Theologicae regulae

Virtue and vice are opposed mediately, not by the position of a middle term, but by the negation of both.

Note that this name, vice, is taken in many ways, negatively, namely, and positively, just as also this name, sin. Vice, then, is sometimes said in omitting what ought to be done; similarly, sometimes in committing what ought not to be done. According to this, then, in that vice is taken negatively, virtue and vice are opposed immediately, as affirmation and negation, like rational and non-rational: I do not say irrational. Since, then, virtue and vice, with regard to the rational creature, are opposed, as affirmation and negation, insofar as vice is taken negatively, whatever rational creature does not have virtue, has vice: and vice versa. Whence, although a Jew and a Pagan may have chastity, temperance, and the other powers which can be virtues, yet, since they do not have them as virtues, they have vices opposed to the virtues by negation. For in this he is vicious, that he does not have the virtues, when he is bound to have them. For just as it is said that failures to go to church, and failures to give alms, are delicts, since we are bound to do these things, and do not do them; and thus vices, or delicts, are said to be, not to have the virtue of temperance, or the virtue of chastity, when we are bound to have it. According to this, however, virtue and vice are not said to be opposed immediately, except according to a determinate time. For we do not say that a boy, before the years of discretion, has virtues, or vices: but when he has come to the years of discretion, if he has not had virtues, he will have vices. Just as we do not say that there is sight, or blindness, in a puppy, before a determinate time. A Jew, then, or a gentile, is not temperate, or not prudent, or not chaste, although he may have political virtues: but he is not intemperate, imprudent, unchaste; for these not only remove, but also imply vicious movements. Similarly concerning this Christian, who is in some mortal sin, for example, in lying, it must be judged: for although he is not moved to lust, he is nevertheless not to be judged chaste, lest chastity be implied as a virtue, nor lustful.

Sometimes, however, vice is taken positively, according to which lust, envy, and anger are called vice. According to this, vice is divided into seven deadly vices: pride, wrath, envy, avarice, sloth, gluttony, lust. According to this, intemperance is called a vice, and imprudence, and injustice. Since lust is called a vice positively, and intemperance is a genus of lust, intemperance is called a vice positively; and according to this virtue and vice are opposed mediately, like chastity and lust: for there is there a middle term by negation, namely non-chastity. Similarly between faith and infidelity, between hope and despair. Just as, then, with the natural physician health and sickness are said to be opposed mediately, and a certain neutrality is there constituted, as it were a middle term, by negation: so with the heavenly physician, between the health of virtue and the sickness of vice, a certain neutrality is constituted, as it were a middle term, by negation; namely, not being virtuous. Nor do we call a movement vicious, because vice is said to have a substantive quality from which it proceeds, just as the movement of virtue has a substantive virtue, from which it proceeds: and thus no quality, which is a vice, is opposed to a quality, which is a virtue; but movement to movement. For we say that a disordered movement is opposed to virtue, by reason of the movement of virtue.