Ontological Proofs for the Existence of God:

(Anselm and Descartes)

I.  Anselm’s Version:

In a nutshell:  God is, by definition, “something than which nothing greater can be thought.”  He is “the greatest conceivable being.”

1.  If God did not exist, than we could conceive of something greater than God.

2.  But by definition, nothing is conceivably greater than God.

3.  Therefore God must exist.

A little more drawn out (Gaunilo’s formulation):

1.  Anselm has heard about a greatest conceivable being, and he knows the meanings of “greatest”, “conceivable”, and “being.”

2.  So Anselm has a conception of a greatest conceivable being.

3.  But since to exist in reality is much greater than to exist merely in the imagination, a conception of anything that doesn’t exist in reality couldn’t be a conception of a greatest conceivable being.

4.  Hence Anselm’s conception of a greatest conceivable being must be a conception of a thing that exists in reality, not just in the imagination.

5.  So the greatest conceivable being must exist in reality,

6.  And God would be the name of that greatest conceivable being.

7.  So God must exist in reality.

Descartes’ Version (From Meditation V):

1.  God, by definition, has all the perfections.

2.  Existence is a perfection.

3.  Therefore God (by definition) has existence.

Some Things to think about:

1.  Possible Counterexamples to this argument form (Gaunilo’s “perfect island”, Beisecker’s “Barney”)

2.  Necessarily referring expressions (“the shortest spy”).

3.  The Cartesian Circle (rears its ugly head toward the end of the 5^th meditation)

I can clearly and distinctly prove the existence of God.  And I can be assured in the soundness of this proof, because the certainty of what I clearly and distinctly conceive is guaranteed by God.