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In linguistics, wh-movement (also known as wh-fronting or wh-extraction or long-distance dependency) concerns special rules of syntax, observed in many languages around the world, involving the placement of interrogative words. The special interrogatives, whatever the language, are known within linguistics as wh-words because most interrogative words in the English language start with a wh-; for example, who(m), whose, what, which, etc. Wh-words are used to form questions, and can also occur in relative clauses. In languages with wh-movement, sentences or clauses with a wh-word show a special word order that has the wh-word (or phrase containing the wh-word) appear at the front of the sentence or clause (Who do you think about?) instead of in a more canonical position later in the sentence (I think about you) The opposite is called wh in situ.
Wh-movement often results in a discontinuity, and in that regard, it is one of (at least) four widely acknowledged discontinuity types, the others being topicalization, scrambling, and extraposition. Wh-movement is found in many languages around the world, and of the various discontinuity types, wh-movement is the one that has been studied the most.
Historically, the name wh-movement stems from early generative grammar (1960s and 1970s) and was a reference to the transformational analysis of the day in which the wh-expression appeared in its canonical position at deep structure and then moved leftward out of that position to land in its derived position at the front of the sentence/clause at surface structure.
Many modern theories of syntax do not acknowledge movement in the transformative sense, but the term wh-movement (also called wh-fronting or wh-extraction) survives and is widely used to denote the observed phenomenon, even by theories that do not acknowledge movement.
The following sentence pairs illustrate wh-movement. Each a-sentence has the canonical word order of a declarative sentence in English, and each b-sentence has experienced wh-movement, whereby the wh-word has been fronted in order to form a question. The relevant words are bolded:
These examples illustrate that wh-fronting occurs when a constituent is questioned that appears to the right of the finite verb in the corresponding declarative sentence. Consider in this regard that when the subject is questioned, there is no obvious reason to assume that wh-fronting has occurred because the default position of the subject is clause-initial:
Despite the fact that such data provide no obvious reason to assume movement, some theories of syntax maintain a movement analysis in the interest of remaining consistent. They assume that the wh-subject has in fact moved up the syntactic hierarchy, although this movement is not apparent from the actual linear order of the words.
Wh-movement typically occurs to form questions in English. There are, however, at least three kinds of questions in which wh-movement does not occur (aside from when the question word serves as the subject and so is already fronted): 1) echo questions (to confirm what you thought you heard), 2) quiz questions, and 3) multiple questions, when there is already one wh-word at the front:
While wh-movement is the rule (and these three cases are the exceptions to the rule) in English, other languages may leave wh-expressions in situ (in base position) more often. In French for instance, wh-movement is often optional in certain matrix clauses.
The examples in the previous section have wh-movement occurring in main clauses (in order to form a question). Wh-movement is not restricted to occurring in main clauses. It frequently appears in subordinate clauses, although its behavior in subordinate clauses differs in a key respect, viz. word order. The following two subsections consider wh-movement in indirect questions and relative clauses.
In English, wh-movement occurs to form a question in both main and subordinate clauses. When the question is expressed with a main clause, it is a direct question. When the question is expressed with a subordinate clause, however, it is an indirect question. While wh-fronting occurs in both direct and indirect questions, there is a key word order difference that distinguishes between the two. This difference is illustrated with the following data:
The subscripts indicate a central word order difference across direct and indirect questions. Wh-fronting in main clauses typically results in V2 word order in English, meaning the finite verb appears in second position, as marked by the 2-subscript in the b-sentences. In indirect questions, however, V3 word order typically obtains, as marked by the 3-subscript in the c-sentences. Despite this systematic word order difference across direct and indirect questions, wh-fronting within the clause is occurring in both cases. Note as well that do-support is often needed in order to enable wh-fronting. Wh-fronting in main clauses is often reliant on subject-auxiliary inversion.
The examples above all involve interrogative clauses (questions). Wh-movement also occurs in relative clauses, however, which cannot be interpreted as questions. Many relative pronouns in English have the same form as the corresponding interrogative words (which, who, where, etc.). Relative clauses are subordinate clauses, so the characteristic V3 word order seen in indirect questions occurs:
The relative pronouns have fronted in the subordinate clauses of the b-examples, just like they are fronted in the indirect questions in the previous sections. The characteristic V3 word order is obligatory. If the V2 word of main clauses occurs, the sentence is bad, as the c-examples demonstrate.
Many instances of wh-fronting involve pied-piping. Pied-piping occurs when a fronted wh-word (or otherwise focused word) pulls an entire encompassing phrase to the front of the clause with it, i.e. it "pied-pipes" the other words of the phrase with it to the front of the clause (see the Pied Piper of Hamelin). The following two subsections consider both obligatory and optional pied-piping.
Pied-piping is sometimes obligatory. That is, in order for a wh-expression to be fronted, an entire encompassing phrase must be fronted with it. The relevant phrase of pied-piping is underlined in the following examples:
These examples illustrate that pied-piping is often necessary when the wh-word is inside a noun phrase (NP) or adjective phrase (AP). Pied-piping is motivated in part by the barriers and islands to extraction (see below). When the wh-word appears underneath a blocking category or in an island, the entire encompassing phrase must be fronted. Pied-piping was first identified by John R. Ross in his 1967 dissertation.
There are cases where pied-piping can be optional. In English, this occurs most notably with prepositional phrases (PPs). The wh-word is the object of a preposition. A formal register will pied-pipe the preposition, whereas more colloquial English prefers to leave the preposition in situ, e.g.
The c-examples are cases of preposition stranding, which is possible in English, but not allowed in many languages that are related to English. For instance, preposition stranding is largely absent from many of the other Germanic languages and it may be completely absent from the Romance languages. Prescriptive grammars often claim that preposition stranding should be avoided in English as well; however, in certain contexts pied-piping of prepositions in English may make a sentence feel artificial or stilted.
