will not insist 
upon this, for I do not wish needlessly to discourage you. And so 
you are satisfied that false opinion is heterodoxy, or the thought 
of something else? 

Theaet. I am. 

Soc. It is possible then upon your view for the mind to conceive 
of one thing as another? 

Theaet. True. 

Soc. But must not the mind, or thinking power, which misplaces them, 
have a conception either of both objects or of one of them? 

Theaet. Certainly. 

Soc. Either together or in succession? 

Theaet. Very good. 

Soc. And do you mean by conceiving, the same which I mean? 

Theaet. What is that? 

Soc. I mean the conversation which the soul holds with herself in 
considering of anything. I speak of what I scarcely understand; but 
the soul when thinking appears to me to be just talking-asking 
questions of herself and answering them, affirming and denying. And 
when she has arrived at a decision, either gradually or by a sudden 
impulse, and has at last agreed, and does not doubt, this is called 
her opinion. I say, then, that to form an opinion is to speak, and 
opinion is a word spoken, -I mean, to oneself and in silence, not aloud 
or to another: What think you? 

Theaet. I agree. 

Soc. Then when any one thinks of one thing as another, he is 
saying to himself that one thing is another? 

Theaet. Yes. 

Soc. But do you ever remember saying to yourself that the noble is 
certainly base, or the unjust just; or, best of all-have you ever 
attempted to convince yourself that one thing is another? Nay, not 
even in sleep, did you ever venture to say to yourself that odd is 



even, or anything of the kind? 

Theaet . Never. 

Soc. And do you suppose that any other man, either in his senses 
or out of them, ever seriously tried to persuade himself that an ox is 
a horse, or that two are one? 

Theaet. Certainly not. 

Soc. But if thinking is talking to oneself, no one speaking and 
thinking of two objects, and apprehending them both in his soul, 
will say and think that the one is the other of them, and I must 
add, that even you, lover of dispute as you are, had better let the 
word "other" alone [i.e., not insist that "one" and "other" are the 
same] . I mean to say, that no one thinks the noble to be base, or 
anything of the kind. 

Theaet. I will give up the word "other," Socrates; and I agree to 
what you say. 

Soc. If a man has both of them in his thoughts, he cannot think that 
the one of them is the other? 

Theat. True. 

Soc. Neither, if he has one of them only in his mind and not the 
other, can he think that one is the other? 

Theaet. True; for we should have to suppose that he apprehends 
that which is not in his thoughts at all. 

Soc. Then no one who has either both or only one of the two 
objects in his mind can think that the one is the other. And 
therefore, he who maintains that false opinion is heterodoxy is 
talking nonsense; for neither in this, any more than in the previous 
way, can false opinion exist in us. 

Theaet. No. 

Soc. But if, Theaetetus, this is not admitted, we shall be driven 
into many absurdities . 

Theaet. What are they? 

Soc. I will not tell you until I have endeavoured to consider the 
matter from every point of view. For I should be ashamed of us if we 
were driven in our perplexity to admit the absurd consequences of 
which I speak. But if we find the solution, and get away from them, we 
may regard them only as the difficulties of others, and the ridicule 

ill not attach to us. On the other hand, if we utterly fail, I 
suppose that we must be humble, and allow the argument to trample us 
under foot, as the sea-sick passenger is trampled upon by the 
sailor, and to do anything to us. Listen, then, while I tell you how I 
hope to find a way out of our difficulty. 

Theaet. Let me hear. 

Soc. I think that we were wrong in denying that a man could think 
what he knew to be what he did not know; and that there is a way in 
which such a deception is possible. 

Theaet. You mean to say, as I suspected at the time, that I may know 
Socrates, and at a distance see some one who is unknown to me, and 
whom I mistake for him-them the deception will occur? 

Soc. But has not that position been relinquished by us, because 
involving the absurdity that we should know and not know the things 
which we know? 

Theaet. True. 

Soc. Let us make the assertion in another form, which may or may not 
have a favourable issue; but as we are in a great strait, every 
argument should be turned over and tested. Tell me, then, whether I am 
right in saying that you may learn a thing which at one time you did 
not know? 

Theaet. Certainly you may. 

Soc. And another and another? 

Theaet. Yes. 

Soc. I would have you imagine, then, that there exists in the mind 
of man a block of wax, which is of different sizes in different men; 
harder, moister, and having more or less of purity in one than 
another, and in some of an intermediate quality. 



w 



Theaet . I see. 

Soc. Let us say that this tablet is a gift of Memory, the mother 
of the Muses; and that when we wish to remember anything which we have 
seen, or heard, or thought in our own minds, we hold the wax to the 
perceptions and thoughts, and in that material receive the 
impression of them as from the seal of a ring; and that we remember 
and know what is imprinted as long as the image lasts; but when the 
image is effaced, or cannot be taken, then we forget and do not know. 

Theaet. Very good. 

Soc. Now, when a person has this knowledge, and is considering 
something which he sees or hears, may not false opinion arise in the 
following manner? 

Theaet. In what manner? 

Soc. When he thinks what he knows, sometimes to be what he knows, 
and sometimes to be what he does not know. We were wrong before in 
denying the possibility of this. 

Theaet. And how would you amend the former statement? 

