I've finally finished a chapter on arguments for the existence of God that I started over a year ago. Ouch. I started to end the chapter by revisiting a version of the ontological argument by Alvin Plantinga. I remember hearing in seminary that it had made some atheists nervous... and I remembered having great difficulty wrapping my head around it.
When I first encountered Anselm's version of the argument, I remember thinking, "Man, I just don't understand it." But I've since concluded it doesn't make sense. Just because we believe in God doesn't mean that every argument for the existence of God makes sense. I used always to assume that I was stupid when I couldn't wrap my head around such things. That of course is still sometimes the case.
But I've also come to realize that sometimes the reason a philosopher or theologian or Bible scholar doesn't make sense to me is because, well, they just don't make sense :-) (P.S. Feel free to invoke this principle when reading my thoughts :-)
Just to remind you of Anselm's argument, it goes something like this:
1. I can conceive of the Greatest Possible Being--the Greatest Possible Being exists in my mind.
2. A Being that exists outside my mind would be greater than one that exists in my mind.
3. Therefore, the Greatest Possible Being must exist outside my mind as well as inside my mind.
This argument doesn't work on more than one level for me. The most significant reason it doesn't work is because it confuses ideas with things, like mixing apples and oranges. For this reason, premises 1 and 2 don't connect. They are like ships passing in the night.
I decided to leave Plantinga mostly out of the chapter because I think his argument is tautologous. His first premise is, in my opinion, exactly what we are trying to prove in the first place.
His argument goes as follows:
1. There is a possible world in which maximal greatness is instantiated.
2. Necessarily, a being is maximally great only if it has maximal excellence in every world (and thus has omniscience, omnipotence, and moral perfection in every world).
3. If premise 1 is true, then it would be impossible for that being not to exist in that possible world.
4. But if it were impossible for that being not to exist in that possible world, it would be impossible for that being to exist in any world.
5. Therefore, that being must exist in all possible worlds.
I have several problems with this argument.
For one, I don't like thinking of God as the greatest possible being because the hidden premise is that we are talking about this universe, inevitably the argument limits God to the limits of to this universe, the greatest possible in this universe, since our conception here is unavoidably limited to our frame of reference. Such a scenario says nothing about the parameters outside this universe and the cosmological argument in any case places God outside of this universe. The entire line of thought is thus ill conceived as a premise for further argument.
It does seem true that if God exists, then God must exist in all possible worlds, understood from our point of reference. We cannot conceive or argue about possibilities beyond our point of reference. Arguments of possible worlds are thus only drawing pads for talking about our world and worlds that might be like ours. This immediately undermines the entire argument as well.
My hunch is that, if we pushed the ontological argument in the right direction, and maybe a nuclear physicist could help out here, we would find that the ontological argument and the argument from necessity turn out to be the same thing as the cosmological argument.
 God, Freedom, and Evil (New York: Harper & Row, 1974). My apologies to Plantinga for leaving out some of the subtleties of his actual argument, but since I consider his argument tautologous, it doesn't really matter.