SOC. Then since they must be in motion, and since absence of motion must be impossible for anything, all things are always in all kinds of motion.

THEO. Necessarily.

SOC. Then just examine this point of their doctrine. Did we not find that they say that heat or whiteness or anything you please arises in some such way as this, namely that each of these moves simultaneously with perception between the active and the passive element, and the passive becomes percipient, but not perception, and the active becomes, not a quality, but endowed with a quality? Now perhaps quality seems an extraordinary word, and you do not understand it when used with general application, so let me give particular examples. For the active element becomes neither heat nor whiteness, but hot or white, and other things in the same way; you probably remember that this was what we said earlier in our discourse, that nothing is in itself unvaryingly one, neither the active nor the passive, but from the union of the two with one another the perceptions and the perceived give birth and the latter become things endowed with some quality while the former become percipient.

THEO. I remember, of course.

SOC. Let us then pay no attention to other matters, whether they teach one thing or another; but let us attend strictly to this only, which is the object of our discussion. Let us ask them, Are all things, according to your doctrine, in motion and flux? Is that so?

THEO. Yes.

SOC. Have they then both kinds of motion which we distinguished? Are they moving in space and also undergoing alteration?

THEO. Of course; that is, if they are to be in perfect motion.

SOC. Then if they moved only in space, but did not undergo alteration, we could perhaps say what qualities belong to those moving things which are in flux, could we not?

THEO. That is right.

SOC. Because I have a reverential fear of examining in a flippant manner Melissus and the others who teach that the universe is one and motionless, and because I reverence still more one man, Parmenides. Parmenides seems to me to be, in Homer’s words, one to be venerated and also awful. Il. 3.172;Od. 8.22; xiv. 234 For I met him when I was very young and he was very old, and he appeared to me to possess an absolutely noble depth of mind. So I am afraid we may not understand his words and may be still farther from understanding what he meant by them; but my chief fear is that the question with which we started, about the nature of knowledge, may fail to be investigated, because of the disorderly crowd of arguments which will burst in upon us if we let them in; especially as the argument we are now proposing is of vast extent, and would not receive its deserts if we treated it as a side issue, and if we treat it as it deserves, it will take so long as to do away with the discussion about knowledge. Neither of these things ought to happen, but we ought to try by the science of midwifery to deliver Theaetetus of the thoughts about knowledge with which he is pregnant.

THEO. Yes, if that is your opinion, we ought to do so.

SOC. Consider, then, Theaetetus, this further point about what has been said. Now you answered that perception is knowledge, did you not?

THEAET. Yes.

SOC. If, then, anyone should ask you, By what does a man see white and black colors and by what does he hear high and low tones? you would, I fancy, say, By his eyes and ears.

THEAET. Yes, I should.

SOC. And will you also be ready to agree that it is impossible to perceive through one sense what you perceive through another; for instance, to perceive through sight what you perceive through hearing, or through hearing what you perceive through sight?

THEAET. Of course I shall.

SOC. Then if you have any thought about both of these together, you would not have perception about both together either through one organ or through the other.

THEAET. No.

SOC. Now in regard to sound and color, you have, in the first place, this thought about both of them, that they both exist?

THEAET. Certainly.

SOC. And that each is different from the other and the same as itself?

SOC. As the talk which the soul has with itself about any subjects which it considers. You must not suppose that I know this that I am declaring to you. But the soul, as the image presents itself to me, when it thinks, is merely conversing with itself, asking itself questions and answering, affirming and denying. When it has arrived at a decision, whether slowly or with a sudden bound, and is at last agreed, and is not in doubt, we call that its opinion; and so I define forming opinion as talking and opinion as talk which has been held, not with someone else, nor yet aloud, but in silence with oneself. How do you define it?

THEAET. In the same way.

SOC. Then whenever a man has an opinion that one thing is another, he says to himself, we believe, that the one thing is the other.

