An ontological argument is an attempt to prove the existence of God using logic alone. It is one of those things that I had come across a few times in the past but never took the time to understand. So, when a blog post by Nathan Schneider on this topic appeared last week in the New York Times, I finally tried to follow the argument. There have been many attempts at an ontological proof throughout history. Schneider wrote about an early one from the eleventh century by an English Catholic Bishop named St. Anslem of Canterbury. I couldn’t really understand Schneider’s somewhat poetic version of the proof but after reading several other versions on the web I think I finally get it. It is actually quite clever although it obviously must make some assumptions that are not self-evident.
Here’s the proof: The first assumption is that God is the greatest possible being that can be conceived. The second assumption is that existing and being conceived is greater than not existing and being conceived. Hence, God must exist, since a God that exists is greater than a God that doesn’t exist. Another way of saying this is that the fact that I can think of a God implies that she must exist. In some sense, this is a precursor to modal realism.
There have been many historical criticisms of this proof. Kant’s critique is that existence is not a predicate. By this he means that existence is not a property of an object. For example, a unicorn has properties such as having a horn, looks like a horse and so forth. But a unicorn could exist or not exist and that doesn’t change what a unicorn is. So existence is something that must be inferred empirically and can never be deduced a priori. I think Kant effectively kills Anslem’s proof. However, another weakness in the argument is that Anslem assumes that the set of all conceived beings has an upper bound. This may not be true as well. There could be an infinite hierarchy of Gods, a possibility that has interesting philosophical consequences as well.