Wh-movement is a syntactic phenomenon whereby interrogative words (sometimes called wh-words) appear at the beginning of an interrogative sentence. The term wh-movement is due to the fact that most English interrogative words start with wh-, for example, what, where, why, etc. The term wh-movement is applied universally, even when the interrogative words of a given language (such as French) do not start with wh-.
According to Joseph Greenberg's linguistic universal No.12, VSO languages always have wh-movement, while SOV languages never do. Many SVO languages have wh-movement too, such as English, but some don't, such as Mandarin. Languages without wh-movement are referred to as wh-in-situ languages.
Wh-movement in English
English is one language that features wh-movement. For example, a declarative sentence in English featuring normal word order would be:
- He buys bread.
The direct object, "bread," of the verb, "to buy," normally follows the verb, however, when the direct object is replaced with a wh-word in order to form a question, the wh-word generally appears at the beginning of the sentence:
- What does he buy?
In English main clauses, a form of "to do" must be used as in the absence of an auxiliary verb. The auxiliary verb (including a form of "to do") occurs after the wh-word and before the subject:
- He should buy bread.
- What should he buy?
In transformational approaches to syntax, wh-movement is analyzed literally in terms of constituent movement, where a moved constituent leaves behind a silent trace (often indicated by a t):
- What does he buy t?
Pied-piping
Pied-piping is a process that occurs when wh-movement affects a phrase larger than a single wh-word. In the case where the wh-word is a determiner such as which or whose, pied-piping refers to the fact that the wh-determiner appears sentence intially along with its complement. For instance, in the following example, the entire phrase "which car" is moved:
- Which car does he like t?
In the transformational analysis, the wh-word which moves to the beginning of the sentence, luring its complement car with it, much like the Pied Piper of Hamelin attracted rats/children that would follow him, hence the term pied-piping.
In the case of determiners, pied-piping is obligatory. For instance, the following sentence would be ungrammatical:
- *Which does he like t car?
However, there are cases where pied-piping can be optional. In English, this is often the case when a wh-word or phrase is the object of a preposition. For instance, the following two examples are both grammatical:
- To whom did she reveal her secret t?
- Whom did she reveal her secret to t?
The second example is a case of preposition stranding, which is possible in English, but not allowed in Latin or other Romance languages. For languages that use postpositions rather than prepositions, stranding is not allowed either.
Prescriptive grammarians often claim that preposition stranding should be avoided in English as well, however in certain contexts, obligatory pied-piping of prepositions in English may make a sentence feel artificial or stilted.
Extraction islands
In many cases, a wh-word can move all the way to the front of a sentence, regardless of how far away it has to move. For example:
- Who does Mary like t?
- Who does Bob know that Mary likes t?
- Who does Carl believe that Bob knows that Mary likes t?
However there are cases in which it is not always possible to perform wh-movement. Clauses from which a wh-word cannot be extracted are referred to as extraction islands.
Adjunct islands
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 because, if, when, and relative clauses. Some examples include:
- Grammatical: You went home because you needed to do what?
- Ungrammatical: *What did you go home because you needed to do t?
- Grammatical: Alex likes the woman who wears what?
- Ungrammatical: *What does Alex like the woman who wears t?
Wh-islands
A wh-island is an island that is created by an embedded sentence which is introduced by a wh-word. For instance, the clause "where Eric went to buy the gift" in the following example, is a wh-island:
- John wonders where Eric went to buy the gift.
Wh-islands are weaker than adjunct islands since extraction is often awkward but not necessarily considered ungrammatical by all speakers.
- Grammatical: John wonders where Eric went to buy what?
- Questionable: ?What does John wonder where Eric went to buy t?
Subject extraction
It is typically easier to extract objects rather than subjects from a clause, especially when an overt complementizer such as "that" or "for" is used. Take the following examples:
- Grammatical: Who do you believe t saw Tom?
- Ungrammatical: *Who do you believe that t saw Tom?
- Grammatical: Who do you believe Jim saw t?
- Grammatical: Who do you believe that Jim saw t?
Subject clauses
Wh-movement does not appear to be possible in clauses that appear in the subject position. For instance, here is a sentence where the clause appears in the object position:
- It is likely that John went home.
Here is the same sentence where the clause appears in the subject position:
- That John went home is likely.
Notice that wh-movement can occur only in the clause that appears in the object position:
- Grammatical: Where is it likely that John went t?
- Ungrammatical: *Where is that John went t likely?