SOC. I will not tell you until I have tried to consider the matter in every way. For I should be ashamed of us, if, in our perplexity, we were forced to make such admissions as those to which I refer. But if we find the object of our quest, and are set free from perplexity, then, and not before, we will speak of others as involved in those absurdities, and we ourselves shall stand free from ridicule. But if we find no escape from our perplexity, we shall, I fancy, become low-spirited, like seasick people, and shall allow the argument to trample on us and do to us anything it pleases. Hear, then, by what means I still see a prospect of success for our quest.

THEAET. Do speak.

SOC. I shall deny that we were right when we agreed that it is impossible for a man to have opinion that the things he does not know are the things which he knows, and thus to be deceived. But there is a way in which it is possible.

THEAET. Do you mean what I myself suspected when we made the statement to which you refer, that sometimes I, though I know Socrates, saw at a distance someone whom I did not know, and thought it was Socrates whom I do know? In such a case false opinion does arise.

SOC. But did not we reject that, because it resulted in our knowing and not knowing the things which we know?

THEAET. Certainly we did.

SOC. Let us, then, not make that assumption, but another; perhaps it will turn out well for us, perhaps the opposite. But we are in such straits that we must turn every argument round and test it from all sides. Now see if this is sensible: Can a man who did not know a thing at one time learn it later?

THEAET. To be sure he can.

SOC. Again, then, can he learn one thing after another?

THEAET. Why not?

SOC. Please assume, then, for the sake of argument, that there is in our souls a block of wax, in one case larger, in another smaller, in one case the wax is purer, in another more impure and harder, in some cases softer, and in some of proper quality.

THEAET. I assume all that.

SOC. Let us, then, say that this is the gift of Memory, the mother of the Muses, and that whenever we wish to remember anything we see or hear or think of in our own minds, we hold this wax under the perceptions and thoughts and imprint them upon it, just as we make impressions from seal rings; and whatever is imprinted we remember and know as long as its image lasts, but whatever is rubbed out or cannot be imprinted we forget and do not know.

THEAET. Let us assume that.

SOC. Now take a man who knows the things which he sees and hears, and is considering some one of them; observe whether he may not gain a false opinion in the following manner.

THEAET. In what manner?

SOC. By thinking that the things which he knows are sometimes things which he knows and sometimes things which he does not know. For we were wrong before in agreeing that this is impossible.

THEAET. What do you say about it now?

SOC. See if you follow me better now. If Socrates knows Theodorus and Theaetetus, but sees neither of them and has no other perception of them, he never could have the opinion within himself that Theaetetus is Theodorus. Am I right or wrong?

THEAET. You are right.

SOC. Now that was the first of the cases of which I spoke.

THEAET. Yes, it was.

SOC. The second is this: knowing one of you and not knowing the other, and not perceiving either of you, I never could think that the one whom I know is the one whom I do not know.

THEAET. Right.

SOC. And this is the third case: not knowing and not perceiving either of you, I could not think that he whom I do not know is someone else whom I do not know. And imagine that you have heard all the other cases again in succession, in which I could never form false opinions about you and Theodorus, either when I know or do not know both of you, or when I know one and not the other; and the same is true if we say perceive instead of know. Do you follow me?

THEAET. I follow you.

SOC. Then the possibility of forming false opinion remains in the following case: when, for example, knowing you and Theodorus, and having on that block of wax the imprint of both of you, as if you were signet-rings, but seeing you both at a distance and indistinctly, I hasten to assign the proper imprint of each of you to the proper vision, and to make it fit, as it were, its own footprint, with the purpose of causing recognition; Aesch. Lib. 197 ff. makes Electra recognize the presence of her brother Orestes by the likeness of his footprints to her own. but I may fail in this by interchanging them, and put the vision of one upon the imprint of the other, as people put a shoe on the wrong foot; or, again, I may be affected as the sight is affected when we use a mirror and the sight as it flows makes a change from right to left, and thus make a mistake; it is in such cases, then, that interchanged opinion occurs and the forming of false opinion arises.

