The other day I was picnicking in Central Park with my 13-year old daughter, when the issue of burden of proof came up. Yeah, I know, what sort of a geeky daughter and overly-intellectual father are we talking about? Nevertheless, Caley (my daughter) knows very well that I am both a skeptic and an atheist, and we occasionally have good humored conversations about these issues.
Specifically, the discussion was about how do I know that there are no ghosts (or other paranormal phenomena). I explained that I don’t know in the sense of certain knowledge, but that there are two major reasons I don’t believe in ghosts: a) Their existence would be at odds with much of what we know from science; and b) I haven’t seen any positive evidence (that has withstood scrutiny) that ghosts exists.
Caley’s response focused on (b) above: “yes, but you also don’t have evidence that ghosts don’t exist, so there.” This is, of course, a classic example of shifting the burden of proof, which is a well known logical fallacy usually described under the heading of “appeal to ignorance.” The idea, as I tried to explain to my daughter, is that the statement “I don’t believe in ghosts because there is no evidence” and the statement “I believe in ghosts because there is no evidence that they don’t exist” are not epistemologically equivalent, so that it is much more reasonable not to believe in ghosts (given the lack of positive evidence).
Although Caley listened to what I was saying, and she is a smart girl, it was clear that I wasn’t getting through. It just seemed logical to her, that it is okay to believe in ghosts if there is no proof that they don’t exist. I then switched tactics and used an example that she could follow more easily. I reminded her of what happens in courts of law (of non fascist countries): the burden of proof is always on the part making a positive claim, not on the one making a negative one. Most especially, one is always presumed innocent unless proven guilty (beyond reasonable doubt, another concept that also nicely fits with skepticism). It would be grossly unfair if we went around presuming people to be guilty of crimes with no other “evidence” than the fact that they can’t prove that they didn’t do it.
Caley paused, clearly understanding the example. But just when I thought I scored one for critical thinking, she went back to her original position: “well, you are making a claim too, that ghosts don’t exist, so don’t you have the burden of proof either?” No, I don’t , but by then it was really time to slice the bread and make our salami and provolone sandwiches, so that was the end of the conversation.
However, I have in fact had similar discussions over and over again — with adults — and have experienced the very same difficulty getting through regarding this concept . Why is it that few people seem to have problems with the burden of proof when it comes to the innocence or guilt of a murder suspect, but then cannot apply the same exact logic to more esoteric issues, such as the existence of ghosts, gods, and the like?
I suspect part of the answer is that in the latter cases most people are attracted to some intuitive (and wrong) notion of epistemic fairness: well, you are making one claim, the other guy is making another claim, the two of you are therefore on equal footing. This seems also to be the underlying philosophy — if there is any — behind the infamous practice by much of the media to “present the two sides,” regardless of how inane one of the two sides actually is. (Incidentally, the latter case is an example of an additional logical fallacy, the false dilemma: why, exactly, would we expect there to be two sides, as opposed to a number of possible, more nuanced, alternatives? Remember “you are either with us or with the terrorists”?)
But if this explanation is correct, then why don’t people also apply the same logic to the legal system? I think that’s because it is our very concept of fairness that shifts in that case: apparently, what is epistemologically fair for impersonal situations is suddenly unfair when people are involved. This may be similar to the case of trolley dilemmas-type thought experiments, which show that people shift from a utilitarian to a deontological ethical system depending on whether they have to make relatively impersonal or very personal decisions about somebody else’s fate (apparently, it’s okay to throw a switch to save five people while killing an innocent bystander, but not okay if you have to physically throw the innocent person in front of the trolley).
The job of the skeptical critical thinker is to convince people that these seemingly different situations are logically equivalent, and that it is therefore not rational to believe in ghosts without evidence at the same time that one wouldn’t dream of convicting a person of a crime just on the basis that she cannot prove her innocence. But as is often the case, human psychology gets in the way of rational thinking.