Theaetetus

Plato

Plato in Twelve Volumes, Vol. 7 translated by Harold North Fowler. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1921.

EU. Just in from the country, Terpsion, or did you come some time ago?

TERP. Quite a while ago; and I was looking for you in the market-place and wondering that I could not find you.

EU. Well, you see, I was not in the city.

TERP. Where then?

EU. As I was going down to the harbor I met Theaetetus being carried to Athens from the camp at Corinth.

TERP. Alive or dead?

EU. Just barely alive; for he is suffering severely from wounds, and, worse than that, he has been taken with the sickness that has broken out in the army.

TERP. You mean the dysentery?

EU. Yes.

TERP. What a man he is who you say is in danger!

EU. A noble man, Terpsion, and indeed just now I heard some people praising him highly for his conduct in the battle.

TERP. That is not at all strange; it would have been much more remarkable if he had not so conducted himself. But why did he not stop here in Megara?

EU. He was in a hurry to get home; for I begged and advised him to stop, but he would not. So I went along with him, and as I was coming back I thought of Socrates and wondered at his prophetic gift, especially in what he said about him. For I think he met him a little before his own death, when Theaetetus was a mere boy, and as a result of acquaintance and conversation with him, he greatly admired his qualities. When I went to Athens he related to me the conversation he had with him, which was well worth hearing, and he said he would surely become a notable man if he lived.

TERP. And he was right, apparently. But what was the talk? Could you relate it?

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.

EU. And I myself went with Theaetetus as far as Erineum, [*](Erineum was between Eleusis and Athens, near the Cephissus. Apparently Eucleides had walked some thirty miles.) so I also should not be sorry to take a rest. Come, let us go, and while we are resting, the boy shall read to us.

TERP. Very well.

EU. Here is the book, Terpsion. Now this is the way I wrote the conversation: I did not represent Socrates relating it to me, as he did, but conversing with those with whom he told me he conversed. And he told me they were the geometrician Theodorus and Theaetetus. Now in order that the explanatory words between the speeches might not be annoying in the written account, such as and I said or and I remarked, whenever Socrates spoke, or he agreed or he did not agree, in the case of the interlocutor, I omitted all that sort of thing and represented Socrates himself as talking with them.

TERP. That is quite fitting, Eucleides.

EU. Come, boy, take the book and read.

SOC. If I cared more for Cyrene and its affairs, Theodorus, I should ask you about things there and about the people, whether any of the young men there are devoting themselves to geometry or any other form of philosophy; but as it is, since I care less for those people than for the people here, I am more eager to know which of our own young men are likely to gain reputation. These are the things I myself investigate, so far as I can, and about which I question those others with whom I see that the young men like to associate. Now a great many of them come to you, and rightly, for you deserve it on account of your geometry, not to speak of other reasons. So if you have met with any young man who is worth mentioning, I should like to hear about him.

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.

THEO. Theaetetus is his name, Socrates; but I believe the property was squandered by trustees. Nevertheless, Socrates, he is remarkably liberal with his money, too.

SOC. It is a noble man that you describe. Now please tell him to come here and sit by us.

THEO. I will. Theaetetus, come here to Socrates.

SOC. Yes, do so, Theaetetus, that I may look at myself and see what sort of a face I have; for Theodorus says it is like yours. Now if we each had a lyre, and he said we had tuned them to the same key, should we take his word for it without more ado, or should we inquire first whether he who said it was a musician?

THEAET. We should inquire.

SOC. Then if we found that he was a musician, we should believe him, but if not, we should refuse to take his word?

THEAET. Yes.

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. But what if he should praise the soul of one of us for virtue and wisdom? Is it not worth while for the one who hears to examine eagerly the one who is praised, and for that one to exhibit his qualities with eagerness?

THEAET. Certainly, Socrates.

SOC. Then, my dear Theaetetus, this is just the time for you to exhibit your qualities and for me to examine them; for I assure you that Theodorus, though he has praised many foreigners and citizens to me, never praised anyone as he praised you just now.

THEAET. A good idea, Socrates; but make sure that he was not speaking in jest.

SOC. That is not Theodorus’s way. But do not seek to draw back from your agreement on the pretext that he is jesting, or he will be forced to testify under oath; for certainly no one will accuse him of perjury. Come, be courageous and hold to the agreement.

THEAET. I suppose I must, if you say so.

SOC. Now tell me; I suppose you learn some geometry from Theodorus?

THEAET. Yes.

