The so-called Ontological Proof goes this way:
• God is the greatest imaginable Being.Now if I understood Plantinga at all (which I wouldn’t be surprised to find isn’t true), the problem with the Ontological Proof is that the fool’s conception is not of a Being who has every quality of God except for existence, since without existence, this god would also not have omnipotence, for instance. My critique rests on much humbler analytical skills. I just can’t buy the definition with which the proof begins, since I can’t imagine God in all of his attributes. Because of this mental limitation, I added some words in brackets to the outline of the proof I drew above; that’s the only way the proof has any chance of making any sense in my view. But I put my addition in brackets; Anselm doesn’t say anything about the real God being “at least as great as” the God the second person imagines. He just says that someone can imagine God to exist, so therefore He exists. But that doesn’t seem right to me at all. What if that second person imagines the existing God to be a powerful, handsome fellow driving a chariot that hauls the sun around the skies? Does the exercise then prove that that God exists? OK, no: I can imagine a God greater than Apollo. So maybe I imagine Zeus. But clearly Anselm wouldn’t say that his reasoning points us to Zeus, either, so I’m still not there and must imagine a yet greater God in order to arrive at the scenario that Anselm describes. But if the proof doesn’t work for any of the gods I’ve imagined so far because they are less than the real God, then the proof can never work: no matter how much I stretch my imagination step by step above these first gods, the thoughts in my head will never reach the real God.
• “The fool says in his heart, ‘There is no God.’ ”
• That fool means something by the word “God,” presumably a very great Being.
• The very great Being about which the fool imagines does not exist. (He clearly states so.)
• One can, by contrast, imagine a God that does exist.
• The God of that second imagination is greater than the nonexisting God of the fool’s imagination, since any existing Being is greater than any nonexisting Being.
• Since God is the greatest imaginable Being, God must be [at least as great as] this second imagined God.
• Therefore, God exists.
Also, I’m not sure that there is a conception of God in the fool’s head. I think his conception is about a thought – a thought that other people have in their heads. I think he really means, “That thought that theists have isn’t true.”
I can’t close without pointing out that discussing this issue took me through very confusing deliberations about whether to capitalize the word made out of g and o and d. I decided that I should capitalize it any time the supposition of the moment seemed intended to point toward the greatest possible Being. I used a lower case initial only when a candidate had been eliminated by the process.