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Extraposition is a mechanism of syntax that alters word order in such a manner that a relatively "heavy" constituent appears to the right of its canonical position.〔For accounts of extraposition, see for instance Guéron (1990), Baltin (1981, 1983), Guéron and May (1984), Stucky (1987), Wittenberg (1987), Culicover and Rochemont (1990), Huck and Na (1990).〕 Extraposing a constituent results in a discontinuity and in this regard, it is unlike shifting, which does not generate a discontinuity. The extraposed constituent is separated from its governor by one or more words that dominate its governor. Two types of extraposition are acknowledged in theoretical syntax: standard cases where extraposition is optional and ''it''-extraposition where extraposition is obligatory. Extraposition is motivated in part by a desire to reduce center embedding by increasing right-branching and thus easing processing, center-embedded structures being more difficult to process. Extraposition occurs frequently in English and related languages. ==Examples== Standard cases of extrapostion are optional, although at times the extraposed version of the sentence is strongly preferred. The following pairs of sentences illustrate "normal" word order first followed by the same sentence with extraposition: ::a. Someone who we don't know left a message. ::b. Someone left a message who we don't know. - Extraposition of relative clause out of subject ::a. Susan said something that nobody expected more than once. ::b. Susan said something more than once that nobody expected. - Extraposition of relative clause out of object ::a. Some guy with red hair was there. ::b. Some guy was there with red hair. - Extraposition of prepositional phrase out of subject ::a. How frustrated with their kids are they? ::b. How frustrated are they with their kids? - Extraposition of prepositional phrase from predicative adjective phrase ::a. ?What that was so entertaining actually happened? ::b. What actually happened that was so entertaining.? - Extraposition of content clause from subject ''wh''-element ::a. ?What that upset everyone do you think they did? ::a. What do you think they did that upset everyone? - Extraposition of content clause from object ''wh''-element These examples illustrate a couple of basic facts about extraposition. One of these facts is that relatively "heavy" constituents are being extraposed (e.g.usually clauses and sometimes prepositional phrases). Another fact is that extraposition can occur out of subjects. This aspect of extraposition is unlike topicalization and ''wh''-fronting, two other mechanisms that often generate discontinuities. Attempts to front expressions out of subjects fail in English. Another fact about extraposition is that sometimes it cannot occur beyond informationally heavy material. ::a. Some guy with red hair was talking excessively. ::b. *Some guy was talking excessively with red hair. - Failed attempt to extrapose prepositional phrase This aspect of extraposition supports the insight that extraposed constituents should be informationally heavy. Extraposition likely fails in this case because ''with red hair'' cannot be construed as important information. 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「extraposition」の詳細全文を読む スポンサード リンク
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