Casuistry, the art in which the Jesuits so much excelled, is, strictly speaking, that branch of theology which treats of cases of conscience, and originally consisted in nothing more than an application of the general precepts of Scripture to particular cases. The ancient casuists, so long as they confined themselves to the simple rules of the Gospel, were at least harmless, and their ingenious writings are still found useful in cases of ecclesiastical discipline; but they gradually introduced into the science of morals the metaphysical jargon of the schools, and instead of aiming at making men moral, contented themselves with disputing about morality.[15] The main source of the aberrations of casuistry lay in the unscriptural dogma of priestly absolution—in the right claimed by man to forgive _sin_, as a transgression of the law of God; and the arbitrary distinction between sins as venial and mortal—a distinction which assigns to the priest the prerogative, and imposes on him the obligation, of drawing the critical line, or fixing a kind of tariff on human actions, and apportioning penance or pardon, as the case may seem to require. In their desperate attempt to define the endless forms of depravity on which they were called to adjudicate, or which the pruriency of the cloister suggested to the imagination, the casuists sank deeper into the mire at every step; and their productions, at length, resembled the common sewers of a city, which, when exposed, become more pestiferous than the filth which they were meant to remove. Even under the best management, such a system was radically bad; in the hands of the Jesuits it became unspeakably worse. To their “modern casuists,” as they were termed, must we ascribe the invention of _probabilism_, _mental reservation_, and the _direction of the intention_, which have been sufficiently explained and rebuked in the Provincial Letters. We shall only remark here, that the actions to which these principles were applied were not only such as have been termed indifferent, and the criminality of which may be doubtful, or dependent on the intention of the actor: the probabilism of the Jesuits was, in fact, a systematic attempt to legalize crime, under the sanction of some grave doctor, who had found out some excuse for it; and their theory of mental reservations, and direction of the intention, was equally employed to sanctify the plainest violations of the divine law. Casuistry, it is true, has generally vibrated betwixt the extremes of impracticable severity and contemptible indulgence; but the charge against the Jesuits was, not that they softened the rigors of ascetic virtue, but that they propagated principles which sapped the foundation of all moral obligation. “They are a people,” said Boileau, “who lengthen the creed and shorten the decalogue.”