Matt Dillahunty on The ontological argument
Dillahunty treats the ontological argument as a logical trick that equivocates between conceptual and actual existence.
Matt Dillahunty has addressed the ontological argument in numerous debates and episodes of The Atheist Experience, and his response is characteristically direct. The argument, he contends, trades on an equivocation between existence as a concept and existence in reality. The fact that we can conceive of a maximally great being tells us something about our capacity for conceptualisation; it tells us nothing about whether such a being actually exists.
Dillahunty often uses the parallel example of a maximally great island or a maximally great pizza to illustrate the problem. If the ontological argument works for God, it should work for anything — and the fact that it obviously does not work for islands and pizzas suggests that something has gone wrong in the reasoning. The argument appears to generate existence from definition, which is a logical impossibility.
He is also critical of the modal version of the ontological argument, associated with Alvin Plantinga, which argues that if it is possible that a maximally great being exists, then it necessarily exists. Dillahunty points out that the key premise — that a maximally great being is possible — is precisely what needs to be demonstrated, not assumed. The argument assumes its conclusion in its first premise, making it circular rather than probative.
“You can't define something into existence. If that worked, I'd define a maximally great bank account and retire.”