Selections
from Plato's Theaetetus
Theaetetus defends Protagoras . . . [Theaetetus.] At any rate, Socrates, after such an exhortation I should be ashamed of not trying to do my best. Now he who knows perceives what he knows, and, as far as I can see at present, knowledge is perception. [Socrates] Bravely said, boy; that is the way in which you should express your opinion. And now, let us examine together this conception of yours, and see whether it is a true birth or a mere wind-egg. You say that knowledge is perception? [Theaet.] Yes. [Soc.] Well, you have delivered yourself of a very important doctrine about knowledge; it is indeed the opinion of Protagoras, who has another way of expressing it, Man, he says, is the measure of all things, of the existence of things that are, and of the non-existence of things that are not:--You have read him? [Theaet.] O yes, again and again. [Soc.] Does he not say that things are to you such as they appear to you, and to me such as they appear to me, and that you and I are men? [Theaet.] Yes, he says so. [Soc.] A wise man is not likely to talk nonsense. Let us try to understand him: the same wind is blowing, and yet one of us may be cold and the other not, or one may be slightly and the other very cold? [Theaet.] Quite true. [Soc.] Now is the wind, regarded not in relation to us but absolutely, cold or not; or are we to say, with Protagoras, that the wind is cold to him who is cold, and not to him who is not? [Theaet.] I suppose the last. [Soc.] Then it must appear so to each of them? [Theaet.] Yes. [Soc.] And "appears to him" means the same as "he perceives." [Theaet.] True. [Soc.] Then appearing and perceiving coincide in the case of hot and cold, and in similar instances; for things appear, or may be supposed to be, to each one such as he perceives them? [Theaet.] Yes. [Soc.] Then perception is always of what exists, and being the same as knowledge is unerring? [Theaet.] Clearly. [Soc.] In the name of the Graces, what an almighty wise man Protagoras must have been! He spoke these things in a parable to the common herd, like you and me, but told the truth, his Truth, in secret to his own disciples. Argument that perception is infallible [Soc.] There is no other object of which I shall ever have the same perception, for another object would give another perception, and would make the perception other and different; nor can that object which affects me, meeting another subject, produce the same perception, or become similar, for that too would produce another result from another subject, and become different. [Theaet.] True. [Soc.] Neither can by myself, have this sensation, nor the object by itself, this quality. [Theaet.] Certainly not. [Soc.] When I perceive I must become percipient of something--there can be no such thing as perceiving and perceiving nothing; the object, whether it become sweet, bitter, or of any other quality, must have relation to a person perceiving it; nothing can become sweet which is sweet to no one. [Theaet.] Certainly not. [Soc.] Then the inference is, that we [the agent and patient] are or become in relation to one another; there is a law which binds us to one another, but not to any other existence, nor each of us to himself; and therefore we can only be bound to one another; so that whether a person says that a thing is or becomes, he must say that it is or becomes to or of or in relation to something else; but he must not say or allow any one else to say that anything is or becomes absolutely: --such is our conclusion. [Theaet.] Very true, Socrates. [Soc.] Then, if that which acts upon me has relation to me and to no other, I and no other am the percipient of it? [Theaet.] Of course. [Soc.] Then my perception is true to me, being inseparable from my own being; and, as Protagoras says, to myself I am judge of what is and-what is not to me. [Theaet.] I suppose so. [Soc.] How then, if I never err, and if my mind never trips in the conception of being or becoming, can I fail of knowing that which I perceive? [Theaet.] You cannot. [Soc.] Then you were quite right in affirming that knowledge is only perception; and the meaning turns out to be the same, whether with Homer and Heracleitus, and all that company, you say that all is motion and flux [everything is always changing], or with the great sage Protagoras, that man is the measure of all things; or with Theaetetus, that, given these premises, perception is knowledge. Am I not right, Theaetetus, and is not this your newborn child, of which I have delivered you? What say you? [Theaet.] I cannot but agree, Socrates. Socrates raises objections [Soc.] Shall I tell you, Theodorus, what amazes me in your acquaintance Protagoras? [Theodorus] What is it? [Soc.] I am charmed with his doctrine, that what appears is to each one, but I wonder that he did not begin his book on Truth with a declaration that a pig or a dog-faced baboon, or some other yet stranger monster which has sensation, is the measure of all things; then he might have shown a magnificent contempt for our opinion of him by informing us at the outset that while we were reverencing him like a God for his wisdom he was no better than a tadpole, not to speak of his fellow-men-would not