Soc. I should begin by making a list of the impossible cases which 
must be excluded. (1) No one can think one thing to be another when he 
does not perceive either of them, but has the memorial or seal of both 
of them in his mind; nor can any mistaking of one thing for another 
occur, when he only knows one, and does not know, and has no 
impression of the other; nor can he think that one thing which he does 
not know is another thing which he does not know, or that what he does 
not know is what he knows; nor (2) that one thing which he perceives 
is another thing which he perceives, or that something which he 
perceives is something which he does not perceive; or that something 
which he does not perceive is something else which he does not 
perceive; or that something which he does not perceive is something 
which he perceives; nor again (3) can he think that something which he 
knows and perceives, and of which he has the impression coinciding 
with sense, is something else which he knows and perceives, and of 
which he has the impression coinciding with sense; -this last case, 
if possible, is still more inconceivable than the others; nor (4) 
can he think that something which he knows and perceives, and of which 
he has the memorial coinciding with sense, is something else which 
he knows; nor so long as these agree, can he think that a thing 
which he knows and perceives is another thing which he perceives; or 
that a thing which he does not know and does not perceive, is the same 
as another thing which he does not know and does not perceive; -nor 
again, can he suppose that a thing which he does not know and does not 
perceive is the same as another thing which he does not know; or 
that a thing which he does not know and does not perceive is another 
thing which he does not perceive : -All these utterly and absolutely 
exclude the possibility of false opinion. The only cases, if any, 
which remain, are the following. 

Theaet. What are they? If you tell me, I may perhaps understand 
you better; but at present I am unable to follow you. 

Soc. A person may think that some things which he knows, or which he 
perceives and does not know, are some other things which he knows 
and perceives; or that some things which he knows and perceives, are 
other things which he knows and perceives. 

Theaet. I understand you less than ever now. 

Soc. Hear me once more, then: -I, knowing Theodorus, and 
remembering in my own mind what sort of person he is, and also what 
sort of person Theaetetus is, at one time see them, and at another 
time do not see them, and sometimes I touch them, and at another 
time not, or at one time I may hear them or perceive them in some 
other way, and at another time not perceive them, but still I remember 
them, and know them in my own mind. 

Theaet. Very true. 

Soc. Then, first of all, I want you to understand that a man may 
or may not perceive sensibly that which he knows. 

Theaet. True. 



Soc. And that which he does not know will sometimes not be perceived 
by him and sometimes will be perceived and only perceived? 

Theaet . That is also true. 

Soc. See whether you can follow me better now: Socrates can 
recognize Theodorus and Theaetetus, but he sees neither of them, nor 
does he perceive them in any other way; he cannot then by any 
possibility imagine in his own mind that Theaetetus is Theodorus. Am I 
not right? 

Theaet. You are quite right. 

Soc. Then that was the first case of which I spoke. 

Theaet. Yes. 

Soc. The second case was, that I, knowing one of you and not knowing 
the other, and perceiving neither, can never think him whom I know 
to be him whom I do not know. 

Theaet. True. 

Soc. In the third case, not knowing and not perceiving either of 
you, I cannot think that one of you whom I do not know is the other 
whom I do not know. I need not again go over the catalogue of excluded 
cases, in which I cannot form a false opinion about you and Theodorus, 
either when I know both or when I am in ignorance of both, or when I 
know one and not the other. And the same of perceiving: do you 
understand me? 

Theaet. I do. 

Soc. The only possibility of erroneous opinion is, when knowing 
you and Theodorus, and having on the waxen block the impression of 
both of you given as by a seal, but seeing you imperfectly and at a 
distance, I try to assign the right impression of memory to the 
right visual impression, and to fit this into its own print: if I 
succeed, recognition will take place; but if I fad and transpose them, 
putting the foot into the wrong shoe-that is to say, putting the 
vision of either of you on to the wrong impression, or if my mind, 
like the sight in a mirror, which is transferred from right to left, 
err by reason of some similar affection, then "heterodoxy" and false 
opinion ensues . 

Theaet. Yes, Socrates, you have described the nature of opinion with 
wonderful exactness. 

Soc. Or again, when I know both of you, and perceive as well as know 
one of you, but not the other, and my knowledge of him does not accord 
with perception-that was the case put by me just now which you did not 
understand 

Theaet. No, I did not. 

Soc. I meant to say, that when a person knows and perceives one of 
you, his knowledge coincides with his perception, he will never 
think him to be some other person, whom he knows and perceives, and 
the knowledge of whom coincides with his perception-f or that also 
was a case supposed. 

Theaet. True. 

Soc. But there was an omission of the further case, in which, as 
we now say, false opinion may arise, when knowing both, and seeing, or 
having some other sensible perception of both, I fail in holding the 
seal over against the corresponding sensation; like a bad archer, I 
miss and fall wide of the mark-and this is called falsehood. 

Theaet. Yes; it is rightly so called. 

Soc. When, therefore, perception is present to one of the seals or 
impressions but not to the other, and the mind fits the seal of the 
absent perception on the one which is present, in any case of this 
sort the mind is deceived; in a word, if our view is sound, there 
can be no error or deception about things which a man does not know 
and has never perceived, but only in things which are known and 
perceived; in these alone opinion turns and twists about, and 
becomes alternately true and false; -true when the seals and 
impressions of sense meet straight and opposite-false when they go 
awry and crooked. 

Theaet. And is not that, Socrates, nobly said? 



Soc. Nobly! yes; but wait a little and hear the explanation, and 
then you will say so with more reason; for to think truly is noble and 
to be deceived is base. 

Theaet . Undoubtedly. 

Soc. And the origin of truth and error is as follows : -When the wax 
in the soul of any one is deep and abundant, and smooth and 
perfectly tempered, then the impressions which pass through the senses 
and sink into the heart of the soul, as Homer says in a parable, 
meaning to indicate the likeness of the soul to wax (Kerh Kerhos); 
these, I say, being pure and clear, and having a sufficient depth of 
wax, are also lasting, and minds, such as these, easily learn and 
easily retain, and are not liable to confusion, but have true 
thoughts, for they have plenty of room, and having clear impressions 
of things, as we term them, quickly distribute them into their 
proper places on the block. And such men are called wise. Do you 
agree? 

Theaet. Entirely. 

