Actually, I don't think its possible to prove that something doesn't exist, outside of some wacky math problem.
When it's logically impossible for something to exist and not leave a certain evidence, and we don't find that evidence in the place where it's logically impossible for it to exist and not be, we know that something doesn't exist.
For instance we can know the Christian god doesn't exist because it would be impossible for that God to exist and not leave certain evidence; since we know the evidence wasn't left we know that God doesn't exist. A benevolent and omnipotent god logically can't be present in the universe that we observe.
Can I know that
all possible gods don't exist? No, I can't, which is why I'm an agnostic atheist. But the existence of any gods described as "benevolent" and "omnipotent" can't logically be consistent with the world as we observe it, at least not if we're going to grant that words have any meaning at all.
The only gods that can exist are useless ones, so I don't waste my time, especially since there's nothing I could know about them. For some gods, we can know that they don't exist. For others no knowledge about their status or nature is possible. Neither one of those are a legitimate basis to even propose that we can know that gods exist. Hence, atheism - no belief in any gods.
So when I say that I'm Catholic, you should have a pretty good idea of my beliefs.
Nonsense. If John Kerry, Andrew Sullivan and the new Pope can all be Catholics, then there's no predictive value to knowing that someone is a Catholic.
But, if after learning about me, you found out that I didn’t think Jesus was the son of god(which I do, btw), wouldn’t you question me saying I was Catholic?
Who am I to judge your religious experience? If you say you're a Catholic, who am I to argue? The Pope might disagree but who is
he to define who is Catholic and who is not?