====== Circular reasoning ======
A form of logical fallacy in which the position that still has to be proven is already presupposed in a premise.
Take for example the following statement:
> The Bible is God’s Word, for it is written [in the Bible] that "all Scripture is inspired by God".
===== Other names =====
* Circular argument
* [[de>logik/fehlannahmen/praemissenfehler/zirkelschluss|Zirkelschluss]]
* Circulus/-um in probando (Lat.: "circle in proving")
* Circulus/-um in demonstrando (Lat.: "circle in the proof")
* Idem per idem (Lat.: "the same by the same")
* hýsteron próteron [Ὕστερον πρότερον] (grc.: "the later [is the] earlier")
Occasionally, the term "[[relevancy:petitio_principii|petitio principii]] " ("postulation of the beginning") is used as a synonym for //circular reasoning//. However, the specific meaning of this expression is inconsistent and has changed over time. It is used here as a [[rhetoric:index|rhetoric]] figure that is analogous to //circular reasoning//.
===== Description =====
The //circular argument// is closely related to the concept of a logical [[glossary:tautology|tautology]], as for both can be said that when the premises are //true// it also holds //true//:
> The sky is blue, because it is blue.
This also includes circular forms of [[logic:inferences:sorites|Sorites]] arguments, in which the last step leads back to the starting point:
> A₁ → A₂ → A₃ → … → Aₙ → A₁
However, //circular reasoning// covers also situation in which further assumptions may be made, which are not //necessarily true//. For an argument to be considered //circular//, it is enough if //one of the premises// already implies what is yet to be proven:
> A ∧ B -> A (from A and B follows A)
===== See also =====
* [[relevancy:petitio_principii|Petitio principii]]
* [[logic:inferences:sorites|Sorites]]
* [[glossary:tautology|Tautology]]
===== More Information =====
* [[wp>Circular reasoning]] on //Wikipedia//