Summa Theologica
Reply to Objection 2: Sciences are differentiated according to the various means through which knowledge is obtained. For the astronomer and the physicist both may prove the same conclusion: that the earth, for instance, is round: the astronomer by means of mathematics (i.e. abstracting from matter), but the physicist by means of matter itself. Hence there is no reason why those things which may be learned from philosophical science, so far as they can be known by natural reason, may not also be taught us by another science so far as they fall within revelation. Hence theology included in sacred doctrine differs in kind from that theology which is part of philosophy.
Whether sacred doctrine is a science?
Objection 1: It seems that sacred doctrine is not a science. For every science proceeds from self-evident principles. But sacred doctrine proceeds from articles of faith which are not self-evident, since their truth is not admitted by all: "For all men have not faith" (2 Thess. 3:2). Therefore sacred doctrine is not a science.
Objection 2: Further, no science deals with individual facts. But this sacred science treats of individual facts, such as the deeds of Abraham, Isaac and Jacob and such like. Therefore sacred doctrine is not a science.
On the contrary, Augustine says (De Trin. xiv, 1) "to this science alone belongs that whereby saving faith is begotten, nourished, protected and strengthened." But this can be said of no science except sacred doctrine. Therefore sacred doctrine is a science.
I answer that, Sacred doctrine is a science. We must bear in mind that there are two kinds of sciences. There are some which proceed from a principle known by the natural light of intelligence, such as arithmetic and geometry and the like. There are some which proceed from principles known by the light of a higher science: thus the science of perspective proceeds from principles established by geometry, and music from principles established by arithmetic. So it is that sacred doctrine is a science because it proceeds from principles established by the light of a higher science, namely, the science of God and the blessed. Hence, just as the musician accepts on authority the principles taught him by the mathematician, so sacred science is established on principles revealed by God.
Reply to Objection 1: The principles of any science are either in themselves self-evident, or reducible to the conclusions of a higher science; and such, as we have said, are the principles of sacred doctrine.
Reply to Objection 2: Individual facts are treated of in sacred doctrine, not because it is concerned with them principally, but they are introduced rather both as examples to be followed in our lives (as in moral sciences) and in order to establish the authority of those men through whom the divine revelation, on which this sacred scripture or doctrine is based, has come down to us.
Whether sacred doctrine is one science?
Objection 1: It seems that sacred doctrine is not one science; for according to the Philosopher (Poster. i) "that science is one which treats only of one class of subjects." But the creator and the creature, both of whom are treated of in sacred doctrine, cannot be grouped together under one class of subjects. Therefore sacred doctrine is not one science.
Objection 2: Further, in sacred doctrine we treat of angels, corporeal creatures and human morality. But these belong to separate philosophical sciences. Therefore sacred doctrine cannot be one science.
On the contrary, Holy Scripture speaks of it as one science: "Wisdom gave him the knowledge [scientiam] of holy things" (Wis. 10:10).