Soc. But when the heart of any one is shaggy-a quality which the 
all-wise poet commends, or muddy and of impure wax, or very soft, or 
very hard, then there is a corresponding defect in the mind -the 
soft are good at learning, but apt to forget; and the hard are the 
reverse; the shaggy and rugged and gritty, or those who have an 
admixture of earth or dung in their composition, have the 
impressions indistinct, as also the hard, for there is no depth in 
them; and the soft too are indistinct, for their impressions are 
easily confused and effaced. Yet greater is the indistinctness when 
they are all jostled together in a little soul, which has no room. 
These are the natures which have false opinion; for when they see or 
hear or think of anything, they are slow in assigning the right 
objects to the right impressions-in their stupidity they confuse them, 
and are apt to see and hear and think amiss-and such men are said to 
be deceived in their knowledge of objects, and ignorant. 

Theaet. No man, Socrates, can say anything truer than that. 

Soc. Then now we may admit the existence of false opinion in us? 

Theaet. Certainly. 

Soc. And of true opinion also? 

Theaet. Yes. 

Soc. We have at length satisfactorily proven beyond a doubt there 
are these two sorts of opinion? 

Theaet. Undoubtedly. 

Soc. Alas, Theaetetus, what a tiresome creature is a man who is fond 
of talking! 

Theaet. What makes you say so? 

Soc. Because I am disheartened at my own stupidity and tiresome 
garrulity; for what other term will describe the habit of a man who is 
always arguing on all sides of a question; whose dulness cannot be 
convinced, and who will never leave off? 

Theaet. But what puts you out of heart? 

Soc. I am not only out of heart, but in positive despair; for I do 
not know what to answer if any one were to ask me : -0 Socrates, have 
you indeed discovered that false opinion arises neither in the 
comparison of perceptions with one another nor yet in thought, but 
in union of thought and perception? Yes, I shall say, with the 
complacence of one who thinks that he has made a noble discovery. 

Theaet. I see no reason why we should be ashamed of our 
demonstration, Socrates. 

Soc. He will say: You mean to argue that the man whom we only 
think of and do not see, cannot be confused with the horse which we do 
not see or touch, but only think of and do not perceive? That I 
believe to be my meaning, I shall reply. 

Theaet. Quite right. 

Soc. Well, then, he will say, according to that argument, the number 
eleven, which is only thought, never be mistaken for twelve, which 
is only thought: How would you answer him? 



Theaet . I should say that a mistake may very likely arise between 
the eleven or twelve which are seen or handled, but that no similar 
mistake can arise between the eleven and twelve which are in the mind. 

Soc. Well, but do you think that no one ever put before his own mind 
five and seven, -I do not mean five or seven men or horses, but five 
or seven in the abstract, which, as we say, are recorded on the 
waxen block, and in which false opinion is held to be impossible; 
did no man ever ask himself how many these numbers make when added 
together, and answer that they are eleven, while another thinks that 
they are twelve, or would all agree in thinking and saying that they 
are twelve? 

Theaet. Certainly not; many would think that they are eleven, and in 
the higher numbers the chance of error is greater still; for I 
assume you to be speaking of numbers in general. 

Soc. Exactly; and I want you to consider whether this does not imply 
that the twelve in the waxen block are supposed to be eleven? 

Theaet. Yes, that seems to be the case. 

Soc. Then do we not come back to the old difficulty? For he who 
makes such a mistake does think one thing which he knows to be another 
thing which he knows; but this, as we said, was impossible, and 
afforded an irresistible proof of the non-existence of false 
opinion, because otherwise the same person would inevitably know and 
not know the same thing at the same time. 

Theaet. Most true. 

Soc. Then false opinion cannot be explained as a confusion of 
thought and sense, for in that case we could not have been mistaken 
about pure conceptions of thought; and thus we are obliged to say, 
either that false opinion does not exist, or that a man may not know 
that which he knows; -which alternative do you prefer? 

Theaet. It is hard to determine, Socrates. 

Soc. And yet the argument will scarcely admit of both. But, as we 
are at our wits' end, suppose that we do a shameless thing? 

Theaet. What is it? 

Soc. Let us attempt to explain the verb "to know." 

Theaet. And why should that be shameless? 

Soc. You seem not to be aware that the whole of our discussion 
from the very beginning has been a search after knowledge, of which we 
are assumed not to know the nature. 

Theaet. Nay, but I am well aware. 

Soc. And is it not shameless when we do not know what knowledge 
is, to be explaining the verb "to know"? The truth is, Theaetetus, 
that we have long been infected with logical impurity. Thousands of 
times have we repeated the words "we know, " and "do not know, " and "we 
have or have not science or knowledge, " as if we could understand what 
we are saying to one another, so long as we remain ignorant about 
knowledge; and at this moment we are using the words "we 
understand, " "we are ignorant, " as though we could still employ them 
when deprived of knowledge or science. 

Theaet. But if you avoid these expressions, Socrates, how will you 
ever argue at all? 

Soc. I could not, being the man I am. The case would be different if 
I were a true hero of dialectic: and that such an one were 
present! for he would have told us to avoid the use of these terms; at 
the same time he would not have spared in you and me the faults 
which I have noted. But, seeing that we are no great wits, shall I 
venture to say what knowing is? for I think that the attempt may be 
worth making. 

Theaet. Then by all means venture, and no one shall find fault 
with you for using the forbidden terms. 

Soc. You have heard the common explanation of the verb "to know"? 

Theaet. I think so, but I do not remember it at the moment. 

Soc. They explain the word "to know" as meaning "to have knowledge." 

Theaet. True. 

Soc. I should like to make a slight change, and say "to possess" 



knowledge . 

Theaet . How do the two expressions differ? 

Soc. Perhaps there may be no difference; but still I should like you 
to hear my view, that you may help me to test it. 

Theaet. I will, if I can. 

Soc. I should distinguish "having" from "possessing": for example, a 
man may buy and keep under his control a garment which he does not 
wear; and then we should say, not that he has, but that he possesses 
the garment. 

Theaet. It would be the correct expression. 

Soc. Well, may not a man "possess" and yet not "have" knowledge in 
the sense of which I am speaking? As you may suppose a man to have 
caught wild birds -doves or any other birds-and to be keeping them 
in an aviary which he has constructed at home; we might say of him 
in one sense, that he always has them because he possesses them, might 
we not? 