SOC. And astronomy and harmony and arithmetic?

THEAET. I try hard to do so.

SOC. And so do I, my boy, from him and from any others who I think know anything about these things. But nevertheless, although in other respects I get on fairly well in them, yet I am in doubt about one little matter, which should be investigated with your help and that of these others. Tell me, is not learning growing wiser about that which one learns?

THEAET. Of course.

SOC. And the wise, I suppose, are wise by wisdom.

THEAET. Yes.

SOC. And does this differ at all from knowledge?

THEAET. Does what differ?

SOC. Wisdom. Or are not people wise in that of which they have knowledge?

THEAET. Of course.

SOC. Then knowledge and wisdom are the same thing?

THEAET. Yes.

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.

THEO. That sort of thing would not be at all rude, Socrates; but tell one of the youths to answer your questions; for I am unused to such conversation and, moreover, I am not of an age to accustom myself to it. But that would be fitting for these young men, and they would improve much more than I; for the fact is, youth admits of improvement in every way. Come, question Theaetetus as you began to do, and do not let him off.

SOC. Well, Theaetetus, you hear what Theodorus says, and I think you will not wish to disobey him, nor is it right for a young person to disobey a wise man when he gives instructions about such matters. Come, speak up well and nobly. What do you think knowledge is?

THEAET. Well, Socrates, I must, since you bid me. For, if I make a mistake, you are sure to set me right.

SOC. Certainly, if we can.

THEAET. Well then, I think the things one might learn from Theodorus are knowledge—geometry and all the things you spoke of just now—and also cobblery and the other craftsmen’s arts; each and all of these are nothing else but knowledge.

SOC. You are noble and generous, my friend, for when you are asked for one thing you give many, and a variety of things instead of a simple answer.

THEAET. What do you mean by that, Socrates?

SOC. Nothing, perhaps; but I will tell you what I think I mean. When you say cobblery you speak of nothing else than the art of making shoes, do you?

THEAET. Nothing else.

SOC. And when you say carpentry? Do you mean anything else than the art of making wooden furnishings?

THEAET. Nothing else by that, either.

SOC. Then in both cases you define that to which each form of knowledge belongs?

THEAET. Yes.

SOC. But the question, Theaetetus, was not to what knowledge belongs, nor how many the forms of knowledge are; for we did not wish to number them, but to find out what knowledge itself really is. Or is there nothing in what I say?

THEAET. Nay, you are quite right.

SOC. Take this example. If anyone should ask us about some common everyday thing, for instance, what clay is, and we should reply that it is the potters’ clay and the oven makers’ clay and the brickmakers’ clay, should we not be ridiculous?

THEAET. Perhaps.

SOC. Yes in the first place for assuming that the questioner can understand from our answer what clay is, when we say clay, no matter whether we add the image-makers’ or any other craftsmen’s. Or does anyone, do you think, understand the name of anything when he does not know what the thing is?

THEAET. By no means.

SOC. Then he does not understand knowledge of shoes if he does not know knowledge.

THEAET. No.

SOC. Then he who is ignorant of knowledge does not understand cobblery or any other art.

THEAET. That is true.

SOC. Then it is a ridiculous answer to the question what is knowledge? when we give the name of some art; for we give in our answer something that knowledge belongs to, when that was not what we were asked.

THEAET. So it seems.

SOC. Secondly, when we might have given a short, everyday answer, we go an interminable distance round; for instance, in the question about clay, the everyday, simple thing would be to say clay is earth mixed with moisture without regard to whose clay it is.

THEAET. It seems easy just now, Socrates, as you put it; but you are probably asking the kind of thing that came up among us lately when your namesake, Socrates here, and I were talking together.

SOC. What kind of thing was that, Theaetetus?

THEAET. Theodorus here was drawing some figures for us in illustration of roots, showing that squares containing three square feet and five square feet are not commensurable in length with the unit of the foot, and so, selecting each one in its turn up to the square containing seventeen square feet and at that he stopped. Now it occurred to us, since the number of roots appeared to be infinite, to try to collect them under one name, by which we could henceforth call all the roots. [*](A simple form of the first statement would be: the square roots of 3, 5, etc., are irrational numbers or surds. The word δύναμις has not the meaning which we give in English to power, namely the result of multiplication of a number by itself, but that which we give to root, i.e. the number which, when multiplied by itself, produces a given result. Here Theaetetus is speaking of square roots only; and when he speaks of numbers and of equal factors he evidently thinks of rational whole numbers only, not of irrational numbers or fractions. He is not giving an exhaustive presentation of his investigation, but merely a brief sketch of it to illustrate his understanding of the purpose of Socrates. Toward the end of this sketch the word δύναμις is limited to the square roots of oblong numbers, i.e. to surds. The modern reader may be somewhat confused because Theaetetus seems to speak of arithmetical facts in geometrical terms. (Cf. Gow, Short History of Greek Mathematics, p. 85.))

