The Absence of Evidence
Quite a few times, recently, I have heard Christians cite the time-worn words “absence of evidence is not evidence of absence”. It’s a catchy sound bite and a highly successful meme, but it is utterly false. Absence of evidence most certainly is evidence of absence.
Before I explain why, I think it’s important to understand the difference between evidence and proof. The two are often used synonymously, to the point where the semantic lines have blurred. Strictly speaking though, evidence is defined as:
Facts or observations presented in support of an assertion.
Proof has a number of definitions, but I think this one is the most appropriate for the point I am trying to illustrate:
That degree of evidence which convinces the mind of any truth or fact, and produces belief; a test by facts or arguments that induce, or tend to induce, certainty of the judgment; conclusive evidence; demonstration.
To summarise this as simply as possible, evidence doesn’t have to be conclusive, it is gradual. In rational terms, the greater the amount and the stronger the nature of the evidence, the more secure becomes the claim it supports. As more evidence becomes available though, the balance can shift either for or against the claim at any one time. One could see it as a sort of ongoing tug of war, where the more ground you take from your opponent, the harder they have to work to recover the position before they can look to take the advantage. Proof, on the other hand, is seen as holding a sense of finality – leaving the truth of the claim beyond any reasonable doubt.
There is a saying (the original source of which I am unable to ascertain) that “proof is for mathematicians and alcoholics”, which is very apt when applied in response to the “absence of evidence” saying. Because, even though they say ‘evidence’, what the people who use the quote really mean is ‘proof’. What they’re saying is: just because there is no evidence that God exists, doesn’t prove that he doesn’t exist. And, of course, they’re right – it doesn’t. It doesn’t show that God does not exist, beyond any reasonable doubt, but it most certainly is evidence against the existence of God.
Let’s say that you are in a large, empty, rectangular room, on your own, or at least as far as you can tell. The claim we will consider as a thought experiment is: there is a twelve piece marching brass band in the room with you. How will you analyse the truth of the claim? Can you see a marching band? Can you hear a marching band? The answer is no, so you are lacking visual or audio evidence of the presence of a marching band. Is there any other evidence that a marching band may be in the room with you? None. There is no evidence whatsoever to support the claim that there is a marching band in the room with you. Is this fact, this absence of evidence, itself evidence that there is no marching band in the room with you? Of course it is! When analysing any claim, the absence of evidence for its truth can automatically be counted as evidence in favour of its falsity. Not conclusive proof, but strong, valid evidence.
The “absence of evidence” quote is normally one of the last resorts before the proposal to agree to disagree. To my mind, it is to all intents and purposes a concession of, and withdrawal from the argument. It translates roughly as: I have no evidence to support my claims, but that doesn’t mean that they’re false. What else could it mean? If someone accuses you of having no evidence for a claim, but you believe that you do have evidence, you don’t start defending your claim as if you didn’t have evidence, you present it. If someone uses that phrase, then it implies agreement that there is no evidence. How can they proceed in a rational discussion if they have just admitted that they have no evidence? What can you say in response? Not an awful lot, in my opinion. If you have stressed the importance of the burden of proof (or should that be burden of evidence?) and that it lies with the positive claimant, and reiterated the points I have tried to make in this article, then I believe that the discussion should end there. You can only hope that the person with whom you have been talking will give some serious thought to the implications of acknowledging the absence of evidence.