One day when I was in graduate school I was walking across campus with a fellow student when we ran into another student who had gone to high school with my friend. They started chatting, catching up, and my friend's friend asked her what classes she was taking. Among the ones she mentioned was the course in metaphysics that I was also taking. Her friend looked surprised and excited.
"You know," she said, "my father is one of the foremost metaphysicians in the country!"
My friend and I exchanged glances. Here we were, enrolled in a graduate-level seminar in metaphysics, and neither one of us had ever heard of one of the foremost metaphysicians in the country. Were we getting a proper education? Was Duke University ripping us off? Was David Sanford, our teacher and himself one of the foremost metaphysicians in the country, really a fraud who had neglected to mention this great metaphysician in class?
Not to worry. It turns out that my friend's friend had a different meaning of "metaphysics" in mind than we had. By "metaphysician" she meant somebody who studied the "occult arts". Her father wrote books about channeling and levitation.
The word "metaphysics" has an interesting history. The discipline itself may be said to go back as far as the 6th century B. C., but we first find the word, if it is a word, associated with a group of treatises by Aristotle. Aristotle himself did not give these treatises the title "Metaphysics". Indeed, he did not even group these treatises together as a single work. Rather, the title derives from the Greek expression ta meta ta phusika, "the things that come after the natural things", and it refers to the fact that the materials contained in this fourteen treatises were thought by somebody somewhere to be appropriate subjects of study to take up after studying the phenomena of the natural world. We don't know who put that title on these treatises. It might have been Andronicus, a 1st century scholar who was among the first to collect the works of Aristotle together and organize them topically. It might have been one of the librarians at Alexandria. (One wag suggested that the title really refers to the place on the library shelf where you might be able to find these treatises: "They're right down there, just after the treatises on nature." Unlikely.)
After antiquity metaphysics became the cornerstone of most philosophical enquiry. It was "the queen of philosophy" just as philosophy itself was the queen of the humanities. Aristotle's own proper name for the subject matter contained in those treatises was "First Philosophy", or "Philosophy in the proper sense of the word", so you can get some idea of how he viewed the topic. Or perhaps I should say "topics", since the fourteen treatises are not marked by the kind of thematic unity one might like to find in a sustained philosophical investigation. Aristotle himself characterized "First Philosophy" in four different ways: the study of first principles; the study of being qua being; the study of substance (in the philosophical, not materialist, sense); and the study of theology.
That last one is rather interesting for the Thomist, since St. Thomas Aquinas, famously, held that theology is not a branch of philosophy at all, but rather philosophy is the tool of theology (this is a rather controversial way of reading the Angelic Doctor's position, but it is enough to point out that he certainly did not regard theology as a department of philosophy). In holding this he was surely right: theology requires a revealed foundation, which philosophy cannot do (there are those who claim that philosophy itself requires logic as a "tool"--this is why, for example, Aristotle's logical works came to be known collectively as "the organon" in the medieval period: "organon" is Greek for "tool" or "instrument"). So a particular metaphysical scheme cannot possibly be a prerequisite for doing theology, since metaphysics itself is a department of philosophy and not something that theology needs to presuppose. Anyone who works in theology knows that they must have some view about metaphysics, of course, but it cannot be a requirement of what they do that they assume this or that metaphysics.
Hence we cannot require, as a matter of orthodoxy or de fide teaching that a Christian theologian adopt Platonic, or Aristotelian, or Thomistic metaphysics. There are some metaphysical schemes that the Christian must reject, but none that he must accept on pain of heresy. Metaphysics will be useful as an explanatory tool, and in certain cases it may be well-advised to declare the rejection of certain metaphysical viewpoints off limits (hence the Tridentine anathema against those who reject transsubstantiation), but the theologian is remarkably free in this particular sphere.
This will be an important thing to keep in mind as we progress in our investigation of Augustine, Maximus, Gregory, and free will.