II. Sources

From the formal object indicated, it is plain that the proper sources of moral theology are revelation, and likewise the magisterium and discipline of the Church, whether they have been consigned to writing or sanctioned only by tradition or use. Now the Church speaks both by her express edicts, and by commending the doctrine of doctors, and by the consent of believers or teachers concerning some doctrine, if it truly exists.¹ Moreover, as we have already noted under I, we shall not pass over principles known by the natural light of reason: both because many obligations occur in life concerning which revelation is silent, and because natural reason itself can bring very much light to those things which have been revealed. And thus it will come about that the whole hall of moral theology is continually and most beautifully illuminated by the doubled light of divine Wisdom, namely both supernatural and natural.

¹ We say "if it truly exists"; for this is sometimes asserted too hastily. Besides, that consent is then only a criterion of Catholic truth if, for a long time and constantly, it presents something as certain and necessarily connected with a dogma of faith. But as regards theological doctrines, insofar as they are handed down in the schools only as such and are defended by authors in books, Cardinal Franzelin says: "It is certainly not repugnant that some opinion, common for some time among theologians, should afterwards, when arguments and documents have been better examined, cease to be common or even become obsolete" (De divina traditione, thesis 17). Cardinal de Lugo says: "An opinion which in this century is very frequent in the schools, and is defended by almost all, in the next century, after the matter has been better examined and new foundations have appeared, is retained by few" (De fide, disputation 20, number 128). Cf. Ter Haar, De systemate morali antiquorum probabilistarum, p. 98.