At the beginning of Meditation 3:
The only thing Descartes knows is that he exists as a thinking thing, and that he has thoughts of various
Question: How can we escape the prison of the mental?
Prove God’s existence
Why does Descartes need to prove God’s existence?
Evil genius hypothesis keeps us from being sure of anything other than existence as a thinking thing.
Unsure about the external world, mathematics, etc.
If a good God existed, he would not deceive us
Descartes’ Ontological Argument
A second argument for God’s existence
Roughly the same as St. Anselm’s (10331109) Ontological Argument from the Proslogion
Uses the essence/existence distinction to prove that God’s essence necessitates his existence.
By reflecting on the concept of God, we can prove that God necessarily exists.
God is the one case for which existence and essence are not separable.
(1) God’s essence is that of an all perfect being.
(2) An all perfect being has every perfection.
(3) Existence is a perfection.
(4) Therefore, God has the perfection of existence; i.e. God exists
Kant’s Objection: Challenge Premise (3): Is existence a perfection?
Existence is not a real defining predicate.
Existence doesn’t anything to the concept of a thing
To say X exists doesn’t change the concept of X
Rather, it says that something exists which fits the concept
Existence claims tell us something about the world, but don’t tell us anything about the concept.