we were just now speaking are supposed to depend: there is nothing but
motion, which has two forms, one active and the other passive, both in
endless number; and out of the union and friction of them there is
generated a progeny endless in number, having two forms, sense and the
object of sense, which are ever breaking forth and coming to the birth at
the same moment. The senses are variously named hearing, seeing, smelling;
there is the sense of heat, cold, pleasure, pain, desire, fear, and many
more which have names, as well as innumerable others which are without
them; each has its kindred object,--each variety of colour has a
corresponding variety of sight, and so with sound and hearing, and with the
rest of the senses and the objects akin to them. Do you see, Theaetetus,
the bearings of this tale on the preceding argument?

THEAETETUS: Indeed I do not.

SOCRATES: Then attend, and I will try to finish the story. The purport is
that all these things are in motion, as I was saying, and that this motion
is of two kinds, a slower and a quicker; and the slower elements have their
motions in the same place and with reference to things near them, and so
they beget; but what is begotten is swifter, for it is carried to fro, and
moves from place to place. Apply this to sense:--When the eye and the
appropriate object meet together and give birth to whiteness and the
sensation connatural with it, which could not have been given by either of
them going elsewhere, then, while the sight is flowing from the eye,
whiteness proceeds from the object which combines in producing the colour;
and so the eye is fulfilled with sight, and really sees, and becomes, not
sight, but a seeing eye; and the object which combined to form the colour
is fulfilled with whiteness, and becomes not whiteness but a white thing,
whether wood or stone or whatever the object may be which happens to be
coloured white. And this is true of all sensible objects, hard, warm, and