Aquinas on Faith & Reason
On the one hand, there are truths that completely surpass the capability of human reason, for example, the doctrine of the Trinity. On the other hand, many truths lie within the grasp of human reason, such as the existence of God. In the first three volumes of the Summa contra gentiles, Thomas attempts to prove these truths of reason, including the existence and nature of God, the orders of creation, the nature and end of man, and so forth. But when he comes to the fourth volume, in which he handles subjects like the Trinity, the incarnation, the sacraments, and the last things, he suddenly changes his method of approach. He states that these things are to be proved by the authority of Holy Scripture, not by natural reason. Because these doctrines surpass reason, they are properly objects of faith.
Now at first blush this seems to suggest that for Aquinas these truths of faith are mysteries, somehow “above logic.” But here we must be very careful. For as I read Aquinas, that’s not how he defines his terms. Rather he seems to mean that truths of faith surpass reason in the sense that they are neither empirically evident nor demonstrable with absolute certainty. He makes no suggestion that truths of faith transcend Aristotelian logic.
Now at first blush this seems to suggest that for Aquinas these truths of faith are mysteries, somehow “above logic.” But here we must be very careful. For as I read Aquinas, that’s not how he defines his terms. Rather he seems to mean that truths of faith surpass reason in the sense that they are neither empirically evident nor demonstrable with absolute certainty. He makes no suggestion that truths of faith transcend Aristotelian logic.
Rather there are just no empirical facts which make these truths evident or from which these truths may be inferred. For example, although the existence of God can be proved from his effects, there are no empirical facts from which the Trinity may be inferred. Or again, the eschatological resurrection of the dead cannot be proved, because there is no empirical evidence for this future event. Elsewhere Thomas makes it clear that truths of faith cannot be demonstrated by reason alone, either. He maintains that we Christians must use only arguments that prove their conclusions with absolute certainty; for if we use mere probability arguments, the insufficiency of those arguments will only serve to confirm the non-Christian in his unbelief.
Thus, the distinction Thomas makes between truths of reason and truths of faith is rather like Augustine’s distinction between seeing and believing. Truths of reason may be “seen”—that is, either proved with rational certainty or accepted as empirically evident—whereas truths of faith must be believed, since they are neither empirically evident nor rationally provable. This does not mean that truths of faith are incomprehensible or “above logic.”
Now because truths of faith can only be believed, does this imply that Thomas is in the end a fideist or an authoritarian? The answer seems clearly no. For like Augustine he proceeds to argue that God provides the signs of miracle and prophecy, which serve to confirm the truths of faith, though not demonstrating them directly.
Thus, the distinction Thomas makes between truths of reason and truths of faith is rather like Augustine’s distinction between seeing and believing. Truths of reason may be “seen”—that is, either proved with rational certainty or accepted as empirically evident—whereas truths of faith must be believed, since they are neither empirically evident nor rationally provable. This does not mean that truths of faith are incomprehensible or “above logic.”
Now because truths of faith can only be believed, does this imply that Thomas is in the end a fideist or an authoritarian? The answer seems clearly no. For like Augustine he proceeds to argue that God provides the signs of miracle and prophecy, which serve to confirm the truths of faith, though not demonstrating them directly.
Because of these signs, Aquinas held that a man can see the truths of faith: “Then they are indeed seen by the one who believes; he would not believe unless he saw that they are worthy of belief on the basis of evident signs or something of this sort.”6 Thomas calls these signs “confirmations,” “arguments,” and “proofs” for the truths of faith.7 This seems to make it clear that Aquinas believed there are good grounds for accepting the truths of faith as a whole. The proofs of miracle and prophecy are compelling, although they are indirect. Thus, for example, the doctrine of the Trinity is a truth of faith because it cannot be directly proved by any argument; nevertheless, it is indirectly proved insofar as the truths of faith taken together as a whole are shown to be credible by the divine signs.
Thomas’s procedure, then, may be summarized in three steps: (1) Fulfilled prophecies and miracles make it credible that the Scriptures taken together as a whole are a revelation from God. (2) As a revelation from God, Scripture is absolutely authoritative. (3) Therefore, those doctrines taught by Scripture that are neither demonstratively provable nor empirically evident may be accepted by faith on the authority of Scripture. Thus, Aquinas can say that an opponent may be convinced of the truths of faith on the basis of the authority of Scripture as confirmed by God with miracles.
Thomas’s procedure, then, may be summarized in three steps: (1) Fulfilled prophecies and miracles make it credible that the Scriptures taken together as a whole are a revelation from God. (2) As a revelation from God, Scripture is absolutely authoritative. (3) Therefore, those doctrines taught by Scripture that are neither demonstratively provable nor empirically evident may be accepted by faith on the authority of Scripture. Thus, Aquinas can say that an opponent may be convinced of the truths of faith on the basis of the authority of Scripture as confirmed by God with miracles.
Again the question arises: How do we know that the purported miracles or fulfilled prophecies ever took place? The medieval thinkers, lacking the historical method, could not answer this question. They developed a philosophical framework in which the signs of credibility confirmed the truths of faith, but they had no way of proving the signs themselves. About the only argument was Augustine’s indirect proof from the miracle of the Church. Thus, Thomas declares,
Now such a wondrous conversion of the world to the Christian faith is a most indubitable proof that such signs did take place. … For it would be the most wondrous sign of all if without any wondrous signs the world were persuaded by simple and lowly men to believe things so arduous, to accomplish things so difficult, and to hope for things so sublime.
A final word might be added. With Aquinas we see the reduction of faith to an epistemological category; that is to say, faith was no longer trust or commitment of the heart, but became a way of knowing, complementary to reason. Faith was essentially intellectual assent to doctrines not provable by reason—hence, Aquinas’s view that a doctrine cannot be both known and believed: if you know it (by reason), then you cannot believe it (by faith). Thus, Aquinas lost the view of faith as trust or commitment. This same intellectualist understanding of faith characterized the documents of the Council of Trent and of Vatican I but was adjusted in the documents of Vatican II.
Craig, W. L. (1994). Reasonable faith : Christian truth and apologetics (Rev. ed., pp. 20–22). Wheaton, Ill.: Crossway Books.
