angels of one species. For it would be necessary for matter to be the
principle of distinction of one from the other, not, indeed, according
to the division of quantity, since they are incorporeal, but according
to the diversity of their powers; and such diversity of matter causes
diversity not merely of species, but of genus.

Reply Obj. 1: "Difference" is nobler than genus, as the determined
is more noble than the undetermined, and the proper than the common,
but not as one nature is nobler than another; otherwise it would be
necessary that all irrational animals be of the same species; or that
there should be in them some form which is higher than the sensible
soul. Therefore irrational animals differ in species according to the
various determined degrees of sensitive nature; and in like manner
all the angels differ in species according to the diverse degrees of
intellectual nature.

Reply Obj. 2: More and less change the species, not according as they
are caused by the intensity or remissness of one form, but according
as they are caused by forms of diverse degrees; for instance, if we
say that fire is more perfect than air: and in this way the angels
are diversified according to more or less.

Reply Obj. 3: The good of the species preponderates over the good
of the individual. Hence it is much better for the species to be
multiplied in the angels than for individuals to be multiplied in
the one species.

Reply Obj. 4: Numerical multiplication, since it can be drawn out
infinitely, is not intended by the agent, but only specific
multiplication, as was said above (Q. 47, A. 3). Hence the perfection
of the angelic nature calls for the multiplying of species, but not
for the multiplying of individuals in one species.
_______________________

FIFTH ARTICLE [I, Q. 50, Art. 5]

Whether the Angels Are Incorruptible?

Objection 1: It would seem that the angels are not incorruptible; for
Damascene, speaking of the angel, says (De Fide Orth. ii, 3) that he
is "an intellectual substance, partaking of immortality by favor, and
not by nature."

Obj. 2: Further, Plato says in the Timaeus: "O gods of gods, whose
maker and father am I: You are indeed my works, dissoluble by nature,
yet indissoluble because I so will it." But gods such as these can
only be understood to be the angels. Therefore the angels are
corruptible by their nature

Obj. 3: Further, according to Gregory (Moral. xvi), "all things would
tend towards