Over at Meta's blog, he has been discussing "extraordinary claims". The idea of "extraordinary proof" is a thing I haven't discussed for a good few years.
If you look at the argument "extraordinary claims require extraordinary proof", the problem is that it creates an endless chain of proof which it makes it literally impossible to satisfy. Let's say we start with a claim that someone calls an "extraordinary" claim, and so they reserve the right to demand "extraordinary" proof. Let's say someone does then bring that extraordinary proof to our arguer. The problem is that the proof itself is "extraordinary" -- it had to be extraordinary. It was part of the conditions to satisfy the arguer that it must be extraordinary. But now, because that proof is extraordinary, the arguer says the proof that they demanded can't be believed either: it's an extraordinary claim. Watch how it works: Someone demands that the proof must be "extraordinary", and reserves the right to throw out that proof precisely because it was extraordinary, precisely because it met the conditions they set. So if you do bring extraordinary proof, it is thrown out unless it has its own proof, and that proof was also extraordinary. And if that next proof was extraordinary, the same cycle repeats all over again. That proof would also be thrown out as an extraordinary claim, as something that requires extraordinary proof of its own. The cycle continues as long as the arguer cares to play, with no way for the responder to satisfy the demands. The demands for proving the next thing would never end. If an argument sets out terms that can never be met, if it lays out conditions that can never be satisfied, it is worthless. For example:
An atheist may say "The existence of God" is extraordinary, and requires extraordinary proof. Ok, let's say God offers up extraordinary proof of his existence: like raising someone from the dead. The burden of extraordinary proof has been met. But wait, the atheist can just say he does not accept the extraordinary proof -- and he rejects it because it's extraordinary, so now he requires extraordinary proof that there really was extraordinary proof. It is a demand which is impossible to satisfy.
Now, for my own part, I don't think the existence of God is an extraordinary claim. But for all that, Jesus had an extraordinary life, and extraordinary teachings. He's all the proof I need: if he says God exists, I'll take his word for it. And if someone wants me to take their word that there isn't a God, they have to top Jesus. If they can't, then Jesus' word is the word I'll be taking for that.