Definition
Plain language
A statement that's true by construction and therefore says nothing.
As stated in the literature
A formula true under every interpretation; reducing a theorem to a tautology yields a compiling proof that carries no mathematical content.
Also called: tautologies, trivial tautology
Why it matters: A proof that has quietly collapsed into a tautology will pass every automated check while establishing absolutely nothing, which makes it a favourite way for a difficult problem to appear solved.
For example, "it will either rain tomorrow or it won't" is always true and tells you nothing about tomorrow's weather.
Heard on the show
“So the structure of the training experiment is a real transfer test, not a tautology.”Episode 180 — The Bug Where Smart Assistants Read a Fact and Still Forget It