Question Two: On the Subject of Habit

St. Thomas, I-II, q. 50.

563. A natural entitative habit is not found in the soul, because the soul is the form completing human nature, and therefore it cannot be disposed to something more perfect according to nature; but there can be found in it a supernatural habit by which it participates in a superior nature: thus through sanctifying grace it participates in the divine nature. - But in the body there is found a natural entitative habit by which it is more or less perfect in its being: such are health, sickness, beauty, deformity, leanness, etc.

564. Principle. Operative habit inheres in an indifferent operative power, that is, one not wholly determined to one thing. - It is proved:

1. It inheres in an operative power. For an operative habit is that which immediately determines to operation; but that must be determined to operation which is the principle of operation.

2. It inheres in an indifferent power. For that which can be disposed in several ways in itself can be ordered and determined in diverse ways to acting.

Hence it is in the powers of the soul which can operate in diverse ways:

1. in the will, which, as a rational power, can be ordered in diverse ways to acting and to a determined good of reason, and of itself is indifferent to acting well or badly;

2. in the intellect, which is in potency to all intelligible things, and undetermined to things not evident;

3. in the sensitive powers, not indeed when they operate from the instinct of nature (thus they are determined to one thing), but when they operate from the command of reason, according as they can be ordered to diverse things and disposed well or badly. But since:

a) the sensitive appetite operates more from the command of reason (and thus is more indifferent) than the internal senses, it follows that habit is found more in the sensitive appetite;

b) nevertheless habits are found in the interior senses, by which man becomes good in memory, or cogitative, or imaginative; but

c) they are not found in the external senses, because by nature they are wholly determined to one thing.

565. Operative habits properly so called are not in the powers of the body, which do not properly operate, but are mere instruments of the soul. For:

a) Operative habit per se does not inhere in the powers of the body, namely, the exterior members, or vegetative powers, or motive powers according to place, because by nature they are determined to one thing.

b) But insofar as they are moved by the soul, in them, and also in the external senses, properly operative habits cannot be, because they do not properly operate, but are mere instruments of the soul, which principally operates in them and which they obey at command.

c) Yet they are said to be in them secondarily, because in them there can be qualities and passive dispositions by which they are materially disposed to serving promptly the operations of the soul. Thus, for example, the motive powers according as the nerves are loosened or contracted; the vegetative powers according as they become accustomed to abstinence or to the use of a determined food.