Theaet. Yes. 

Soc. And yet, in another sense, he has none of them; but they are in 
his power, and he has got them under his hand in an enclosure of his 
own, and can take and have them whenever he likes; -he can catch any 
which he likes, and let the bird go again, and he may do so as often 
as he pleases . 

Theaet. True. 

Soc. Once more, then, as in what preceded we made a sort of waxen 
figment in the mind, so let us now suppose that in the mind of each 
man there is an aviary of all sorts of birds-some flocking together 
apart from the rest, others in small groups, others solitary, flying 
anywhere and everywhere. 

Theaet. Let us imagine such an aviary-and what is to follow? 

Soc. We may suppose that the birds are kinds of knowledge, and 
that when we were children, this receptacle was empty; whenever a 
man has gotten and detained in the enclosure a kind of knowledge, he 
may be said to have learned or discovered the thing which is the 
subject of the knowledge: and this is to know. 

Theaet. Granted. 

Soc. And further, when any one wishes to catch any of these 
knowledges or sciences, and having taken, to hold it, and again to let 
them go, how will he express himself ?-will he describe the 
"catching" of them and the original "possession" in the same words? 
I will make my meaning clearer by an example: -You admit that there 
is an art of arithmetic? 

Theaet. To be sure. 

Soc. Conceive this under the form of a hunt after the science of odd 
and even in general . 

Theaet. I follow. 

Soc. Having the use of the art, the arithmetician, if I am not 
mistaken, has the conceptions of number under his hand, and can 
transmit them to another. 

Theaet. Yes. 

Soc. And when transmitting them he may be said to teach them, and 
when receiving to learn them, and when receiving to learn them, and 
when having them in possession in the aforesaid aviary he may be 
said to know them. 

Theaet. Exactly. 

Soc. Attend to what follows: must not the perfect arithmetician know 
all numbers, for he has the science of all numbers in his mind? 

Theaet. True. 

Soc. And he can reckon abstract numbers in his head, or things about 
him which are numerable? 

Theaet. Of course he can. 

Soc. And to reckon is simply to consider how much such and such a 
number amounts to? 

Theaet. Very true. 

Soc. And so he appears to be searching into something which he 



knows, as if he did not know it, for we have already admitted that 
he knows all numbers ; -you have heard these perplexing questions 
raised? 

Theaet . I have. 

Soc. May we not pursue the image of the doves, and say that the 
chase after knowledge is of two kinds? one kind is prior to possession 
and for the sake of possession, and the other for the sake of taking 
and holding in the hands that which is possessed already. And thus, 
when a man has learned and known something long ago, he may resume and 
get hold of the knowledge which he has long possessed, but has not 
at hand in his mind. 

Theaet. True. 

Soc. That was my reason for asking how we ought to speak when an 
arithmetician sets about numbering, or a grammarian about reading? 
Shall we say, that although he knows, he comes back to himself to 
learn what he already knows? 

Theaet. It would be too absurd, Socrates. 

Soc. Shall we say then that he is going to read or number what he 
does not know, although we have admitted that he knows all letters and 
all numbers? 

Theaet. That, again, would be an absurdity. 

Soc. Then shall we say that about names we care nothing?-any one may 
twist and turn the words "knowing" and "learning" in any way which 
he likes, but since we have determined that the possession of 
knowledge is not the having or using it, we do assert that a man 
cannot not possess that which he possesses; and, therefore, in no case 
can a man not know that which he knows, but he may get a false opinion 
about it; for he may have the knowledge, not of this particular thing, 
but of some other; -when the various numbers and forms of knowledge are 
flying about in the aviary, and wishing to capture a certain sort of 
knowledge out of the general store, he takes the wrong one by mistake, 
that is to say, when he thought eleven to be twelve, he got hold of 
the ringdove which he had in his mind, when he wanted the pigeon. 

Theaet. A very rational explanation. 

Soc. But when he catches the one which he wants, then he is not 
deceived, and has an opinion of what is, and thus false and true 
opinion may exist, and the difficulties which were previously raised 
disappear. I dare say that you agree with me, do you not? 

Theaet. Yes. 

Soc. And so we are rid of the difficulty of a man's not knowing what 
he knows, for we are not driven to the inference that he does not 
possess what he possesses, whether he be or be not deceived. And yet I 
fear that a greater difficulty is looking in at the window. 

Theaet. What is it? 

Soc. How can the exchange of one knowledge for another ever become 
false opinion? 

Theaet. What do you mean? 

Soc. In the first place, how can a man who has the knowledge of 
anything be ignorant of that which he knows, not by reason of 
ignorance, but by reason of his own knowledge? And, again, is it not 
an extreme absurdity that he should suppose another thing to be 
this, and this to be another thing; -that, having knowledge present 
with him in his mind, he should still know nothing and be ignorant 
of all things?-you might as well argue that ignorance may make a man 
know, and blindness make him see, as that knowledge can make him 
ignorant . 

Theaet. Perhaps, Socrates, we may have been wrong in making only 
forms of knowledge our birds: whereas there ought to have been forms 
of ignorance as well, flying about together in the mind, and then he 
who sought to take one of them might sometimes catch a form of 
knowledge, and sometimes a form of ignorance; and thus he would have a 
false opinion from ignorance, but a true one from knowledge, about the 
same thing. 

Soc. I cannot help praising you, Theaetetus, and yet I must beg 



you to reconsider your words. Let us grant what you say-then, 
according to you, he who takes ignorance will have a false 
opinion-am I right? 

Theaet. Yes. 

Soc. He will certainly not think that he has a false opinion? 

Theaet. Of course not. 

Soc. He will think that his opinion is true, and he will fancy 
that he knows the things about which he has been deceived? 

Theaet. Certainly. 

Soc. Then he will think that he has captured knowledge and not 
ignorance? 

