Illustrating the burden of proof - pay me!

[John 6IX Breezy]

The aphorism 'extraordinary claims require extraordinary evidence' has been brought up as an example of arguing from incredulity. It can (and has) been misused that way, 'extraordinary' is very ambiguous in common language. But it isn't meant to be a prop for personal incredulity, the term 'extraordinary claim' should be be understood as a claim contrary to what known prior evidence supports, and 'extraordinary evidence' is evidence sufficient to indicate the claim is correct in the face of evidence to the contrary.

I agree with your general comments on the matter; but I wish to add my own take:

We have a tendency to ascribe more truth than is warranted to bits of wisdom that come wrapped in poetic and pleasant speech. During a class, one of my professors passed out slips of paper which reported some research about romantic relationships. The students were then asked to raise their hands if they agreed with the finding, and everyone did. The catch was that for half the students the conclusion said Research has found that opposites attract, while the other half said Research has found that birds of a feather flock together.

The same holds true for the spiderman-esque quip that Extraordinary claims require extraordinary evidence. Adjectives such as Extraordinary are both subjective and immeasurable. And no proposition, regardless of how extraordinary or mundane, has a predetermined amount of evidence it requires. In fact, the quicker we get rid of words such as evidence and proof from our vocabulary, the less mistakes we are likely to make. Words such as Consistent with are better alternatives.