Whether it is Self-Evident that God Exists
We proceed to the first article thus:
1. It seems to be self-evident that God exists. Things are said to be self-evident when the knowledge of them is naturally in us, as is obviously the case with first principles. Now the Damascene says that |the knowledge that God exists is naturally inborn in all men| (1 De Fid. Orth. I, 3). It is therefore self-evident that God exists.
2. Again, as the philosopher says of the first principles of demonstration, whatever is known as soon as the terms are known is self-evident (1 Post. An., ch.2). Thus we know that any whole is greater than its part as soon as we know what a whole is, and what a part is. Now when it is understood what the term |God| signifies, it is at once understood that God exists. For the term |God| means that than which nothing greater can be signified, and that which exists in reality is greater than that which exists only in the intellect. Hence since |God| exists in the intellect as soon as the term is understood, it follows that God exists also in reality. It is therefore self-evident that God exists.
3. Again, it is self-evident that truth exists. For truth exists if anything at all is true, and if anyone denies that truth exists, he concedes that it is true that it does not exist, since if truth does not exist it is then true that it does not exist. Now God is truth itself, according to John 14:6: |I am the way, and the truth, and the life.| It is therefore self-evident that God exists.
On the other hand: no one can conceive the opposite of what is self-evident, as the philosopher explains in dealing with the first principles of demonstration (4 Metaph., text 9; 1 Post. An., texts 5 and ult.). Now the opposite of |God exists| can be conceived, according to Ps.53:1: |The fool hath said in his heart, There is no God.| It follows that it is not self-evident that God exists.
I answer: there are two ways in which a thing may be self-evident. It may be self-evident in itself, but not self-evident to us. It may also be self-evident both in itself and to us. A proposition is self-evident when its predicate is contained in the meaning of its subject. For example, the proposition |man is an animal| is self-evident, because |animal| is contained in the meaning of |man.| Hence if the predicate and the subject are known to everyone, the proposition will be self-evident to everyone. This is obviously the case with regard to the first principles of demonstration, whose terms are universals known to everyone, such as being and not-being, whole, part, and the like. But when there are some to whom the predicate and the subject are unknown, the proposition will not be self-evident to them, however self-evident it may be in itself. Thus Boethius says (Lib. de Hebd. -- Whether all Existence is Good): |it happens that some universal concepts of mind are self-evident only to the wise, e.g., that the incorporeal is not in space.| I say, then, that this proposition |God exists| is self-evident in itself, since its predicate is the same with its subject. For God is his existence, as we shall show in Q.3, Art.4. But since we do not know what God is, it is not self-evident to us, but must be proved by means of what is better known to us though less well known to nature, i.e., by means of the effects of God.
On the first point: the knowledge that God exists is inborn in us in a general and somewhat confused manner. For God is the final beatitude of man, and a man desires beatitude naturally, and is also naturally aware of what he desires. But this is not absolute knowledge that God exists, any more than to know that someone is coming is to know that Peter is coming, even though it should actually be Peter who comes. Many indeed think that riches are man's perfect good, and constitute his beatitude. Others think that pleasures are his perfect good, and others again something else.
On the second point: he who hears the term |God| may not understand it to mean that than which nothing greater can be conceived, since some have believed that God is a body. But given that one understands the term to mean this, it does not follow that he understands that that which the term signifies exists in the nature of things, but only that it exists in the intellect. Neither can it be argued that God exists in reality, unless it is granted that that than which nothing greater can be conceived exists in reality, which is not granted by those who suppose that God does not exist.
On the third point: it is self-evident that truth in general exists. But it is not self-evident to us that the first truth exists.