itself, as
stated in _Ethic._ vi, 1: and to these applies what we have said of
science and opinion. Some, however, viz. the moral virtues, are in
the appetitive part of the soul; and the same may be said of the
contrary vices. Now the habits of the appetitive part are caused
therein because it is natural to it to be moved by the reason.
Therefore a habit either of virtue or of vice, may be corrupted by a
judgment of reason, whenever its motion is contrary to such vice or
virtue, whether through ignorance, passion or deliberate choice.

Reply Obj. 1: As stated in _Ethic._ vii, 10, a habit is like a second
nature, and yet it falls short of it. And so it is that while the
nature of a thing cannot in any way be taken away from a thing, a
habit is removed, though with difficulty.

Reply Obj. 2: Although there is no contrary to intelligible species,
yet there can be a contrary to assertions and to the process of
reason, as stated above.

Reply Obj. 3: Science is not taken away by movement of the body, if
we consider the root itself of the habit, but only as it may prove an
obstacle to the act of science; in so far as the intellect, in its
act, has need of the sensitive powers, which are impeded by corporal
transmutation. But the intellectual movement of the reason can
corrupt the habit of science, even as regards the very root of the
habit. In like manner a habit of virtue can be corrupted.
Nevertheless when it is said that "virtue is more lasting than
learning," this must be understood in respect, not of the subject or
cause, but of the act: because the use of virtue continues through
the whole of life, whereas the use of learning does not.
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SECOND ARTICLE [I-II, Q. 53, Art. 2]

Whether a Habit Can Diminish?

Objection 1: It would seem that a habit cannot diminish. Because a
habit is a simple quality and form. Now a simple thing is possessed
either wholly or not at all. Therefore although a habit can be lost
it cannot diminish.

Obj. 2: Further, if a thing is befitting an accident, this is by
reason either of the accident or of its subject. Now a habit does not
become more or less intense by reason of itself; else it would follow
that a species might be predicated of its individuals more or less.
And if it can become less intense as to its participation by its
subject, it would follow that something is accidental to a habit,
proper thereto and not common to the habit and its subject. Now
w