EU. No, by Zeus, at least not offhand. But I made notes at the time as soon as I reached home, then afterwards at my leisure, as I recalled things, I wrote them down, and whenever I went to Athens I used to ask Socrates about what I could not remember, and then I came here and made corrections; so that I have pretty much the whole talk written down.

TERP. That is true. I heard you say so before; and really I have been waiting about here all along intending to ask you to show it to me. What hinders us from reading it now? Certainly I need to rest, since I have come from the country.

THEO. Truly, Socrates, it is well worth while for me to talk and for you to hear about a splendid young fellow, one of your fellow-citizens, whom I have met. Now if he were handsome, I should be very much afraid to speak, lest someone should think I was in love with him. But the fact is—now don’t be angry with me—he is not handsome, but is like you in his snub nose and protruding eyes, only those features are less marked in him than in you. You see I speak fearlessly. But I assure you that among all the young men I have ever met—and I have had to do with a great many—I never yet found one of such marvelously fine qualities. He is quick to learn, beyond almost anyone else, yet exceptionally gentle, and moreover brave beyond any other; I should not have supposed such a combination existed, and I do not see it elsewhere. On the contrary, those who, like him, have quick, sharp minds and good memories, have usually also quick tempers; they dart off and are swept away, like ships without ballast; they are excitable rather than courageous; those, on the other hand, who are steadier are somewhat dull when brought face to face with learning, and are very forgetful. But this boy advances toward learning and investigation smoothly and surely and successfully, with perfect gentleness, like a stream of oil that flows without a sound, so that one marvels how he accomplishes all this at his age.

SOC. That is good news; but which of our citizens is his father?

THEO. I have heard the name, but do not remember it. However, it does not matter, for the youth is the middle one of those who are now coming toward us. He and those friends of his were anointing themselves in the outer course, The scene is evidently laid in a gymnasium; the young men have been exercising. and now they seem to have finished and to be coming here. See if you recognize him.

SOC. Yes, I do. He is the son of Euphronius of Sunium, who is a man of just the sort you describe, and of good repute in other respects; moreover he left a very large property. But the youth’s name I do not know.

SOC. But now, if we are concerned about the likeness of our faces, we must consider whether he who speaks is a painter, or not.

THEAET. I think we must.

SOC. Well, is Theodorus a painter?

THEAET. Not so far as I know.

SOC. Nor a geometrician, either?

THEAET. Oh yes, decidedly, Socrates.

SOC. And an astronomer, and an arithmetician, and a musician, and in general an educated man?

THEAET. I think so.

SOC. Well then, if he says, either in praise or blame, that we have some physical resemblance, it is not especially worth while to pay attention to him.

THEAET. Perhaps not.

SOC. Well, it is just this that I am in doubt about and cannot fully grasp by my own efforts—what knowledge really is. Can we tell that? What do you say? Who of us will speak first? And he who fails, and whoever fails in turn, shall go and sit down and be donkey, as the children say when they play ball; and whoever gets through without failing shall be our king and shall order us to answer any questions he pleases. Why are you silent? I hope, Theodorus, I am not rude, through my love of discussion and my eagerness to make us converse and show ourselves friends and ready to talk to one another.

THEAET. The numbers between these, such as three and five and all numbers which cannot be formed by multiplying equal factors, but only by multiplying a greater by a less or a less by a greater, and are therefore always contained in unequal sides, we represented by the shape of the oblong rectangle and called oblong numbers.

SOC. Very good; and what next?

THEAET. All the lines which form the four sides of the equilateral or square numbers we called lengths, and those which form the oblong numbers we called surds, because they are not commensurable with the others in length, but only in the areas of the planes which they have the power to form. And similarly in the case of solids. That is, cubes and cube roots.

SOC. Most excellent, my boys! I think Theodorus will not be found liable to an action for false witness.

THEAET. But really, Socrates, I cannot answer that question of yours about knowledge, as we answered the question about length and square roots. And yet you seem to me to want something of that kind. So Theodorus appears to be a false witness after all.

