(In Four Articles)

After treating of human acts and passions, we now pass on to the
consideration of the principles of human acts, and firstly of
intrinsic principles, secondly of extrinsic principles. The intrinsic
principle is power and habit; but as we have treated of powers in the
First Part (Q. 77, seqq.), it remains for us to consider them in general:
in the second place we shall consider virtues and vices and other like
habits, which are the principles of human acts.

Concerning habits in general there are four points to consider: First,
the substance of habits; second, their subject; third, the cause of
their generation, increase, and corruption; fourth, how they are
distinguished from one another.

Under the first head, there are four points of inquiry:

(1) Whether habit is a quality?

(2) Whether it is a distinct species of quality?

(3) Whether habit implies an order to an act?

(4) Of the necessity of habit.
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FIRST ARTICLE [I-II, Q. 49, Art. 1]

Whether Habit Is a Quality?

Objection 1: It would seem that habit is not a quality. For Augustine
says (QQ. lxxxiii, qu. 73): "this word 'habit' is derived from the
verb 'to have.'" But "to have" belongs not only to quality, but also
to the other categories: for we speak of ourselves as "having"
quantity and money and other like things. Therefore habit is not a
quality.

Obj. 2: Further, habit is reckoned as one of the predicaments; as may
be clearly seen in the _Book on the Predicaments_ (Categor. vi). But
one predicament is not contained under another. Therefore habit is
not a quality.

Obj. 3: Further, "every habit is a disposition," as is stated in the
_Book of the Predicaments_ (Categor. vi). Now disposition is "the
order of that which has parts," as stated in _Metaph._ v, text. 24.
But this belongs to the predicament Position. Therefore habit is not
a quality.

_On the contrary,_ The Philosopher says in the Book of Predicaments
(Categor. vi) that "habit is a quality which is difficult to change."

_I answer that,_ This word _habitus_ (habit) is derived from _habere_
(to have). Now habit is taken from this word in two ways; in one way,
inasmuch as man, or any other thing, is said to "have" something; in
another way, inasmuch as a particular thing has a relation (_se
habet_) either in regard to itself, or in regard to something else.

Concerning the first, we must observe that "to have," as said in
regard to anythi