While still a Christian, I had no need for proofs of God - faith was central to my, well, faith. As a mathematician, I was aware of Godel's ontological proof of God; but knowing what a fruit-bat Godel had been, I never bothered to investigate.
So, following my Damascus Road conversion to atheism, I have been reading up on the ontological arguments of Anselm, Descarte, Plantinga, and of course, Godel, to find out what all the fuss is about...
My first impression was simple confirmation of something I had long suspected: logic in the hands of philosophers tends to result in the use of very precise and well defined rules to push around exceptionally nebulous and ill-defined concepts. The ideas of maximal goodness, maximal greatness, maximal perfection, etc, suggest extremely naive one-dimensional thinking, almost certainly inspired by the age-old tenets of the faith held by the philosopher in question.
My second impression, primarily from reading Plantinga and associated apologetics (e.g. William Land Craig), is just how blatently dishonest the argument appears. The bait-and-switch on the term "possible" is a text-book case. The modern Plantinga argument (put into readable english) is:
- 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.
The possible of the first line looks innocuous enough, and on a generous day some of us may even make grudging acceptance. Possible is this context tends to be taken as "not definitely impossible". BUT the use of possible in the second line is very different. This is now the "possible" of modal logic, with very different meaning: something that is "possible" must occur in some plausible example of existance (the "possible world" mentioned.)
If we agree up front that the first "possible" is in the colloquial sense, then the argument fails immediately as the "possible"s of lines 1 and 2 are now different. If it is in the modal logic sense, then we have essentially begged the question, as we have essentially agreed as premise that this "maximally great being" is necessary.
And finally (for now), the "possible worlds" of modal logic are a perfectly sound concept when looking at strictly defined systems with specific parameter spaces, but their applicability is extremely questionable when it comes to considering possible examples of Existence. We even have no surety that there is any such thing as a possible example of existence that is not our own!