In the Popular Delusions series, I have explored just a few varieties of the vast number of nonsensical beliefs which afflict humanity. From the belief that astronomical bodies millions of light-years distant control our destiny here on Earth, to the belief that water remembers what substances were once dissolved in it, to the belief that reality is just a construct of the mind and can be altered by wishing hard enough, it seems there is no kind of absurdity a skeptic could dream up that has not already been outdone by someone who sincerely believes something even more ridiculous.
While I intend to continue cataloguing some of our species’ more prominent delusions, trying to debunk every single one would be a fool’s errand. Since there are a potentially infinite number of false claims, as opposed to a finite and very limited set of true ones, there is literally no limit to the ridiculous ideas people can and will dream up. If we are ever to establish a community of reason among humanity, we rationalists will have to do more than clearing away intellectual rubbish one piece at a time. Instead, we will have to teach and disseminate a general set of principles for critical thinking, one that will give all people a mental toolkit to recognize and reject superstitious ideas of all kinds so that they never take root. In this post series, I intend to assemble such a toolkit.
The first and most important principle of being a critical thinker is maintaining a well-honed sense of plausibility. Far too many absurd claims succeed only because many people have no mental impediment to credulously accepting almost anything they are told. The educated critical thinker, however, knows that just because a claim is made does not make it likely to be true. The quickest and most reliable way to judge the plausibility of some startling new claim is to check whether it fits in with other facts that are already known. The more numerous and the more well-established are the facts which a new claim contradicts, the stronger the evidence for that claim must be in order for it to overturn conventional wisdom and be accepted. Or, in short: Extraordinary claims require extraordinary evidence.
There are several ways to conceptualize this. One could be a set of balance scales; on one side is the weight of conventional wisdom and the evidence supporting it, on the other a new and extraordinary claim and the evidence in its favor. Whichever side has the more weight and tips the balance, that is the side that we should believe. As the philosopher David Hume put it in a famous passage from his 1748 book, An Enquiry Concerning Human Understanding:
The plain consequence is (and it is a general maxim worthy of our attention), “That no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavours to establish; and even in that case there is a mutual destruction of arguments, and the superior only gives us an assurance suitable to that degree of force, which remains, after deducting the inferior.” When anyone tells me, that he saw a dead man restored to life, I immediately consider with myself, whether it be more probable, that this person should either deceive or be deceived, or that the fact, which he relates, should really have happened. I weigh the one miracle against the other; and according to the superiority, which I discover, I pronounce my decision, and always reject the greater miracle.
Alternatively, we can conceive of the evidence as a web, each individual piece forming one strand that is linked together with many others. Discordant claims stretch and distort the weave, while those that accord with other evidence fit in neatly. Again, the more strongly a new claim would stretch or sever the interconnected strands of this web, the more skepticism with which it should be viewed.
Of course, just because something is an extraordinary claim does not mean it is false. Many assertions that clashed strongly with conventional wisdom turned out to be correct in the end. As Hume says, the inhabitants of a hot, tropical climate who had never seen ice or snow would justifiably find it an extraordinary claim that water can turn into a rock-hard solid. We should not rationally expect them to believe this until they have seen water freeze with their own eyes and can examine the evidence for themselves.
On the other hand, for an example of an extraordinary claim that is far more likely to be false, consider this thread from the Unexplained Mysteries forum, where several participants state their belief that TV magician Criss Angel can truly and genuinely levitate people:
As for the levitations he did…it all looked pretty clear cut to me. No strange camera angles, no tables or cables…people freaking out…plus levitating total strangers never mind himself.
It seems to me that this man is offering the proof so many are asking for. He also demonstrates telekinetic abilities. I’ve seen many on this board say “if someone has these abilities, they would be in the media, on camera proving it!”… well, here it is.
This is a perfect example of someone whom the critical thinking principles described in this post could have helped. Let me begin by listing the obvious facts: ordinary people, as a rule, cannot float up off the ground by will alone. Levitation is neither a commonplace feat nor an uncommon but known ability possessed by a minority of individuals. There is no known physiological mechanism that would enable a person to do such a thing without physical support or the application of an external propulsive force. We have studied the law of gravity in detail and found no obvious exceptions that would permit its usual operation to be suspended. And, lastly, Criss Angel is a magician, a profession whose function it is to find unusual and clever ways of deceiving people for purposes of entertainment.
Given all these widely agreed-upon and uncontested facts, what should we conclude when presented with one single photo, or even video, of a person apparently levitating off the ground? Should we take the one over the many, throwing aside a huge quantity of evidence we thought we had about the way the universe works, and conclude that this single observation establishes an entirely new paradigm? Or is it a far more rational conclusion that one puzzling observation is not enough to outweigh the vast quantity of evidence attesting to the fact that people cannot levitate, and that Criss Angel has come up with a way to trick people into believing he has accomplished something he has not in fact accomplished, even if we cannot state with confidence precisely what the trick is?
The participants on the UM board have done the former, a clear demonstration of irrational thinking. To rewrite one’s entire worldview every time an apparently discordant piece of evidence comes alone is not just terminally credulous, it would leave one unable to function in the world. How could a person choose any action if they were completely revising the base of their knowledge every time they turned around?
This is not to say that extraordinary claims can never be proven. As with the ice example, applicability of past experience should be the default assumption, but it should not be the final conclusion. Claims that violate or apparently violate laws of nature should be viewed with skepticism at first, but they should be tested rather than rejected outright. And if repeated evidence showed that people could indeed levitate without support – evidence obtained under reliable, controlled conditions, when tricks and cheating could be conclusively ruled out – then we would have to conclude that we had learned something new about the way the universe works. In the meantime, our provisional conclusion should be that this extraordinary claim is, at best, not proved.
Other posts in this series: