Definition

(Summa Theologica, I-II, qq. 55-70.)

Definition.—A virtue is a good habit of the free powers of the soul, that is a principle of good conduct, and never of conduct that is evil. Hence, the following are not virtues: (a) an occasional inclination to good, for this is not a fixed habit; (b) good habits of the body or of the vegetative powers, etc. (such as beauty and health), for these are not free; (c) knowledge of the right or affection for it without any reference to practice, for virtue is a principle of right living; (d) habits that can be applied indifferently to good or bad conduct, such as human opinion.