still remains to be considered an objection which may be raised
about dreams and diseases, in particular about madness, and the
various illusions of hearing and sight, or of other senses. For you
know that in all these cases the esse-percipi theory appears to be
unmistakably refuted, since in dreams and illusions we certainly
have false perceptions; and far from saying that everything is which
appears, we should rather say that nothing is which appears.

  Theaet. Very true, Socrates.

  Soc. But then, my boy, how can any one contend that knowledge is
perception, or that to every man what appears is?

  Theaet. I am afraid to say, Socrates, that I have nothing to answer,
because you rebuked me just now for making this excuse; but I
certainly cannot undertake to argue that madmen or dreamers think
truly, when they imagine, some of them that they are gods, and
others that they can fly, and are flying in their sleep.

  Soc. Do you see another question which can be raised about these
phenomena, notably about dreaming and waking?

  Theaet. What question?

  Soc. A question which I think that you must often have heard persons
ask:-How can you determine whether at this moment we are sleeping, and
all our thoughts are a dream; or whether we are awake, and talking
to one another in the waking state?

  Theaet. Indeed, Socrates, I do not know how to prove the one any
more than the other, for in both cases the facts precisely
correspond;-and there is no difficulty in supposing that during all
this discussion we have been talking to one another in a dream; and
when in a dream we seem to be narrating dreams, the resemblance of the
two states is quite astonishing.

  Soc. You see, then, that a doubt about the reality of sense is
easily raised, since there may even be a doubt whether we are awake or
in a dream. And as our time is equally divided between sleeping and
waking, in either sphere of existence the soul contends that the
thoughts which are present to our minds at the time are true; and
during one half of our lives we affirm the truth of the one, and,
during the other half, of the other; and are equally confident of
both.

  Theaet. Most true.

  Soc. And may not the same be said of madness and other disorders?
the difference is only that the times are not equal.