====== 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:

> <u questionable "Circular reasoning">The Bible is God’s Word, for it is written [in the Bible] that "all Scripture is inspired by God".</u>

===== Other names =====

  * Circular argument
  * <i :la "Lat.: circle in proving">Circulus/-um in probando</i> (Lat.: "circle in proving")
  * <i :la "Lat.: circle in the proof">Circulus/-um in demonstrando</i> (Lat.: "circle in the proof")
  * <i :la "Lat.: the same by the same">Idem per idem</i> (Lat.: "the same by the same")
  * <i :grc-Latn>hýsteron próteron</i> [<span :grc "hýsteron próteron">Ὕστερον πρότερον</span>] (grc.: "the later [is the] earlier")

Occasionally, the term "<i :la>[[relevance:petitio_principii|petitio principii]]</i> " ("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//. 

<aside info filled rounded>
**Note:** also the terms <i :la "Lat.: vicious circle">circulus vitiosus</i> and its translation "vicious circle" are sometimes understood as synonyms for //circular reasoning//. However, as these terms mainly refer to //negative feedback systems//, they are not recommended for use in this context.
</aside>

===== 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//:

> <u questionable "Tautology">The sky is blue, because it is blue.</u>

This also includes circular forms of [[logic:inferences:sorites|Sorites]] arguments, in which the last step leads back to the starting point:

> <u questionable "Circular argument"><var>A₁</var> → <var>A₂</var> → <var>A₃</var> → … → <var>Aₙ</var> → <var>A₁</var></u>

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:

> <u questionable "From A and B follows A (circular argument)"><var>A</var> ∧ <var>B</var> -> <var>A</var></u> (from <var>A</var> and <var>B</var> follows <var>A</var>)

===== More examples =====
==== The Wiki-AI Loop ====

Being a publicly accessible wiki, this website has also ended up in the training data used by AI systems. Setting aside the problems this raises regarding copyright, it also presents an interesting challenge when it comes to continuing work on this project:

If the author asks an AI for an assessment – for example, regarding language usage (“Is this term actually used in this sense?”) or other topics on this website – there is a risk that the AI has derived its knowledge, among other sources, from existing content on this site. The “language usage” it is now supposed to verify could ultimately be a (possibly incorrect) usage that was once listed on this very site.

The underlying logic would therefore be: (use on this site) → (training the AI) → <u invalid "circular reasoning">(use on this site)</u>

In other words: a perfect circular argument. Or to put it another way: the AI cannot be trusted in this case.

<aside info>**Note:** As a general rule, //any// fact provided by AI should //always// be verified using independent sources.

Keeping this in mind, using AI systems as “writing and research assistants” can still hugely lighten the workload. Ultimately, however, the user must retain control over and take responsibility for the content.

On this website, this is handled as follows: The AI checks existing articles for gaps and ambiguities, but the text is always written by a human. Nothing is included in the content that has not been fully understood and reviewed by a human author.</aside>

===== See also =====

  * <i :la>[[relevance:petitio_principii|Petitio principii]]</i>
  * [[logic:inferences:sorites|Sorites]]
  * [[glossary:tautology|Tautology]]

===== More Information =====

  * [[wp>Circular reasoning]] on //Wikipedia//