Circular reasoning
Circular reasoning is a logical fallacy in which the reasoner begins with what they are trying to end with. 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. As a consequence, the argument becomes a matter of faith and fails to persuade those who do not already accept it. 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. Circular reasoning is closely related to begging the question, and in modern usage the two generally refer to the same thing.
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.
An example of circular reasoning is: “This statement is correct because it says it is correct.”
Common forms
Circular reasoning can appear in several common forms, each illustrating a different way the conclusion and premise reinforce each other without independent support.;Restatement : The conclusion is simply a rephrasing of the premise.
;Character or trait loop: A personal quality is justified by behavior, which is then justified by the same quality.
;Definition loop: A term is defined in a way that refers back to itself.
;Rule or authority loop: A rule or authority is justified by reference to itself or the rule it establishes.
History
The problem of circular reasoning has been noted in Western philosophy at least as far back as the Pyrrhonist philosopher Agrippa who includes the problem of circular reasoning among his Five Tropes of Agrippa. The Pyrrhonist philosopher Sextus Empiricus described the problem of circular reasoning as "the reciprocal trope":The reciprocal trope occurs when what ought to be confirmatory of the object under investigation needs to be made convincing by the object under investigation; then, being unable to take either in order to establish the other, we suspend judgement about both.