CLE [I, Q. 87, Art. 2]

Whether Our Intellect Knows the Habits of the Soul by Their Essence?

Objection 1: It would seem that our intellect knows the habits of the
soul by their essence. For Augustine says (De Trin. xiii, 1): "Faith
is not seen in the heart wherein it abides, as the soul of a man may
be seen by another from the movement of the body; but we know most
certainly that it is there, and conscience proclaims its existence";
and the same principle applies to the other habits of the soul.
Therefore the habits of the soul are not known by their acts, but by
themselves.

Obj. 2: Further, material things outside the soul are known by their
likeness being present in the soul, and are said therefore to be
known by their likenesses. But the soul's habits are present by their
essence in the soul. Therefore the habits of the soul are known by
their essence.

Obj. 3: Further, "whatever is the cause of a thing being such is
still more so." But habits and intelligible species cause things to
be known by the soul. Therefore they are still more known by the soul
in themselves.

_On the contrary,_ Habits like powers are the principles of acts. But
as is said (De Anima ii, 4), "acts and operations are logically prior
to powers." Therefore in the same way they are prior to habits; and
thus habits, like the powers, are known by their acts.

_I answer that,_ A habit is a kind of medium between mere power and
mere act. Now, it has been said (A. 1) that nothing is known but as
it is actual: therefore so far as a habit fails in being a perfect
act, it falls short in being of itself knowable, and can be known
only by its act; thus, for example, anyone knows he has a habit from
the fact that he can produce the act proper to that habit; or he may
inquire into the nature and idea of the habit by considering the act.
The first kind of knowledge of the habit arises from its being
present, for the very fact of its presence causes the act whereby it
is known. The second kind of knowledge of the habit arises from a
careful inquiry, as is explained above of the mind (A. 1).

Reply Obj. 1: Although faith is not known by external movement of
the body, it is perceived by the subject wherein it resides, by the
interior act of the heart. For no one knows that he has faith unless
he knows that he believes.

Reply Obj. 2: Habits are present in our intellect, not as its object
since, in the present state of life, our intellect's object is t