Thomas Aquinas, Summa Theologiae

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 (Article 1). Therefore sin is incompatible with virtue.

Objection 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.

Objection 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 (Question 51, Article 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 (Question 63, Article 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 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.

Accordingly, mortal sin is incompatible with the infused virtues, but is consistent with acquired virtue: while venial sin is compatible with virtues, whether infused or acquired.

Reply to Objection 1: Sin is contrary to virtue, not by reason of itself, but by reason of its act. Hence sin is incompatible with the act, but not with the habit, of virtue.

Reply to Objection 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 to Objection 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.

Articulus 4

Argumentum 1

Ad quartum sic proceditur. Videtur quod actus vitiosus, sive peccatum, non possit simul esse cum virtute. Contraria enim non possunt esse simul in eodem. Sed peccatum quodammodo contrariatur virtuti, ut dictum est.

Ergo peccatum non potest simul esse cum virtute.

Argumentum 2

Praeterea, peccatum est peius quam vitium, idest actus malus quam habitus malus. Sed vitium non potest simul esse in eodem cum virtute. Ergo neque peccatum.

Argumentum 3

Praeterea, sicut peccatum accidit in rebus voluntariis, ita et in rebus naturalibus, ut dicitur in II physic..

Sed nunquam in rebus naturalibus accidit peccatum nisi per aliquam corruptionem virtutis naturalis, sicut monstra accidunt corrupto aliquo principio in semine, ut dicitur in II physic..

Ergo etiam in rebus voluntariis non accidit peccatum nisi corrupta aliqua virtute animae.

Et sic peccatum et virtus non possunt esse in eodem.

Sed Contra

Sed contra est quod philosophus dicit, in II ethic., quod per contraria virtus generatur et corrumpitur.

Sed unus actus virtuosus non causat virtutem, ut supra habitum est.

Ergo neque unus actus peccati tollit virtutem.

Possunt ergo simul in eodem esse.

Corpus

Respondeo dicendum quod peccatum comparatur ad virtutem sicut actus malus ad habitum bonum. Aliter autem se habet habitus in anima, et forma in re naturali. Forma enim naturalis ex necessitate producit operationem sibi convenientem, unde non potest esse simul cum forma naturali actus formae contrariae; sicut non potest esse cum calore actus infrigidationis, neque simul cum levitate motus descensionis, nisi forte ex violentia exterioris moventis. Sed habitus in anima non ex necessitate producit suam operationem, sed homo utitur eo cum voluerit. Unde simul habitu in homine existente, potest non uti habitu, aut agere contrarium actum. Et sic potest habens virtutem procedere ad actum peccati. Actus autem peccati, si comparetur ad ipsam virtutem prout est habitus quidam, non potest ipsam corrumpere, si sit unus tantum, sicut enim non generatur habitus per unum actum, ita nec per unum actum corrumpitur, ut supra dictum est.

Sed si comparetur actus peccati ad causam virtutum, sic possibile est quod per unum actum peccati aliquae virtutes corrumpantur.

Quodlibet enim peccatum mortale contrariatur caritati, quae est radix omnium virtutum infusarum, inquantum sunt virtutes, et ideo per unum actum peccati mortalis, exclusa caritate, excluduntur per consequens omnes virtutes infusae, quantum ad hoc quod sunt virtutes. Et hoc dico propter fidem et spem, quarum habitus remanent informes post peccatum mortale, et sic non sunt virtutes. Sed peccatum veniale, quod non contrariatur caritati nec excludit ipsam, per consequens etiam non excludit alias virtutes. Virtutes vero acquisitae non tolluntur per unum actum cuiuscumque peccati. Sic igitur peccatum mortale non potest simul esse cum virtutibus infusis, potest tamen simul esse cum virtutibus acquisitis. Peccatum vero veniale potest simul esse et cum virtutibus infusis, et cum acquisitis.

Ad 1

Ad primum ergo dicendum quod peccatum non contrariatur virtuti secundum se, sed secundum suum actum.

Et ideo peccatum non potest simul esse cum actu virtutis, potest tamen simul esse cum habitu.

Ad 2

Ad secundum dicendum quod vitium directe contrariatur virtuti, sicut et peccatum actui virtuoso. Et ideo vitium excludit virtutem, sicut peccatum excludit actum virtutis.

Ad 3

Ad tertium dicendum quod virtutes naturales agunt ex necessitate, et ideo, integra existente virtute, nunquam peccatum potest in actu inveniri. Sed virtutes animae non producunt actus ex necessitate, unde non est similis ratio.