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In linguistics, crossover effects are restrictions on possible binding or coreference found between certain phrases and pronouns.〔 The crossover phenomenon was first explored in detail by Postal (1971).〕 Coreference (or coindexation) that is normal and natural when a pronoun follows its antecedent becomes impossible, or at best just marginally possible, when "crossover" is deemed to have occurred, e.g. ''?Who1 do his1 friends admire __1?'' The term itself refers to the traditional transformational analysis of sentences containing leftward movement (e.g. wh-movement, topicalization), whereby it appears as though the fronted constituent crosses over the expression (usually a pronoun) with which it is coindexed on its way to the front of the clause. Crossover effects are divided into strong crossover (SCO) and weak crossover (WCO).〔The distinction between strong and weak crossover is due to Wasow (1972).〕 The phenomenon occurs in English and related languages, and it may be present in all natural languages that allow fronting. ==Examples== The following sentences illustrate crossover phenomena. The a-sentences are questions in which crossover has not occurred and are given here for the sake of comparison, and the b-sentences illustrate crossover. The subscripts mark coindexation (≈coreference); they indicate that the words bearing the subscripts are supposed to refer to the same one person. The gaps in the b-sentences mark the canonical position of the wh-expression (before movement): ::a. Who1 said he1 was hungry? - Crossover absent, intentional coreferential reading available ::b. *Who1 did he1 say __1 was hungry. - Crossover present (strong), intentional coreferential reading unavailable ::a. Who told Jill1 that Fred would call her1? - Crossover absent, intentional coreferential reading available ::b. *Who1 did Jill1 say that Fred should call __1? - Crossover present (strong), intentional coreferential reading unavailable ::a. Who1 will call his1 mother? - Crossover absent, coreferential reading available ::b. ?Who1 will his1 mother call __1? - Crossover present (weak), coreferential reading unlikely ::a. Which student1 called her1 instructor? - Crossover absent, coreferential reading available ::b. ?Which student1 did her1 instructor call __1 - Crossover present (weak), coreferential reading unlikely The acceptability contrast here is curious upon first analysis. In both the a- and b-sentences, the order of the wh-expression and the coindexed pronoun is the same, the wh-expression preceding the pronoun. But only the reading indicated with the a-sentences is (fully) possible. Note that the first two b-sentences actually allow an accidental coreferential reading. This accidental reading is, however, unlike the intentional coreferential reading that the a-sentences allow. The relevant difference is that in the b-sentences, the wh-expression appears to have been moved across the pronoun on its way to the front of the sentence, whereas there is no such crossover in the a-sentences. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crossover effects」の詳細全文を読む スポンサード リンク
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