Virtue is a habit of doing moral good. A natural habit is acquired by repeated acts, but a supernatural virtue is infused by the grace of God. At the outset the will may be opposed by the defects of temperament, by the evil inclinations of passion, and even by sinful habits in the practice of virtue; but, by systematically waging war on these perverse inclinations in a Christian manner, man may gradually overcome their combined opposition and cultivate voluntary good habits, or virtues. By striving thus man contributes his part to the development of the corresponding supernatural virtue, of which grace is always the efficient cause.
A moral virtue is the golden mean between the vices of excess and defect. This mean is marked out by right reason, that is, by reason free from error, prejudice, and delusion, especially when this reason is enlightened by faith. The virtues that unite us directly to God are called theological; those that govern our actions in the way of rectitude are called moral. There are three of the former and four of the latter. The theological virtues are: faith, hope and charity. The principal moral virtues are: prudence, justice, temperance, and fortitude. The latter are called cardinal virtues, because all other moral virtues are sub- ordinated to them.