SECOND ARTICLE [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 the

nature of a material thing as stated above (Q. 84, A. 7), but as that

by which it understands.

Reply Obj. 3: The axiom, "whatever is the cause of a thing being

such, is still more so," is true of things that are of the same

order, for instance, of the same kind of cause; for example, we may

say that health is desirable on account of life, and therefore life

is more desirable still. But if we take things of different orders

the axiom is not true: for we may say that health is caused by

medicine, but it does not follow that medicine is more desirable than

health, for health belongs to the order of final causes, whereas

medicine belongs to the order of efficient causes. So of two things

belonging essentially to the order of the objects of knowledge, the

one which is the cause of the other being known, is the more known,

as principles are more known than conclusions. But habit as such does

not belong to the order of objects of knowledge; nor are things known

on account of the habit, as on account of an object known, but as on

account of a disposition or form whereby the subject knows: and

therefore the argument does not prove.

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Summa Theologica, Part I (Prima Pars) From the Complete American Edition · 第 543 / 722 题