THEAET. I think it does, Socrates. You describe what happens to opinion marvelously well.

SOC. There is still the further case, when, knowing both of you, I perceive one in addition to knowing him, but do not perceive the other, and the knowledge which I have of that other is not in accord with my perception. This is the case I described in this way before, and at that time you did not understand me.

THEAET. No, I did not.

SOC. This is what I meant, that if anyone knows and perceives one of you, and has knowledge of him which accords with the perception, he will never think that he is someone else whom he knows and perceives and his knowledge of whom accords with the perception. That was the case, was it not?

THEAET. Yes.

SOC. But we omitted, I believe, the case of which I am speaking now—the case in which we say the false opinion arises: when a man knows both and sees both (or has some other perception of them), but fails to hold the two imprints each under its proper perception; like a bad archer he shoots beside the mark and misses it; and it is just this which is called error or deception.

THEAET. And properly so.

SOC. Now when perception is present to one of the imprints but not to the other, and the mind applies the imprint of the absent perception to the perception which is present, the mind is deceived in every such instance. In a word, if our present view is sound, false opinion or deception seems to be impossible in relation to things which one does not know and has never perceived; but it is precisely in relation to things which we know and perceive that opinion turns and twists, becoming false and true—true when it puts the proper imprints and seals fairly and squarely upon one another, and false when it applies them sideways and aslant.

THEAET. Well, then, Socrates, is that view not a good one?

SO.So also do those whose wax is hard; for the imprints lack depth. And imprints in soft wax are also indistinct, because they melt together and quickly become blurred; but if besides all this they are crowded upon one another through lack of room, in some mean little soul, they are still more indistinct. So all these men are likely to have false opinions. For when they see or hear or think of anything, they cannot quickly assign things to the right imprints, but are slow about it, and because they assign them wrongly they usually see and hear and think amiss. These men, in turn, are accordingly said to be deceived about realities and ignorant.

SOC. Well, then, do you think that anyone ever considered in his own mind five and seven,— I do not mean by setting before his eyes seven men and five men and considering them, or anything of that sort, but seven and five in the abstract, which we say are imprints in the block of wax, and in regard to which we deny the possibility of forming false opinions—taking these by themselves, do you imagine that anybody in the world has ever considered them, talking to himself and asking himself what their sum is, and that one person has said and thought eleven, and another twelve, or do all say and think that it is twelve?

THEAET. No, by Zeus; many say eleven, and if you take a larger number for consideration, there is greater likelihood of error. For I suppose you are speaking of any number rather than of these only.

SOC. You are right in supposing so; and consider whether in that instance the abstract twelve in the block of wax is not itself imagined to be eleven.

THEAET. It seems so.

SOC. Have we not, then, come back again to the beginning of our talk? For the man who is affected in this way imagines that one thing which he knows is another thing which he knows. This we said was impossible, and by this very argument we were forcing false opinion out of existence, that the same man might not be forced to know and not know the same things at the same time.

THEAET. Very true.

SOC. Then we must show that forming false opinion is something or other different from the interchange of thought and perception. For if it were that, we should never be deceived in abstract thoughts. But as the case now stands, either there is no false opinion or it is possible for a man not to know that which he knows. Which alternative will you choose?

THEAET. There is no possible choice, Socrates.

SOC. But shall we say that he is going to read or count that which he does not know, when we have granted that he knows all letters and all numbers?

SOC. It is not easy, Theaetetus, to refrain from praising you. However, examine your suggestion once more. Let it be as you say: the man who catches the ignorance will, you say, have false opinion. Is that it?

THEAET. Yes.

SOC. But surely he will not also think that he has false opinion.

THEAET. Certainly not.

SOC. No, but true opinion, and will have the attitude of knowing that about which he is deceived.

THEAET. Of course.