Theaet. Clearly. 

Soc. And thus, after going a long way round, we are once more face 
to face with our original difficulty. The hero of dialectic will 
retort upon us:-"0 my excellent friends, he will say, laughing, if a 
man knows the form of ignorance and the form of knowledge, can he 
think that one of them which he knows is the other which he knows? or, 
if he knows neither of them, can he think that the one which he 
knows not is another which he knows not? or, if he knows one and not 
the other, can he think the one which he knows to be the one which 
he does not know? or the one which he does not know to be the one 
which he knows? or will you tell me that there are other forms of 
knowledge which distinguish the right and wrong birds, and which the 
owner keeps in some other aviaries or graven on waxen blocks according 
to your foolish images, and which he may be said to know while he 
possesses them, even though he have them not at hand in his mind? 
And thus, in a perpetual circle, you will be compelled to go round and 
round, and you will make no progress." What are we to say in reply, 
Theaetetus? 

Theaet. Indeed, Socrates, I do not know what we are to say. 

Soc. Are not his reproaches just, and does not the argument truly 
show that we are wrong in seeking for false opinion until we know what 
knowledge is; that must be first ascertained; then, the nature of 
false opinion? 

Theaet. I cannot but agree with you, Socrates, so far as we have yet 
gone . 

Soc. Then, once more, what shall we say that knowledge is?-for we 
are not going to lose heart as yet. 

Theaet. Certainly, I shall not lose heart, if you do not. 

Soc. What definition will be most consistent with our former views? 

Theaet. I cannot think of any but our old one, Socrates. 

Soc. What was it? 

Theaet. Knowledge was said by us to be true opinion; and true 
opinion is surely unerring, and the results which follow from it are 
all noble and good. 

Soc. He who led the way into the river, Theaetetus, said "The 
experiment will show"; and perhaps if we go forward in the search, 
we may stumble upon the thing which we are looking for; but if we stay 
where we are, nothing will come to light. 

Theaet. Very true; let us go forward and try. 

Soc. The trail soon comes to an end, for a whole profession is 
against us . 

Theaet. How is that, and what profession do you mean? 

Soc. The profession of the great wise ones who are called orators 
and lawyers; for these persuade men by their art and make them think 
whatever they like, but they do not teach them. Do you imagine that 
there are any teachers in the world so clever as to be able to 
convince others of the truth about acts of robbery or violence, of 
which they were not eyewitnesses, while a little water is flowing in 
the clepsydra? 

Theaet. Certainly not, they can only persuade them. 

Soc. And would you not say that persuading them is making them 
have an opinion? 

Theaet. To be sure. 



Soc. When, therefore, judges are justly persuaded about matters 
which you can know only by seeing them, and not in any other way, 
and when thus judging of them from report they attain a true opinion 
about them, they judge without knowledge and yet are rightly 
persuaded, if they have judged well. 

Theaet . Certainly. 

Soc. And yet, my friend, if true opinion in law courts and 
knowledge are the same, the perfect judge could not have judged 
rightly without knowledge; and therefore I must infer that they are 
not the same. 

Theaet. That is a distinction, Socrates, which I have heard made 
by some one else, but I had forgotten it. He said that true opinion, 
combined with reason, was knowledge, but that the opinion which had no 
reason was out of the sphere of knowledge; and that things of which 
there is no rational account are not knowable-such was the singular 
expression which he used-and that things which have a reason or 
explanation are knowable. 

Soc. Excellent; but then, how did he distinguish between things 
which are and are not "knowable"? I wish that you would repeat to me 
what he said, and then I shall know whether you and I have heard the 
same tale. 

Theaet. I do not know whether I can recall it; but if another person 
would tell me, I think that I could follow him. 

Soc. Let me give you, then, a dream in return for a dream: -Methought 
that I too had a dream, and I heard in my dream that the primeval 
letters or elements out of which you and I and all other things are 
compounded, have no reason or explanation; you can only name them, but 
no predicate can be either affirmed or denied of them, for in the 
one case existence, in the other non-existence is already implied, 
neither of which must be added, if you mean to speak of this or that 
thing by itself alone. It should not be called itself, or that, or 
each, or alone, or this, or the like; for these go about everywhere 
and are applied to all things, but are distinct from them; whereas, if 
the first elements could be described, and had a definition of their 
own, they would be spoken of apart from all else. But none of these 
primeval elements can be defined; they can only be named, for they 
have nothing but a name, and the things which are compounded of 
them, as they are complex, are expressed by a combination of names, 
for the combination of names is the essence of a definition. Thus, 
then, the elements or letters are only objects of perception, and 
cannot be defined or known; but the syllables or combinations of 
them are known and expressed, and are apprehended by true opinion. 
When, therefore, any one forms the true opinion of anything without 
rational explanation, you may say that his mind is truly exercised, 
but has no knowledge; for he who cannot give and receive a reason 
for a thing, has no knowledge of that thing; but when he adds rational 
explanation, then, he is perfected in knowledge and may be all that 
I have been denying of him. Was that the form in which the dream 
appeared to you? 

Theaet. Precisely. 

Soc. And you allow and maintain that true opinion, combined with 
definition or rational explanation, is knowledge? 

Theaet. Exactly. 

Soc. Then may we assume, Theaetetus, that to-day, and in this casual 
manner, we have found a truth which in former times many wise men have 
grown old and have not found? 

Theaet. At any rate, Socrates, I am satisfied with the present 
statement . 

Soc. Which is probably correct-for how can there be knowledge 
apart from definition and true opinion? And yet there is one point 
in what has been said which does not quite satisfy me. 

Theaet. What was it? 

Soc. What might seem to be the most ingenious notion of all: -That 
the elements or letters are unknown, but the combination or 



syllables known. 

Theaet . And was that wrong? 

Soc. We shall soon know; for we have as hostages the instances which 
the author of the argument himself used. 

Theaet. What hostages? 

