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Theaet. What do you mean, Socrates?
Soc. 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
Theaet. I think so.
Soc. And who could take up arms against such a great army having
Homer for its general, and not appear ridiculous?
Theaet. Who indeed, Socrates?
Soc. 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 friction, which is a kind of
motion;-is not this the origin of fire?
Theaet. It is.
Soc. And the race of animals is generated in the same way?
Theaet. Certainly.
Soc. And is not the bodily habit spoiled by rest and idleness, but
preserved for a long time by motion and exercise?
Theaet. True.
Soc. 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?
Theaet. True.
Soc. Then motion is a good, and rest an evil, to the soul as well as
to the body?
Theaet. Clearly.
Soc. 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.
Theaet. I believe, Socrates, that you have truly explained his
Soc. 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.
Theaet. Then what is colour?
Soc. 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

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