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Self-reference occurs in natural or formal languages when a sentence, idea or formula refers to itself. The reference may be expressed either directly—through some intermediate sentence or formula—or by means of some encoding. In philosophy, it also refers to the ability of a subject to speak of or refer to himself, herself, or itself: to have the kind of thought expressed by the first person pronoun, the word "I" in English.
Self-reference also occurs in literature and film when an author refers to his work in the context of the work itself. Famous examples include Cervantes's Don 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, Luigi Pirandello's Six Characters in Search of an Author, and Federico Fellini's 8½ . This is closely related to the concepts of breaking the fourth wall and meta-reference, which often involve self-reference.
The surrealist painter René Magritte is famous for his self-referential works. His painting The Treachery of Images, includes the words this is not a pipe, the truth of which depends entirely on whether the word "ceci" (in English, "this") refers to the pipe depicted—or to the painting or the sentence itself.
In computer science, self-reference occurs in reflection, where a program can read or modify its own instructions like any other data. Numerous programming languages support reflection to some extent with varying degrees of expressiveness. Additionally, self-reference is seen in recursion (related to the mathematical recurrence relation), where a code structure refers back to itself during computation.
In language 
A word that describes itself is called an autological word (or autonym). This generally applies to adjectives, for example sesquipedalian, but can also apply to other parts of speech, such as TLA, as a three-letter abbreviation for "three-letter abbreviation", and PHP which is a recursive acronym for "PHP: Hypertext Preprocessor".
A reflexive sentence has the same subject and object (e.g., "The man washed himself"). In contrast, a transitive sentence requires the subject and object to be non-identical (e.g., "The man hit John").
There is a special case of meta-sentence in which the content of the sentence in the metalanguage and the content of the sentence in the object language are the same. Such a sentence is referring to itself. However some meta-sentences of this type can lead to paradoxes. "This is a sentence." can be considered to be a self-referential meta-sentence which is obviously true. However "This sentence is false" is a meta-sentence which leads to a self-referential paradox.
Fumblerules are a list of rules of good grammar and writing, demonstrated through sentences that violate those very rules, such as "Avoid cliches like the plague" and "Don't use no double negatives". The term was coined in a published list of such rules by William Safire.
In mathematics 
In popular culture 
- The sub-genre of "recursive science fiction" is now so extensive that it has fostered a fan-maintained bibliography at the New England Science Fiction Association's website; some of it is about science fiction fandom, some about science fiction and its authors.
See also 
- Hofstadter, D. R. (1980). Gödel, Escher, Bach: an Eternal Golden Braid. New York, Vintage Books.
- Smullyan, Raymond (1994), Diagonalization and Self-Reference, Oxford Science Publications, ISBN 0-19-853450-7