d them, as they are in themselves, but by its
own mode, according as it apprehends composite things; and in this way
also it apprehends God (Q. 3).

Reply Obj. 1: It is difference which constitutes the species. Now
everything is constituted in a species according as it is determined
to some special grade of being because "the species of things are
like numbers," which differ by addition and subtraction of unity, as
the Philosopher says (Metaph. viii, text 10). But in material things
there is one thing which determines to a special grade, and that is
the form; and another thing which is determined, and this is the
matter; and hence from the latter the genus is derived, and from
the former the "difference." Whereas in immaterial things there is
no separate determinator and thing determined; each thing by its
own self holds a determinate grade in being; and therefore in them
genus and "difference" are not derived from different things, but
from one and the same. Nevertheless, this differs in our mode of
conception; for, inasmuch as our intellect considers it as
indeterminate, it derives the idea of their genus; and inasmuch
as it considers it determinately, it derives the idea of their
"difference."

Reply Obj. 2: This reason is given in the book on the _Fount of
Life,_ and it would be cogent, supposing that the receptive mode of
the intellect and of matter were the same. But this is clearly false.
For matter receives the form, that thereby it may be constituted in
some species, either of air, or of fire, or of something else. But
the intellect does not receive the form in the same way; otherwise
the opinion of Empedocles (De Anima i, 5, text 26) would be true, to
the effect that we know earth by earth, and fire by fire. But the
intelligible form is in the intellect according to the very nature of
a form; for as such is it so known by the intellect. Hence such a way
of receiving is not that of matter, but of an immaterial substance.

Reply Obj. 3: Although there is no composition of matter and form in
an angel, yet there is act and potentiality. And this can be made
evident if we consider the nature of material things which contain a
twofold composition. The first is that of form and matter, whereby
the nature is constituted. Such a composite nature is not its own
existence but existence is its act. Hence the nature itself is
related to its own existence as potentiality to act. Therefore if
there be no matter, and supp