SOC. And did you find such a name?

THEAET. I think we did. But see if you agree.

SOC. Speak on.

THEAET. We divided all number into two classes. The one, the numbers which can be formed by multiplying equal factors, we represented by the shape of the square and called square or equilateral numbers.

SOC. Well done!

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. Nonsense! If he were praising your running and said he had never met any young man who was so good a runner, and then you were beaten in a race by a full grown man who held the record, do you think his praise would be any less truthful?

THEAET. Why, no.

SOC. And do you think that the discovery of knowledge, as I was just now saying, is a small matter and not a task for the very ablest men?

THEAET. By Zeus, I think it is a task for the very ablest.

SOC. Then you must have confidence in yourself, and believe that Theodorus is right, and try earnestly in every way to gain an understanding of the nature of knowledge as well as of other things.

THEAET. If it is a question of earnestness, Socrates, the truth will come to light.

SOC. Well then—for you pointed out the way admirably just now—take your answer about the roots as a model, and just as you embraced them all in one class, though they were many, try to designate the many forms of knowledge by one definition.

THEAET. But I assure you, Socrates, I have often tried to work that out, when I heard reports of the questions that you asked, but I can neither persuade myself that I have any satisfactory answer, nor can I find anyone else who gives the kind of answer you insist upon; and yet, on the other hand, I cannot get rid of a feeling of concern about the matter.

SOC. Yes, you are suffering the pangs of labor, Theaetetus, because you are not empty, but pregnant.

THEAET. I do not know, Socrates; I merely tell you what I feel.

SOC. Have you then not heard, you absurd boy, that I am the son of a noble and burly midwife, Phaenarete?

THEAET. Yes, I have heard that.

SOC. And have you also heard that I practise the same art?

THEAET. No, never.

SOC. But I assure you it is true; only do not tell on me to the others; for it is not known that I possess this art. But other people, since they do not know it, do not say this of me, but say that I am a most eccentric person and drive men to distraction. Have you heard that also?

THEAET. Yes, I have.

SOC. Shall I tell you the reason then?

THEAET. Oh yes, do.

SOC. Just take into consideration the whole business of the midwives, and you will understand more easily what I mean. For you know, I suppose, that no one of them attends other women while she is still capable of conceiving and bearing but only those do so who have become too old to bear.

THEAET. Yes, certainly.

SOC. They say the cause of this is Artemis, because she, a childless goddess, has had childbirth allotted to her as her special province. Now it would seem she did not allow barren women to be midwives, because human nature is too weak to acquire an art which deals with matters of which it has no experience, but she gave the office to those who on account of age were not bearing children, honoring them for their likeness to herself.

THEAET. Very likely.

SOC. Is it not, then, also likely and even necessary, that midwives should know better than anyone else who are pregnant and who are not?

THEAET. Certainly.

SOC. And furthermore, the midwives, by means of drugs and incantations, are able to arouse the pangs of labor and, if they wish, to make them milder, and to cause those to bear who have difficulty in bearing; and they cause miscarriages if they think them desirable.

THEAET. That is true.

SOC. Well, have you noticed this also about them, that they are the most skillful of matchmakers, since they are very wise in knowing what union of man and woman will produce the best possible children?

THEAET. I do not know that at all.

SOC. But be assured that they are prouder of this than of their skill in cutting the umbilical cord. Just consider. Do you think the knowledge of what soil is best for each plant or seed belongs to the same art as the tending and harvesting of the fruits of the earth, or to another?

THEAET. To the same art.

SOC. And in the case of a woman, do you think, my friend, that there is one art for the sowing and another for the harvesting?

THEAET. It is not likely.

SOC. No; but because there is a wrongful and unscientific way of bringing men and women together, which is called pandering, the midwives, since they are women of dignity and worth, avoid matchmaking, through fear of falling under the charge of pandering. And yet the true midwife is the only proper match-maker.

THEAET. It seems so.

