In rhetoric, a tautology (from Greek ταὐτός, "the same" and λόγος, "word/idea") is a logical argument constructed in such a way, generally by repeating the same concept or assertion using different phrasing or terminology, that the proposition as stated is logically irrefutable, while obscuring the lack of evidence or valid reasoning supporting the stated conclusion. (A rhetorical tautology should not be confused with a tautology in propositional logic.)[a]
Circular reasoning differs from tautologies in that circular reasoning restates the premise as the conclusion, instead of deriving the conclusion from the premise. A tautology states the same thing twice.
^Rhetorical tautologies state the same thing twice, while appearing to state two or more different things; logical tautologies state the same thing twice, and must do so by logical necessity. The inherent meanings and subsequent conclusions in rhetorical and logical tautologies or logical necessities are very different. By axiomatic necessity, logical tautologies are neither refutable nor verifiable under any condition.