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.
_______________________

SECOND ARTICLE [I, Q. 75, Art. 2]

Whether the Human Soul Is Something Subsistent?

Objection 1: It would seem that the human soul is not something
subsistent. For that which subsists is said to be "this particular
thing." Now "this particular thing" is said not of the soul, but of
that which is composed of soul and body. Therefore the soul is not
something subsistent.

Obj. 2: Further, everything subsistent operates. But the soul does
not operate; for, as the Philosopher says (De Anima i, 4), "to say
that the soul feels or understands is like saying that the soul
weaves or builds." Therefore the soul is not subsistent.

Obj. 3: Further, if the soul were subsistent, it would have some
operation apart from the body. But it has no operation apart from the
body, not even that of understanding: for the act of understanding
does not take place without a phantasm, which cannot exist apart from
the body. Therefore the human soul is not something subsistent.

_On the contrary,_ Augustine says (De Trin. x, 7): "Who understands
that the nature of the soul is that of a substance and not that of a
body, will see that those who maintain the corporeal nature of the
soul, are led astray through associating with the soul tho