On the contrary, Holy Scripture speaks of it as one science: "Wisdom gave him the knowledge [scientiam] of holy things" (Wis. 10:10).
I answer that, Sacred doctrine is one science. The unity of a faculty or habit is to be gauged by its object, not indeed, in its material aspect, but as regards the precise formality under which it is an object. For example, man, ass, stone agree in the one precise formality of being colored; and color is the formal object of sight. Therefore, because Sacred Scripture considers things precisely under the formality of being divinely revealed, whatever has been divinely revealed possesses the one precise formality of the object of this science; and therefore is included under sacred doctrine as under one science.
Reply Obj. 1: Sacred doctrine does not treat of God and creatures equally, but of God primarily, and of creatures only so far as they are referable to God as their beginning or end. Hence the unity of this science is not impaired.
Reply Obj. 2: Nothing prevents inferior faculties or habits from being differentiated by something which falls under a higher faculty or habit as well; because the higher faculty or habit regards the object in its more universal formality, as the object of the common sense is whatever affects the senses, including, therefore, whatever is visible or audible. Hence the common sense, although one faculty, extends to all the objects of the five senses. Similarly, objects which are the subject-matter of different philosophical sciences can yet be treated of by this one single sacred science under one aspect precisely so far as they can be included in revelation. So that in this way, sacred doctrine bears, as it were, the stamp of the divine science which is one and simple, yet extends to everything. _______________________
FOURTH ARTICLE [I, Q. 1, Art. 4]
Whether Sacred Doctrine Is a Practical Science?
Objection 1: It seems that sacred doctrine is a practical science; for
a practical science is that which ends in action according to the
Philosopher (Metaph. ii). But sacred doctrine is ordained to action:
"Be ye doers of the word, and not hearers only" (James 1:22).
Therefore sacred doctrine is a practical science.
Obj. 2: Further, sacred doctrine is divided into the Old and the
New Law. But law implies a moral science which is a practical science.
Therefore sacred doctrine is a practical science.
On the contrary, Every practical science is concerned with human operations; as moral science is concerned with human acts, and architecture with buildings. But sacred doctrine is chiefly concerned with God, whose handiwork is especially man. Therefore it is not a practical but a speculative science.
I answer that, Sacred doctrine, being one, extends to things which belong to different philosophical sciences because it considers in each the same formal aspect, namely, so far as they can be known through divine revelation. Hence, although among the philosophical sciences one is speculative and another practical, nevertheless sacred doctrine includes both; as God, by one and the same science, knows both Himself and His works. Still, it is speculative rather than practical because it is more concerned with divine things than with human acts; though it does treat even of these latter, inasmuch as man is ordained by them to the perfect knowledge of God in which consists eternal bliss. This is a sufficient answer to the Objections. _______________________