Entry 0373: Is the Proposition “God exists” a Self-Evident Proposition?
Several times in his writings, Saint Thomas Aquinas answered the question “Is it self-evident that God exists?” by saying that the proposition “God exists” is self-evident in itself, but not self-evident with respect to us. (1)
(3) See Aquinas, Commentary on Boethius’ De Hebdomadibus, lecture 1.
Self-evident propositions are propositions that are known as soon as their terms are known. A self-evident proposition emerges when subject and predicate disclose their own intelligibilities by themselves, without the need for recourse to the mediating intelligibility of other terms. (2)
For example, Aquinas tells us that the affirmation, “the remainders of equals subtracted from equals are equal,” is self-evident in itself because the terms that enter into the proposition disclose their own intelligibilities by themselves. (3) This can be seen easily as follows:
If you pour exactly 16 milliliters of water into each of two identical glasses and then take exactly 4 milliliters of water away from each glass, you are left with two glasses each containing exactly 12 milliliters of water.
The cognitive sequence is the following: (a) everyone understands what it is to be equal, and (b) everyone understands what it is to be subtracted. Therefore, (c) everyone understands that “if you take equals away from equals, the remainders are equal.”
The convincing force of a self-evident proposition is grasped automatically. A self-evident proposition needs no proof. Its meaning is obvious. And, once the terms are understood, the mind instantly assents to the truth of a self-evident proposition.
Why, then, did Aquinas say that the proposition “God exists” is self-evident in itself, but not self-evident with respect to us?
Even when a proposition is self-evident in itself, for those who are not able to comprehend the intelligibility of the terms, the truth of the proposition remains unknown, and thus for them the proposition is not self-evident.
The predicate “exists” belongs indeed to the understanding of the subject “God,” but since the subject “God” is beyond our comprehension, the connection that exists between the subject “God” and the predicate “exists” is not instantly perceived by the human mind.
Our initial contact with the term “God” and our efforts to understand the intelligibility of the term “God” do not result in our understanding automatically the validity and certainty of a connection between the subject “God” and the predicate “exists.” The validity and certainty of this connection has to be derived and established through the mediation of the intelligibility of other terms.
For this reason, we see that throughout the centuries thinkers have used the tools of demonstration and reasoning to come up with arguments for the existence of God.
The truth of the existence of God is a conclusion established through reasoning. The proposition “God exists” is not a self-evident proposition with respect to us.
(1) See Thomas Aquinas, Summa theologiae, part I, question 2, article 1; De veritate, question 10, article 12; De potentia, question 7, article 2, ad 9; Summa contra gentiles, book 1, chapter 11, nos. 1-4; and In I Sententiarum, distinction 3, article 2.
(2) See Michael V. Dougherty, “Thomas Aquinas on the Manifold Senses of Self-Evidence,” The Review of Metaphysics 59 (2006): 601-630; and Joseph M. Christianson, “Aquinas: The Necessity and Some Characteristics of the Habit of First Indemonstrable (Speculative) Principles,” The New Scholasticism 62 (1988): 249-296.