Soc. The letters, which are the elements; and the syllables, which 
are the combinations; -he reasoned, did he not, from the letters of the 
alphabet? 

Theaet. Yes; he did. 

Soc. Let us take them and put them to the test, or rather, test 
ourselves : -What was the way in which we learned letters? and, first of 
all, are we right in saying that syllables have a definition, but that 
letters have no definition? 

Theaet. I think so. 

Soc. I think so too; for, suppose that some one asks you to spell 
the first syllable of my name : -Theaetetus, he says, what is SO? 

Theaet. I should reply S and 0. 

Soc. That is the definition which you would give of the syllable? 

Theaet. I should. 

Soc. I wish that you would give me a similar definition of the S. 

Theaet. But how can any one, Socrates, tell the elements of an 
element? I can only reply, that S is a consonant, a mere noise, as 
of the tongue hissing; B, and most other letters, again, are neither 
vowel-sounds nor noises. Thus letters may be most truly said to be 
undefined; for even the most distinct of them, which are the seven 
vowels, have a sound only, but no definition at all. 

Soc. Then, I suppose, my friend, that we have been so far right in 
our idea about knowledge? 

Theaet. Yes; I think that we have. 

Soc. Well, but have we been right in maintaining that the 
syllables can be known, but not the letters? 

Theaet. I think so. 

Soc. And do we mean by a syllable two letters, or if there are more, 
all of them, or a single idea which arises out of the combination of 
them? 

Theaet. I should say that we mean all the letters. 

Soc. Take the case of the two letters S and 0, which form the 
first syllable of my own name; must not he who knows the syllable, 
know both of them? 

Theaet. Certainly. 

Soc. He knows, that is, the S and 0? 

Theaet. Yes. 

Soc. But can he be ignorant of either singly and yet know both 
together? 

Theaet. Such a supposition, Socrates, is monstrous and unmeaning. 

Soc. But if he cannot know both without knowing each, then if he 
is ever to know the syllable, he must know the letters first; and thus 
the fine theory has again taken wings and departed. 

Theaet. Yes, with wonderful celerity. 

Soc. Yes, we did not keep watch properly. Perhaps we ought to have 
maintained that a syllable is not the letters, but rather one single 
idea framed out of them, having a separate form distinct from them. 

Theaet. Very true; and a more likely notion than the other. 

Soc. Take care; let us not be cowards and betray a great and 
imposing theory. 

Theaet. No, indeed. 

Soc. Let us assume then, as we now say, that the syllable is a 
simple form arising out of the several combinations of harmonious 
elements-of letters or of any other elements. 

Theaet. Very good. 

Soc. And it must have no parts. 

Theaet. Why? 

Soc. Because that which has parts must be a whole of all the 
parts. Or would you say that a whole, although formed out of the 



parts, is a single notion different from all the parts? 

Theaet . I should. 

Soc. And would you say that all and the whole are the same, or 
different? 

Theaet. I am not certain; but, as you like me to answer at once, I 
shall hazard the reply, that they are different. 

Soc. I approve of your readiness, Theaetetus, but I must take time 
to think whether I equally approve of your answer. 

Theaet. Yes; the answer is the point. 

Soc. According to this new view, the whole is supposed to differ 
from all? 

Theaet. Yes. 

Soc. Well, but is there any difference between all [in the plural] 
and the all [in the singular]? Take the case of number: -When we say 
one, two, three, four, five, six; or when we say twice three, or three 
times two, or four and two, or three and two and one, are we 
speaking of the same or of different numbers? 

Theaet. Of the same. 

Soc. That is of six? 

Theaet. Yes. 

Soc. And in each form of expression we spoke of all the six? 

Theaet. True. 

Soc. Again, in speaking of all [in the plural] is there not one 
thing which we express? 

Theaet. Of course there is. 

Soc. And that is six? 

Theaet. Yes. 

Soc. Then in predicating the word "all" of things measured by 
number, we predicate at the same time a singular and a plural? 

Theaet. Clearly we do. 

Soc. Again, the number of the acre and the acre are the same; are 
they not? 

Theaet. Yes. 

Soc. And the number of the stadium in like manner is the stadium? 

Theaet. Yes. 

Soc. And the army is the number of the army; and in all similar 
cases, the entire number of anything is the entire thing? 

Theaet. True. 

Soc. And the number of each is the parts of each? 

Theaet. Exactly. 

Soc. Then as many things as have parts are made up of parts? 

Theaet. Clearly. 

Soc. But all the parts are admitted to be the all, if the entire 
number is the all? 

Theaet. True. 

Soc. Then the whole is not made up of parts, for it would be the 
all, if consisting of all the parts? 

Theaet. That is the inference. 

Soc. But is a part a part of anything but the whole? 

Theaet. Yes, of the all. 

Soc. You make a valiant defence, Theaetetus. And yet is not the 
all that of which nothing is wanting? 

Theaet. Certainly. 

Soc. And is not a whole likewise that from which nothing is 
absent? but that from which anything is absent is neither a whole 
nor all; -if wanting in anything, both equally lose their entirety of 
nature . 

Theaet. I now think that there is no difference between a whole 
and all . 

Soc. But were we not saying that when a thing has parts, all the 
parts will be a whole and all? 

Theaet. Certainly. 

Soc. Then, as I was saying before, must not the alternative be 
that either the syllable is not the letters, and then the letters 



are not parts of the syllable, or that the syllable will be the same 
with the letters, and will therefore be equally known with them? 

Theaet . You are right. 

Soc. And, in order to avoid this, we suppose it to be different from 
them? 

Theaet. Yes. 

Soc. But if letters are not parts of syllables, can you tell me of 
any other parts of syllables, which are not letters? 

Theaet. No, indeed, Socrates; for if I admit the existence of 
parts in a syllable, it would be ridiculous in me to give up letters 
and seek for other parts . 

