This is the first in what will be a series of short note about things that annoy me.
One often hears that phrase when dealing with people claiming to be skeptics that “Extraordinary Claims require Extraordinary Proof”. The phrase has its origin from Marcello Truzzi and was later popularized by Carl Sagan.
The general interpretation is that if you are claiming something wildly different from what is accepted you must meet a burden of proof that is proportionately as rigorous as the claim is unconventional.
This, on a quick listen, seems to make sense but it is completely wrong. The level of proof for any claim is the same. If I say “a ‘bigfoot’ ran through my back yard yesterday’” or I say “a dog ran through my back yard yesterday” the level of proof is the same. The difference is not the proof required but the difficulty of gathering and producing evidence. The more common claim will, by its nature, have more evidence already present. I can, for example, offer as evidence the presence of dogs that are known to live in my neighborhood where I’d have a much more difficult time providing a list of ‘bigfoot’ known to live nearby.
For decades the coelacanth was ‘known’ to be extinct and the claim of seeing a specimen was considered about the same as seeing a dinosaur. When one was caught in 1938 the proof needed to back up the claim was the fishermen producing the dead fish. The level of proof was the same as if they’d caught an otherwise common variety of mackerel that hadn’t previously been found in that region. The claim was extraordinary, the burden of proof was not.
Where the Truzzi canard presents a problem is that it merely provides a bias against new information and a bias toward what is already “known”. This is neither “science” nor “skeptical” but is merely adding inertia toward commonly held “common sense” and against change and innovation. It’s a fancy way of admitting that the “skeptic” prefers to only be told things they already agree with and that is precisely the opposite of being a skeptic.
Extraordinary claims require the same proof as anything else. It’s just that it’s generally extraordinarily hard to get that proof.