Extraordinary Claims

David Hume said a wise person proportions belief to the evidence. A report of a marvel has to be weighed against the wider experience that made the marvel surprising. The evidence should be as strong as the claim is strange, not just as exciting.

Carl Sagan made the idea famous in a sentence that is easy to remember and easy to misuse. “Extraordinary claims require extraordinary evidence” does not mean “new claims are guilty.” It means the support has to scale with how much else would have to be rewritten.

An ordinary claim can rest on ordinary checks. A marvel needs those checks plus a reason to think the usual errors, such as a trick, a mistake or a hoax, do not explain it.

The blurry photo

A friend shares a blurry photo and says it shows a craft that rewrites physics. The photo has no original file, no date, no other witness, and no measurement. The claim, if true, would touch every textbook. The support would not survive a second look.

The fair response is not a sneer. It is a list of the evidence that would match the size of the rewrite: instruments, repeats, and a record someone hostile could inspect.

Try this today Next time you see a marvel online, ask what extra evidence would make it believable.