SOC. Hence he will fancy that he has caught, and has, knowledge, not ignorance.

THEAET. Evidently.

SOC. Then, after our long wanderings, we have come round again to our first difficulty. For the real reasoner will laugh and say, Most excellent Sirs, does a man who knows both knowledge and ignorance think that one of them, which he knows, is another thing which he knows; or, knowing neither of them, is he of opinion that one, which he does not know, is another thing which he does not know; or, knowing one and not the other, does he think that the one he does not know is the one he knows; or that the one he knows is the one he does not know? Or will you go on and tell me that there are kinds of knowledge of the kinds of knowledge and of ignorance, and that he who possesses these kinds of knowledge and has enclosed them in some sort of other ridiculous aviaries or waxen figments, knows them, so long as he possesses them, even if he has them not at hand in his soul? And in this fashion are you going to be compelled to trot about endlessly in the same circle without making any progress? What shall we reply to this, Theaetetus?

THEAET. By Zeus, Socrates, I don’t know what to say.

SOC. Then, my boy, is the argument right in rebuking us and in pointing out that we were wrong to abandon knowledge and seek first for false opinion? It is impossible to know the latter until we have adequately comprehended the nature of knowledge.

THEAET. As the case now stands, Socrates, we cannot help thinking as you say.

SOC. To begin, then, at the beginning once more, what shall we say knowledge is? For surely we are not going to give it up yet, are we?

THEAET. Not by any means, unless, that is, you give it up.

SOC. Tell us, then, what definition will make us contradict ourselves least.

SOC. The man who was leading the way through the river, A man who was leading the way through a river was asked if the water was deep. He replied αὐτὸ δείξει, the event itself will show (i.e. you can find out by trying). The expression became proverbial. Theaetetus, said: The result itself will show; and so in this matter, if we go on with our search, perhaps the thing will turn up in our path and of itself reveal the object of our search; but if we stay still, we shall discover nothing.

THEAET. You are right; let us go on with our investigation.

SOC. Well, then, this at least calls for slight investigation; for you have a whole profession which declares that true opinion is not knowledge.

THEAET. How so? What profession is it?

SOC. The profession of those who are greatest in wisdom, who are called orators and lawyers; for they persuade men by the art which they possess, not teaching them, but making them have whatever opinion they like. Or do you think there are any teachers so clever as to be able, in the short time allowed by the water-clock, The length of speeches in the Athenian law courts was limited by a water-clock. satisfactorily to teach the judges the truth about what happened to people who have been robbed of their money or have suffered other acts of violence, when there were no eyewitnesses?

THEAET. I certainly do not think so; but I think they can persuade them.

SOC. And persuading them is making them have an opinion, is it not?

THEAET. Of course.

SOC. Then when judges are justly persuaded about matters which one can know only by having seen them and in no other way, in such a case, judging of them from hearsay, having acquired a true opinion of them, they have judged without knowledge, though they are rightly persuaded, if the judgement they have passed is correct, have they not?

THEAET. Certainly.

SOC. But, my friend, if true opinion and knowledge were the same thing in law courts, the best of judges could never have true opinion without knowledge; in fact, however, it appears that the two are different.

THEAET. Oh yes, I remember now, Socrates, having heard someone make the distinction, but I had forgotten it. He said that knowledge was true opinion accompanied by reason, but that unreasoning true opinion was outside of the sphere of knowledge; and matters of which there is not a rational explanation are unknowable—yes, that is what he called them—and those of which there is are knowable.

SOC. I am glad you mentioned that. But tell us how he distinguished between the knowable and the unknowable, that we may see whether the accounts that you and I have heard agree.

THEAET. But I do not know whether I can think it out; but if someone else were to make the statement of it, I think I could follow.

SOC. Listen then, while I relate it to you—a dream for a dream. I in turn used to imagine that I heard certain persons say that the primary elements of which we and all else are composed admit of no rational explanation;