Chapter 6 — That God’s existence is necessary in itself

The same line of reasoning shows that it is necessary for God to exist. For everything that has the possibility of existing and not existing is mutable. But God is absolutely immutable, as has been demonstrated. Therefore, God does not have the possibility of existing and not existing. But anything that exists, and does not have the possibility of not existing, exists necessarily, since to exist necessarily and to be unable not to exist mean the same thing. Therefore, it is necessary for God to exist.

Moreover, everything that has the possibility of existing and of not existing needs something else to make it exist, for in itself it stands indifferently toward either alternative. But that which causes another thing to exist is prior to that thing. Hence there is something prior to anything that has the possibility of existing and of not existing. However, nothing is prior to God. Therefore, he does not have the possibility of existing and of not existing, but he must necessarily exist. And since there are some necessary things that have a cause of their necessity, which cause must be prior to them, God, who is the first of all, has no cause of his own necessity. Hence God’s existence is necessary by his very nature.