Several people suggested that we must first agree upon a definition of the supernatural. We could perhaps agree among ourselves that the supernatural encompasses things that aren't real or that have no evidence or are made up, like the world of Harry Potter or Tolkein or the Bible, but religious folks would never accept such a definition, and unless we're content just to talk among ourselves we need a definition that they accept, and that we ourselves accept. Is that even possible?
My first reaction to this is to look back through history and understand how the viewed the intersection of the supernatural and natural. I can't help but notice that the definition of supernatural has changed quite a bit.
A couple of millenia ago no one really viewed the natural and supernatural as distinct realms. Rather, the world around us was awash with the supernatural. As Stephen Weinberg puts it, "Once nature seemed inexplicable without a nymph in every brook and a dryad in every tree."[1] Many scientific historians agree that the demystification of nature is what allowed science to flourish.
As science has progressed the supernatural has been pushed back until those who believe in the supernatural are now forced to claim that the supernatural is a separate realm. I really don't think this is a matter of practice. It is a matter of keeping a belief alive through whatever means necessary, including a redefinition of what the supernatural is.
If believers are going to push for the inclusion of the supernatural into a practical method then we must focus on the practical definition. In practice, the supernatural is equivalent to fantasy. They are indistinguishable.
But complex theories, whether about God or science, rarely have that one piece of confirming evidence. Ask yourself what is the one piece of evidence that proves the sun is at the center of the solar system. And Tycho Brahe spent a lifetime gathering the evidence used by Kepler to derive the laws of planetary motion.
The answer is stellar paralax. Even Tycho Brahe agreed that such an observation would falsify a geocentric solar system, and with advances in telescope technology stellar paralax was observed.
The problem with the supernatural, as it is defined in practice by believers, is that any and all observations can be consistent with the supernatural. There is no equivalent to stellar paralax when it comes to the supernatural.
As obvious as the conclusion that there is no Christian God might seem to us, proving that all this evidence actually supports that conclusion and not its opposite is no simple task.
This is why I often ask pointed questions. This is why I always ask what observations, if made, would be inconsistent with the existence of ___ (insert deity here)____. When believers fail to address the question then the conclusion is all too obvious. Evidence doesn't matter. It never has.
[1]
Dreams of a Final Theory, Stephen Weinberg.