“Now, there are some objects of speculation that depend on matter for their being, for they can only exist in matter. And these are subdivided. Some depend on matter both for their being and for their being understood, as do those things whose definition contains sensible matter and which, as a consequence, cannot be understood without sensible matter. For example, it is necessary to include flesh and bones in the definition of man. It is things of these sort that physics or natural science studies. On the other hand, there are some things that, although dependent upon matter for their being, do not depend on it for their being understood, because sensible matter is not included in their definitions. This is the case with lines and numbers—the kinds of objects with which mathematics deals. There are still other objects of speculative knowledge that do not depend upon matter for their being because they can exist without matter; either they never exist in matter, as in the case of God and the angels, or they exist in matter in some instances and not in others, as in the case of substance, quality, potency, act, one and many, and the like. The science that treats of all these is theology or divine science, which is so called because its principal object is God. By another name it is called metaphysics; that is to say, beyond physics, because it ought to be learned by us after physics, for we have to proceed from sensible things to those that are non-sensible. It is also called first philosophy, inasmuch as all the other sciences, receiving their principles from it, come after it….”
~St. Thomas Aquinas: Commentary on Boethius’s De Trinitate, q. 5, a. 3, Reply.
(From An Aquinas Reader, ed. Mary T. Clark)
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