The Complete Aristotle (eng.)

and brain—having a distinct
existence, however, from one another, and no less real than the
infinite bodies, and each infinite: which is contrary to
reason.
    The statement that complete separation never will take place is
correct enough, though Anaxagoras is not fully aware of what it
means. For affections are indeed inseparable. If then colours and
states had entered into the mixture, and if separation took place,
there would be a ‘white’ or a ‘healthy’ which was nothing but white
or healthy, i.e. was not the predicate of a subject. So his ‘Mind’
is an absurd person aiming at the impossible, if he is supposed to
wish to separate them, and it is impossible to do so, both in
respect of quantity and of quality—of quantity, because there is no
minimum magnitude, and of quality, because affections are
inseparable.
    Nor is Anaxagoras right about the coming to be of homogeneous
bodies. It is true there is a sense in which clay is divided into
pieces of clay, but there is another in which it is not. Water and
air are, and are generated ‘from’ each other, but not in the way in
which bricks come ‘from’ a house and again a house ‘from’ bricks;
and it is better to assume a smaller and finite number of
principles, as Empedocles does.
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5
    All thinkers then agree in making the contraries principles,
both those who describe the All as one and unmoved (for even
Parmenides treats hot and cold as principles under the names of
fire and earth) and those too who use the rare and the dense. The
same is true of Democritus also, with his plenum and void, both of
which exist, be says, the one as being, the other as not-being.
Again he speaks of differences in position, shape, and order, and
these are genera of which the species are contraries, namely, of
position, above and below, before and behind; of shape, angular and
angle-less, straight and round.
    It is plain then that they all in one way or another identify
the contraries with the principles. And with good reason. For first
principles must not be derived from one another nor from anything
else, while everything has to be derived from them. But these
conditions are fulfilled by the primary contraries, which are not
derived from anything else because they are primary, nor from each
other because they are contraries.
    But we must see how this can be arrived at as a reasoned result,
as well as in the way just indicated.
    Our first presupposition must be that in nature nothing acts on,
or is acted on by, any other thing at random, nor may anything come
from anything else, unless we mean that it does so in virtue of a
concomitant attribute. For how could ‘white’ come from ‘musical’,
unless ‘musical’ happened to be an attribute of the not-white or of
the black? No, ‘white’ comes from ‘not-white’-and not from any
‘not-white’, but from black or some intermediate colour. Similarly,
‘musical’ comes to be from ‘not-musical’, but not from any thing
other than musical, but from ‘unmusical’ or any intermediate state
there may be.
    Nor again do things pass into the first chance thing; ‘white’
does not pass into ‘musical’ (except, it may be, in virtue of a
concomitant attribute), but into ‘not-white’-and not into any
chance thing which is not white, but into black or an intermediate
colour; ‘musical’ passes into ‘not-musical’-and not into any chance
thing other than musical, but into ‘unmusical’ or any intermediate
state there may be.
    The same holds of other things also: even things which are not
simple but complex follow the same principle, but the opposite
state has not received a name, so we fail to notice the fact. What
is in tune must come from what is not in tune, and vice versa; the
tuned passes into untunedness-and not into any untunedness, but
into the corresponding opposite. It does not matter whether we take
attunement, order, or composition for our illustration; the
principle is obviously the same in all, and in fact applies equally
to the production of a house, a statue, or any other complex. A
house comes from certain things in a certain state of separation
instead of conjunction, a statue (or any other thing that has been
shaped) from shapelessness-each of these objects being partly order
and partly composition.
    If then this is true, everything that comes to be or passes away
from, or passes into, its contrary or an intermediate state. But
the