Ontological Argument

Apriori, deductive.

1. God = that than which nothing greater can be conceived. 

2. Even a fool (atheist) understands, b/c admits in intellectu but not in re. 

3. Greater to exist in both mind and reality. 

4. Greatest conceivable being, if genuinely great, must exist in both.

5. T/f, since God is 'greatest conceivable being, must exist in both. 

- Fool really a fool if denying existence of smth that is genuinely greatest (reductio ad absurdum).

Gaunilo of Marmoutier: On behalf of the Fool.

Counter-example of perfect island, structured similarly. If you imagine perfect island, must exist due to perfetion. No such island in existence unless found.

H/e; incoherent, as conceptions subjective in nature. No problems reflected in idea of perfect being = 3 O's.

God who cannot be thought not to exist > God who can be thought of as not existing

Idea of non-existent greatest conceivable being = contradictory. 

2 types of existence:

Contingent: Islands etc. Depend on other physical things for existence. Changes may stop it from existing. 

Necessary: Depends on nothing else - had to exist. Anselm believes Gaunilo's arg fails b/c God = necessarily exists. 

Revived after Aquinas' cosmological arg.

1. God is the supremely perfect being.

2. A supremely perfect being contains all supereme perfections.

3. Existence, (+ 3 O's), is a supreme perfection.

4. Conclusion (2 + 3) = God, a supremely perfect being, exists.

Relies on definition of God - existence essential property of perfect being.

'God exists' = true by definition. 

Existence is a predicate - necessary.

Even if existence is necessary predicate of God, doesn't mean God exists.

To accept a triangle but reject three angles = self-contradictory. But, if whole triangle is rejected, predicates are too, t/f, irrelevant. Applies to necessary being - rejected, predicates (existence) rejected, no contradiction.

Same point made earlier by David Hume:

what we can concieve existent, we can also conceive as non-existent.

Existence is not a predicate. Predicates should tell us something a/b nature of obj/add something to its description. Saying 'exists' does not do this. 

While Anselm's first argument cannot treat existence as a predicate, second can b/c of 'necessary'. 

1) God is a supremely perfect being.

2) A supremely perfect being possesses every perfection.

3) Necessary existence is a perfection.

4) T/f, God possesses necessary existence.

5) God necessarily exists.

'Possible worlds'

Maximally great being, only so if exists in every poss world.

Maximal excellence:

M.G entails M.E incl. omnipotence, omniscience + moral perf. 

1) There is a poss world in which there is a being that is maximally great.

2) If M.G, exists in our world.

3) Being has M.E, as M.G entails M.E.

4) So, there is a omnipotent, omniscient and morally perfect in our world.

5) There is a God.

Obj to this:

We are still only looking at the possibility, nothing in actuality. - Maximal excellence possible. 

Syllogism:

Anselm used 'exist' wrongly. Can't be predicate. Can be given to fictional things as well.

1) Donkey's exist.

2) Eeyore is a donkey.

3) Eeyore exists. 

• Quite unsuccessful.
• Definitions limited - say things in terms of the possibility, not real.
• Difficulty in establishing definition for God - limited to finite human terms not adequate to describe God.