Moving the goalposts
Also called: Shifting the standard
Changing what would count as proof after the earlier standard has been met.
How to spot it
Was the test agreed before the evidence arrived? Did it quietly get harder afterwards?
Example
“Show me one study.” (You do.) “Fine, but I meant a large one.” (You do.) “But not from that country.”
How to answer it
Ask up front what evidence would change their mind, and say it back to them.
Related
- No true Scotsman: Protecting a claim by redefining the group so counterexamples don't count.
- Shifting the burden of proof: Claiming something is true because it hasn't been disproved, and asking others to disprove it.