_I answer that,_ In accordance with what has been already shown (Q.
54, A. 3; Q. 77, A. 1) it is necessary to say that the intellect is
a power of the soul, and not the very essence of the soul. For then
alone the essence of that which operates is the immediate principle
of operation, when operation itself is its being: for as power is to
operation as its act, so is the essence to being. But in God alone
His action of understanding is His very Being. Wherefore in God alone
is His intellect His essence: while in other intellectual creatures,
the intellect is a power.

Reply Obj. 1: Sense is sometimes taken for the power, and sometimes
for the sensitive soul; for the sensitive soul takes its name from
its chief power, which is sense. And in like manner the intellectual
soul is sometimes called intellect, as from its chief power; and thus
we read (De Anima i, 4), that the "intellect is a substance." And in
this sense also Augustine says that the mind is spirit and essence
(De Trin. ix, 2; xiv, 16).

Reply Obj. 2: The appetitive and intellectual powers are different
genera of powers in the soul, by reason of the different formalities
of their objects. But the appetitive power agrees partly with the
intellectual power and partly with the sensitive in its mode of
operation either through a corporeal organ or without it: for
appetite follows apprehension. And in this way Augustine puts the
will in the mind; and the Philosopher, in the reason (De Anima iii,
9).

Reply Obj. 3: In the angels there is no other power besides the
intellect, and the will, which follows the intellect. And for this
reason an angel is called a "mind" or an "intellect"; because his
whole power consists in this. But the soul has many other powers,
such as the sensitive and nutritive powers, and therefore the
comparison fails.

Reply Obj. 4: The immateriality of the created intelligent substance
is not its intellect; and through its immateriality it has the power
of intelligence. Wherefore it follows not that the intellect is the
substance of the soul, but that it is its virtue and power.
_______________________

SECOND ARTICLE [I, Q. 79, Art. 2]

Whether the Intellect Is a Passive Power?

Objection 1: It would seem that the intellect is not a passive power.
For everything is passive by its matter, and acts by its form. But the
intellectual power results from the immateriality of the intelligent
substance. Therefore it seems that the intellect