IV. Method

A threefold method can be distinguished in treating moral theology: the speculative-scholastic method, which dwells on elucidating and proving principles, and thus provides the foundation on which casuists, as they are called, can rely; the casuistic method, which, after briefly setting forth the principles, inquires what is lawful or unlawful in various circumstances, especially in complicated ones; and the mixed method, which joins both methods. The latter method, that is, the mixed method, is to be preferred. For since moral theology is indeed a science, but one that is plainly directed to practice, it is clear that in learning and handing it down, not only the speculative-scholastic method, which deduces more general rules of morals from principles, but also the casuistic method must be employed. For this latter method supplies a very useful and almost necessary exercise for rightly weighing the minute circumstances in which human actions often happen to be immersed. Nor therefore can it be excluded, provided that the solutions of the proposed questions are exhibited with the greatest discretion and with perpetual attention to the principles themselves. Indeed, you will rightly call casuistry the very collection of decisions of ecclesiastical authority which regard the manifold practical cases of the Christian life; and no one fails to see that the study of this is necessary in itself.

To the point St. Alphonsus says: "They assert that knowledge of principles is enough, and that, for acquiring moral theology, it is sufficient to turn through only those books which, bearing before themselves a display of erudition, think that the whole sequence of this long art consists in general principles, while necessary questions and doubts are passed over, and while they loftily and foolishly despise the authorities of the more celebrated authors; but they are entirely mistaken.... For the greatest difficulty of this science consists in this: that principles be well applied to particular cases, and in a different way according as different circumstances occur, on which the variation of resolutions depends" (Dissertation on the moderate use of probable opinions). And already the Angelic Doctor observed: "Universal moral discourses are less useful, because actions are in particulars" (II-II, Prologue).