Coreference resolution
In linguistics, coreference, sometimes written co-reference, occurs when two or more expressions in a text refer to the same person or thing; they have the same referent, e.g. Bill said he would come; the proper noun Bill and the pronoun he refer to the same person, namely to Bill. Coreference is the main concept underlying binding phenomena in the field of syntax. The theory of binding explores the syntactic relationship that exists between coreferential expressions in sentences and texts. When two expressions are coreferential, the one is usually a full form (the antecedent) and the other is an abbreviated form (a proform or anaphor). Linguists use indices to show coreference, as with the i index in the example Billi said hei would come. The two expressions with the same reference are coindexed, hence in this example Bill and he are coindexed, indicating that they should be interpreted as coreferential.
When exploring coreference, there are numerous distinctions that can be made, e.g. anaphora, cataphora, split antecedents, coreferring noun phrases, etc. When dealing with proforms (pronouns, pro-verbs, pro-adjectives, etc.), one distinguishes between anaphora and cataphora. When the proform follows the expression to which it refers, anaphora is present (the proform is an anaphor), and when it precedes the expression to which it refers, cataphora is present (the proform is a cataphor). These notions are illustrated as follows:
Semanticists and logicians sometimes draw a distinction between coreference and what is known as a bound variable. An instance of a bound variable can look like coreference, but from a technical standpoint, one can argue that it actually is not. Bound variables occur when the antecedent to the proform is an indefinite quantified expression, e.g.
Quantified expressions such as every student and no student are, from a technical standpoint, not referential. The subjects every student and no student are grammatically singular, but they do not pick out single referents in the discourse world. Thus since the antecedents to the possessive adjective his is not referential, one also cannot say that his is referential. Instead, one says it is a variable that is bound by its antecedent. Its reference varies based upon which of the students in the discourse world is thought of. If Jack, John, and Jerry are the three students in the discourse world, then the meaning of his varies based upon whether Jack, John, or Jerry is the focus of the minds eye. The existence of bound variables is perhaps more apparent with the following example:
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