Carl Sagan suggested they do and it is an oft repeated phrase, which I myself have repeated on numerous occasions. However, in a discussion on another message forum, a good example was brought up that challenges this assertion. Let's say I claim to be 6 feet tall. A simple measurement can prove whether my claim is true.
Now, let's say I claim to be 100 feet tall. This is certainly an extraordinary claim, is it not? However, the only evidence I need is the same tape measure used when I claimed to be 6 feet tall.
Suppose you claim you have a friend who is 100 feet tall, and you have measured him yourself, and you can show everyone the tape measure. But he's shy and does not want to come out and be measured or photographed by other people.
I don't think people would accept that.
Another example: I used to volunteer as a timer for Masters swim meets. For an ordinary meet, an ordinary stopwatch would do. But if we thought it was possible that someone would break an age-group record (e.g. fastest 100-yd butterfly in the 70-74 year old age group) we needed another timer and the timers had to sign more forms to attest that the timings were correct.
Was this by any chance a Christian message forum you heard this from because it's silly talk. Yes, extraordinary claims always require extraordinary evidence. The tape measure analogy doesn't even apply.
It wasn't a Christian forum, but it was a Christian person who said it.
Now that I've thought about it some more, I can see where it falls short. If some claimed their cousin was 6 feet tall, you'd accept it as being likely true without even seeing them. We see people who are 6 feet tall all of the time, afterall. On the other hand, if they claimed their cousin to be 100 feet tall, we'd demand to see them in person. A tape measure wouldn't even come in to the equation. It's not their exact height that we'd be questioning, but their height so far askew from the norm.
It depends on how one defines "extraordinary" as it applies to claims and to evidence. Relatively speaking, being one hundred feet in height is fucking incredible for a human, though not so much for a building.
Of course, for certain definitions of "extraordinary claim" and "extraordinary evidence" Sagan's quote will fall flat, but then so will any truism if you turn certain definitions all the way to 11. *shrug*
In any case, the claims that we have in mind when we regurgitate that line are extraordinary and do require extraordinary evidence. All that this means, if anything, that the requirement for ordinary evidence in satisfying such an extraordinary claim is not inherent to the extraordinariness that's, y'know, going on, but rather due to the particular evidence that's needed being extraordinary by an ordinary definition of "extraordinary".
In other words: "Okay, I give up, but you still know what I mean, you nose-picker!"
"Extraordinary claims require extraordinary methods for testing evidence" was not the Sagan quote.
It's just like theists to distort whatever they can to gain some kind of argument for their absurd position. Did this clown really throw you off with this crap? I'm not trying to put you down or anything, it just seems like you let your guard down, gave him way too much rope, and he hung you with it.