Theaetetus (153)

SOC. Then who could still contend with such a great host, led by Homer as general, and not make himself ridiculous?

THEAET. It is not easy, Socrates.

SOC. No, Theaetetus, it is not. For the doctrine is amply proved by this, namely, that motion is the cause of that which passes for existence, that is, of becoming, whereas rest is the cause of non-existence and destruction; for warmth or fire, which, you know, is the parent and preserver of all other things, is itself the offspring of movement and friction, and these two are forms of motion. Or are not these the source of fire?

THEAET. Yes, they are.

SOC. And furthermore, the animal kingdom is sprung from these same sources.

THEAET. Of course.

SOC. Well, then, is not the bodily habit destroyed by rest and idleness, and preserved, generally speaking, by gymnastic exercises and motions?

THEAET. Yes.

SOC. And what of the habit of the soul? Does not the soul acquire information and is it not preserved and made better through learning and practice, which are motions, whereas through rest, which is want of practice and of study, it learns nothing and forgets what it has learned?

THEAET. Certainly.

SOC. Then the good, both for the soul and for the body, is motion, and rest is the opposite?

THEAET. Apparently.

SOC. Now shall I go on and mention to you also windless air, calm sea, and all that sort of thing, and say that stillness causes decay and destruction and that the opposite brings preservation? And shall I add to this the all-compelling and crowning argument that Homer by the golden chain [*] refers to nothing else than the sun, and means that so long as the heavens and the sun go round everything exists and is preserved, among both gods and men, but if the motion should stop, as if bound fast, everything would be destroyed and would, as the saying is, be turned upside down?

THEAET. Yes, Socrates, I think he means what you say he does.

SOC. Then, my friend, you must apply the doctrine in this way: first as concerns vision, the color that you call white is not to be taken as something separate outside of your eyes, nor yet as something inside of them; and you must not assign any place to it, for then it would at once be in a definite position and stationary and would have no part in the process of becoming.

THEAET. But what do you mean?