to which one is bound. Now no man is bound to the impossible:
wherefore no man sins by omission, if he does not do what he cannot.
Accordingly she who is violated after vowing virginity, is guilty of
an omission, not through not having virginity, but through not
repenting of her past sin, or through not doing what she can to
fulfil her vow by observing continence. Again a priest is not bound
to say Mass, except he have a suitable opportunity, and if this be
lacking, there is no omission. And in like manner, a person is bound
to restitution, supposing he has the wherewithal; if he has not and
cannot have it, he is not guilty of an omission, provided he does
what he can. The same applies to other similar cases.

Reply Obj. 3: Just as the sin of transgression is opposed to negative
precepts which regard the avoidance of evil, so the sin of omission
is opposed to affirmative precepts, which regard the doing of good.
Now affirmative precepts bind not for always, but for a fixed time,
and at that time the sin of omission begins. But it may happen that
then one is unable to do what one ought, and if this inability is
without any fault on his part, he does not omit his duty, as stated
above (ad 2; I-II, Q. 71, A. 5). On the other hand if this inability
is due to some previous fault of his (for instance, if a man gets
drunk at night, and cannot get up for matins, as he ought to), some
say that the sin of omission begins when he engages in an action that
is illicit and incompatible with the act to which he is bound. But
this does not seem to be true, for supposing one were to rouse him by
violence and that he went to matins, he would not omit to go, so
that, evidently, the previous drunkenness was not an omission, but
the cause of an omission. Consequently, we must say that the omission
begins to be imputed to him as a sin, when the time comes for the
action; and yet this is on account of a preceding cause by reason of
which the subsequent omission becomes voluntary.

Reply Obj. 4: Omission is directly opposed to justice, as stated
above; because it is a non-fulfilment of a good of virtue, but only
under the aspect of due, which pertains to justice. Now more is
required for an act to be virtuous and meritorious than for it to be
sinful and demeritorious, because "good results from an entire cause,
whereas evil arises from each single defect" [*Dionysius, De Div.
Nom. iv]. Wherefore the merit of justice requires an act, whereas a