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{{selfref|For the Wikipedia policy, please see [[Wikipedia:Avoid self-references]]}}

[[Image:ouroboros.png|thumb|150px|The [[Ouroboros]], a dragon that bites its tail, is a symbol for self-reference.]]
'''Self-reference''' is a phenomenon in [[natural language|natural]] or [[formal languages]] consisting of a [[Sentence (linguistics)|sentence]] or [[formula]] referring to itself directly, through some intermediate sentence or formula, or by means of some [[Semantics encoding|encoding]].<ref>Wikipedia, http://en.wikipedia.org/wiki/Self-referential</ref> In philosophy, it also refers to the ability of a subject to speak of or refer to themself: to have the kind of thought expressed in English by "[[I (pronoun)|I]]". 

Self-reference is possible when there are two logical levels, a level and a meta-level. It is most commonly used in [[mathematics]], [[philosophy]], [[computer programming]], and [[linguistics]]. Self-referential statements can lead to [[paradox]]es (but see [[antinomy]] for limits on the significance of these).

==Usage==
An example of a self-reference situation is the one of [[autopoiesis]], as the logical organization produces itself the physical structure which create itself.

In [[metaphysics]], self-reference is [[subjectivity]], while "hetero-reference", as it is called (see [[Niklas Luhmann]]), is objectivity.

Self-reference also occurs in [[literature]] when an author refers to his  work in the context of the work itself. Famous examples include [[Cervantes]]'s [[Quixote]], [[Denis Diderot]]'s ''[[Jacques le fataliste et son maître]]'', [[Italo Calvino]]'s ''[[If on a winter's night a traveler]]'', many stories by [[Nikolai Gogol]], [[Lost in the Funhouse]] by [[John Barth]], and [[Luigi Pirandello]]'s ''[[Six Characters in Search of an Author]]''. This is closely related to the concept of ''breaking the [[fourth wall]]'' or [[meta-reference]] (which often involve self-reference). 

The [[surrealistic]] [[painter]] [[René Magritte]] is famous for his self-referential works. [[Image:MagrittePipe.jpg|thumb|150px|"[[The Treachery Of Images]]" (1928-9) by [[René Magritte]] depicts a pipe along with text meaning, "This is not a pipe."]] "[[The Treachery of Images]]," shown at right, includes words claiming, in French, it is not a pipe, the truth of which depend entirely on what the word "ceci" (in English, "this") is taken to refer to. Is it the pipe depicted&mdash;or is it the painting or even the sentence itself?

Self-reference is also employed in [[tautology (rhetoric)|tautology]] and in ''licensed terminology''. When a word defines itself (e.g., "Machine: any objects put together mechanically"), the result is a tautology. Such self-references can be quite complex, include full propositions rather than simple words, and produce arguments and terms that require license (accepting them as proof of themselves).

Self-reference in [[computer science]] is seen in the concept of [[recursion]], where a program unit relies on instances of itself to perform a computation.  The [[Lisp programming language]] is especially designed to exploit recursion. Object oriented languages use special keywords to refer to the current instance of an object: <code>[[this (computer science)|this]]</code> in [[C++]], [[Java (programming language)|Java]], and [[PHP]]; <code>self</code> in [[Smalltalk]] and [[Objective C]]; and <code>Me</code> in [[Visual Basic]].

==Examples==<!-- This section is linked from [[Self-reference]] -->

Many of the following examples appear in [[Douglas Hofstadter]]'s [[Gödel, Escher, Bach: an Eternal Golden Braid]] or [[Metamagical Themas]].

===Mathematics===

* [[Tupper's self-referential formula]]

===Sentences===

*This statement is short.
*I am not the subject of this sentence.
*"I" is the subject of this sentence.
*Which question is also its own answer?
*[[Quine's paradox|"Yields falsehood when preceded by its quotation" yields falsehood when preceded by its quotation.]] (This is a version of the [[liar paradox]], an example of [[indirect self-reference]] through a [[quines|quine]], which leads to a [[paradox]].)
*The statement that the word "false" should be interpreted as "not true" is false. (another version of the liar paradox)
*[[Russell's paradox]]: The set of all sets which are not elements of themselves (which includes, and therefore does not, and therefore does include itself)
*The [[Self-reference#Examples|Examples section of this article]] refers to itself.
*This sentence exemplifies cacozelia (using rare/foreign words to appear learned).
*[[Click here]]
*Do not read this.
*This page intentionally left blank.

