Ontological Arguments

An Interpretation of Anselm's Ontological Argument

D1: x is God =df. x is the being than which none greater can be conceived.

D2: x exists in reality =df. x actually, really, in fact exists.

D3: x exists in the intellect =df. someone thinks about, conceives, or imagines x.

Anselm's Ontological Axiom: If x and y are alike in all respects except that x exists in reality, and y exists only in the intellect, then x is greater than y.

1. If God exists only in the intellect, then we can conceive of a being greater than God.
2. It’s not the case that we can conceive of a being greater than God.
3. Therefore, it's not the case that God exists only in the intellect. [1,2 MT]
4. Either God exists in reality or God exists only in the intellect.
5. Therefore, God exists in reality. [3,4 DS]

• Be able to provide a rationale for each of the premises.

The Logical Form of Disjunctive Syllogism:

1. P or Q
2. It's not the case that Q
3. Therefore, P

Gaunilo's Parody of Anselm's Ontological Argument

D4: x is the Lost Isle =df. x is the island than which none greater can be conceived.

1. If the Lost Isle exists only in the intellect, then we can conceive of and island greater than the Lost Isle.
2. We cannot conceive of an island greater than the Lost Isle.
3. Therefore, it's not the case that the Lost Isle exists only in the intellect. [1,2 MT]
4. Either the Lost Isle exists in reality or the Lost Isle exists only in the intellect.
5. Therefore, the Lost Isle exists in reality. [3,4 DS]

• Be able to provide a rationale for each of the premises.
• Does this parody of Anselm's Ontological Argument demonstrate that Anselm's argument is unsound? Why or Why not?
• Be able to present an objection against one of the premises in both Anselm's and Gaunilo's arguments.

Descartes' Ontological Argument

1. God has all perfections.
2. Necessary existence is a perfection.
3. Therefore, (1) and (2). [1,2 Conj.]
4. If (1) and (2), then God has necessary existence.
5. If God has necessary existence, then God exists.
6. Therefore, God exists. [3,4,5 MMP]

• Be able to provide a rationale for each of these premise based on passages from Descartes' Fifth Meditation and the Preliminaries of the Philosophy of Religion Handout.
• Be able to present an objection against one of these premises.