Extraposition

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. 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.

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:

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.

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.

A further widely acknowledged fact about extraposition is that it is clause-bound. This aspect of extraposition is known as the Right Roof Constraint. There is a "right roof" above which extraposition cannot occur. In other words, extraposition cannot occur out of an embedded clause:

This aspect of extraposition is unlike fronting discontinuities (topicialization and wh-fronting), which can easily front a constituent out of an (argument) clause, e.g.

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