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Originally Posted by jposamen  Carl Sagan has been quoted to say, "Extraordinary claims require extraordinary evidence." Generalizing this idea, I think it's widely accepted that the rigor or extent of evidence should be proportional to the extraordinariness of the claim it supports. What are the problems with this notion? |
The degree to which a claim is extraordinary depends on background knowledge. Therefore, what is an extraordinary claim for Carl Sagan may be an ordinary claim for someone else. For example, if you believe that the content of
The Bible is true then the resurrection of the dead may not seem so extraordinary to you as it would to Carl Sagan, or if you lived in the 15th Century Columbus' claim that the earth was spherical may have been extraordinary, but today the same claim is anything but extraordinary. In other words, if a claim contradicts a great deal of your background knowledge then it is extraordinary, and if it is consistent with your background knowledge then it is ordinary, so extraordinariness is a function of what you already believe, not an impartial quality of a claim.