In linguistics, wh-movement (also known as wh-fronting, wh-extraction, wh-raising) concerns rules of syntax involving the placement of interrogative words. In plain terms, it refers to an asymmetry between the syntactical arrangement of words or morphemes in a question and the form of answers to that question; specifically, the placement of the question word. An example in English is "What are you doing?", a response to which could be "I am editing Wikipedia."; in which the answer (editing Wikipedia) is at the end of the sentence but the question word (What) is at the beginning.
Interrogative forms are known within English linguistics as wh-words because most question words in the English language start with a wh-; such as what, when, where, who, and why. In English, only one interrogative word does not begin with wh-, namely how. In languages with wh-movement, sentences or clauses with a wh-word show a special word order that places the wh-word (or phrase containing the wh-word) at the front of the sentence or clause (Whom are you thinking about?) instead of the canonical position later in the sentence (I am thinking about you). Leaving the wh-word in its canonical position 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. It is observed in many of the world's languages, and plays a key role in the theories of long-distance dependencies.
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 appears in its canonical position at deep structure and then moves leftward from that position to a derived position at the front of the sentence/clause at surface structure. Although many theories of syntax do not use the mechanism of movement in the transformative sense, the term wh-movement (or equivalent terms such as wh-fronting, wh-extraction, wh-raising) is widely used to denote the phenomenon, even in theories that do not model long-distance dependencies as movement.
What needs to be considered is that wh-movement does not occur solely due to interrogative words. Wh-words are used to form questions, and can also occur in relative clauses. Wh-movement occurs from the existing EPP (Extended projection principle). There are three types of wh-expressions overall- Interrogative, Relative, and Pseudo-cleft wh-expressions.
The following examples of sentence pairs illustrate wh-movement: each (a) example has the canonical word order of a declarative sentence in English; each (b) sentence has undergone wh-movement, whereby the wh-word has been fronted in order to form a question. The relevant words are bolded.
wh-fronting of whom, which corresponds to the direct object Tesnière (1a) Tom has been reading Tesnière. (1b) Whom has Tom been reading?
wh-fronting of what, which corresponds to the prepositional object syntax (2a) She should stop talking about syntax. (2b) What should she stop talking about?
The examples in (1) through (7) 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 occurs in ex situ forms, where the structure moves from the base to the Spec C with the help of EPP.
Each one of the Wh-words is responsible for a certain description or target.
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):
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 such as in Slavic Languages. In French for instance, wh-movement is often optional in certain matrix clauses.
The EPP (Extended projection principle) plays a great role in the case of wh-movement. For those languages that leave wh-expressions in situ, we may see a pattern in that EPP does not exist in the structure itself- unlike ex situ where movement is allowed and the EPP is present.
Some example of languages that possess Wh-expressions without wh-movement (are in situ) are Chinese and Slavic languages- languages that are most commonly used as examples are Mandarin and Russian.
It also needs to be considered that in situ questions are different from wh-fronted questions as they follow two different paths:
1) Typically, in situ expressions result from no movement at all which tends to be morphologically or pragmatically conditioned 
2) Wh-expressions/words are always moved 
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 whom 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 and violating them results in the sentence sounding ungrammatical to the native speaker.
The b-sentences are strongly marginal/unacceptable because one has attempted to extract an expression out of a wh-island.
The reason why this occurs is because both wh-words are part of a DP. It would not be possible to move the bottom wh-word to the top of the structure, as they would both interfere. In order to get a grammatical result, a proper wh-movement must occur. However, because the wh-word is taking up the Spec- C position, it is not possible to move the competing wh-word higher by skipping the higher DP as wh-movement is a cyclic process.
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.
Syntax trees are visual breakdowns of sentences that include dominating heads for every segment (word/constituent) in the tree itself. In the Wh-Movement, there are additional segments that are added- EPP ( Extended projection principle ) and the Question Feature [+Q] that represents a question sentence.
The Wh-movement is motivated by a Question Feature/EPP at C (Complementizer), which promotes movement of a Wh-word from the canonical base position to Spec-C. This movement could be considered as “Copy + Paste + Delete” movement as we are copying the interrogative word from the bottom, pasting it to Spec-C, and then deleting it from the bottom so that it solely remains at the top (now taking the position of Spec-C). Overall, the highest C will be the target position of the Wh-Raising.
The interrogatives that are used in the Wh-Movement do not all share headedness. This is important to consider when making the syntax trees, as there are three different heads that may be used
Determiner Phrase (DP): Who, What
Prepositional Phrase (PP): Where, When, Why
Adverb Phrase (AdvP): How
When creating the Syntax Tree for the Wh-movement, consider the subject-aux inversion in the word that was raised from T (Tense) to C (Complementizer).
The location of the EPP (Extended Projection Principle):
The EPP allows movement of the Wh-word from the bottom canonical position of the syntax tree to Spec C. The EPP is a great indicator when it comes to distinguishing between in-situ trees and ex-situ. Ex situ trees allow the movement to Spec C, while in situ do not as the head C lacks the EPP feature.
