When they can muster no positive evidence for the existence of a god, religious people will often not cede the point, but will say something like, “Okay, so it isn’t possible to prove that god exists, but you can’t prove he doesn’t exist either.” That announcement is supposed to be the magical moment where the atheist admits defeat, or is forced to concede that his “belief” in atheism is, at the very least, in equal standing with that of the religious believer. However, what such religious people don’t know is that they have just engaged in a common logical error which relies on an even more common logical fallacy.
The logical error has to do with a principle, known in Latin as onus probandi (“burden of proof”), which states that the one making a claim bears the burden for proving that claim, it is not the responsibility of the one denying the claim to disprove it. In fact, claims of “there isn’t any evidence for it, but you can’t disprove it either” are logically impossible to disprove, which is why religious people often use them in effort to keep their faith “safe” from crticism or standards of evidence. However, neglecting one’s burden of proof – or attempting to shift it to the other party – is usually the result of a logical fallacy known as argumentum ad ignorantiam (“an argument from ignorance”), in which someone holds that a claim is proven true because it has not [yet] been proven false or that a claim is false because it has not [yet] been proven true.
However, when confronted with more obvious examples of this fallacy, even religious people will readily deny wild claims for which there is no evidence, but have not been disproved. Consider the following conversation:
A. I believe that god exists.
B. What is the evidence for such a belief?
A. Well, there isn’t any direct evidence, but I feel that it must be true. Besides, you can’t prove that god doesn’t exist, so how can you say that you don’t believe that there is a god?
B. True. It is impossible to prove a negative. Do you know what I believe?
B. I believe that beneath the atmosphere of Venus, there are unicorns mating and binge-watching episodes of “Cheers.” It’s just that the atmosphere is opaque and we can’t see them.
A. That is ridiculous.
A. Because there is no evidence for that at all.
B. Yes, but you can’t prove that those unicorns aren’t on Venus watching Hulu, can you?
Even the most religious person will readily object to such a claim, but in the same instance will exempt their belief in god from the same standard of proof and logical tenability.