1. Arguments for The Existence of God
Ontological
Cosmological
Teleological

2. God’s Existence Not subjective Not unprovable in principle
Natural Theology: Knowing God through reason
Biblical Theology: Knowing God through revelation

3. The Ontological Argument
A priori (vs. a posteriori)
God exists by definition
If you think about the concept of God hard enough, you’ll see that he must exist

4. Descartes (1596–1650) God is a perfect being
A perfect being must contain all perfections
Existence is a perfection.
God exists.

5. Anselm (1033–1109) Proslogion (“Discourse)
Originally “Faith Seeking Understanding”
I understand in order to believe vs.
I believe in order to understand.

6. Anselm’s Version Reductio ad absurdum
Indirect proof - show that atheism leads to a contradiction, so theism must be true

7. Anselm’s Version Assume God doesn’t exist God exists only in the mind
The Greatest Conceivable Being (GCB) exists only in the mind
But this can’t be true because there is a greater being, which exists not only in the mind but in reality as well

8. Anselm’s Version The GCB exists ONLY in the mind The GCB isn’t the GCB
A is not A <-- Contradiction
Atheism leads to a contradiction
Atheism is false
It’s not true that God doesn’t exist
God exists

9. Anselm’s Version Assume not-G. If not-G, then GCB = not-GCB Not-not-G

10. Gaunillo’s Objection
The Greatest Conceivable Island Objection (Perfect Island, Lost Island)
Assume the GCI exists only in the mind.
If the GCI exists only in the mind, then a greater island can be imagined, which exists not only in the mind but in reality
The GCI isn’t really the GCI (contrad.)
The GCI must exist.

11. Gaunillo’s Objection
Anselm: My argument doesn’t work for the greatest conceivable kind of type of being, just the greatest conceivable being in general.
Once the limiting, imperfect particulars of the island are eliminated, the Island starts to look like God.

12. Kant’s Objection Existence isn’t a property (real predicate)
The concept of a real $100 is the same as an imaginary $100; it’s just that one is instantiated.
Existence applies to a thing and it’s properties together; it is not itself a property.

13. Malcolm’s Modal Version
God is a necessary being.
If God’s existence is possible, then it’s actual.
God’s existence is possible.
God must exist.
Objection: Maybe God’s existence isn’t possible.

14. Other Objections God doesn’t’ exist in the mind.
Exist “in the mind” equivocates on the term “exists.”
The terms “greater” and “greatest” are vague, value-laden or assume a Platonic metaphysics with degrees of reality.
Which is greater Jupiter or the DNA molecule?