Soc. Quite true, Theaetetus, and therefore, according to our present 
view, a syllable must surely be some indivisible form? 

Theaet. True. 

Soc. But do you remember, my friend, that only a little while ago we 
admitted and approved the statement, that of the first elements out of 
which all other things are compounded there could be no definition, 
because each of them when taken by itself is uncompounded; nor can one 
rightly attribute to them the words "being" or "this," because they 
are alien and inappropriate words, and for this reason the letters 
or elements were indefinable and unknown? 

Theaet. I remember. 

Soc. And is not this also the reason why they are simple and 
indivisible? I can see no other. 

Theaet. No other reason can be given. 

Soc. Then is not the syllable in the same case as the elements or 
letters, if it has no parts and is one form? 

Theaet. To be sure. 

Soc. If, then, a syllable is a whole, and has many parts or letters, 
the letters as well as the syllable must be intelligible and 
expressible, since all the parts are acknowledged to be the same as 
the whole? 

Theaet. True. 

Soc. But if it be one and indivisible, then the syllables and the 
letters are alike undefined and unknown, and for the same reason? 

Theaet . I cannot deny that . 

Soc. We cannot, therefore, agree in the opinion of him who says that 
the syllable can be known and expressed, but not the letters. 

Theaet. Certainly not; if we may trust the argument. 

Soc. Well, but will you not be equally inclined to, disagree with 
him, when you remember your own experience in learning to read? 

Theaet. What experience? 

Soc. Why, that in learning you were kept trying to distinguish the 
separate letters both by the eye and by the car, in order that, when 
you heard them spoken or saw them written, you might not be confused 
by their position. 

Theaet. Very true. 

Soc. And is the education of the harp-player complete unless he 
can tell what string answers to a particular note; the notes, as every 
one would allow, are the elements or letters of music? 

Theaet. Exactly. 

Soc. Then, if we argue from the letters and syllables which we 
know to other simples and compounds, we shall say that the letters 
or simple elements as a class are much more certainly known than the 
syllables, and much more indispensable to a perfect knowledge of any 
subject; and if some one says that the syllable is known and the 
letter unknown, we shall consider that either intentionally or 
unintentionally he is talking nonsense? 

Theaet. Exactly. 

Soc. And there might be given other proofs of this belief, if I am 
not mistaken. But do not let us in looking for them lose sight of 
the question before us, which is the meaning of the statement, that 
right opinion with rational definition or explanation is the most 
perfect form of knowledge. 



Theaet . We must not. 

Soc. Well, and what is the meaning of the term "explanation"? I 
think that we have a choice of three meanings. 

Theaet. What are they? 

Soc. In the first place, the meaning may be, manifesting one's 
thought by the voice with verbs and nouns, imaging an opinion in the 
stream which flows from the lips, as in a mirror or water. Does not 
explanation appear to be of this nature? 

Theaet. Certainly; he who so manifests his thought, is said to 
explain himself. 

Soc. And every one who is not born deaf or dumb is able sooner or 
later to manifest what he thinks of anything; and if so, all those who 
have a right opinion about anything will also have right 
explanation; nor will right opinion be anywhere found to exist apart 
from knowledge. 

Theaet. True. 

Soc. Let us not, therefore, hastily charge him who gave this account 
of knowledge with uttering an unmeaning word; for perhaps he only 
intended to say, that when a person was asked what was the nature of 
anything, he should be able to answer his questioner by giving the 
elements of the thing. 

Theaet. As for example, Socrates...? 

Soc. As, for example, when Hesiod says that a waggon is made up of a 
hundred planks. Now, neither you nor I could describe all of them 
individually; but if any one asked what is a waggon, we should be 
content to answer, that a waggon consists of wheels, axle, body, rims, 
yoke . 

Theaet. Certainly. 

Soc. And our opponent will probably laugh at us, just as he would if 
we professed to be grammarians and to give a grammatical account of 
the name of Theaetetus, and yet could only tell the syllables and 
not the letters of your name-that would be true opinion, and not 
knowledge; for knowledge, as has been already remarked, is not 
attained until, combined with true opinion, there is an enumeration of 
the elements out of which is composed. 

Theaet. Yes. 

Soc. In the same general way, we might also have true opinion 
about a waggon; but he who can describe its essence by an 
enumeration of the hundred planks, adds rational explanation to true 
opinion, and instead of opinion has art and knowledge of the nature of 
a waggon, in that he attains to the whole through the elements. 

Theaet. And do. you not agree in that view, Socrates? 

Soc. If you do, my friend; but I want to know first, whether you 
admit the resolution of all things into their elements to be a 
rational explanation of them, and the consideration of them in 
syllables or larger combinations of them to be irrational-is this your 
view? 

Theaet. Precisely. 

Soc. Well, and do you conceive that a man has knowledge of any 
element who at one time affirms and at another time denies that 
clement of something, or thinks that, the same thing is composed of 
different elements at different times? 

Theaet. Assuredly not. 

Soc. And do you not remember that in your case and in of others this 
often occurred in the process of learning to read? 

Theaet. You mean that I mistook the letters and misspelt the 
syllables? 

Soc. Yes. 

Theaet. To be sure; I perfectly remember, and I am very far from 
supposing that they who are in this condition, have knowledge. 

Soc. When a person, at the time of learning writes the name of 
Theaetetus, and thinks that he ought to write and does write Th and e; 
but, again meaning to write the name of Theododorus, thinks that he 
ought to write and does write T and e-can we suppose that he knows the 



first syllables of your two names? 

Theaet . We have already admitted that such a one has not yet 
attained knowledge. 

Soc. And in like manner be may enumerate without knowing them the 
second and third and fourth syllables of your name? 

Theaet. He may. 

Soc. And in that case, when he knows the order of the letters and 
can write them out correctly, he has right opinion? 

Theaet. Clearly. 

Soc. But although we admit that he has right opinion, he will 
still be without knowledge? 

Theaet. Yes. 

