In linguistics, anaphora () is the use of an expression whose interpretation depends upon another expression in context (its antecedent or postcedent). In a narrower sense, anaphora is the use of an expression that depends specifically upon an antecedent expression and thus is contrasted with cataphora, which is the use of an expression that depends upon a postcedent expression. The anaphoric (referring) term is called an anaphor. For example, in the sentence Sally arrived, but nobody saw her, the pronoun her is an anaphor, referring back to the antecedent Sally. In the sentence Before her arrival, nobody saw Sally, the pronoun her refers forward to the postcedent Sally, so her is now a cataphor (and an anaphor in the broader, but not the narrower, sense). Usually, an anaphoric expression is a pro-form or some other kind of deictic (contextually dependent) expression. Both anaphora and cataphora are species of endophora, referring to something mentioned elsewhere in a dialog or text. Anaphora is an important concept for different reasons and on different levels: first, anaphora indicates how discourse is constructed and maintained; second, anaphora binds different syntactical elements together at the level of the sentence; third, anaphora presents a challenge to natural language processing in computational linguistics, since the identification of the reference can be difficult; and fourth, anaphora partially reveals how language is understood and processed, which is relevant to fields of linguistics interested in cognitive psychology. Nomenclature and examples The term anaphora is actually used in two ways. In a broad sense, it denotes the act of referring. Any time a given expression (e.g. a pro-form) refers to another contextual entity, anaphora is present. In a second, narrower sense, the term anaphora denotes the act of referring backwards in a dialog or text, such as referring to the left when an anaphor points to its left toward its antecedent in languages that are written from left to right. Etymologically, anaphora derives from Ancient Greek ἀναφορά (anaphorá, "a carrying back"), from ἀνά (aná, "up") + φέρω (phérō, "I carry"). In this narrow sense, anaphora stands in contrast to cataphora, which sees the act of referring forward in a dialog or text, or pointing to the right in languages that are written from left to right: Ancient Greek καταφορά (kataphorá, "a downward motion"), from κατά (katá, "downwards") + φέρω (phérō, "I carry"). A pro-form is a cataphor when it points to its