===The Fumblerules===
Fumblerules state rules of good grammar and writing through sentences that violate those very rules.  George L. Trigg and William Safire have made their own lists, but anyone knowledgable on grammar can do the same.  See [[List of Fumblerules]] for a comprehensive (yet non-exhaustive) list.

===Literature===
{{main|Metafiction}}
*"beware: do not read this poem" by [[Ishmael Reed]] - "the hunger of this poem is legendary, it has taken in many victims"
*[[The Monster at the End of This Book: Starring Lovable, Furry Old Grover|The Monster at the End of This Book]] references itself in the title, as well as throughout the story.
*[[Steal This Book]] by Abbie Hoffman
*[[The Cat Who Walks Through Walls]] by [[Robert A. Heinlein]] considers the universe ([[multiverse]]) as an author-manipulated object including the plot in the book itself.
*[[Sophie's World]] by [[Jostein Gaarder]], in which the titular character realizes she is the character of a book.
*[[Neverending Story]] by [[Michael Ende]] uses self-reference of the book prominently, when a character (Atreyu) of a story within the story (also called 'Neverending Story') finds a book called the same, and it is the same book the reader is reading.

===Other===
*[[Pangram#Self-enumerating pangrams|Self-enumerating pangrams]]
*A Wikipedia Article entitled Self Reference.
* [[Irish Constitution#Transitory Provisions|Article 52 of the Irish Constitution]] has prohibited publication of Article 52 in official texts since 1938 despite continuing to have the force of law

==References==
{{reflist|2}}
*[[Douglas Hofstadter|Hofstadter, D. R.]] (1980). ''[[Gödel, Escher, Bach: an Eternal Golden Braid]]''. New York, Vintage Books.
*[[Raymond Smullyan]] ([[1994]]), ''Diagonalization and Self-Reference'', Oxford Science Publications, ISBN 0-19-853450-7
*{{cite encyclopedia
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 | encyclopedia = {{SITENAME}}
 | title = Self-reference
 | url = {{fullurl: Self-reference}}
 | accessdate = {{CURRENTYEAR}}-{{CURRENTMONTH}}-{{CURRENTDAY2}}
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}}

==See also==
{{col-begin}}
{{col-break}}
*[[Circular reference]]
*[[Diagonal lemma]]
*[[Gödel's incompleteness theorem]]
*[[Grelling-Nelson paradox]]
*[[Indirect self-reference]]
*[[List of autological words]]
*[[Meta-reference]]
{{col-break}}
*[[Object of the mind]]
*[[Optical feedback]]
*[[Recursion]]
*[[Reference work]]
*[[Russell's paradox]]
*[[Self-coup]]
*[[Self-similarity]]
*[[Self-reference]]
*[[Self-refuting idea]]
*[[Use–mention distinction]]
*[[Self-insertion]]
{{col-end}}

==External links==
*''[http://www.earlham.edu/~peters/writing/psa/ The Paradox of Self-Amendment:  A Study of Logic, Law, Omnipotence, and Change]'', by Peter Suber (Peter Lang Publishing, 1990).  A book-length study of self-reference in law.  (The book is OP but the full text is free online.)
*''[http://www.math.wisc.edu/%7Epropp/srat-Q Self-Referential Aptitude Test]'', by Jim Propp
*''[http://www.cut-the-knot.org/selfreference/index.shtml Self-reference and apparent self-reference]''
*''[http://niquette.com/books/sophmag/elegance.htm "Elegancelessness"] A collection of self-references by Paul Niquette''
*Parody site [[Uncyclopedia]]'s [[uncyclopedia:Category:Self-reference|self-reference]] have some good examples of self-reference
*[http://cgi.cs.indiana.edu/~oracle/digest.cgi?N=1353#1353-01|A Self-Referential Story], from the [[The Internet Oracle|Internet Oracularities]] #1353
*[http://www.maths.unsw.edu.au/~jim/selfref.html Self-reference jokes]

[[Category:Grammar]]
[[Category:Theory of computation]]
[[Category:Logic]]
[[Category:Philosophy of language]]

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