Reply Obj. 1: Nothing hinders one thing from standing above another simply, and below it in some respect. Now a thing is deemed above another simply if it surpasses it in a point which is proper to both; while it is deemed above it in a certain respect, if it surpasses it in something which is accidental to both. Now it has been shown from the very nature of act and habit, that act surpasses habit both in goodness and in badness. Whereas the fact that habit is more lasting than act, is accidental to them, and is due to the fact that they are both found in a nature such that it cannot always be in action, and whose action consists in a transient movement. Consequently act simply excels in goodness and badness, but habit excels in a certain respect.
Reply Obj. 2: A habit is several acts, not simply, but in a certain respect, i.e. virtually. Wherefore this does not prove that habit precedes act simply, both in goodness and in badness.
Reply Obj. 3: Habit causes act by way of efficient causality: but act causes habit, by way of final causality, in respect of which we consider the nature of good and evil. Consequently act surpasses habit both in goodness and in badness. ________________________
FOURTH ARTICLE [I-II, Q. 71, Art. 4]
Whether Sin Is Compatible with Virtue?
Objection 1: It would seem that a vicious act, i.e. sin, is incompatible with virtue. For contraries cannot be together in the same subject. Now sin is, in some way, contrary to virtue, as stated above (A. 1). Therefore sin is incompatible with virtue.
Obj. 2: Further, sin is worse than vice, i.e. evil act than evil habit. But vice cannot be in the same subject with virtue: neither, therefore, can sin.
Obj. 3: Further, sin occurs in natural things, even as in voluntary matters (Phys. ii, text. 82). Now sin never happens in natural things, except through some corruption of the natural power; thus monsters are due to corruption of some elemental force in the seed, as stated in Phys. ii. Therefore no sin occurs in voluntary matters, except through the corruption of some virtue in the soul: so that sin and virtue cannot be together in the same subject.
On the contrary, The Philosopher says (Ethic. ii, 2, 3) that "virtue is engendered and corrupted by contrary causes." Now one virtuous act does not cause a virtue, as stated above (Q. 51, A. 3): and, consequently, one sinful act does not corrupt virtue. Therefore they can be together in the same subject.
I answer that, Sin is compared to virtue, as evil act to good habit. Now the position of a habit in the soul is not the same as that of a form in a natural thing. For the form of a natural thing produces, of necessity, an operation befitting itself; wherefore a natural form is incompatible with the act of a contrary form: thus heat is incompatible with the act of cooling, and lightness with downward movement (except perhaps violence be used by some extrinsic mover): whereas the habit that resides in the soul, does not, of necessity, produce its operation, but is used by man when he wills. Consequently man, while possessing a habit, may either fail to use the habit, or produce a contrary act; and so a man having a virtue may produce an act of sin. And this sinful act, so long as there is but one, cannot corrupt virtue, if we compare the act to the virtue itself as a habit: since, just as habit is not engendered by one act, so neither is it destroyed by one act as stated above (Q. 63, A. 2, ad 2). But if we compare the sinful act to the cause of the virtues, then it is possible for some virtues to be destroyed by one sinful act. For every mortal sin is contrary to charity, which is the root of all the infused virtues, as virtues; and consequently, charity being banished by one act of mortal sin, it follows that all the infused virtues are expelled as virtues. And I say [this] on account of faith and hope, whose habits remain unquickened after mortal sin, so that they are no longer virtues. On the other hand, since venial sin is neither contrary to charity, nor banishes it, as a consequence, neither does it expel the other virtues. As to the acquired virtues, they are not destroyed by one act of any kind of sin.