Soc. And yet he will have explanations, as well as right opinion, 
for he knew the order of the letters when he wrote; and this we 
admit be explanation. 

Theaet. True. 

Soc. Then, my friend, there is such a thing as right opinion 
united with definition or explanation, which does not as yet attain to 
the exactness of knowledge. 

Theaet. It would seem so. 

Soc. And what we fancied to be a perfect definition of knowledge 
is a dream only. But perhaps we had better not say so as yet, for were 
there not three explanations of knowledge, one of which must, as we 
said, be adopted by him who maintains knowledge to be true opinion 
combined with rational explanation? And very likely there may be found 
some one who will not prefer this but the third. 

Theaet. You are quite right; there is still one remaining. The first 
was the image or expression of the mind in speech; the second, which 
has just been mentioned, is a way of reaching the whole by an 
enumeration of the elements. But what is; the third definition? 

Soc. There is, further, the popular notion of telling the mark or 
sign of difference which distinguishes the thing in question from 
all others . 

Theaet. Can you give me any example of such a definition? 

Soc. As, for example, in the case of the sun, I think that you would 
be contented with the statement that the sun is, the brightest of 
the heavenly bodies which revolve about the earth. 

Theaet. Certainly. 

Soc. Understand why: -the reason is, as I was just now saying, that 
if you get at the difference and distinguishing characteristic of each 
thing, then, as many persons affirm, you will get at the definition or 
explanation of it; but while you lay hold only of the common and not 
of the characteristic notion, you will only have the definition of 
those things to which this common quality belongs. 

Theaet. I understand you, and your account of definition is in my 
judgment correct. 

Soc. But he, who having right opinion about anything, can find out 
the difference which distinguishes it from other things will know that 
of which before he had only an opinion. 

Theaet. Yes; that is what we are maintaining. 

Soc. Nevertheless, Theaetetus, on a nearer view, I find myself quite 
disappointed; the picture, which at a distance was not so bad, has now 
become altogether unintelligible. 

Theaet. What do you mean? 

Soc. I will endeavour to explain: I will suppose myself to have true 
opinion of you, and if to this I add your definition, then I have 
knowledge, but if not, opinion only. 

Theaet. Yes. 

Soc. The definition was assumed to be the interpretation of your 
difference . 

Theaet. True. 

Soc. But when I had only opinion, I had no conception of your 
distinguishing characteristics. 

Theaet. I suppose not. 



Soc. Then I must have conceived of some general or common nature 
which no more belonged to you than to another. 

Theaet. True. 

Soc. Tell me, now-How in that case could I have formed a judgment of 
you any more than of any one else? Suppose that I imagine Theaetetus 
to be a man who has nose, eyes, and mouth, and every other member 
complete; how would that enable me to distinguish Theaetetus from 
Theodorus, or from some outer barbarian? 

Theaet. How could it? 

Soc. Or if I had further conceived of you, not only as having nose 
and eyes, but as having a snub nose and prominent eyes, should I 
have any more notion of you than of myself and others who resemble me? 

Theaet. Certainly not. 

Soc. Surely I can have no conception of Theaetetus until your 
snub-nosedness has left an impression on my mind different from the 
snub-nosedness of all others whom I have ever seen, and until your 
other peculiarities have a like distinctness; and so when I meet you 
tomorrow the right opinion will be re-called? 

Theaet. Most true. 

Soc. Then right opinion implies the perception of differences? 

Theaet. Clearly. 

Soc. What, then, shall we say of adding reason or explanation to 
right opinion? If the meaning is, that we should form an opinion of 
the way in which something differs from another thing, the proposal is 
ridiculous . 

Theaet. How so? 

Soc. We are supposed to acquire a right opinion of the differences 
which distinguish one thing from another when we have already a 
right opinion of them, and so we go round and round: -the revolution of 
the scytal, or pestle, or any other rotatory machine, in the same 
circles, is as nothing compared with such a requirement; and we may be 
truly described as the blind directing the blind; for to add those 
things which we already have, in order that we may learn what we 
already think, is like a soul utterly benighted. 

Theaet. Tell me; what were you going to say just now, when you asked 
the question? 

Soc. If, my boy, the argument, in speaking of adding the definition, 
had used the word to "know," and not merely "have an opinion" of the 
difference, this which is the most promising of all the definitions of 
knowledge would have come to a pretty end, for to know is surely to 
acquire knowledge. 

Theaet. True. 

Soc. And so, when the question is asked, What is knowledge? this 
fair argument will answer "Right opinion with knowledge, "-knowledge, 
that is, of difference, for this, as the said argument maintains, is 
adding the definition. 

Theaet. That seems to be true. 

Soc. But how utterly foolish, when we are asking what is 
knowledge, that the reply should only be, right opinion with knowledge 
of difference or of anything! And so, Theaetetus, knowledge is neither 
sensation nor true opinion, nor yet definition and explanation 
accompanying and added to true opinion? 

Theaet. I suppose not. 

Soc. And are you still in labour and travail, my dear friend, or 
have you brought all that you have to say about knowledge to the 
birth? 

Theaet. I am sure, Socrates, that you have elicited from me a good 
deal more than ever was in me. 

Soc. And does not my art show that you have brought forth wind, 
and that the offspring of your brain are not worth bringing up? 

Theaet. Very true. 

Soc. But if, Theaetetus, you should ever conceive afresh, you will 
be all the better for the present investigation, and if not, you 
will be soberer and humbler and gentler to other men, and will be 



too modest to fancy that you know what you do not know. These are 
the limits of my art; I can no further go, nor do I know aught of 
the things which great and famous men know or have known in this or 
former ages. The office of a midwife I, like my mother, have 
received from God; she delivered women, I deliver men; but they must 
be young and noble and fair. 

And now I have to go to the porch of the King Archon, where I am 
to meet Meletus and his indictment. To-morrow morning, Theodorus, I 
shall hope to see you again at this place. 

-THE END-