What does it take to convince an atheist that God exists? This question has been asked and answered again and again. But no matter what reasonable response an atheist gives, it is automatically rejected by the religionists. If an atheist suggests that some supernatural event would be convincing to him, that suggestion will be met with one of two possible responses from the religionist: either "That's unreasonable because you're asking to see something that is never going to happen" or "You wouldn't really accept that as being convincing because your own belief system doesn't allow it as a possibility". The religionist will never simply take the atheist's answer at face value, because that would be tantamount to admitting that the atheist is being reasonable. That's something religionists will never admit, regardless of how reasonable the atheist's position might actually be.
First, let's describe the kind of events that atheists suggest would be convincing to them. Invariably, they are things that would be considered supernatural. Now, I understand that there may be considerable disagreement as to what constitutes a supernatural event. Theists may consider all kinds of things to be supernatural simply because they are caused by God. But many such things can't be distinguished form natural. For example, they think the human mind is part of the soul, a supernatural entity that is entirely (or at least partly) immaterial. That's fine for them, but materialists see mind as being completely natural. The reason is that nothing about it violates the regularities of nature that we call physical laws. Anything that doesn't violate the natural laws of physics is something that atheists will consider to be natural. So this isn't what they're talking about.
But there could be other phenomena that an atheist would describe as supernatural, should he ever witness such a thing. As Victor Reppert points out, Keith Parsons answer was that if he saw stars change their position in the sky to spell out a message to him from God: "Turn or burn, Parsons this means you," then he would see that as reason to believe. The important point about this example is that it would violate the laws of physics. Stars don't just move is such a way. And note that it's not a question of whether they could form a message like that in a natural way. Yes, they could. But they don't just suddenly move in the sky in violation of physical laws. Other atheists have suggested a variety of things that they would see as obviously supernatural events. They all share the common feature of violating physical laws. That's the key element that atheists are looking for as a reason to believe, because a clearly supernatural event can't be explained by natural causes, so it implies a supernatural cause, and that opens the door for God.
But that's not good enough for religionists. Some of them complain: "You just demand to see that kind of thing because you know it will never happen." Well, no - we don't "know" it will never happen, we just believe that. And why do we believe that? Because we believe the world is natural, and there is no supernatural entity like God causing supernatural events. What's interesting is that the religionist also believes it will never happen. This is someone who believes the stories of the New Testament, including the miraculous feats of Jesus, and his resurrection, which is a blatant violation of thermodynamic laws. So it's not that he thinks a supernatural event couldn't happen, or that they haven't happened. He just thinks it won't happen in a way that we can all witness. So it's OK for the religionist to base his beliefs on miracles that he never witnessed, but he thinks it is unreasonable for an atheist say that he should base similar beliefs of something that he can see. This simply boils down to: "If you demand that that faith be based on observable evidence, you are being unreasonable."
And then we have the kind of response that Victor gives:
But if someone were to go from spelling stars to a theological explanation, they could be immediately accused of committing the god of the gaps fallacy. If we, on principle, have to prefer an unknown naturalistic explanation over a theological one in every case, then we ought to follow that rule even in this case. If that is true, then saying "you don't have any evidence" takes on a different flavor than we would ordinarily think. The complaint usually sounds like "God could do something to give us adequate evidence for his existence, so why doesn't he?" But if we follow a strict ban on gap arguments, then there is nothing God can do to give us adequate evidence of his existence. Poor guy, he's omnipotent, but he can't prove his existence to us to save his life. It isn't that there isn't enough evidence, it's that, by the very nature of the idea of God, God cannot give us enough evidence if he tried his very hardest. I find this to be an extremely paradoxical position, though apparently Dawkins has embraced it. - ReppertVictor doesn't understand the difference between natural and supernatural, and he apparently doesn't understand what is meant by the term "God of the gaps". God-of-the-gaps reasoning only applies to things that could (at least in principle) be explained by natural means. The human mind is a good example of this. As I noted, there is nothing miraculous about it. It does not violate any laws of physics. But so far it has defied a complete scientific explanation. Not that there could never be such an explanation. But the present gap in scientific knowledge is exploited as an opening for God to fill in as the go-to explanation for theists whenever they find a hole in scientific understanding of natural phenomena. That's God of the gaps.
On the other hand, the kind of event that Parsons described would be genuinely supernatural. It violates the laws of physics. There is no scientific explanation for such a thing. If we ever witnessed such an event, it would require a whole new paradigm of understanding reality. Science, as we know it, would no longer be valid. In that case, there would be no substantial framework of scientific understanding with gaps here and there that could be filled in by God. God of the gaps would no longer apply. Our whole framework of understanding would be different, and science, as we know it, would cease to be part of that framework.
But this is something that Victor doesn't understand, because he sees science as a religion rather than a means of understanding the realities of our world. Rather than trying to see where there might be holes in his own reasoning, he'd rather just accuse atheists of being incoherent or unreasonable. Lack of objective, observable evidence is not a hindrance to religious faith. Anyone who doesn't accept that faith is deemed to be unreasonable by definition. It makes no difference what reason we might give. When trying to reason with a religionist, it's "Heads I lose, tails you win."
Let me say that if the evidence bears it, any truly reasonable person should reexamine his beliefs, and change them accordingly. If the evidence shows that there are supernatural things, then so be it. There is no sacred rule in science that overrides evidence. This is what people like Parsons have been saying. It's what Coyne and Dawkins, and many others are saying. For them, belief is based on evidence, and we have to go where the evidence leads. That's why we're atheists in the first place. As it happens, science is fully consistent with the available evidence. Give me a reason to think otherwise.