Once again the claim has surfaced: “extraordinary claims require extraordinary evidence.” And once again I have had to shoot it down. Now what could be the problem with a principle so symmetrically reasonable? Grey days produce grey moods. Cold weather requires a cold weather jacket. Why wouldn’t extraordinary claims require extraordinary evidence?
The problem starts with this: who decides what is “extraordinary”? Without an absolute, objective standard this principle collapses into “Anything that appears really implausible to me requires extraordinary evidence” and that in turn collapses into “No evidence will be good enough to convince me of something I find really implausible”. In other words, this is a recipe for an irrational dismissal of any evidence counter to what one already accepts.
One of the reasons atheists, naturalists, agnostics and other skeptics feel free to invoke this most dubious principle is because they naively think whatever they happen to find extraordinary is objectively extraordinary. But first you need to defend that position, and few even know how to begin mounting a defense for it.
The most basic problem however is that “extraordinary” claims, like all other claims, require good evidence. That’s it. Let’s say your claim is that you were abducted by aliens. Extraordinary? I’d say so. But then you provide good, solid evidence for it. Then I ought to believe it, or at least be reasonably open to it (barring the possibility that I have defeaters to that evidence).
Here’s a final illustration. I was picking up dog poo in the backyard today when a finger broke through the bag and was soiled by the feces. My first reaction was to amputate the finger, but I quickly reminded myself that this was an unreasonable response. Feces, like dirt, simply requires soap and water. And so I washed the soiled finger just like I would wash a finger smeared with dirt. Granted, I still had an impulse to keep washing, but that was not rational. A finger soiled with something “extraordinarily” unclean like dog poo, requires the same soap and water that cleans a finger soiled with something “ordinarily” unclean like dirt.