SOC. So great, then, is the importance of midwives; but their function is less important than mine. For women do not, like my patients, bring forth at one time real children and at another mere images which it is difficult to distinguish from the real. For if they did, the greatest and noblest part of the work of the midwives would be in distinguishing between the real and the false. Do you not think so?

THEAET. Yes, I do.

SOC. All that is true of their art of midwifery is true also of mine, but mine differs from theirs in being practised upon men, not women, and in tending their souls in labor, not their bodies. But the greatest thing about my art is this, that it can test in every way whether the mind of the young man is bringing forth a mere image, an imposture, or a real and genuine offspring. For I have this in common with the midwives: I am sterile in point of wisdom, and the reproach which has often been brought against me, that I question others but make no reply myself about anything, because I have no wisdom in me, is a true reproach; and the reason of it is this: the god compels me to act as midwife, but has never allowed me to bring forth. I am, then, not at all a wise person myself, nor have I any wise invention, the offspring born of my own soul; but those who associate with me, although at first some of them seem very ignorant, yet, as our acquaintance advances, all of them to whom the god is gracious make wonderful progress, not only in their own opinion, but in that of others as well. And it is clear that they do this, not because they have ever learned anything from me, but because they have found in themselves many fair things and have brought them forth. But the delivery is due to the god and me. And the proof of it is this: many before now, being ignorant of this fact and thinking that they were themselves the cause of their success, but despising me, have gone away from me sooner than they ought, whether of their own accord or because others persuaded them to do so. Then, after they have gone away, they have miscarried thenceforth on account of evil companionship, and the offspring which they had brought forth through my assistance they have reared so badly that they have lost it; they have considered impostures and images of more importance than the truth, and at last it was evident to themselves, as well as to others, that they were ignorant.

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. It is likely that a wise man is not talking nonsense; so let us follow after him. Is it not true that sometimes, when the same wind blows, one of us feels cold, and the other does not? or one feels slightly and the other exceedingly cold?

THEAET. Certainly.

SOC. Then in that case, shall we say that the wind is in itself cold or not cold or shall we accept Protagoras’s saying that it is cold for him who feels cold and not for him who does not?

THEAET. Apparently we shall accept that.

SOC. Then it also seems cold, or not, to each of the two?

THEAET. Yes.

SOC. But seems denotes perceiving?

THEAET. It does.

SOC. Then seeming and perception are the same thing in matters of warmth and everything of that sort. For as each person perceives things, such they are to each person.

THEAET. Apparently.

SOC. Perception, then, is always of that which exists and, since it is knowledge, cannot be false.

THEAET. So it seems.

SOC. By the Graces! I wonder if Protagoras, who was a very wise man, did not utter this dark saying to the common herd like ourselves, and tell the truth [*](An allusion to the title of Protagoras’s book, Truth.) in secret to his pupils.

THEAET. Why, Socrates, what do you mean by that?

SOC. I will tell you and it is not a bad description, either, that nothing is one and invariable, and you could not rightly ascribe any quality whatsoever to anything, but if you call it large it will also appear to be small, and light if you call it heavy, and everything else in the same way, since nothing whatever is one, either a particular thing or of a particular quality; but it is out of movement and motion and mixture with one another that all those things become which we wrongly say are—wrongly, because nothing ever is, but is always becoming. And on this subject all the philosophers, except Parmenides, may be marshalled in one line—Protagoras and Heracleitus and Empedocles—and the chief poets in the two kinds of poetry, Epicharmus, in comedy, and in tragedy, Homer, who, in the line

  1. 0ceanus the origin of the gods, and Tethys their mother,
Hom. Il. 14.201, 302has said that all things are the offspring of flow and motion; or don’t you think he means that?

THEAET. I think he does.

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?

THEAET. Yes, they are.

SOC. And furthermore, the animal kingdom is sprung from these same sources.

THEAET. Of course.

SOC. Well, then, is not the bodily habit destroyed by rest and idleness, and preserved, generally speaking, by gymnastic exercises and motions?

THEAET. Yes.

SOC. And what of the habit of the soul? Does not the soul acquire information and is it not preserved and made better through learning and practice, which are motions, whereas through rest, which is want of practice and of study, it learns nothing and forgets what it has learned?

THEAET. Certainly.

SOC. Then the good, both for the soul and for the body, is motion, and rest is the opposite?

THEAET. Apparently.

