My preferred version of this (which so far as I know is original to me; see http://www.mccaughan.org.uk/g/log/2009/ontological.html http://www.mccaughan.org.uk/

My preferred version of this (which so far as I know is original to me; see http://www.mccaughan.org.uk/g/log/2009/ontological.html http://www.mccaughan.org.uk/g/log/2009/ontological.html): Consider a proof of God's existence than which no worse can be conceived. Proofs that are merely wrong (bad logic, false premises, etc.) are two a penny; clearly the worst possible proof would in fact have to conclusively refute the proposition it was trying to prove. As St Anselm has taught us, clearly a worst-possible proof "exists in the understanding". But a proof so bad that it actually refutes its intended conclusion is clearly much worse if it actually exists in reality. Hence such a proof that exists only in the understanding is not worst-possible after all. Hence, there exists (in reality, not merely "in the understanding") a proof of God's existence so bad that it conclusively proves that there is no God. And, of course, if there is a conclusive proof that there is no God, there is in fact no God. Hence, there is no God. Thanks, St Anselm!