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.

Standard cases of extraposition are optional, although at times the extraposed version of the sentence is strongly preferred.

One of these facts is that relatively "heavy" constituents are being extraposed (e.g.usually clauses and sometimes prepositional phrases).

This aspect of extraposition is unlike topicalization and wh-fronting, two other mechanisms that often generate discontinuities.

In other words, it is pro-form of a sort; its appearance pushes the clause that it stands for to the end of the sentence.

[4][citation needed] When extraposition occurs, it inevitably reduces center embedding and thus increases right-branching.

[5] To increase right-branching it then moves rightward (and upward in the case of the phrase structure analysis) to its surface position.

[6] The words in red in the dependency tree qualify as a concrete unit of syntax; they form a catena.