(CG 1/009). The Order and Mode of Procedure in this Work (Book 1: Of God As He Is In Himself) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THIS opinion rests on the following grounds:

1. Those truths are self-evident which are recognised at once, as soon as the terms in which they are expressed are known. Such a truth is the assertion that God exists: for by the name 'God' we understand something greater than which nothing can be thought. This notion is formed in the understanding by whoever hears and understands the name 'God,' so that God must already exist at least in the mind. Now He cannot exist in the mind only: for what is in the mind and in reality is greater than that which is in the mind only; but nothing is greater than God, as the very meaning of the name shows: it follows that the existence of God is a self evident truth, being evidenced by the mere meaning of the name.

2. The existence of a being is conceivable, that could not be conceived not to exist; such a being is evidently greater than another that could be conceived not to exist. Thus then something greater than God is conceivable if He could be conceived not to exist; but anything 'greater than God' is against the meaning of the name 'God.' It remains then that the existence of God is a self-evident truth.

3. Those propositions are most self-evident which are either identities, as 'Man is man,' or in which the predicates are included in the definitions of the subjects, as 'Man is an animal.' But in God of all beings this is found true, that His existence is His essence, as will be shown later (Chap. XXII); and thus there is one and the same answer to the question 'What is He?' and 'Whether He is.' Thus then, when it is said 'God is,' the predicate is either the same with the subject or at least is included in the definition of the subject; and thus the existence of God will be a self-evident truth.

4. Things naturally known are self-evident: for the knowledge of them is not attained by enquiry and study. But the existence of God is naturally known, since the desire of man tends naturally to God as to his last end, as will be shown further on (B. 111, Chap. XXV).

5. That must be self-evident whereby all other things are known; but such is God; for as the light of the sun is the principle of all visual perception, so the divine light is the principle of all intellectual cognition.