Metaphysics
by Aristotle
Written circa 350 B.C.
Translated by W. D. Ross
Book III.5
Those who really feel the difficulties have been led to this
opinion by observation of the sensible world. (1) They think that
contradictories or contraries are true at the same time, because
they see contraries coming into existence out of the same thing. If,
then, that which is not cannot come to be, the thing must have existed
before as both contraries alike, as Anaxagoras says all is mixed in
all, and Democritus too; for he says the void and the full exist alike
in every part, and yet one of these is being, and the other non-being.
To those, then, whose belief rests on these grounds, we shall say that
in a sense they speak rightly and in a sense they err. For 'that which
is' has two meanings, so that in some sense a thing can come to be out
of that which is not, while in some sense it cannot, and the same
thing can at the same time be in being and not in being-but not in the
same respect. For the same thing can be potentially at the same time
two contraries, but it cannot actually. And again we shall ask them to
believe that among existing things there is also another kind of
substance to which neither movement nor destruction nor generation
at all belongs.
And (2) similarly some have inferred from observation of the
sensible world the truth of appearances. For they think that the truth
should not be determined by the large or small number of those who
hold a belief, and that the same thing is thought sweet by some when
they taste it, and bitter by others, so that if all were ill or all
were mad, and only two or three were well or sane, these would be
thought ill and mad, and not the others.