this have produced an over-powering effect? For if truth is only sensation, and no man can discern another's feelings better than he, or has any superior right to determine whether his opinion is true or false, but each, as we have several times repeated, is to himself the sole judge, and everything that he judges is true and right, why, my friend, should Protagoras be preferred to the place of wisdom and instruction, and deserve to be well paid, and we poor ignoramuses have to go to him, if each one is the measure of his own wisdom? Must he not be talking ad captandum in all this? I say nothing of the ridiculous predicament in which my own midwifery and the whole art of dialectic is placed; for the attempt to supervise or refute the notions or opinions of others would be a tedious and enormous piece of folly, if to each man his own are right; and this must be the case if Protagoras Truth [truth as defined by Protagoras] is the real truth, and the philosopher is not merely amusing himself by giving oracles out of the shrine of his book. Objection based on memory [Soc.] And the way will be to ask whether perception is or is not the same as knowledge; for this was the real point of our argument, and with a view to this we raised (did we not?) those many strange questions. [Theaet.] Certainly. [Soc.] Shall we say that we know every thing which we see and hear? for example, shall we say that not having learned, we do not hear the language of foreigners when they speak to us? or shall we say that we not only hear, but know what they are saying? Or again, if we see letters which we do not understand, shall we say that we do not see them? or shall we aver that, seeing them, we must know them? [Theaet.] We shall say, Socrates, that we know what we actually see and hear of them-that is to say, we see and know the figure and color of the letters, and we hear and know the elevation or depression of the sound of them; but we do not perceive by sight and hearing, or know, that which grammarians and interpreters teach about them. [Soc.] Wonderful, Theaetetus; and about this there shall be no dispute, because I want you to grow; but there is another difficulty coming, which you will also have to repulse. [Theaet.] What is it? [Soc.] Some one will say, Can a man who has ever known anything, and still has and preserves a memory of that which he knows, not know that which he remembers at the time when he remembers? I have, I fear, a tedious way of putting a simple question, which is only, whether a man who has learned, and remembers, can fail to know? [Theaet.] Impossible, Socrates; the supposition is monstrous. [Soc.] Am I talking nonsense, then? Think about it: is not seeing perceiving, and is not sight perception? [Theaet.] True. [Soc.] And if our recent definition holds, every man knows that which he has seen? [Theaet.] Yes. [Soc.] And you would admit that there is such a thing as memory? [Theaet.] Yes. [Soc.] And is memory of something or of nothing? [Theaet.] Of something, surely. [Soc.] Of things learned and perceived, that is? [Theaet.] Certainly. [Soc.] Often a man remembers that which he has seen? [Theaet.] True. [Soc.] And if he closed his eyes, would he forget? [Theaet.] Who, Socrates, would dare to say so? [Soc.] But we must say so, if the previous argument is to be maintained. [Theaet.] What do you mean? I am not quite sure that I understand you, though I have a strong suspicion that you are right. [Soc.] As thus: he who sees knows, as we say, that which he sees; for perception and sight and knowledge are admitted to be the same. [Theaet.] Certainly. [Soc.] But he who saw, and has knowledge of that which he saw, remembers, when he closes his eyes, that which he no longer sees. [Theaet.] True. [Soc.] And seeing is knowing, and therefore not-seeing is not-knowing? [Theaet.] Very true. [Soc.] Then the inference is, that a man may have attained the knowledge, of something, which he may remember and yet not know, because he does not see; and this has been affirmed by us to be a monstrous supposition. [Theaet.] Most true. [Soc.] Thus, then, the assertion that knowledge and perception are one, involves a manifest impossibility? [Theaet.] Yes. [Soc.] Then they must be distinguished? [Theaet.] I suppose that they must. Are there false opinions? [Soc.] In the first place, let us return to our old objection, and see whether we were right in blaming and taking offence at Protagoras on the ground that he assumed all to be equal and sufficient in wisdom; although he admitted that there was a better and worse, and that in respect of this, he said that some who excelled others were wise. [Theod.] Very true. [Soc.] Had Protagoras been living and answered for himself, instead of our answering for him, there would have been no need of our reviewing or reinforcing the argument. But as he is not here, and some one may accuse us of speaking without authority on his behalf, had we not better come to a clearer agreement about his meaning, for a great deal may be at stake? [Theod.] True. [Soc.] Then let us obtain, not through any third person, but from his own statement and in the fewest words possible, the basis of agreement. [Theod.] In what way? [Soc.] In this way:--His words