SOC. One of these was Aristeides, the son of Lysimachus, and there are very many more. When such men come back and beg me, as they do, with wonderful eagerness to let them join me again, the spiritual monitor that comes to me forbids me to associate with some of them, but allows me to converse with others, and these again make progress. Now those who associate with me are in this matter also like women in childbirth; they are in pain and are full of trouble night and day, much more than are the women; and my art can arouse this pain and cause it to cease. Well, that is what happens to them. But in some cases, Theaetetus, when they do not seem to me to be exactly pregnant, since I see that they have no need of me, I act with perfect goodwill as match-maker and, under God, I guess very successfully with whom they can associate profitably, and I have handed over many of them to Prodicus, and many to other wise and inspired men. Now I have said all this to you at such length, my dear boy, because I suspect that you, as you yourself believe, are in pain because you are pregnant with something within you. Apply, then, to me, remembering that I am the son of a midwife and have myself a midwife’s gifts, and do your best to answer the questions I ask as I ask them. And if, when I have examined any of the things you say, it should prove that I think it is a mere image and not real, and therefore quietly take it from you and throw it away, do not be angry as women are when they are deprived of their first offspring. For many, my dear friend, before this have got into such a state of mind towards me that they are actually ready to bite me, if I take some foolish notion away from them, and they do not believe that I do this in kindness, since they are far from knowing that no god is unkind to mortals, and that I do nothing of this sort from unkindness, either, and that it is quite out of the question for me to allow an imposture or to destroy the true. And so, Theaetetus, begin again and try to tell us what knowledge is. And never say that you are unable to do so; for if God wills it and gives you courage, you will be able.

THEAET. Well then, Socrates, since you are so urgent it would be disgraceful for anyone not to exert himself in every way to say what he can. I think, then, that he who knows anything perceives that which he knows, and, as it appears at present, knowledge is nothing else than perception.

SOC. Good! Excellent, my boy! That is the way one ought to speak out. But come now, let us examine your utterance together, and see whether it is a real offspring or a mere wind-egg. Perception, you say, is knowledge?

THEAET. Yes.

SOC. And, indeed, if I may venture to say so, it is not a bad description of knowledge that you have given, but one which Protagoras also used to give. Only, he has said the same thing in a different way. For he says somewhere that man is the measure of all things, of the existence of the things that are and the non-existence of the things that are not. You have read that, I suppose?

THEAET. Yes, I have read it often.

SOC. Well, is not this about what he means, that individual things are for me such as they appear to me, and for you in turn such as they appear to you —you and I being man?

THEAET. Yes, that is what he says.

SOC. Then who could still contend with such a great host, led by Homer as general, and not make himself ridiculous?

THEAET. It is not easy, Socrates.

SOC. No, Theaetetus, it is not. For the doctrine is amply proved by this, namely, that motion is the cause of that which passes for existence, that is, of becoming, whereas rest is the cause of non-existence and destruction; for warmth or fire, which, you know, is the parent and preserver of all other things, is itself the offspring of movement and friction, and these two are forms of motion. Or are not these the source of fire?

SOC. Let us stick close to the statement we made a moment ago, and assume that nothing exists by itself as invariably one: then it will be apparent that black or white or any other color whatsoever is the result of the impact of the eye upon the appropriate motion, and therefore that which we call color will be in each instance neither that which impinges nor that which is impinged upon, but something between, which has occurred, peculiar to each individual. Or would you maintain that each color appears to a dog, or any other animal you please, just as it does to you?

THEAET. No, by Zeus, I wouldn’t.

SOC. Well, does anything whatsoever appear the same to any other man as to you? Are you sure of this? Or are you not much more convinced that nothing appears the same even to you, because you yourself are never exactly the same?

THEAET. Yes, I am much more convinced of the last.

SOC. Then, if that with which I compare myself in size, or which I touch, were really large or white or hot, it would never have become different by coming in contact with something different, without itself changing; and if, on the other hand, that which did the comparing or the touching were really large or white or hot, it would not have become different when something different approached it or was affected in some way by it, without being affected in some way itself. For nowadays, my friend, we find ourselves rather easily forced to make extraordinary and absurd statements, as Protagoras and everyone who undertakes to agree with him would say.

THEAET. What do you mean? What statements?

SOC. And so should I. But since this is the case, and we have plenty of time, shall we not quietly, without any impatience, but truly examining ourselves, consider again the nature of these appearances within us? And as we consider them, I shall say, I think, first, that nothing can ever become more or less in size or number, so long as it remains equal to itself. Is it not so?

THEAET. Yes.

SOC. And secondly, that anything to which nothing is added and from which nothing is subtracted, is neither increased nor diminished, but is always equal.

THEAET. Certainly.

THEAET. Truly, Socrates, those you speak of are very stubborn and perverse mortals.

