Chastity is a moral virtue which moderates the unruly desires of the flesh. Of all the appetites that we received from nature, one of the most violent is the one which pushes one sex towards the other. Sexual appetite is something which we have in common with animals of all species, because nature has not watched over the conservation of animal species any less than over that of man. And no less over the conservation of harmful animals and over those we call beneficial . But with man, this animal above all others, something happened that has never been observed among other animals: it is cheating nature by enjoying the pleasure that it attached to the procreation of the human species, but neglecting its goal. This is where the essence of impurity resides and, consequently, the essence of the opposing virtue will consist in profiting wisely from what nature gave us and never separate the goals from the means. Chastity will then exist outside marriage as well as within: within marriage by satisfying all that nature asks from us and all that religion and the laws of the state have authorized; and in celibacy, by resisting those impulses of nature which, pressing us without regard for time, place, circumstances, propriety, religion, customs or laws, would drive us towards illicit actions.

Chastity must not be mistaken for abstinence . A chaste person, is the one who is not abstemious, and reciprocally, the abstemious person is not chaste . Chastity is the same in all times, all periods of life and all ranks; abstinence is only a matter of celibacy, and celibacy is nearly always an obligation. See Celibacy. Age makes old men necessarily abstemious; it rarely makes them chaste .

This is all that philosophy teaches us about chastity . But the laws of the Christian religion are much stricter: an ill-intentioned word, a glance, an expression, or even a gesture can offend Christian chastity . The Christian achieves true chastity only when he has managed to preserve himself in a state of angelical purity, despite the perpetual temptations of the demons of the flesh. The Christian spirit views anything that favors the efforts of this enemy of our innocence as an obstacle to chastity . Some such obstacles are eating and drinking in excess, socializing with persons of ill-repute, or even simply persons of the opposite sex, the sight of an indecent object, a questionable speech, an indecent reading, a free thought, etc. See Celibacy, Marriage [Marriage (Natural Law), Marriage (Jurisprudence)), Marriage (Theology)] and other articles in this work, where the duties of man towards himself are discussed, for how chastity ought to be judged.