SOC. Now shall I go on and mention to you also windless air, calm sea, and all that sort of thing, and say that stillness causes decay and destruction and that the opposite brings preservation? And shall I add to this the all-compelling and crowning argument that Homer by the golden chain [*](Hom. Il. 8.18 ff. especially 26. In this passage Zeus declares that all the gods and goddesses together could not, with a golden chain, drag him from on high, but that if he pulled, he would drag them, with earth and sea, would then bind the chain round the summit of Olympus, and all the rest would hang aloft. This crowning argument is a reductio ad absurdum of the habit of using texts from Homer in support of all kinds of doctrine.) refers to nothing else than the sun, and means that so long as the heavens and the sun go round everything exists and is preserved, among both gods and men, but if the motion should stop, as if bound fast, everything would be destroyed and would, as the saying is, be turned upside down?

THEAET. Yes, Socrates, I think he means what you say he does.

SOC. Then, my friend, you must apply the doctrine in this way: first as concerns vision, the color that you call white is not to be taken as something separate outside of your eyes, nor yet as something inside of them; and you must not assign any place to it, for then it would at once be in a definite position and stationary and would have no part in the process of becoming.

THEAET. But what do you mean?

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. Take a little example and you will know all I have in mind. Given six dice, for instance, if you compare four with them, we say that they are more than the four, half as many again, but if you compare twelve with them, we say they are less, half as many; and any other statement would be inadmissible; or would you admit any other?

THEAET. Not I.

SOC. Well then, if Protagoras, or anyone else, ask you, Theaetetus, can anything become greater or more in any other way than by being increased? what reply will you make?

THEAET. If I am to say what I think, Socrates, with reference to the present question, I should say no, but if I consider the earlier question, I should say yes, for fear of contradicting myself.

SOC. Good, by Hera! Excellent, my friend! But apparently, if you answer yes it will be in the Euripidean spirit; for our tongue will be unconvinced, but not our mind. [*](Eur. Hipp. 612ἡ γλῶσσ’ ὀμώμοχ’, ἡ δὲ φρὴν ἀνώμοτος, my tongue has sworn, but my mind is unsworn.)

THEAET. True.

SOC. Well, if you and I were clever and wise and had found out everything about the mind, we should henceforth spend the rest of our time testing each other out of the fulness of our wisdom, rushing together like sophists in a sophistical combat, battering each other’s arguments with counter arguments. But, as it is, since we are ordinary people, we shall wish in the first place to look into the real essence of our thoughts and see whether they harmonize with one another or not at all.

THEAET. Certainly that is what I should like.

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.

SOC. And should we not say thirdly, that what was not previously could not afterwards be without becoming and having become?

THEAET. Yes, I agree.

SOC. These three assumptions contend with one another in our minds when we talk about the dice, or when we say that I, who do not, at my age, either increase in size or diminish, am in the course of a year first larger than you, who are young, and afterwards smaller, when nothing has been taken from my size, but you have grown. For I am, it seems, afterwards what I was not before, and I have not become so; for it is impossible to have become without becoming, and without losing anything of my size I could not become smaller. And there are countless myriads of such contradictions, if we are to accept these that I have mentioned. You follow me, I take it, Theaetetus, for I think you are not new at such things.

THEAET. By the gods, Socrates, I am lost in wonder when I think of all these things, and sometimes when I regard them it really makes my head swim.

SOC. Theodorus seems to be a pretty good guesser about your nature. For this feeling of wonder shows that you are a philosopher, since wonder is the only beginning of philosophy, and he who said that Iris was the child of Thaumas [*](Hes. Theog. 750 Iris is the messenger of heaven, and Plato interprets the name of her father as Wonder (θαῦμα).) made a good genealogy. But do you begin to understand why these things are so, according to the doctrine we attribute to Protagoras, or do you not as yet?

THEAET. Not yet, I think.

SOC. And will you be grateful to me if I help you to search out the hidden truth of the thought of a famous man or, I should say, of famous men?

THEAET. Of course I shall be grateful, very grateful.

SOC. Look round and see that none of the uninitiated is listening. The uninitiated are those who think nothing is except what they can grasp firmly with their hands, and who deny the existence of actions and generation and all that is invisible.

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.

SOC. Let us, then, not neglect a point in which it is defective. The defect is found in connection with dreams and diseases, including insanity, and everything else that is said to cause illusions of sight and hearing and the other senses. For of course you know that in all these the doctrine we were just presenting seems admittedly to be refuted, because in them we certainly have false perceptions, and it is by no means true that everything is to each man which appears to him; on the contrary, nothing is which appears.