SOC. So they are, my boy, quite without culture. But others are more clever, whose secret doctrines I am going to disclose to you. For them the beginning, upon which all the things we were just now speaking of depend, is the assumption that everything is real motion and that there is nothing besides this, but that there are two kinds of motion, each infinite in the number of its manifestations, and of these kinds one has an active, the other a passive force. From the union and friction of these two are born offspring, infinite in number, but always twins, the object of sense and the sense which is always born and brought forth together with the object of sense. Now we give the senses names like these: sight and hearing and smell, and the sense of cold and of heat, and pleasures and pains and desires and fears and so forth. Those that have names are very numerous, and those that are unnamed are innumerable. Now the class of objects of sense is akin to each of these; all sorts of colors are akin to all sorts of acts of vision, and in the same way sounds to acts of hearing, and the other objects of sense spring forth akin to the other senses. What does this tale mean for us, Theaetetus, with reference to what was said before? Do you see?

THEAET. Not quite, Socrates.

SOC. Just listen; perhaps we can finish the tale. It means, of course, that all these things are, as we were saying, in motion, and their motion has in it either swiftness or slowness. Now the slow element keeps its motion in the same place and directed towards such things as draw near it, and indeed it is in this way that it begets. But the things begotten in this way are quicker; for they move from one place to another, and their motion is naturally from one place to another. Now when the eye and some appropriate object which approaches beget whiteness and the corresponding perception—which could never have been produced by either of them going to anything else—then, while sight from the eye and whiteness from that which helps to produce the color are moving from one to the other, the eye becomes full of sight and so begins at that moment to see, and becomes, certainly not sight, but a seeing eye, and the object which joined in begetting the color is filled with whiteness and becomes in its turn, not whiteness, but white, whether it be a stick or a stone, or whatever it be the hue of which is so colored.

SOC. And all the rest—hard and hot and so forth—must be regarded in the same way: we must assume, we said before, that nothing exists in itself, but all things of all sorts arise out of motion by intercourse with each other; for it is, as they say, impossible to form a firm conception of the active or the passive element as being anything separately; for there is no active element until there is a union with the passive element, nor is there a passive element until there is a union with the active; and that which unites with one thing is active and appears again as passive when it comes in contact with something else. And so it results from all this, as we said in the beginning, that nothing exists as invariably one, itself by itself, but everything is always becoming in relation to something, and being should be altogether abolished, though we have often—and even just now—been compelled by custom and ignorance to use the word. But we ought not, the wise men say, to permit the use of something or somebody’s or mine or this or that or any other word that implies making things stand still, but in accordance with nature we should speak of things as becoming and being made and being destroyed and changing; for anyone who by his mode of speech makes things stand still is easily refuted. And we must use such expressions in relation both to particular objects and collective designations, among which are mankind and stone and the names of every animal and class. Do these doctrines seem pleasant to you, Theaetetus, and do you find their taste agreeable?

THEAET. I don’t know, Socrates; besides, I can’t tell about you, either, whether you are preaching them because you believe them or to test me.

SOC. You forget, my friend, that I myself know nothing about such things, and claim none of them as mine, but am incapable of bearing them and am merely acting as a midwife to you, and for that reason am uttering incantations and giving you a taste of each of the philosophical theories, until I may help to bring your own opinion to light. And when it is brought to light, I will examine it and see whether it is a mere wind-egg or a real offspring. So be brave and patient, and in good and manly fashion tell what you think in reply to my questions.

THEAET. Very well; ask them.

SOC. Then say once more whether the doctrine pleases you that nothing is, but is always becoming—good or beautiful or any of the other qualities we were just enumerating.

THEAET. Why, when I hear you telling about it as you did, it seems to me that it is wonderfully reasonable and ought to be accepted as you have presented it.

THEAET. What you say is very true, Socrates.

SOC. What argument is left, then, my boy, for the man who says that perception is knowledge and that in each case the things which appear are to the one to whom they appear?

THEAET. I hesitate to say, Socrates, that I have no reply to make, because you scolded me just now when I said that. But really I cannot dispute that those who are insane or dreaming have false opinions, when some of them think they are gods and others fancy in their sleep that they have wings and are flying.

SOC. Don’t you remember, either, the similar dispute about these errors, especially about sleeping and waking?

THEAET. What dispute?

SOC. One which I fancy you have often heard. The question is asked, what proof you could give if anyone should ask us now, at the present moment, whether we are asleep and our thoughts are a dream, or whether we are awake and talking with each other in a waking condition.

