Whether a Body Can Be Active?
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."
Obj. 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.
Obj. 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.
Obj. 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.
Obj. 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 (Q. 45, A. 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 Obj. 1: This passage of Augustine is to be understood of the
whole corporeal nature considered as a whole, which 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 Obj. 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 Obj. 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 Obj. 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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