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| (Sterling State Park) |
The Internet Encyclopedia of Philosophy article by Kenneth Himma is good on explaining the Modal Version of the Ontological Argument for God's Existence.. Here is Plantinga's OA for God's existence, via Himma.
Plantinga defines two properties: "maximal excellence" and "maximal greatness."
P1. A being is maximally excellent in a world W if and only if it is omnipotent, omniscient, and morally perfect in W.
P2. A being is maximally great in a world W if and only if it is maximally excellent in every possible world.
"Thus, maximal greatness entails existence in every possible world: since a being that is maximally great at W is omnipotent at every possible world and non-existent beings can't be omnipotent, it follows that a maximally great being exists in every logically possible world." If, then, a maximally great being exists in some possible world, then it exists in every possible world, to include our actual world.
Is it logically possible that a maximally great being exists in some possible world? Plantinga thinks so. To think this is not possible one would have to show that the concept of "maximally great being" is logically contradictory, like "square circle." Therefore, the concept of a "maximally great being" is logically possible; i.e., possibly instantiated. It follows, therefore, that a maximally great being (i.e., God) exists in every possible world.
Himma now formulates Plantinga' argument as follows:
1. The concept of a maximally great being is self-consistent.
2. If 1, then there is at least one logically possible world in which a maximally great being exists.
3. Therefore, there is at least one logically possible world in which a maximally great being exists.
4. If a maximally great being exists in one logically possible world, it exists in every logically possible world.
5. Therefore, a maximally great being (i.e., God) exists in every logically possible world.
As P2 affirms, maximal greatness entails existence in every possible world. If it is possible that such a being exists in one possible world, then it exists in every possible world. Since our world is a possible world, God exists in our world.
See Himma's entire essay for more, including objections.
