ontological argument writes:
- It is possible that a maximally great being exists.
- If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.
- If a maximally great being exists in some possible world, then it exists in every possible world.
- If a maximally great being exists in every possible world, then it exists in the actual world.
- If a maximally great being exists in the actual world, then a maximally great being exists.
- Therefore, a maximally great being exists
Let's try it backwards. Plantinga would mean something like "a necessary, omniscient, omnipotent, omnipresent and perfectly good being" by "maximally great".
- It is possible that a maximally great being doesn't exist.
-If it is possible that a maximally great being doesn't exist, then in at least one possible world no such being would be necessary.
-By definition, in order to be maximally great, the being must necessarily exist in all possible worlds.
-Therefore, a maximally great being cannot exist in any world it if could not exist in one.
-Plantinga's God doesn't exist.