In my opinion, the greatest Christian thinker of all time, after the apostles died, was Thomas Aquinas. Etienne Gilson, in his work The Christian Philosophy Of St Thomas Aquinas, takes on the task of defining what distinguished theology from philosophy for Aquinas.
This issue comes up again and again when I hear cultists and even Christians claim that Christian teaching was hijacked by philosophy during the Middle Ages. We’re told that Plato and Aristotle took center stage and that biblical revelation was shoved aside.
Is it true that men like Aquinas did not take the Bible seriously, that they placed the philosophies of Plato and Arsitotle in judgment over revealed theological truths?
Gilson explains that in the case of Aquinas, nothing could be further from the truth. So how did Aquinas distinguish between theology and philosophy?
It has become customary to label “theological” any conclusion whose premises presuppose faith in a divinely revealed truth, and to label “philosophical” any conclusion whose premises are purely rational , that is, known by the light of natural reason alone. This is not the point of view stated by St. Thomas himself at the beginning of his Prologue to the Second Book of his commentary on the Sentences of Peter Lombard. According to him, the philosopher considers the nature of things as they are in themselves, whereas the theologian considers them in their relation to God conceived as being both their origin and their end.
From this point of view, every conclusion concerning God himself, or the relations of being to God, is theological in its own right. Some of these conclusions presuppose an act of faith in the divine revelation, but some of them do not. All of them are theological; those, among them, which are purely rational, belong to theology no less than the others. The only difference is that, since these do not presuppose faith , they can be extracted from their theological context and judged, from the point of view of natural reason, as purely philosophical conclusions.
To repeat, philosophy considers the “nature of things as they are in themselves” whereas theology considers the nature of things “in their relation to God conceived as being both their origin and their end.” Thus every conclusion about God or about the world in relation to God is theological first and foremost. Any theological conclusion which does not presuppose faith (is purely rational) is also a philosophical conclusion.
Gilson explains why this distinction is important:
This is an extremely important point in that it enables us to understand how strictly metaphysical knowledge can be included within a theological structure without losing its purely philosophical nature. Everything in the Summa [Theologiae, Aquinas’s most famous work,] is theological, yet, elements of genuinely philosophical nature are part and parcel of Thomistic theology precisely because, according to St. Thomas himself, the distinction between theology and philosophy does not adequately answer the distinction between faith and reason.
Now we come to Aquinas’s concerns with mixing philosophy and theology. Gilson writes that critics of Aquinas often misunderstand what Aquinas was trying to do.
According to some of his modern interpreters, St. Thomas thought of himself as a philosopher who was not anxious to compromise the purity of his philosophy by admitting into it the slightest mixture of theology. But as a matter of fact , the real St. Thomas was afraid of doing just the reverse. In the Summa Theologiae, his problem was not how to introduce philosophy into theology without corrupting the essence of philosophy; it was rather how to introduce philosophy into theology without corrupting the essence of theology (emphasis added).
Not only the hostility of the “Biblicists” of his time warned him of the problem , but he was himself quite as much aware of it as they were. And the more freely he made use of philosophy, the more was he aware of the problem. As he himself understands it, theology must be conceived as a science of Revelation. Its source is the word of God. Its basis is faith in the truth of this word. . . . For theologians who were not in the least worried about philosophy, no problem actually arose. Persuaded that they should add nothing human to the bare deposit of revelation, they could rest assured that they were respecting the integrity and the unity of the Sacred Science. They proceeded from faith to faith, by faith.
For St. Thomas Aquinas the problem was rather different. It was a question of how to integrate philosophy into sacred science, not only without allowing either the one or the other to suffer essentially thereby, but to the greater benefit of both. In order to achieve this result, he had to integrate a science of reason with a science of revelation without corrupting at the same time both the purity of reason and the purity of revelation.
Thus Aquinas was eminently aware of the dangers of mixing theology and philosophy. Rather than placing philosophy above theology, he did just the opposite. One can argue about how successful he was, but there can be no argument that Aquinas allowed philosophical considerations to knowingly trump revealed biblical truth.