|Portrait of Leibniz|
Edward Feser, in his book Five Proofs of the Existence of God, (Chapter 5, “The Rationalist Proof”), explains how Leibniz’s conception of PSR can be deployed to prove the existence of God. Feser’s argument is that when everything has a cause, then there has to be an ultimate cause from which all other causes (and their effects) follow. The ultimate cause must go outside the series of must go outside the series of contingencies and must be necessary—this ultimate cause is God.
He offers a 27 point formal statement of the argument, in which he makes the leap towards proving the God’s existence in point 14: “But that there are any contingent things at all must have some explanation, given PSR; and the only remaining explanation is in terms of a necessary being as cause.”
In the final paragraph, Feser says:
“The universe’s existence cannot be explained in terms of its own nature, because it is not purely actual (given that it has potentialities), not simple (given that it has parts), and not subsistent existence itself (since it is as contingent as its parts are). Its explanation must therefore be found in something distinct from it. The difference between God and the world then is that not only one has an explanation and the other lacks it, but rather that one is self-explanatory while the other is not.”