St. Thomas Aquinas’ Commentary on Boethius’s De Trinitate, q. 5, a. 1, reply

The theoretical or speculative intellect is properly distinguished from the operative or practical intellect by the fact that the speculative intellect has for its end the truth that it contemplates, while the practical intellect directs the truth under consideration to activity as to an end. So the Philosopher says in the De Anima that they differ from each other by their ends; and in the Metaphysics he states that “the end of speculative knowledge is truth, but the end of practical knowledge is action.” Now, since matter must be proportionate to the end, the subject-matter of the practical sciences must be things that can be made or done by us, so that we can direct the knowledge of them to activity as to an end.

On the other hand, the subject-matter of the speculative sciences must be things that cannot be made or done by us, so that our knowledge of them cannot be directed to activity as to an end. And the speculative sciences must differ according to the distinctions among these things.

Now we must realize that when habits or powers are differentiated by their objects they do not differ according to just any distinction among these objects, but according to the distinctions that are essential to the objects as objects. For example, it is incidental to a sense object as such whether it be an animal or a plant. Accordingly, the distinction between the senses is not based upon this difference but rather upon the difference between color and sound. So the speculative sciences must be divided according to differences between objects of speculation, considered precisely as such. Now an object of this kind ─ namely, an object of a speculative power ─ derives one characteristic from the side of the power of intellect and another from the side of the habit of science that perfects the intellect. From the side of the intellect it has the fact that it is immaterial, because the intellect itself is immaterial. From the side of habit of science it has the fact that it is necessary, for science treats of necessary matters, as is shown in the Posterior Analytics. Now everything that is necessary is, as such, immobile, because everything changeable is, as such, able to be or not to be, either absolutely or in a certain respect, as is said in the Metaphysics. Consequently, separation from matter and motion, or connection with them, essentially belongs to an object of speculation, which is the object of speculative science. As a result, the speculative sciences are differentiated according to their degree of separation from matter and motion.

(1) Now there are some objects of speculation that depend on matter for their being, for they can exist only in matter. And these are subdivided. (a) 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 this sort that physics or natural science studies. (b) On the other hand, there are some things that, Although dependent upon matter for their being, do not depend upon it for their being understood, because sensible matter is not included in their definitions. This is the case with lines and numbers ─ the kind of objects with which mathematics deals. (2) There are still other objects of speculative knowledge that do not depend upon matter for their being, because they can exist without matter; (a) either they never exist in matter, as in the case of God and the angels, or (b) they exist in matter in some instances and not in others, as in the case of substance, quality, being, 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. Now there can be nothing that depends upon matter for its being understood but not for its being, because by its very nature the intellect is immaterial. So there is no fourth kind of philosophy besides the ones mentioned.

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Return to Lesson 29: Yes, There Is a Theory of Everything