Whether the Soul Is a Body?
Objection 1: It would seem that the soul is a body. For the soul is
the moving principle of the body. Nor does it move unless moved.
First, because seemingly nothing can move unless it is itself moved,
since nothing gives what it has not; for instance, what is not hot
does not give heat. Secondly, because if there be anything that moves
and is not moved, it must be the cause of eternal, unchanging
movement, as we find proved Phys. viii, 6; and this does not appear to
be the case in the movement of an animal, which is caused by the soul.
Therefore the soul is a mover moved. But every mover moved is a body.
Therefore the soul is a body.
Obj. 2: Further, all knowledge is caused by means of a likeness.
But there can be no likeness of a body to an incorporeal thing. If,
therefore, the soul were not a body, it could not have knowledge of
corporeal things.
Obj. 3: Further, between the mover and the moved there must be
contact. But contact is only between bodies. Since, therefore, the
soul moves the body, it seems that the soul must be a body.
_On the contrary,_ Augustine says (De Trin. vi, 6) that the soul "is
simple in comparison with the body, inasmuch as it does not occupy
space by its bulk."
_I answer that,_ To seek the nature of the soul, we must premise that
the soul is defined as the first principle of life of those things
which live: for we call living things "animate," [*i.e. having a
soul] and those things which have no life, "inanimate." Now life is
shown principally by two actions, knowledge and movement. The
philosophers of old, not being able to rise above their imagination,
supposed that the principle of these actions was something corporeal:
for they asserted that only bodies were real things; and that what is
not corporeal is nothing: hence they maintained that the soul is
something corporeal. This opinion can be proved to be false in many
ways; but we shall make use of only one proof, based on universal and
certain principles, which shows clearly that the soul is not a body.
It is manifest that not every principle of vital action is a soul,
for then the eye would be a soul, as it is a principle of vision; and
the same might be applied to the other instruments of the soul: but
it is the _first_ principle of life, which we call the soul. Now,
though a body may be a principle of life, as the heart is a principle
of life in an animal, yet nothing corporeal can be the first
principle of life. For it is clear that to be a principle of life, or
to be a living thing, does not belong to a body as such; since, if
that were the case, every body would be a living thing, or a
principle of life. Therefore a body is competent to be a living thing
or even a principle of life, as "such" a body. Now that it is
actually such a body, it owes to some principle which is called its
act. Therefore the soul, which is the first principle of life, is not
a body, but the act of a body; thus heat, which is the principle of
calefaction, is not a body, but an act of a body.
Reply Obj. 1: As everything which is in motion must be moved by
something else, a process which cannot be prolonged indefinitely, we
must allow that not every mover is moved. For, since to be moved is
to pass from potentiality to actuality, the mover gives what it has
to the thing moved, inasmuch as it causes it to be in act. But, as
is shown in _Phys._ viii, 6, there is a mover which is altogether
immovable, and not moved either essentially, or accidentally; and
such a mover can cause an invariable movement. There is, however,
another kind of mover, which, though not moved essentially, is moved
accidentally; and for this reason it does not cause an invariable
movement; such a mover, is the soul. There is, again, another mover,
which is moved essentially--namely, the body. And because the
philosophers of old believed that nothing existed but bodies, they
maintained that every mover is moved; and that the soul is moved
directly, and is a body.
Reply Obj. 2: The likeness of a thing known is not of necessity
actually in the nature of the knower; but given a thing which knows
potentially, and afterwards knows actually, the likeness of the thing
known must be in the nature of the knower, not actually, but only
potentially; thus color is not actually in the pupil of the eye, but
only potentially. Hence it is necessary, not that the likeness of
corporeal things should be actually in the nature of the soul, but
that there be a potentiality in the soul for such a likeness. But the
ancient philosophers omitted to distinguish between actuality and
potentiality; and so they held that the soul must be a body in order
to have knowledge of a body; and that it must be composed of the
principles of which all bodies are formed in order to know all bodies.
Reply Obj. 3: There are two kinds of contact; of "quantity," and of
"power." By the former a body can be touched only by a body; by the
latter a body can be touched by an incorporeal thing, which moves
that body.
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