Aquinas on Faith and Reason

Editor’s note: This post originally appeared on Think Apologetics. Tabernacle of David considers this resource trustworthy and Biblically sound.


Thomas Aquinas (1224–1274) was a theologian, philosopher, and the consummate apologist of the medieval church. Born in Italy, he joined the Dominican order. He was canonized by the Roman church in 1326. Aquinas wrote De anima (On the Soul), De Ente et Essentia (On Being and Essence), De veritate (On Truth), On the Power of God, Summa contra Gentiles, and The Unity of the Intellect Against the Averoeists. By far his most important and influential writing went into his magnum opus systematic theology, Summa Theologica, which was still unfinished at his death.

The thought of Aquinas is rich and varied. He wrote on many topics, including faith and reason, revelation, knowledge, reality, God creation human beings, government, and ethics. His mind was intensely analytical, making his arguments difficult for the modern reader to follow. His writing style is sometimes dialectical and highly complex, especially in Summa Theologica. This is less true in Summa contra Gentiles.

One area of Aquinas thought I wanted to mention is the relationship between faith and reason:

Aquinas did not believe that human reason was without limitations. In fact he offered many arguments as to why reason is insufficient and revelation/faith is needed.

Following Jewish philosopher Moses Maimonides, Aquinas set forth five reasons why we must first believe what we may later be able to provide good evidence for (Maimonides, 1.34):
1. The object of spiritual understanding is deep and subtle, far removed from sense perception.
2. Human understanding is weak as it fights through these issues.
3. A number of things are needed for conclusive spiritual proof. It takes time to discern them.
4. Some people are disinclined to rigorous philosophical investigation.
5. It is necessary to engage in other occupations besides philosophy and science to provide the necessities of life (On Truth, 14.10, reply).

Aquinas said it is clear that, “if it were necessary to use a strict demonstration as the only way to reach a knowledge of the things which we must know about God, very few could ever construct such a demonstration and even these could do it only after a long time.”

Elsewhere, Aquinas lists only three basic reasons divine revelation is needed.
1. Few possess the knowledge of God, some do not have the disposition for philosophical study, and others do not have the time or are indolent.
2. Time is required to find the truth. This truth is very profound, and there are many things that must be presupposed. During youth the soul is distracted by “the various movements of the passions.”
3. It is difficult to sort out what is false in the intellect. Our judgment is weak in sorting true from false concepts. Even in demonstrated propositions there is a mingling of false.
“That is why it was necessary that the unshakable certitude and pure truth concerning divine things should be presented to men by way of faith” (Gentiles, 1.4, 2–5).

The Noetic Effects of Sin

Aquinas also understood the Noetic Effects of Sin. Clearly, the mind falls far short when it comes to the things of God. As examples of weakness Aquinas looked at the philosophers and their errors and contradictions. “To the end, therefore, that a knowledge of God, undoubted and secure, might be present among men, it was necessary that divine things be taught by way of faith, spoken as it were by the Word of God who cannot lie” (ibid., 2a2ae. 2, 4). For “the searching of natural reason does not fill mankind’s need to know even those divine realities which reason could prove”(ibid., 2a2ae.2, 4, reply).

As a result of the noetic effects of sin, grace is needed. Aquinas concluded that “If for something to be in our power means that we can do it without the help of grace, then we are bound to many things that are not within our power without healing grace—for example to love God or neighbor.” The same is true of belief. But with the help of grace we do have this power (ibid., 2a2ae.2, 6, ad 1).

However, Aquinas did not believe that sin destroyed human rational ability. “Sin cannot destroy man’s rationality altogether, for then he would no longer be capable of sin” (ibid., 1a2ae.85, 2).

Not only is faith necessary because of human depravity, but also because some things simply go beyond the power of reason. That does not mean they are contrary to reason, but that they are not fully comprehensible. Just because we have no reasons for things that go beyond reason does not mean they are not rational. Every belief that is not self-evident can be defended as necessary. We may not know the argument, but it exists. It at least is known to God “and to the blessed who have vision and not faith about these things” (De Trinitate, 1.1.4; On Truth, 14.9, ad 1).

While human reason cannot attain to the things of faith, it is the preface to them. While “philosophical truths cannot be opposed to truths of faith, they fall short indeed, yet they also admit common analogies; and some moreover are foreshadowing, for nature is the preface of grace” (De Trinitate, 2.3).

Aquinas does not believe that reason alone can bring anyone to faith. Salvation is accomplished only by the grace of God. Faith can never be based on reason. At best it can only be supported by reason. Thus, reason and evidence never coerce faith. There is always room for unbelievers not to believe in God, even though a believer can construct a valid proof that God exists. Reason can be used to demonstrate that God exists, but it can never in itself persuade someone to believe in God. Only God can do this, working in and through their free choice.

Sources: Geisler, N. L. (1999). BECA Grand Rapids, Mich.: Baker Books., 725-728.

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