SOCRATES: But now, since not even white continues to flow white, and whiteness itself is a flux or change which is passing into another colour, and is never to be caught standing still, can the name of any colour be rightly used at all? THEODORUS: How is that possible, Socrates, either in the case of this or of any other quality--if while we are using the word the object is escaping in the flux? SOCRATES: And what would you say of perceptions, such as sight and hearing, or any other kind of perception? Is there any stopping in the act of seeing and hearing? THEODORUS: Certainly not, if all things are in motion. SOCRATES: Then we must not speak of seeing any more than of not-seeing, nor of any other perception more than of any non-perception, if all things partake of every kind of motion? THEODORUS: Certainly not. SOCRATES: Yet perception is knowledge: so at least Theaetetus and I were saying. THEODORUS: Very true. SOCRATES: Then when we were asked what is knowledge, we no more answered what is knowledge than what is not knowledge? THEODORUS: I suppose not. SOCRATES: Here, then, is a fine result: we corrected our first answer in our eagerness to prove that nothing is at rest. But if nothing is at rest, every answer upon whatever subject is equally right: you may say that a thing is or is not thus; or, if you prefer, 'becomes' thus; and if we say 'becomes,' we shall not then hamper them with words expressive of rest. THEODORUS: Quite true. SOCRATES: Yes, Theodorus, except in saying 'thus' and 'not thus.' But you ought not to use the word 'thus,' for there is no motion in 'thus' or in 'not thus.' The maintainers of the doctrine have as yet no words in which to express themselves, and must get a new language. I know of no word that will suit them, except perhaps 'no how,' which is perfectly indefinite. THEODORUS: Yes, that is a manner of speaking in which they will be quite at home. SOCRATES: And so, Theodorus, we have got rid of your friend without assenting to his doctrine, that every man is the measure of all things--a wise man only is a measure; neither can we allow that knowledge is perception, certainly not on the hypothesis of a perpetual flux, unless perchance our friend Theaetetus is able to convince us that it is. THEODORUS: Very good, Socrates; and now that the argument about the doctrine of Protagoras has been completed, I am absolved from answering; for this was the agreement. THEAETETUS: Not, Theodorus, until you and Socrates have discussed the doctrine of those who say that all things are at rest, as you were proposing. THEODORUS: You, Theaetetus, who are a young rogue, must not instigate your elders to a breach of faith, but should prepare to answer Socrates in the remainder of the argument. THEAETETUS: Yes, if he wishes; but I would rather have heard about the doctrine of rest. THEODORUS: Invite Socrates to an argument--invite horsemen to the open plain; do but ask him, and he will answer.