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Objection 1: It would seem that no bodies are active. For
Augustine says (De Civ. Dei v, 9): "There are things that
are acted upon, but do not act; such are bodies: there is one Who
acts but is not acted upon; this is God: there are things that both
act and are acted upon; these are the spiritual substances."
Objection 2: Further, every agent except the first agent requires
in its work a subject susceptible of its action. But there is not
substance below the corporeal substance which can be susceptible of the
latter's action; since it belongs to the lowest degree of beings.
Therefore corporeal substance is not active.
Objection 3: Further, every corporeal substance is limited by
quantity. But quantity hinders substance from movement and action,
because it surrounds it and penetrates it: just as a cloud hinders the
air from receiving light. A proof of this is that the more a body
increases in quantity, the heavier it is and the more difficult to
move. Therefore no corporeal substance is active.
Objection 4: Further, the power of action in every agent is
according to its propinquity to the first active cause. But bodies,
being most composite, are most remote from the first active cause,
which is most simple. Therefore no bodies are active.
Objection 5: Further, if a body is an agent, the term of its
action is either a substantial, or an accidental form. But it is not
a substantial form; for it is not possible to find in a body any
principle of action, save an active quality, which is an accident;
and an accident cannot be the cause of a substantial form, since the
cause is always more excellent than the effect. Likewise, neither is
it an accidental form, for "an accident does not extend beyond its
subject," as Augustine says (De Trin. ix, 4). Therefore no
bodies 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 which passes from this body to
that. Hence such an action is effected by the contact of two bodies.
But this opinion of Avicebron goes further than that of Plato. For
Plato held only substantial forms to be separate; while he referred
accidents to the material principles which are "the great" and "the
small," which he considered to be the first contraries, by others
considered to the "the rare" and "the dense." Consequently both
Plato and Avicenna, who follows him to a certain extent, held that
corporeal agents act through their accidental forms, by disposing
matter for the substantial form; but that the ultimate perfection
attained by the introduction of the substantial form is due to an
immaterial principle. And this is the second opinion concerning the
action of bodies; of which we have spoken above when treating of the
creation (Question 45, Article 8).
The third opinion is that of Democritus, who held that action takes
place through the issue of atoms from the corporeal agent, while
passion consists in the reception of the atoms in the pores of the
passive body. This opinion is disproved by Aristotle (De Gener.
i, 8,9). For it would follow that a body would not be passive as
a whole, and the quantity of the active body would be diminished
through its action; which things are manifestly untrue.
We must therefore say that a body acts forasmuch as it is in act, on a
body forasmuch as it is in potentiality.
Reply to Objection 1: This passage of Augustine is to be
understood of the whole corporeal nature considered as a whole, while
thus has no nature inferior to it, on which it can act; as the
spiritual nature acts on the corporeal, and the uncreated nature on the
created. Nevertheless one body is inferior to another, forasmuch as
it is in potentiality to that which the other has in act.
From this follows the solution of the second objection. But it must
be observed, when Avicebron argues thus, "There is a mover who is
not moved, to wit, the first maker of all; therefore, on the other
hand, there exists something moved which is purely passive," that
this is to be conceded. But this latter is primary matter, which is a
pure potentiality, just as God is pure act. Now a body is composed
of potentiality and act; and therefore it is both active and passive.
Reply to Objection 3: Quantity does not entirely hinder the
corporeal form from action, as stated above; but from being a
universal agent, forasmuch as a form is individualized through being in
matter subject to quantity. The proof taken from the weight of bodies
is not to the purpose. First, because addition of quantity does not
cause weight; as is proved (De Coelo et Mundo iv, 2).
Secondly, it is false that weight retards movement; on the contrary,
the heavier a thing, the greater its movement, if we consider the
movement proper thereto. Thirdly, because action is not effected by
local movement, as Democritus held: but by something being reduced
from potentiality to act.
Reply to Objection 4: A body is not that which is most distant from
God; for it participates something of a likeness to the Divine
Being, forasmuch as it has a form. That which is most distant from
God is primary matter; which is in no way active, since it is a pure
potentiality.
Reply to Objection 5: The term of a body's action is both an
accidental form and a substantial form. For the active quality, such
as heat, although itself an accident, acts nevertheless by virtue of
the substantial form, as its instrument: wherefore its action can
terminate in a substantial form; thus natural heat, as the instrument
of the soul, has an action terminating in the generation of flesh.
But by its own virtue it produces an accident. Nor is it against the
nature of an accident to surpass its subject in acting, but it is to
surpass it in being; unless indeed one were to imagine that an accident
transfers its identical self from the agent to the patient; thus
Democritus explained action by an issue of atoms.
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