This chapter from Groothuis' Christian Apologetics on the ontological argument will probably boggle my mind forever. Here's what I've got, though.
The first premise below is okay, because the idea of a perfect being is conceivable (not contradictory).
Anselm's first ontological argument:
1. God is the greatest possible being.
2. Actual existence is better than possible (mental) existence.
3. Because 1 & 2, therefore God, as the greatest possible being, does not merely have possible (mental) existence, but also actual.
Question: What if the greatest actual being is not the greatest possible being?
The third premise below is okay because there is nothing contradictory about a maximally great being.
Anselm's second ontological argument:
1. God is maximally great--a Perfect Being.
2. --that is either impossible or (if possible/actual) necessary (can't be contingent).
3. It's not impossible.
4. Therefore, it's necessary.
5. Therefore, God exists.
Kant's criticism that existence is not necessary to the idea of God (or that existence cannot function as a predicate for the subject of God) fails, because God is a possibly existing thing whose existence is a legitimate question (not all conclude he does exist).
Question: What if the greatest actual being is not a maximally great/perfect being?
Question: Is being "necessary" the same as being "logically necessary"? If so, then even if the ontological argument fails, it does not rule out God's being logically necessary, as there are other arguments that can stand in for that (cosmological, moral, etc.).
Interlude: The paradox of the stone fails because it is logically impossible to make a stone he can't lift--power is about logical possibles being actualized.
Plantinga's ontological argument:
1. It is possible a maximally great being exists (it isn't contradictory).
2. A maximally great being exists in some possible world.
3. So, a maximally great being exists in every possible world.
4. Therefore, a maximally great being exists in the actual world.
Question: What if it's possible a maximally great being does NOT exist (in some, therefore any, possible world)...?
The "perfect island" parody/argument fails because there are no maximal or necessary islands.
Cool: These scriptures point to God's necessity: Acts 17:24-25; John 5:26.