Article 8: “Whether Sacred Doctrine is a matter of argument?”
In the eighth article Thomas makes the explicit case for something he has already implied, which is that sacred doctrine is a matter of argument, by which he means that it is demonstrative in the Aristotelian sense: it logically proves its conclusions from the first principles revealed in sacred scripture. What this further means is that Sacred Doctrine uses reason. As Thomas puts it, “sacred doctrine makes use even of human reason, not indeed, to prove faith… but to make clear other things that are put forward in this doctrine.” We use reason, in other words, to make inferences about what is logically entailed in the teaching of Sacred Scripture. Reason is also valuable in its role of providing a manifestatio, or rational clarification or illumination of the inherent reasonableness or intelligibility of the faith. A good example of this role of reason within theology occurs in St. Thomas’s discussion of the Trinity: we can’t know by reason that God is a Trinity of persons, yet reason is effective in elucidating the coherence of this doctrine.
To summarize the first question of the Summa, then, what makes theology to be theology for St. Thomas? In good Aristotelian fashion, we can distinguish the following “four causes” of theology:
- theology’s material cause: Scripture is its data, its material cause; it is that “out of which” theology is made.
- theology’s efficient cause: this is God’s act of revealing himself through Scripture; if God doesn’t reveal himself, there can be no sacred doctrine.
- theology’s formal cause: what is the form or species of sacred doctrine? What kind of thing is it? What is its essence? It is a science, which is to say, an ordered body of knowledge of causes. What is theology? It is thinking causally (from premises to conclusions) about the articles of faith, asking how this doctrine logically causes or entails that doctrine. This is how theology proceeds; this is the theological method of the Aristotelian Christianity of the Scholastic Middle Ages.
- theology’s final cause: what’s the goal of sacred doctrine? At a speculative level it is simply the knowledge and truth of God; at the practical level, the goal is human salvation.
 Peter Kreeft, Summa of the Summa.