Circular reasoning

Circular reasoning (Latin: circulus in probando, "circle in proving";[1] also known as circular logic) is a logical fallacy in which the reasoner begins with what they are trying to end with.[2] Circular reasoning is not a formal logical fallacy, but a pragmatic defect in an argument whereby the premises are just as much in need of proof or evidence as the conclusion, and as a consequence the argument fails to persuade. Other ways to express this are that there is no reason to accept the premises unless one already believes the conclusion, or that the premises provide no independent ground or evidence for the conclusion.[3] Circular reasoning is closely related to begging the question, and in modern usage the two generally refer to the same thing.[4]

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Circular reasoning is often of the form: "A is true because B is true; B is true because A is true." Circularity can be difficult to detect if it involves a longer chain of propositions.