are, "What seems to a man, is to him." [Theod.] Yes, so he says. [Soc.] And are not we, Protagoras, uttering the opinion of man, or rather of all mankind, when we say that every one thinks himself wiser than other men in some things, and their inferior in others? In the hour of danger, when they are in perils of war, or of the sea, or of sickness, do they not look up to their commanders as if they were gods, and expect salvation from them, only because they excel them in knowledge? Is not the world full of men in their several employments, who are looking for teachers and rulers of themselves and of the animals? And there are plenty who think that they are able to teach and able to govern. Now, in all this is implied that ignorance and wisdom exist among them. [Theod.] Certainly. [Soc.] And wisdom is assumed by them to be true thought, and ignorance to be false opinion. [Theod.] Exactly. [Soc.] How then, Protagoras, would you have us treat the argument? Shall we say that the opinions of men are always true, or sometimes true and sometimes false? In either case, the result is the same, and their opinions are not always true, but sometimes true and sometimes false. For tell me, Theodorus, do you suppose that you yourself, or any other follower of Protagoras, would contend that no one deems another ignorant or mistaken in his opinion? [Theod.] The thing is incredible, Socrates. [Soc.] And yet that absurdity is necessarily involved in the thesis which declares man to be the measure of all things. [Theod.] How so? [Soc.] Why, suppose that you determine in your own mind something to be true, and declare your opinion to me; let us assume, as he argues, that this is true to you. Now, if so, you must either say that the rest of us are not the judges of this opinion or judgment of yours, or that we judge you always to have a true opinion: But are there not thousands upon thousands who, whenever you form a judgment, take up arms against you and are of an opposite judgment and opinion, deeming that you judge falsely? [Theod.] Yes, indeed, Socrates, thousands and tens of thousands, as Homer says, who give me a world of trouble. [Soc.] Well, but are we to assert that what you think is true to you and false to the ten thousand others? [Theod.] No other inference seems to be possible. [Soc.] And how about Protagoras himself? If neither he nor the multitude thought, as indeed they do not think, that man is the measure of all things, must it not follow that the Truth of which Protagoras wrote would be true to no one? But if you suppose that he himself thought this, and that the multitude does not agree with him, you must begin by allowing that in whatever proportion the many are more than one, in that proportion his truth is more untrue than true. [Theod.] That would follow if the truth is supposed to vary with individual opinion. [Soc.] And the best of the joke is, that he acknowledges the truth of their opinion who believe his own opinion to be false; for he admits that the opinions of all men are true. [Theod.] Certainly. [Soc.] And does he not allow that his own opinion is false, if he admits that the opinion of those who think him false is true? [Theod.] Of course. [Soc.] Whereas the other side do not admit that they speak falsely? [Theod.] They do not. [Soc.] And he, as may be inferred from his writings, agrees that this opinion is also true. [Theod.] Clearly. [Soc.] Then all mankind, beginning with Protagoras, will contend, or rather, I should say that he will allow, when he concedes that his adversary has a true opinion -- Protagoras, I say, will himself allow that neither a dog nor any ordinary man is the measure of anything which he has not learned -- am I not right? [Theod.] Yes. [Soc.] And the Truth of Protagoras being doubted by all, will be true neither to himself to any one else? [Theod.] I think, Socrates, that we are running my old friend too hard. [Soc.] But do not know that we are going beyond the truth. Doubtless, as he is older, he may be expected to be wiser than we are. And if he could only just push his head out of the ground under which he rests, he would have overthrown both of us again and again, me for talking nonsense and you for assenting to me, and have been off and underground in a trice. But as he is not within call, we must make the best use of our own faculties, such as they are, and speak out what appears to us to be true. And one thing which no one will deny is, that there are great differences in the understandings of men. [Theod.] In that opinion I quite agree. [Soc.] And is there not most likely to be firm ground in the distinction which we were indicating on behalf of Protagoras, viz., that most things, and all immediate sensations, such as hot, dry, sweet, are only such as they appear; if however difference of opinion is to be allowed at all, surely we must allow it in respect of health or disease? for every woman, child, or living creature has not such a knowledge of what conduces to health as to enable them to cure themselves. [Theod.] I quite agree. Perception distinguished from knowledge [Soc.] Then now, Theaetetus, take another view of the subject: you answered that knowledge is perception? [Theaet.] I did. [Soc.] And if any one were to ask you: With what does a man see black and white colors? and with what does he hear high and low sounds?