Dialogues

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? Theaetetus Yes. Socrates 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 nonexistence of things that are not:⁠—You have read him? Theaetetus O yes, again and again. Socrates 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? Theaetetus Yes, he says so. Socrates 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? Theaetetus Quite true. Socrates 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? Theaetetus I suppose the last. Socrates Then it must appear so to each of them? Theaetetus Yes. Socrates And “appears to him” means the same as “he perceives.” Theaetetus True. Socrates 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? Theaetetus Yes. Socrates Then perception is always of existence, and being the same as knowledge is unerring? Theaetetus Clearly. Socrates 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,”305 in secret to his own disciples. Theaetetus What do you mean, Socrates? Socrates

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

“Ocean whence sprang the gods, and mother Tethys,”

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

Theaetetus I think so. Socrates And who could take up arms against such a great army having Homer for its general, and not appear ridiculous?306 Theaetetus Who indeed, Socrates? Socrates Yes, Theaetetus; and there are plenty of other proofs which will show that motion is the source of what is called being and becoming, and inactivity of not-being and destruction; for fire and warmth, which are supposed to be the parent and guardian of all other things, are born of movement and of friction, which is a kind of motion;307⁠—is not this the origin of fire? Theaetetus It is. Socrates And the race of animals is generated in the same way? Theaetetus Certainly. Socrates And is not the bodily habit spoiled by rest and idleness, but preserved for a long time308 by motion and exercise? Theaetetus True. Socrates And what of the mental habit? Is not the soul informed, and improved, and preserved by study and attention, which are motions; but when at rest, which in the soul only means want of attention and study, is uninformed, and speedily forgets whatever she has learned? Theaetetus True. Socrates Then motion is a good, and rest an evil, to the soul as well as to the body? Theaetetus Clearly. Socrates I may add, that breathless calm, stillness and the like waste and impair, while wind and storm preserve; and the palmary argument of all, which I strongly urge, is the golden chain in Homer, by which he means the sun, thereby indicating that so long as the sun and the heavens go round in their orbits, all things human and divine are and are preserved, but if they were chained up and their motions ceased, then all things would be destroyed, and, as the saying is, turned upside down. Theaetetus I believe, Socrates, that you have truly explained his meaning. Socrates Then now apply his doctrine to perception, my good friend, and first of all to vision; that which you call white colour is not in your eyes, and is not a distinct thing which exists out of them. And you must not assign any place to it: for if it had position it would be, and be at rest, and there would be no process of becoming. Theaetetus Then what is colour? Socrates Let us carry the principle which has just been affirmed, that nothing is self-existent, and then we shall see that white, black, and every other colour, arises out of the eye meeting the appropriate motion, and that what we call a colour is in each case neither the active nor the passive element, but something which passes between them, and is peculiar to each percipient; are you quite certain that the several colours appear to a dog or to any animal whatever as they appear to you? Theaetetus Far from it. Socrates Or that anything appears the same to you as to another man? Are you so profoundly convinced of this? Rather would it