Whextraction

Wh-extraction refers to a syntactic process in which a wh-word (who, what, which) is moved from its original position inside a clause to the front of the clause to form questions or certain relative clauses. The wh word creates a dependency with a displaced position often described as a trace or a null operator at the base position. In many theories, the movement is successive cyclic, moving through intermediate positions within embedded clauses until it reaches a prominent, clause-initial position.

In English, wh-extraction is common in questions and some relative clauses. For example, in "What did you say that Mary bought __?" the word What is moved to the front, leaving a gap that corresponds to the object of bought. Prepositions can be integrated through pied-piping, yielding forms like "Which book did you go to the library with __?" In other languages, wh words may appear in place (in situ) and rely on particles, intonation, or other grammatical devices to signal a question.

Wh-extraction is subject to locality constraints. Certain extractions from within islands or complex syntactic structures are degraded or ungrammatical, reflecting limits on how far a wh-phrase can travel and where it can originate. Cross-linguistically, languages vary in how they realize wh dependencies: some front the wh word, others use particles or alternative word orders, and some permit multiple wh-words to be extracted in a single clause.

The concept is central to theories of movement and the architecture of grammar, and it remains a focus of cross-linguistic and psycholinguistic study.