are
active.

_On the contrary,_ Dionysius says (Coel. Hier. xv) that among other
qualities of corporeal fire, "it shows its greatness in its action
and power on that of which it lays hold."

_I answer that,_ It is apparent to the senses that some bodies are
active. But concerning the action of bodies there have been three
errors. For some denied all action to bodies. This is the opinion of
Avicebron in his book on _The Fount of Life,_ where, by the arguments
mentioned above, he endeavors to prove that no bodies act, but that
all the actions which seem to be the actions of bodies, are the
actions of some spiritual power that penetrates all bodies: so that,
according to him, it is not fire that heats, but a spiritual power
which penetrates, by means of the fire. And this opinion seems to be
derived from that of Plato. For Plato held that all forms existing in
corporeal matter are participated thereby, and determined and limited
thereto; and that separate forms are absolute and as it were
universal; wherefore he said that these separate forms are the causes
of forms that exist in matter. Therefore inasmuch as the form which
is in corporeal matter is determined to this matter individualized by
quantity, Avicebron held that the corporeal form is held back and
imprisoned by quantity, as the principle of individuality, so as to
be unable by action to extend to any other matter: and that the
spiritual and immaterial form alone, which is not hedged in by
quantity, can issue forth by acting on something else.

But this does not prove that the corporeal form is not an agent, but
that it is not a universal agent. For in proportion as a thing is
participated, so, of necessity, must that be participated which is
proper thereto; thus in proportion to the participation of light is
the participation of visibility. But to act, which is nothing else
than to make something to be in act, is essentially proper to an act
as such; wherefore every agent produces its like. So therefore to the
fact of its being a form not determined by matter subject to
quantity, a thing owes its being an agent indeterminate and
universal: but to the fact that it is determined to this matter, it
owes its being an agent limited and particular. Wherefore if the form
of fire were separate, as the Platonists supposed, it would be, in a
fashion, the cause of every ignition. But this form of fire which is
in this corporeal matter, is the cause of this ignition whic