Islands in Syntax Trees:
Within Syntax trees, islands do not allow movement to occur- if movement is attempted, the sentence would then be perceived as ungrammatical to the native speaker of the observed language. Islands are typically noted as being a boxed node on the tree. The movement in the Wh-Island syntax tree is unable to occur because in order to move out of an embedded clause, a Determiner Phrase (DP) must move through the Spec C position. This cannot occur, as the Determiner Phrase (DP) is already occupied.
“She said [who bought what]?”. We see that “who” takes the place of DP and restricts “what” from rising up to the respected Spec C. Native speakers may confirm this as well as it will sound ungrammatical * ”What did she say [bought what?]”.
In languages, a sentence can contain more than one wh-question. These interrogative constructions are called multiple wh-questions, 
e.g: Who ate what at the restaurant?
In the following English example, a strikeout-line and trace-movement co-indexation symbols - [Whoi ...
who ti ...]- are used to indicate the underlying raising-movement of the closest wh-phrase. This movement produces an overt sentence word order with one fronted wh-question:
e.g: [Whoi did you help
who ti make what?]
In the underlying syntax, the wh-phrase closest to Spec-CP is raised to satisfy selectional properties of the CP: the [+Q] and [+Wh-EPP] feature requirements of C. The wh-phrase farther away from Spec-CP stays in its base position (in situ).
The superiority condition determines which wh-phrase moves in a clause that contains multiple wh-phrases. This is the outcome of applying the attract closest principle, where only the closest candidate is eligible for movement to the attracting head that selects for it. If the farther wh-phrase moves instead of the preceding wh-phrase, an ungrammatical structure is created (in English). Not all languages have instances of multiple-wh movement governed by the superiority condition, most have variations. There is no uniformity found across languages concerning the superiority condition.
For example, see the following English phrases:
a. [Whoi did you ask
whoti to buy what?]
b. *[Whati did you ask who to buy
The subscript "ti" or "i" are used to mark coreference. "t" represents a trace, while both "ti" and "i" represent that the words refer to each other and the same entity.
In a., the closer wh-phrase [who] moves up towards Spec-CP from being the subject of the VP [who to buy what]. The second wh-phrase [what] remains in-situ (as the direct object of the VP[who to buy what]). This is to satisfy the [+Q Wh] feature in the Spec-CP.
In b., the farther wh-phrase [what] has incorrectly moved from the direct object position of the VP[who to buy
what] into the Spec-CP position. The closer wh-phrase to Spec-CP [who] has remained in-situ as the subject of the VP[ who to buy what]. This sentence contains a violation of the attract closest principle, as the closest candidate was not moved, rather the farther candidate. This sentence is ungrammatical which is marked by the asterisk (*).
German does not show the expected effects of the superiority condition during clauses with multiple wh-phrases. German appears to have a process that allows the farther wh-phrase to "cross-over" the closer wh-phrase and move, not remaining in-situ.  This movement is tolerated and has less consequences than when compared with English.
For example, see the following German phrases:
In a., the gloss shows that the wh-phrase [what] has "crossed over" wh-phrase [who] and is now in Spec,CP to satisfy the [+Q Wh] feature. This movement is a violation of the attract closest principle, which is what the superiority condition is based upon.
Mandarin is a wh-in-situ language, which means that it does not exhibit wh-movement in constituent questions. In other words, wh-words in Mandarin remain at the end of the sentence, contrasting with wh-movement in English where the wh-word would move in constituent questions.
The following example illustrates multiple wh-movement in Mandarin, and is written in pinyin for the sake of simplicity and clarity:
|Translation||'What do you wonder why Mary bought it?'|
This example demonstrates that the wh-word "what" in Mandarin remains in-situ at Surface structure, while the wh-word "why" in Mandarin moves to proper scope position and, in doing so, c-commands the wh-word that stays in-situ.
The scope of wh-questions in Mandarin is also subject to other conditions depending on the kind of wh-phrase involved. The following example can translate into two meanings:
|Translation||'What is the thing x such that you wonder who bought x?'
'Who is the person x such that you wonder what x bought?'
This example illustrates the way certain wh-words such as "who" and "what" can freely obtain matrix scope in Mandarin.
In reference to the Attract Closest principle, where the head adopts the closest candidate available to it, the overt wh-phrase in Mandarin moves to proper scope position while the other wh-phrase stays in-situ as it is c-commanded by the wh-phrase first mentioned. This can be seen in the following example, where the word for "what" stays in-situ since it is c-commanded by the phrase in Mandarin meaning "at where":
|Example #3||Ni||xiang||zhidao||Mali||zai nali||maile||shenme|
|Translation||'What is the thing x such that you wonder where Mary bought x?'
'Where is the place x such that you wonder what Mary bought at x?'
