we say that heat is the act of what is
hot, and light of what is lucid; not as though lucid and light were
two separate things, but because a thing is made lucid by the light.
In like manner, the soul is said to be the "act of a body," etc.,
because by the soul it is a body, and is organic, and has life
potentially. Yet the first act is said to be in potentiality to the
second act, which is operation; for such a potentiality "does not
reject"--that is, does not exclude--the soul.

Reply Obj. 2: The soul does not move the body by its essence, as the
form of the body, but by the motive power, the act of which
presupposes the body to be already actualized by the soul: so that
the soul by its motive power is the part which moves; and the animate
body is the part moved.

Reply Obj. 3: We observe in matter various degrees of perfection, as
existence, living, sensing, and understanding. Now what is added is
always more perfect. Therefore that form which gives matter only the
first degree of perfection is the most imperfect; while that form
which gives the first, second, and third degree, and so on, is the
most perfect: and yet it inheres to matter immediately.

Reply Obj. 4: Avicenna held that the substantial forms of the
elements remain entire in the mixed body; and that the mixture is
made by the contrary qualities of the elements being reduced to an
average. But this is impossible, because the various forms of the
elements must necessarily be in various parts of matter; for the
distinction of which we must suppose dimensions, without which matter
cannot be divisible. Now matter subject to dimension is not to be
found except in a body. But various bodies cannot be in the same
place. Whence it follows that elements in the mixed body would be
distinct as to situation. And then there would not be a real mixture
which is in respect of the whole; but only a mixture apparent to
sense, by the juxtaposition of particles.

Averroes maintained that the forms of elements, by reason of their
imperfection, are a medium between accidental and substantial forms,
and so can be "more" or "less"; and therefore in the mixture they are
modified and reduced to an average, so that one form emerges from
them. But this is even still more impossible. For the substantial
being of each thing consists in something indivisible, and every
addition and subtraction varies the species, as in numbers, as stated
in _Metaph._ viii (Did. vii, 3); and cons