THEAET. Really, Socrates, I don’t see what proof can be given; for there is an exact correspondence in all particulars, as between the strophe and antistrophe of a choral song. Take, for instance, the conversation we have just had: there is nothing to prevent us from imagining in our sleep also that we are carrying on this conversation with each other, and when in a dream we imagine that we are relating dreams, the likeness between the one talk and the other is remarkable.

SOC. So you see it is not hard to dispute the point, since it is even open to dispute whether we are awake or in a dream. Now since the time during which we are asleep is equal to that during which we are awake, in each state our spirit contends that the semblances that appear to it at any time are certainly true, so that for half the time we say that this is true, and for half the time the other, and we maintain each with equal confidence.

THEAET. Certainly.

SOC. And may not, then, the same be said about insanity and the other diseases, except that the time is not equal?

THEAET. Yes.

SOC. Well, then, shall truth be determined by the length or shortness of time?

THEAET. It is impossible for it to be the same in anything, either in quality or in any other respect whatsoever, when it is wholly other.

SOC. Must we not, then, necessarily agree that such a thing is also unlike?

THEAET. It seems so to me.

SOC. Then if anything happens to become like or unlike anything—either itself or anything else—we shall say that when it becomes like it becomes the same, and when it becomes unlike it becomes other?

THEAET. We must.

SOC. Well, we said before, did we not, that the active elements were many—infinite in fact—and likewise the passive elements?

THEAET. Yes.

SOC. And furthermore, that any given element, by uniting at different times with different partners, will beget, not the same, but other results?

SOC. Then I shall never have this perception of any other thing; for a perception of another thing is another perception, and makes the percipient different and other: nor can that which acts on me ever by union with another produce the same result or become the same in kind; for by producing another result from another passive element it will become different in kind.

THEAET. That is true.

SOC. And neither shall I, furthermore, ever again become the same as I am, nor will that ever become the same as it is.

THEAET. No.

SOC. And yet, when I become percipient, I must necessarily become percipient of something, for it is impossible to become percipient and perceive nothing; and that which is perceived must become so to someone, when it becomes sweet or bitter or the like; for to become sweet, but sweet to no one, is impossible.

THEAET. Perfectly true.

SOC. The result, then, I think, is that we (the active and the passive elements) are or become, whichever is the case, in relation to one another, since we are bound to one another by the inevitable law of our being, but to nothing else, not even to ourselves. The result, then, is that we are bound to one another; and so if a man says anything is, he must say it is to or of or in relation to something, and similarly if he says it becomes; but he must not say it is or becomes absolutely, nor can he accept such a statement from anyone else. That is the meaning of the doctrine we have been describing.

THEAET. Yes, quite so, Socrates.

SOC. Then, since that which acts on me is to me and to me only, it is also the case that I perceive it, and I only?

THEAET. Of course.

SOC. Then to me my perception is true; for in each case it is always part of my being; and I am, as Protagoras says, the judge of the existence of the things that are to me and of the non-existence of those that are not to me.

THEAET. So it seems.

SOC. Well, we have at last managed to bring this forth, whatever it turns out to be; and now that it is born, we must in very truth perform the rite of running round with it in a circle— The rite called took place a few days after the birth of a child. After some ceremonies of purification the nurse, in the presence of the family, carried the infant rapidly about the family hearth, thereby introducing him, as it were, to the family and the family deities. At this time the father decided whether to bring up the child or to expose it. Sometimes, perhaps, the child was named on this occasion. In the evening relatives assembled for a feast at which shell-fish were eaten. the circle of our argument—and see whether it may not turn out to be after all not worth rearing, but only a wind-egg, an imposture. But, perhaps, you think that any offspring of yours ought to be cared for and not put away; or will you bear to see it examined and not get angry if it is taken away from you, though it is your first-born?

THEO. Theaetetus will bear it, Socrates, for he is not at all ill-tempered. But for heaven’s sake, Socrates, tell me, is all this wrong after all?

SOC. You are truly fond of argument, Theodorus, and a very good fellow to think that I am a sort of bag full of arguments and can easily pull one out and say that after all the other one was wrong; but you do not understand what is going on: none of the arguments comes from me, but always from him who is talking with me. I myself know nothing, except just a little, enough to extract an argument from another man who is wise and to receive it fairly. And now I will try to extract this thought from Theaetetus, but not to say anything myself.

THEO. That is the better way, Socrates; do as you say.

SOC. Do you know, then, Theodorus, what amazes me in your friend Protagoras?