o the soul; but not in relation to the body, except in so far as the
body has relation to the soul. Hence the first object of our
consideration will be the soul. And since Dionysius (Ang. Hier. xi)
says that three things are to be found in spiritual
substances--essence, power, and operation--we shall treat first of
what belongs to the essence of the soul; secondly, of what belongs to
its power; thirdly, of what belongs to its operation.

Concerning the first, two points have to be considered; the first is
the nature of the soul considered in itself; the second is the union
of the soul with the body. Under the first head there are seven
points of inquiry.

(1) Whether the soul is a body?

(2) Whether the human soul is a subsistence?

(3) Whether the souls of brute animals are subsistent?

(4) Whether the soul is man, or is man composed of soul and body?

(5) Whether the soul is composed of matter and form?

(6) Whether the soul is incorruptible?

(7) Whether the soul is of the same species as an angel?
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FIRST ARTICLE [I, Q. 75, Art. 1]

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 th