The existence of God is known from the consideration of his nature alone.
Demonstration
To say that an attribute is contained in the nature or in the concept of a thing is the same as to say that this attribute is true of this thing, and that it may be affirmed to be in it. (Definition IX )
But necessary existence is contained in the nature or in the concept of God (by Axiom X ).
Hence it may with truth be said that necessary existence is in God, or that God exists.
And this syllogism is the same as that of which I made use in my reply to the sixth article of these objections; and its conclusion may be known without proof by those who are free from all prejudice, as has been said in Postulate V . But because it is not so easy to reach so great perspicacity of mind, we shall essay to establish the same thing by other modes.
Proposition II
The existence of God is demonstrated, a posteriori , from this alone, that his idea is in us.
Demonstration
The objective reality of each of our ideas requires a cause in which this same reality is contained, not simply objectively, but formally or eminently (by Axiom V ).
But we have in us the idea of God (by Definitions II and VIII ), and of this idea the objective reality is not contained in us, either forrnally or eminently (by Axiom VI ), nor can it be contained in any other except in God himself (by Definition VIII ).