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. That would be absurd in many ways.

SOC. But can you show clearly in any other way which of the two sets of opinions is true?

THEAET. I do not think I can.

SOC. Listen, then, while I tell you what would be said about them by those who maintain that what appears at any time is true for him to whom it appears. They begin, I imagine, by asking this question: Theaetetus, can that which is wholly other have in any way the same quality as its alternative? And we must not assume that the thing in question is partially the same and partially other, but wholly other.

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?

THEAET. Certainly.

SOC. Well, then, let us take me, or you, or anything else at hand, and apply the same principle—say Socrates in health and Socrates in illness. Shall we say the one is like the other, or unlike?

THEAET. When you say Socrates in illness do you mean to compare that Socrates as a whole with Socrates in health as a whole?

SOC. You understand perfectly; that is just what I mean.

THEAET. Unlike, I imagine.

SOC. And therefore other, inasmuch as unlike?

THEAET. Necessarily.

SOC. And you would say the same of Socrates asleep or in any of the other states we enumerated just now?

THEAET. Yes.

SOC. Then each of those elements which by the law of their nature act upon something else, will, when it gets hold of Socrates in health, find me one object to act upon, and when it gets hold of me in illness, another?

THEAET. How can it help it?

SOC. And so, in the two cases, that active element and I, who am the passive element, shall each produce a different object?

THEAET. Of course.

SOC. So, then, when I am in health and drink wine, it seems pleasant and sweet to me?

THEAET. Yes.

SOC. The reason is, in fact, that according to the principles we accepted a while ago, the active and passive elements produce sweetness and perception, both of which are simultaneously moving from one place to another, and the perception, which comes from the passive element, makes the tongue perceptive, and the sweetness, which comes from the wine and pervades it, passes over and makes the wine both to be and to seem sweet to the tongue that is in health.

THEAET. Certainly, such are the principles we accepted a while ago.

SOC. But when it gets hold of me in illness, in the first place, it really doesn’t get hold of the same man, does it? For he to whom it comes is certainly unlike.

THEAET. True.

SOC. Therefore the union of the Socrates who is ill and the draught of wine produces other results: in the tongue the sensation or perception of bitterness, and in the wine—a bitterness which is engendered there and passes over into the other; the wine is made, not bitterness, but bitter, and I am made, not perception, but perceptive.

THEAET. Certainly.

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. How, then, if I am an infallible judge and my mind never stumbles in regard to the things that are or that become, can I fail to know that which I perceive?

THEAET. You cannot possibly fail.

SOC. Therefore you were quite right in saying that knowledge is nothing else than perception, and there is complete identity between the doctrine of Homer and Heracleitus and all their followers—that all things are in motion, like streams—the doctrine of the great philosopher Protagoras that man is the measure of all things—and the doctrine of Theaetetus that, since these things are true, perception is knowledge. Eh, Theaetetus? Shall we say that this is, so to speak, your new-born child and the result of my midwifery? Or what shall we say?

THEAET. We must say that, Socrates.

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 amphidromiatook 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?

THEO. What is it?

SOC. In general I like his doctrine that what appears to each one is to him, but I am amazed by the beginning of his book. I don’t see why he does not say in the beginning of his Truth [*](Truthwas apparently the title, or part of the title, of Protagoras’s book.) that a pig or a dog-faced baboon or some still stranger creature of those that have sensations is the measure of all things. Then he might have begun to speak to us very imposingly and condescendingly, showing that while we were honoring him like a god for his wisdom, he was after all no better in intellect than any other man, or, for that matter, than a tadpole. What alternative is there, Theodorus? For if that opinion is true to each person which he acquires through sensation, and no one man can discern another’s condition better than he himself, and one man has no better right to investigate whether another’s opinion is true or false than he himself, but, as we have said several times, each man is to form his own opinions by himself, and these opinions are always right and true, why in the world, my friend, was Protagoras wise, so that he could rightly be thought worthy to be the teacher of other men and to be well paid, and why were we ignorant creatures and obliged to go to school to him, if each person is the measure of his own wisdom? Must we not believe that Protagoras was playing to the gallery in saying this? I say nothing of the ridicule that I and my science of midwifery deserve in that case,—and, I should say, the whole practice of dialectics, too. For would not the investigation of one another’s fancies and opinions, and the attempt to refute them, when each man’s must be right, be tedious and blatant folly, if the Truth of Protagoras is true and he was not jesting when he uttered his oracles from the shrine of his book?