Reply Obj. 2:  Vice is directly contrary to virtue, even as sin to virtuous act:  and so vice excludes virtue, just as sin excludes acts of virtue.

Reply Obj. 3:  The natural powers act of necessity, and hence so long as the power is unimpaired, no sin can be found in the act.  On the other hand, the virtues of the soul do not produce their acts of necessity; hence the comparison fails. ________________________

FIFTH ARTICLE [I-II, Q. 71, Art. 5]

Whether Every Sin Includes an Action?

Objection 1:  It would seem that every sin includes an action.  For as merit is compared with virtue, even so is sin compared with vice.  Now there can be no merit without an action.  Neither, therefore, can there be sin without action.

Obj. 2:  Further, Augustine says (De Lib.  Arb. iii, 18) [Cf.  De Vera Relig. xiv.]:  So “true is it that every sin is voluntary, that, unless it be voluntary, it is no sin at all.”  Now nothing can be voluntary, save through an act of the will.  Therefore every sin implies an act.

Obj. 3:  Further, if sin could be without act, it would follow that a man sins as soon as he ceases doing what he ought.  Now he who never does something that he ought to do, ceases continually doing what he ought.  Therefore it would follow that he sins continually; and this is untrue.  Therefore there is no sin without an act.

On the contrary, It is written (James 4:17):  “To him . . . who knoweth to do good, and doth it not, to him it is a sin.”  Now “not to do” does not imply an act.  Therefore sin can be without act.

I answer that, The reason for urging this question has reference to the sin of omission, about which there have been various opinions.  For some say that in every sin of omission there is some act, either interior or exterior—­interior, as when a man wills not to go to church, when he is bound to go—­exterior, as when a man, at the very hour that he is bound to go to church (or even before), occupies himself in such a way that he is hindered from going.  This seems, in a way, to amount to the same as the first, for whoever wills one thing that is incompatible with this other, wills, consequently, to go without this other:  unless, perchance, it does not occur to him, that what he wishes to do, will hinder him from that which he is bound to do, in which case he might be deemed guilty of negligence.  On the other hand, others say, that a sin of omission does not necessarily suppose an act:  for the mere fact of not doing what one is bound to do is a sin.

Now each of these opinions has some truth in it.  For if in the sin of omission we look merely at that in which the essence of the sin consists, the sin of omission will be sometimes with an interior act, as when a man wills not to go to church: while sometimes it will be without any act at all, whether interior or exterior, as when a man, at the time that he is bound to go to church, does not think of going or not going to church.