The Burden of Proof

It seems like everyone has a simplistic idea of who bears the burden of proof and it drives me freakin' nuts -- almost as much as people using "begs the question" to mean "forces us to ask."* The simplistic idea is that the person making a claim must bear the burden of proof, while the person who denies the claim does not. This is the standard in formal debates to keep them from going too far afield. Courts of law apply it as well because our justice system is premised on the "innocent until proven guilty" standard. So it's not unreasonable to mistake it as the universal standard, but it's still a mistake.

In philosophy burden of proof issues are notoriously difficult. Sometimes the person making a claim bears the burden of proof, but sometimes the person denying a claim bears it. Sometimes all parties bear it. It depends. And there's no absolute standard agreed upon by philosophers, although there are some clear examples. One traditional philosophical issue is the problem of other minds. How do we know that other people are really sparks of self-consciousness? The simplistic idea of burden of proof would say the person who denies other minds exist (solipsism) does not shoulder any of the burden of proof, but in this case he shoulders all of it. The person who affirms that other minds exist does not need to prove anything.

One objection people raise is that you can't prove a negative. Except you can. Of course you can. I can prove there is no full-sized elephant in this room right now. I can prove that there is not an army of fifty foot tall badgers ransacking downtown Portland as we speak. In fact, Karl Popper's philosophy of science says that all science can do is falsify claims, not prove them, in which case, science only proves negatives. It can't prove the positive claim "All swans are white" but it can prove the negative claim "Not all swans are white" by finding one example of a swan that isn't white. What you cannot do is empirically prove a universal negative. But you can still empirically prove a non-universal negative (like "Not all swans are white") and you can logically prove a universal negative (if it's a logical contradiction).

Another objection people raise is Bertrand Russell's suggestion of a teapot orbiting the sun between Earth and Mars. The person making this claim shoulders the burden of proof because in the absence of any evidence or reason to think such a teapot exists, the rational response is to disbelieve it, not just to be agnostic about it. We don't need a reason to disbelieve it, since in the absence of evidence we don't shoulder any burden of proof. But we do have a reason to disbelieve it: it's completely ad hoc or contrived. The more ad hoc a suggestion is, the less likely it is true. The teapot apologist must provide evidence to overcome the ad hoc-ness of the claim. Contrast this with the problem of other minds: there the solipsist is making the ad hoc claim and so must bear the burden of proof.

Most claims end up somewhere in between orbiting teapots and other minds (orbiting minds?), meaning that burden of proof is difficult to establish. The more ad hoc a claim is, the larger the share of the burden of proof one has, and sometimes denying a claim is more ad hoc than affirming it, not least because denying some claims can have repercussions that are outrageous. Carl Sagan said, "Incredible claims require incredible evidence," which is also simplistic and false, but if we restate it as "Ad hoc claims require sufficient evidence to counter their ad hoc-ness" then it can be salvaged, although it may not work as well as an aphorism.

* Incidentally, "begs the question" means you're arguing in a circle. You are assuming (begging) what is at question. So if I said "Trump is the most honest President ever," and when you asked why I believe that, I said, "Trump said so, and the most honest President ever wouldn't lie about something like that," I would be begging the question. The question is whether Trump is honest and my reasoning assumes he is in order to conclude he is. It argues in a circle, it begs the question. I actually wrote about this on Quodlibeta back in the day.