Thomas Aquinas

“ 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. ”

“ 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 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. ”

“ The sin of omission is contrary to an affirmative precept which binds always, but not for always. Hence, by omitting to act, a man sins only for the time at which the affirmative precept binds him to act. ”

“ This is also made clear from the fact that a habit is not called good or bad, save in so far as it induces to a good or bad act: wherefore a habit is called good or bad by reason of the goodness or badness of its act: so that an act surpasses its habit in goodness or badness, since "the cause of a thing being such, is yet more so." ”

“ Now the presence of vices and sins in man is owing to the fact that he follows the inclination of his sensitive nature against the order of his reason.
Reply to Objection 4: Whatever is irregular in a work of art, is unnatural to the art which produced that work. Now the eternal law is compared to the order of human reason, as art to a work of art. Therefore it amounts to the same that vice and sin are against the order of human reason, and that they are contrary to the eternal law. ”

“ 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. ”

“ More things are required for good than for evil, since "good results from a whole and entire cause, whereas evil results from each single defect," as Dionysius states (Div. Nom. iv) : so that sin may arise from a man doing what he ought not, or by his not doing what he ought; while there can be no merit, unless a man do willingly what he ought to do: wherefore there can be no merit without act, whereas there can be sin without act. ”

“ There is a twofold nature in man, rational nature, and the sensitive nature. And since it is through the operation of his senses that man accomplishes acts of reason, hence there are more who follow the inclinations of the sensitive nature, than who follow the order of reason: because more reach the beginning of a business than achieve its completion. ”

“ 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. ”

“ Further, a thing is said to be forbidden, because it is contrary to the law. Now not all sins are evil through being forbidden, but some are forbidden because they are evil. Therefore sin in general should not be defined as being against the law of God. ”

“ The Philosopher is speaking there of a thing being against nature, in so far as "being against nature" is contrary to "being from nature": and not in so far as "being against nature" is contrary to "being in accord with nature," in which latter sense virtues are said to be in accord with nature, in as much as they incline us to that which is suitable to nature. ”

“ For whenever a man is ill-disposed inwardly, through some inordinate affection, he is rendered thereby unfit for fulfilling his duties: since "a tree is known by its fruit," i.e. man by his works, according to Mat. ”