A characteristic feature of natural languages is the fact that certain syntactic categories are systematically found "out of place." Normally, in English, a direct object follows the verb on which it depends (one says I had seen it rather than I had it seen or It I had seen). Nonetheless, if the object is interrogated, a wh-word (so called because most interrogative words in English begin with the letters wh -- who, what, which, when, where, why, etc.) is used and "displaced" to first position in (root or subordinate) interrogative sentences (What had you seen? I asked what you had seen).

Such wh-movement is found in other contructions as well (relatives, exclamatives, concessives, etc.: The film which you had seen . . . ; What a nice house you have!Whatever you do, . . . , etc.) and is but an instance of a more general movement operation which "displaces" syntactic categories other than wh-phrases: for instance, nominal phrases and verbs (on the latter, see HEAD MOVEMENT).

After Chomsky 1977, 1986, 1995, and the references cited there, a better understanding is available of many of the properties of wh-movement; for example, (a) the nature of the position the wh-phrase moves to; (b) the rationale for such a movement; and (c) the conditions under which such movement is permitted or blocked.

Modern linguistic theory considers sentence structure as characterized by the alternation of a head (a syntactic atom such as a verb, noun, adjective, determiner, complementizer -- that is, a subordinating conjunction -- etc.) and a phrase (a larger syntactic unit built around a head), which can serve as a complement or as a specifier of another head (see X-BAR THEORY, Chomsky 1970; Kayne 1994). The simplified structure is thus:

(1) [Phrase Complementizer [Phrase Agreement [Phrase Tense [Phrase (subject) Verb Phrase (object) ]]]]

(The phrase to the immediate left of each (italicized) head is its specifier).

An object wh-phrase is displaced from the complement position on the right of the verb to the specifier position on the left of the complementizer. This, for example, accounts for its occupying the first position of the (interrogative) sentence (as no other head precedes the complementizer), as well as for the fact that in certain languages the wh-phrase co-occurs with (and precedes) the complementizer itself (e.g., Middle English: This bok which that I make mencioun of . . .). In root interrogatives (in English and other languages), the finite verb (a head) is necessarily in second position, immediately after the wh-phrase (What have you seen?). This can be made sense of if it too is displaced to the complementizer head. The rationale for the movement of a wh-phrase appears to be related to the way a wh-phrase is interpreted. A question like Which persons have you met? means roughly "Tell me which is the value of x, where x ranges over the class of persons such that you have met x." In other terms, which is a sort of quantifier extracted from the object and binding a variable in the object position, much as in the (Polish) notation of standard predicate logic (see QUANTIFIERS). The displacement of a wh-phrase can thus be seen as a way of partially building in the syntax a representation of the LOGICAL FORM of the sentence, although not all languages displace their wh-phrases overtly in the syntax or have a special morphological way that distinguishes them from indefinite phrases (see Cheng 1991).

The displacement of wh-phrases is severely constrained. Although wh-movement gives the impression of taking place over an unbounded number of sentences (How do you think that they said that they wanted to repair it?, where how is moved from the sentence containing the verb repair), there is evidence that it proceeds stepwise through the specifier of each complementizer (at least in the case of phrases other than subjects and complements). This is shown by the fact that whenever the specifier of some intermediate complementizer is filled by another wh-phrase, such movement becomes impossible (*How do you wonder why he repaired it?). Only subjects and complements can (marginally) skip over one such intermediate specifier (cf. ??Which one of his brothers did you wonder why they invited?).

Such stepwise movement of wh-phrases is constrained in another fashion. In essence, it can apply only when the subordinate sentence is a complement of the next higher verb (for refinements, see Rizzi 1990 and Cinque 1990). As witnessed by the fact that they seem to involve a quantifier/variable interpretation, and that they are subject to the same constraints as overt wh-movement constructions, a number of other constructions have been analyzed as containing a covert type of wh-movement (see Chomsky 1977). These comprise comparative (He buys more books than his father used to buy), topicalized (This film, I think that they saw), "easy-to-please" (John is easy for everybody to succeed in convincing), and other constructions.

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-- Guglielmo Cinque


Cheng, L. L. (1991). On the Typology of Wh-Questions. Ph.D. diss., MIT.

Chomsky, N. (1970). Remarks on nominalization. In R. A. Jacobs and P. Rosenbaum, Eds., Readings in English Transformational Grammar. Waltham, MA: Ginn and Co., pp.184-221.

Chomsky, N. (1977). On wh-movement. In P. Culicover, T. Wasow, and A. Akmajian, Eds., Formal Syntax. New York: Academic Press, pp. 71-132.

Chomsky, N. (1986). Barriers. Cambridge, MA: MIT Press.

Chomsky, N. (1995). The Minimalist Program. Cambridge, MA: MIT Press.

Cinque, G. (1990). Types of A-bar Dependencies. Cambridge, MA: MIT Press.

Jackendoff, R. (1977). X-bar Syntax: A Study of Phrase Structure. Cambridge, MA: MIT Press.

Kayne, R. (1994). The Antisymmetry of Syntax. Cambridge, MA: MIT Press.

Rizzi, L. (1990). Relativized Minimality. Cambridge, MA: MIT Press .