Summa summae S. Thomae sive compendium theologiae

A proposition is called per se nota whose truth becomes known through itself and without a medium distinct from itself, just as the sun is called per se visible, because it is seen by itself and not through another, more luminous medium.

I say: This proposition, God is, is self-evident in itself, not to us.¹

The first part is proved. That proposition is per se known quoad se whose predicate is included in the ratio of the subject, as its definition or a part of the definition, as this one: « Man is an animal; » for by that very fact it is immediate and lacks an a priori middle for proof. But the existence of God is thus included in the ratio of God; for God is essentially His own esse, or is necessarily and essentially a being that exists, as we shall prove below. Therefore.

The second part is proved. That proposition is not self-known as regards us in which the quiddity of the subject does not become known to us from the first and common apprehension of the terms, but requires discourse in order to become known to us; because then it cannot become known to us at once whether the predicate belongs to the subject. But the quiddity of God does not become known to us from the first and common apprehension of the terms, but through discourse. Therefore. — The minor is evident: because what God is, we do not understand as soon as we hear this word, God, just as from the utterance of these terms, whole and part, being and non-being, we at once understand what a whole is, what a part is, what being is, what non-being is; but what God is, even the wise themselves understand through discourse and very imperfectly. Therefore.

Here you have refuted the opinion of those more recent thinkers who say that the notion of the existence of God is innate in us; for by this innate notion of God they understand nothing other than that, without discursus, even an easy one, from the sole apprehension of the terms themselves, a sound and attentive mind understands that God exists, just as from the sole apprehension of the terms, without discursus, the first principles are understood: Whatever is, either is or is not, the whole is greater than its part, as Honoratus Tournely himself, the defender of this opinion, explains. But this is the same as saying that it is per se notum quoad nos that God exists: which we attacked in the second part of the conclusion.

[What the cause was why certain men asserted that « for God to exist is self-known, so that its contrary cannot be thought, and thus that God exists cannot be demonstrated, » the Angelic Doctor explains thus, I Contra gentes, c. 10 and 11: « The aforesaid opinion arises partly indeed from custom, by which from the beginning men have been accustomed to hear and invoke the name of God. But custom, and especially that which is from the beginning, acquires the force of nature: whence it comes about that those things with which the mind is imbued from մանկություն, are held so firmly as if they were naturally and self-known. But partly it comes about from this, that there is no distinction made between what is self-known simply and what is known with respect to us. For simply indeed that God exists is self-known, since this very thing which God is, is His own esse (existence). But because we cannot conceive in mind this very thing which God is, that is, the essence, it remains unknown with respect to us. »]