Saint Thomas Aquinas: Reason does not lead to the Trinity

Saint Thomas Aquinas confirmed Islamic theology

By Ibn Anwar, BHsc (Hons), MCollT

The Doctor Angelicus of the Roman Catholic church postulated rational argumentation for the existence of God in his so called quinque viæ (five ways). Saint Aquinas contends that with reason, one can be rest assured that God is absolutely one– the common denominator between Judaism and Islam. Although orthodox Christianity affirms the statement “God is One,” the church expanded the concept to include three persons (i.e., the Father, the Son and the Holy Spirit) creating what is known as the Trinity. The Trinitarians adamantly insist that to believe in anything less than the Trinity is heretical and blasphemous. In orthodox Christianity, then, the fundamental concept of God is not simply that “He is One” but that “He is THREE in ONE.” Without getting into the complexities that such a doctrine entails in this short article, it is important to note that in Saint Aquinas’s rational postulation, he comes to the conclusion that through reason, one can only reach the conclusion that God is One but never that He is a Trinity.

Distinguished Professor of Philosophy at Fordham University Dr. Brian Davies writes:

“As I have noted, Aquinas claims that the doctrine of the Trinity cannot be arrived by reason. His consistently upheld position is that reason can lead us to know that there is but one God, though it cannot prove that there is distinction in God as proclaimed by the doctrine of the Trinity.” [1]

According to Saint Aquinas, who is without a doubt one of the greatest of Catholic thinkers hence the title given to him by Saint Antoninus, i.e., Doctor Angelicus (Angelic Doctor), the doctrine of the Trinity cannot be proven or appreciated through reason. Since reasoning cannot bring us to the Trinity, it must be correctly regarded as an unreasonable doctrine.


[1] Davies, B. (2016). Thomas Aquinas’s Summa Contra Gentiles: A Guide and Commentary. New York: Oxford University Press. p. 445 fn. 14

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