In many cases, a wh-expression can occur at the front of a sentence regardless of how far away its canonical location is, e.g.
The wh-word who is the direct object of the verb likes in each of these sentences. There appears to be no limit on the distance that can separate the fronted expression from its canonical position. In more technical terms, we can say that the dependency relation between the gap (the canonical, empty position) and its filler (the wh-expression) is unbounded in the sense that there is no upper bound on how deeply embedded within the given sentence the gap may appear.
However, there are cases in which this is not possible. Certain kinds of phrases do not seem to allow a gap. The phrases from which a wh-word cannot be extracted are referred to as extraction islands or simply islands. The following subsections briefly consider seven types of islands: 1) adjunct islands, 2) wh-islands, 3) subject islands, 4) left branch islands, 5) coordinate structure islands, 6) complex NP islands, and 7) non-bridge islands. These island types were all originally identified in Ross' seminal dissertation. The islands in the examples that follow are underlined in the a-sentences.
An adjunct island is a type of island formed from an adjunct clause. Wh-movement is not possible out of an adjunct clause. Adjunct clauses include clauses introduced by because, if, and when, as well as relative clauses. Some examples include:
Wh-movement fails in the b-sentences because the gap appears in an adjunct clause.
A wh-island is created by an embedded sentence which is introduced by a wh-word. Wh-islands are weaker than adjunct islands since extraction is often quite awkward, but they are not necessarily considered to be ungrammatical by all speakers.
The b-sentences are strongly marginal/unacceptable because one has attempted to extract an expression out of a wh-island.
Wh-movement is not (or hardly) possible out of subjects, at least not in English. This is particularly true for subject clauses, and to a somewhat lesser extent out of subject phrases, e.g.
The important insight here is that wh-extraction out of object clauses and phrases is quite possible. There is therefore an asymmetry across subjects and objects with respect to wh-movement.
Modifiers that would appear on a left branch under a noun (i.e. they precede the noun that they modify) cannot be extracted. The relevant constraint is known as the Left Branch Condition, and Ross (1967) is again credited with having discovered it. The left branch constraint captures the fact that possessive determiners and attributive adjectives in English and many related languages necessarily pied-pipe the entire noun phrase when they are fronted, e.g.
Extraction fails in the b-sentences because the extracted expression corresponds to a left-branch modifier of a noun. Left branch islands are cross-linguistically variable. While they exist in English, they are absent from many other languages, most notably, from the Slavic languages.
In coordination, extraction out of a conjunct of a coordinate structure is possible only if this extraction affects all the conjuncts of the coordinate structure equally. The relevant constraint is known as the coordinate structure constraint. Extraction must extract the same syntactic expression out of each of the conjuncts simultaneously. This sort of extraction is said to occur across the board (ATB-extraction), e.g.
Wh-extraction out of a conjunct of a coordinate structure is only possible if it can be interpreted as occurring equally out all the conjuncts simultaneously, that is, if it occurs across the board.
Extraction is difficult from out of a noun phrase. The relevant constraint is known as the complex NP constraint, and comes in two varieties, the first banning extraction from the clausal complement of a noun, and the second banning extraction from a relative clause modifying a noun:
Sentential complement to a noun:
Extraction out of object that-clauses serving as complements to verbs may show island-like behavior if the matrix verb is a non-bridge verb (Erteschik-Shir 1973). Non-bridge verbs include manner-of-speaking verbs, such as whisper or shout, e.g.
Wh-movement is also found in many other languages around the world. Most European languages also place wh-words at the beginning of a clause. Furthermore, many of the facts illustrated above are also valid for other languages. The systematic difference in word order across main wh-clauses and subordinate wh-clauses shows up in other languages in varying forms. The islands to wh-extraction are also present in other languages, but there will be some variation. The following example illustrates wh-movement of an object in Spanish:
|John||bought||meat.||'John bought meat.'|
|what||bought||John||'What did John buy?'|
The following examples illustrates wh-movement of an object in German:
|He||reads||Tesnière||every||evening.||'He reads Tesnière every evening.'|
|who||reads||he||every||evening||'Who does he read every evening?'|
The following examples illustrate wh-movement an object in French:
|they||have||seen||Peter||'They saw Peter.'|
|Who||is it that||they||have||seen||'Who did they see?'|
|Who||have||they||seen||'Who did they see?'|
All the examples are quite similar to the English examples and demonstrate that wh-movement is a general phenomenon in numerous languages. As stated however, the behavior of wh-movement can vary, depending on the individual language in question.
Wh-movement typically results in a discontinuity: the "moved" constituent ends up in a position that is separated from its canonical position by material that syntactically dominates the canonical position, which means there seems to be a discontinuous constituent and a long distance dependency present. Such discontinuities challenge any theory of syntax, and any theory of syntax is going to have a component that can address these discontinuities. In this regard, theories of syntax tend to explain discontinuities in one of two ways, either via movement or via feature passing.
Theories that posit movement have a long and established tradition that reaches back to early Generative Grammar (1960s and 1970s). They assume that the displaced constituent (e.g. the wh-expression) is first generated in its canonical position at some level or point in the structure generating process below the surface. This expression is then moved or copied out of this base position and placed in its surface position where it actually appears in speech. Movement is indicated in tree structures using one of a variety of means (e.g. a trace t, movement arrows, strikeouts, lighter font shade, etc.).
The alternative to the movement approach to wh-movement and discontinuities in general is feature passing. This approach rejects the notion that movement in any sense has occurred. The wh-expression is base generated in its surface position, and instead of movement, information passing (i.e. feature passing) occurs up or down the syntactic hierarchy to and from the position of the gap.