I meant to write something deep and inspiring to start the new year, but at least so far I haven’t come up with that yet, so here’s this instead.
Imagine the following situation: A person, whom we can call Bob, believes something strongly. It could be anything, such as that aliens have visited the Earth, or that John has a crush on Pauline. And it’s no wonder Bob believes it — he’s got plenty of evidence about it. Facts A, B, C, D and E all point to its being true. None of them might prove it for certain, but put together, they’re highly suggestive. So Bob has good reason to be convinced.
Then along comes a sceptic, who says that Bob’s notion requires proof to be believed. Well, he’s got plenty of items. But after he’s done enumerating them, the sceptic points out that A actually doesn’t prove anything. Bob is at least willing to make some concessions, and admits the sceptic’s reasoning. It doesn’t really matter since so much other evidence still proves his belief. Then the sceptic points out that B just isn’t true at all, and after seeing the evidence Bob concedes to that as well. The can’t reach an agreement about C, with Bob considering it valid evidence but the sceptic not so. D turns out to be rather suspect as well.
Bob is only really left with E, which he never considered sufficient evidence by itself in the first place. He doesn’t change his opinion, however. As the items of evidence drop out, he has increasingly begun to emphasize that it could still be true. His faith hasn’t shaken because the sceptic hasn’t proven his belief to be untrue. It still appears quite believable to him. He can see how all this evidence could be invalid even if the belief were still true. Maybe abduction stories are usually obtained unreliable through hypnosis and no-one’s ever provided any material evidence of their having happened, meaning he can’t use them as proof of the nature of the aliens. Maybe psychology proves that perfectly normal people can make unreliable observations coloured by their imaginations, disproving his claim that there must be something extraordinary behind extraordinary sightings. That still doesn’t prove that flying saucers haven’t visited the Earth. Extraordinary sightings could still have extraordinary reason. And maybe the humanoids are just too clever to leave behind proper evidence of their abductions.
Believers of different stripes are often accused of shifting the burden of proof to the wrong side; instead of giving evidence for their beliefs, they demand that sceptics prove them wrong. The above mechanism seems to go some way towards explaining this tendency. It often appears that there is evidence for some thing (especially when these have a tendency to pop up spontaneously among believers; more on this in another article). Based on those, one’s belief may for all they know have perfectly good basis to be accepted, or at least be able to cleverly disguise itself as such. But once a strong belief has already formed, it apparently has a tendency to get stuck in the brain. Other things are interpreted through this belief which, I suspect, makes it circularly look more credible — it fits with other things that are known, and with ways of understanding things, but in reality this may just be because it has affected them itself. This may at least in part also explain the tendency people have of noticing evidence for but not that against their held beliefs (confirmation bias).
In the case of “Bob”, the belief has already been accepted, perhaps quite genuinely for the reason that the evidence appeared so strong. Now it would take separate evidence to counter it. But what Bob is missing here is that if the original collection of evidence is disproven, the reason to believe in the first place also disappears. Instead he hangs onto his belief and demands that it be disproven before he give it up. It of course helps here, and may play an important part, if he has some ulterior motivation to believe in the thing in question — but this kind of thing need not always be explained by just that.
Don’t do this. Always keep in mind what the reason is that you have to believe in something. If someone or something challenges your belief, always compare the counterarguments to your reasons for believing. If they counter the reasons, there is no need to demand anything further. Otherwise you will only end up claiming that you have proven something just by proving it to be possible.