by Him, and are by Him reducible from
existence to non-existence.

If, however, a thing is called mutable by a power in itself, thus also
in some manner every creature is mutable. For every creature has a
twofold power, active and passive; and I call that power passive which
enables anything to attain its perfection either in being, or in
attaining to its end. Now if the mutability of a thing be considered
according to its power for being, in that way all creatures are not
mutable, but those only in which what is potential in them is
consistent with non-being. Hence, in the inferior bodies there is
mutability both as regards substantial being, inasmuch as their matter
can exist with privation of their substantial form, and also as
regards their accidental being, supposing the subject to coexist with
privation of accident; as, for example, this subject _man_ can exist
with _not-whiteness_ and can therefore be changed from white to
not-white. But supposing the accident to be such as to follow on the
essential principles of the subject, then the privation of such an
accident cannot coexist with the subject. Hence the subject cannot be
changed as regards that kind of accident; as, for example, snow cannot
be made black. Now in the celestial bodies matter is not consistent
with privation of form, because the form perfects the whole
potentiality of the matter; therefore these bodies are not mutable as
to substantial being, but only as to locality, because the subject is
consistent with privation of this or that place. On the other hand
incorporeal substances, being subsistent forms which, although with
respect to their own existence are as potentiality to act, are not
consistent with the privation of this act; forasmuch as existence is
consequent upon form, and nothing corrupts except it lose its form.
Hence in the form itself there is no power to non-existence; and so
these kinds of substances are immutable and invariable as regards
their existence. Wherefore Dionysius says (Div. Nom. iv) that
"intellectual created substances are pure from generation and from
every variation, as also are incorporeal and immaterial substances."
Still, there remains in them a twofold mutability: one as regards
their potentiality to their end; and in that way there is in them a
mutability according to choice from good to evil, as Damascene says
(De Fide ii, 3,4); the other as regards place, inasmuch as by their
finite power they attain to cer