"Oh dear," says God, "I hadn't thought of that," and promptly disappears in a puff of logic.—The Hitchhiker's Guide to the Galaxy
I was watching an interview with Colin McGinn where he said that he thought the ontological argument is interesting because nobody's ever managed to pinpoint exactly what's wrong with it even though it's wholly unconvincing to everybody who hears it. There are lots of ways to show it's absurd (e.g. Guanilo's Island), but none are concise and direct enough to seem like the problem with it.
Well, a line of reasoning recently occurred to me that I'd like to put forth as the problem with the ontological argument. The normal version goes something like this:
- God is defined as the most perfect being conceivable.
- If he didn't exist, he would be less perfect than a being who did exist.
- Therefore, God exists.
- God is defined as a being who exists.
- Therefore God exists.
The trick is in confusing the levels, and losing the difference between a definition and reality. If you dream that you woke up, it doesn't mean you're awake. By the same token, a being that's defined to exist doesn't necessarily exist (nor a being that's defined as "a being defined to exist"). The part about "what it means to be perfect" just acts as misdirection from the meat of the argument enough to block your common sense.
There's no contradiction whatsoever within the definition, nothing wrong with it even, but every definition is a hypothetical of sorts, just a label to tell me what you mean when you use the word.
I did happen to notice that Kant looks to have proposed almost the same counterargument, but his version seems wordier and was one of four bullet points in his argument. I wonder if Colin McGinn is familiar with Kant's refutation...