CRITIAS: I do not think so.

SOCRATES: Then you consider that a man never wants any of these things for
the use of the body?

CRITIAS: Certainly not.

SOCRATES: And if they appear useless to this end, ought they not always to
appear useless? For we have already laid down the principle that things
cannot be at one time useful and at another time not, in the same process.

CRITIAS: But in that respect your argument and mine are the same. For you
maintain if they are useful to a certain end, they can never become
useless; whereas I say that in order to accomplish some results bad things
are needed, and good for others.

SOCRATES: But can a bad thing be used to carry out a good purpose?

CRITIAS: I should say not.

SOCRATES: And we call those actions good which a man does for the sake of
virtue?

CRITIAS: Yes.

SOCRATES: But can a man learn any kind of knowledge which is imparted by
word of mouth if he is wholly deprived of the sense of hearing?

CRITIAS: Certainly not, I think.