Definition of tautology
1a : needless repetition of an idea, statement, or word Rhetorical repetition, tautology ('always and for ever'), banal metaphor, and short paragraphs are part of the jargon.— Philip Howard
b : an instance of such repetition The phrase "a beginner who has just started" is a tautology.
2 logic : a statement that is true by virtue of its logical form alone A logical combination of sentences that is always true, regardless of the truth or falsity of the constituent sentences, is known as a "tautology."— Rudy Rucker … now the objection was raised that the entire theory of natural selection rested on a tautology: "Who survives? The fittest. Who are the fittest? Those that survive."— Ernst Mayr
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