It’s an annoying type of argument that tends to show up when theists are backed into a corner. Other people have covered it pretty well. I feel like adding a little bit of my own thoughts. If you’re not familiar with it, one goes something like this:
1. I can imagine something of maximum greatness.
2. It’d be even greater if that thing I’m imagining was real.
3. Maximum greatness means the thing I’m imagining must exist.
Okay, so I mangled it a little, but I think my summary helps bring out one of the problems I prefer to focus on: It assumes the universe cares about what humans define as “great.” I think that’s a pretty arrogant leap to make. Of course, the arrogance seems greater when we’re talking about what certain humans think of as “great.”
To illustrate the latter part of that, let’s move into the world of fiction for a moment. Comic books, specifically. Compare Superman and Batman. Everyone’s entitled to their own opinion, but generally I’m a bigger fan of Bats than I am of Superman. While many comic heroes have innate powers granted by alien origins, mutations, lab accidents, and so on, Batman is the Ur-example of a “Badass Normal.” Sure, he’s smart, athletic, and has the bank account to afford all of those wonderful toys, but he’s still a “mere” human. And yet, despite the relative handicap of lacking innate powers, he can still pull his weight among his superpowered allies. That’s part of what I think makes Batman a great heroic character.
And theists generally want me to accept a lazy super non-hero (if not outright villain, depending on how much cherrypicking the theist does) as the greatest being in existence, and use that alleged greatness as a foundation for asserting its existence. Kind of falls flat with me.
Another ontological argument goes like this:
1. It’s possible that there is a necessary being.
2. If it’s possible that there is a necessary being, then a necessary being exists.
3. Therefore, a necessary being exists.
I may not know as much nuance about types of logic as the source I quoted, but a question that seems obvious to me is “what do you mean by ‘necessary?'” Naturally, another observation for both of these ontological arguments made in the Debunking Christianity links I’ve added is this: Being able to conceive of something, or of a possibility for something doesn’t make it real.
The fact that theists (Christian or otherwise) use these kinds of arguments make me wonder who they’re trying to convince: Atheists, or themselves?