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In rhetoric, a tautology (from Greek ταὐτός, "the same" and λόγος, "word/idea") is an argument which repeats an assertion using different phrasing. The proposition, as stated, is thus logically irrefutable, while obscuring the lack of evidence or valid reasoning supporting the stated conclusion.
On the surface, tautology in rhetoric and in logic are similar. In rhetoric, an assertion is supported by a superficially distinct premise, while effectively stating the same thing twice. In formal logic, a tautology makes a single statement, which is true by logical necessity. Axiomatically, logical tautologies are neither refutable nor verifiable under any condition, effectively stating the identity of an assertion. In contrast, rhetoric deals with more tangible assertions, and tautologies in this context may be refuted or verified.
In circular reasoning a premise is restated as a conclusion. Similarly to beg the question is to assume the truth of the conclusion of an argument in the premises in order for the conclusion to follow. In contrast, a tautology simply states the same thing twice, thus typically being redundancies only comprising part of a statement.