--you would say, if I am not mistaken, "With the eyes and with the ears." [Theaet.] I should. [Soc.] The free use of words and phrases, rather than minute precision, is generally characteristic of a liberal education, and the opposite is pedantic; but sometimes precision. is necessary, and I believe that the answer which you have just given is open to the charge of incorrectness; for which is more correct, to say that we see or hear with the eyes and with the ears, or through the eyes and through the ears. [Theaet.] I should say "through," Socrates, rather than "with." [Soc.] Yes, my boy, for no one can suppose that in each of us, as in a sort of Trojan horse, there are perched a number of unconnected senses, which do not all meet in some one nature, the mind, or whatever we please to call it, of which they are the instruments, and with which through them we perceive objects of sense. [Theaet.] I agree with you in that opinion. [Soc.] The reason why I am thus precise is, because I want to know whether, when we perceive black and white through the eyes, and again, other qualities through other organs, we do not perceive them with one and the same part of ourselves, and, if you were asked, you might refer all such perceptions to the body. Perhaps, however, I had better allow you to answer for yourself and not interfere; Tell me, then, are not the organs through which you perceive warm and hard and light and sweet, organs of the body? [Theaet.] Of the body, certainly. [Soc.] And you would admit that what you perceive through one faculty you cannot perceive through another; the objects of hearing, for example, cannot be perceived through sight, or the objects of sight through hearing? [Theaet.] Of course not. [Soc.] If you have any thought about both of them, this common perception cannot come to you, either through the one or the other organ? [Theaet.] It cannot. [Soc.] How about sounds and colors: in the first place you would admit that they both exist? [Theaet.] Yes. [Soc.] And that either of them is different from the other, and the same with itself? [Theaet.] Certainly. [Soc.] And that both are two and each of them one? [Theaet.] Yes. [Soc.] You can further observe whether they are like or unlike one another? [Theaet.] I dare say. [Soc.] But through what do you perceive all this about them? for neither through hearing nor yet through seeing can you apprehend that which they have in common. Let me give you an illustration of the point at issue:-If there were any meaning in asking whether sounds and colors are saline or not, you would be able to tell me what faculty would consider the question. It would not be sight or hearing, but some other. [Theaet.] Certainly; the faculty of taste. [Soc.] Very good; and now tell me what is the power which discerns, not only in sensible objects, but in all things, universal notions, such as those which are called being and not-being, and those others about which we were just asking-what organs will you assign for the perception of these notions? [Theaet.] You are thinking of being and not being, likeness and unlikeness, sameness and difference, and also of unity and other numbers which are applied to objects of sense; and you mean to ask, through what bodily organ the soul perceives odd and even numbers and other arithmetical conceptions. [Soc.] You follow me excellently, Theaetetus; that is precisely what I am asking. [Theaet.] Indeed, Socrates, I cannot answer; my only notion is, that these, unlike objects of sense, have no separate organ, but that the mind, by a power of her own, contemplates the universals in all things. . . . [Soc.] The simple sensations which reach the soul through the body are given at birth to men and animals by nature, but their reflections on the being and use of them are slowly and hardly gained, if they are ever gained, by education and long experience. [Theaet.] Assuredly. [Soc.] And can a man attain truth who fails of attaining being? [Theaet.] Impossible. [Soc.] And can he who misses the truth of anything, have a knowledge of that thing? [Theaet.] He cannot. [Soc.] Then knowledge does not consist in impressions of sense, but in reasoning about them; in that only, and not in the mere impression, truth and being can be attained? [Theaet.] Clearly. [Soc.] And would you call the two processes by the same name, when there is so great difference between them? [Theaet.] That would certainly not be right. [Soc.] And what name would you give to seeing, hearing, smelling, being cold and being hot? [Theaet.] I should call all of them perceiving-what other name could be given to them? [Soc.] Perception would be the collective name of them? [Theaet.] Certainly. [Soc.] Which, as we say, has no part in the attainment of truth any more of being? [Theaet.] Certainly not. [Soc.] And therefore not in. science or knowledge? [Theaet.] No. [Soc.] Then perception, Theaetetus, can never be the same as knowledge or science? [Theaet.] Clearly not, Socrates; and knowledge has now been most distinctly proved to be different from perception. . . .
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