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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?
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 non-existence 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,' (In allusion to a book of Protagoras' which bore this title.) 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? (Compare Cratylus.)
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;—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 time 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 not be true that it never appears exactly the same to you, because you are never exactly the same?
THEAETETUS: The latter.
SOCRATES: And if that with which I compare myself in size, or which I apprehend by touch, were great or white or hot, it could not become different by mere contact with another unless it actually changed; nor again, if the comparing or apprehending subject were great or white or hot, could this, when unchanged from within, become changed by any approximation or affection of any other thing. The fact is that in our ordinary way of speaking we allow ourselves to be driven into most ridiculous and wonderful contradictions, as Protagoras and all who take his line of argument would remark.
