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]
Rhetorical tautology vs. circular reasoning
Circular reasoning differs from tautologies in that circular reasoning restates the premise as the conclusion, instead of deriving the conclusion from the premise. (This is often conflated with begging the question, in which the premise relies on the assumption of the conclusion). A tautology simply states the same thing twice.
Rhetorical tautologies typically present themselves as redundancies only comprising part of a statement.
Circular reasoning: "God exists because the Bible says so, and the Bible is God's word."
Rhetorical tautology: "A tautology is anything that is tautological."
- 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.
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