Question I
THE DUTIES OF ALL CLASSES OF MEN
744. Good habits, specifically different, are all reducible to seven most general virtues (see 150, 151), and hence in studying these seven virtues, we shall at the same time study all the common duties of man.
745. The properties of the seven infused virtues are chiefly four:
(a) In the first place, these virtues may be increased: “This I pray, that your charity may more and more abound” (Phil, i. 9). The increase takes place _ex opere operato_ through the Sacraments, or _ex opere operantis_ through meritorious works—that is, whenever sanctifying grace, their root, is increased.
(b) A second property of the infused virtues is that they may be lost: “I have somewhat against thee, because thou hast left thy first charity” (Apoc., ii. 4); “Some have made shipwreck concerning the faith” (I Tim., i. 19). The loss is caused by the contrary of the virtue: faith is lost by disbelief, hope by despair; charity and the moral virtues are lost by any mortal sin, for they are built on sanctifying grace, which mortal sin destroys.
(c) A third property of the infused virtues is that they cannot be diminished directly. If we leave out of consideration their opposites (which, as just said, remove these virtues entirely), there is nothing else that can act directly upon them. Mere failure to exercise them cannot lessen them, since they are caused by divine infusion, not by human exercise; venial sin cannot lessen them, since it does not lessen grace on which they depend.
(d) A fourth property of the infused virtues is that they are diminished indirectly. Failure to practise them or venial sin does diminish the ease and fervor with which the acts of these virtues are exercised; and thus indirectly—that is, by preparing the way for acts that are directly contrary—neglect or venial sin diminishes the habits themselves.