When people have pointed out the complete lack of evidence for certain claims, such as the existence of gods, others have responded that the absence of evidence is not evidence of absence. But is that always the case? One of the reasons why it’s a rather weak objection is that there are countless claims for which there may be no “evidence of absence”. To insist on believing all of these things merely because there’s no evidence to the contrary would be absurd, and to selectively believe in only some of them is simply arbitrary, and shows that these beliefs have nothing to do with evidence in the first place.
Beyond that, the absence of evidence for gods can sometimes be considered evidence of their absence depending on the evidence we would expect to see if a certain god existed. For some definitions of gods, this is a trivial matter. For instance, the evidence at hand does not show that the world was formed in the span of six days. It does not show that a massive flood covered the entire earth within human history. And it does not show that humans were simply created without having evolved from any ancestors. Any god whose existence would result in these things being observed can thus be ruled out, because the evidence we would expect to see if these gods existed is absent.
But there are also definitions of gods which state that their existence would have no observable effect, and whether these gods exist or not, the evidence would remain the same. In this case, the choice to believe in such a god is, once again, not rooted in evidence. To argue about evidence in the face of this belief would be pointless, and moreover, there’s no reason for those who hold such a belief to debate the evidence or the absence thereof when their beliefs have no basis in it anyway.
This demand for “evidence of absence” implies that no evidence is needed in order to believe in something for which there is no evidence, yet evidence is needed in order to not believe in something for which there is no evidence. This is precisely backwards – if there is no evidence of something, no additional evidence is needed to simply not believe in it. Here, the principle applies to itself: the absence of evidence of absence is not evidence of the absence of absence.
Another potential source of confusion is the failure to distinguish between the absence of any evidence regarding a phenomenon, and the absence of confirming evidence of a phenomenon. It’s the difference between just not bothering to look for something, and looking for it but not finding any evidence of it. If there’s only an absence of evidence because you haven’t taken the time to search for it, then of course that absence of evidence wouldn’t mean anything. But if we do attempt to seek out confirming evidence and still fail to find it, the evidence that we did acquire in the process is still evidence, not an “absence of evidence”.
Evidence that does not confirm a given claim is evidence nonetheless. To accept only confirming evidence as evidence, while ignoring all other evidence by calling it the “absence of evidence”, would be a mistake. If the presence of evidence in favor of a phenomenon would lead us to believe in it, then why shouldn’t the absence of that evidence sway our beliefs in the other direction?
Finally, it’s important to note that the absence of evidence cannot be treated as proof of absence. Just because there’s no evidence of something does not mean we can conclude with perfect confidence that it doesn’t exist. That would be an argument from ignorance. But the absence of evidence can still be evidence. It may be weaker or stronger evidence depending on the validity, accuracy and scope of our efforts to verify or falsify a certain claim, but it is evidence. And because this is evidence and not absolute proof, it always leaves open the possibility that new evidence could be discovered which would require us to update and change our beliefs.
Some people have taken this as a license to say that there might be evidence of gods, and we just haven’t found it yet. And that’s entirely possible. But the possibility that such evidence might be discovered some day is only fatal to the claim that this has been definitively and permanently ruled out with total certainty. That possibility alone does nothing whatsoever to undermine the fact that the evidence as it stands reflects the nonexistence of gods and not the existence of gods. And insofar as we intend to base our beliefs on evidence, this means using actual evidence and not imaginary evidence. We work from the evidence we have, not the evidence we don’t have. There’s no point to believing things that might be true if there were evidence of them. Our beliefs are sourced from what we know is true because there’s evidence of it. And sometimes, that evidence is evidence of absence.
The evidence for the absence of gods, even if you consider it to be very weak, is still vastly greater than the evidence for the presence of gods. And unless later findings should happen to alter this, it’s plain to see where the evidence is pointing us – assuming we care to follow it.