As these examples show, Mandarin is a wh-in-situ language, exhibits no movement of wh-phrases at Surface structure, is subject to other conditions based on the type of wh-phrase involved in the question, and adheres to the Attract Closest principle.
ln Bulgarian, the [+ wh] feature of C motivates multiple Wh-word movements, which leads to multiple specifiers. It requires formation of clusters of wh-phrases in [Spec,CP] in the matrix clause. This is different from English because in English, only one Wh-word moves to [Spec,CP] when there is multiple wh-words in a clause. This is because in Bulgarian, unlike English, all movements of wh-elements take place in the syntax, where movement is shown overtly. The phrase structure for Wh-words in Bulgarian would look like is shown in Figure 1 below, where a Wh-cluster is formed under [Spec, CP].
In Bulgarian and Romanian, a Wh-element is attracted into [Spec,CP] and the other Wh-elements are adjoined into the first Wh-word in [Spec,CP].
|Translation||Who sees whom?|
In Example 1, we see that the both Wh-words underwent movement and are in a [Spec,CP] cluster.
The Attract Closest is a principle of the Superiority Condition where the head which attracts a certain feature adopts the closest candidate available to it. This usually leads to the movement of the closest candidate.
Slavic languages are grouped in to two different S-structures concerning the movement of Wh-elements at [Spec,CP] (Rudin, 1998). One group includes the languages: Serbo-Croatian, Polish, and Czech where there is only one Wh-element in [Spec,CP] at S-structure. The other group contains Bulgarian and Romanian which have all of their Wh-elements in [Spec,CP] at S-structure. In the first group mentioned, the Attract Closest principle is present and the Wh-word that is closest to the attracting head undergoes movement while the rest of the Wh-elements remain in-situ. The second group of languages, the Attract Closest principle occurs in a slightly different way. The orderof the way the Wh-word moves is dictated by their proximity to [Spec,CP]. The closest Wh-word to the attracting head undergoes movement first and the next closest one follows suit, and on and on. In that way the Superiority effect is present in Serbo-Croation, Polish, and Czech in the first Wh-element, while in Bulgarian and Romanian, it is present in all of the Wh-elements in the clause.
|Translation||How did Ivan what?|
The Attract Closest principle explains a crucial detail about the order of which Wh-words move first in the tree. Since the closest Wh-word is moved first, there is a particular order that appears. Wh-Subjects goes before Wh-objects and Wh-adjuncts (Grewendorf, 2001). This is seen in Example #2 and Example #3. Example #3 also shows that there can be more than two Wh-words in [Spec,CP] and that no matter how many Wh-words are in the clause they would all have to undergo movement.
|Translation||Who kissed whom how?|
In Bulgarian, we see in Example #4, that to defer from forming a sequence of the same Wh-words, a Wh-element is allowed to remain in-situ as a last resort (Bošković, 2002).
|Translation||What conditions what?|
In summary, Bulgarian has Multiple Wh-Movement in the syntax and the Wh-words move overtly. We also see that while all Wh-words in a clause moves under [Spec,CP] because of the [+ wh] feature, there is still a certain order in how they are appear in the clause.
In French, multiple wh-questions have the following patterns:
a) In some French interrogative sentences, wh-movement can be optional. 
1.The closest wh-phrase to Spec CP can be fronted (i.e., moved to Spec CP from its covert base position in deep structure to its overt phonological form in surface-structure word order);
|Translation||'What have you sent to who(m)? '|
In the example sentences above, examples (#1) and (#2) are both grammatical and share the same meaning in French. Here the choice of using one form of question over the other is optional; either sentence can be used to ask about the two particular DP constituents expressed by two wh-words. In French, the second sentence could also be used as an echo question.  By contrast, in English the grammatical structure of the second sentence is only acceptable as an echo question: a question we ask to clarify the information we hear (or mishear) in someone's utterance, or that we use to express our shock or disbelief in reaction to a statement made by someone. For echo questions in English, it is typical for speakers to emphasize the wh-words prosodically by using rising intonation (e.g.,You sent WHAT to WHO?). These special instances of using multiple wh-questions in English are essentially "requests for the repetition of that utterance".
b) In other French interrogative sentences, wh-movement is required. 
The option of using wh-in-situ in French sentences with multiple wh-questions is limited to specific conditions. There exists "a very limited distribution" of its usage.
French wh-in-situ can occur only:
Wh-in situ usage is not allowed in French when these criteria are not met.
Wh-in-situ is not allowed:
|Translation||* 'André has asked you have eaten what.'|
|Translation||'André has asked what you have eaten.'|
2. in questions with overt complementizers
|Translation||* 'What have you eaten what?'|
|Translation||'What you have eaten?'|
3. in 'long-distance' questions
|Translation||* 'Michelle and Pierre think that André has eaten what?'|
|Translation||'What do Michelle and Peter think that André has eaten?'|
To summarize, in French sentences with multiple wh-questions, the choice between wh-movement and wh-in-situ is not arbitrary; it is constrained by specific conditions.
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.
Many languages do not have wh-movement. Instead, these languages keep the symmetry of the question and answer sentences.
For example, topic questions in Chinese have the same sentence structure as their answers:
The response to which could be:
It needs to be considered that Chinese in fact have a wh-particle. However, there is no wh-movement.
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. The EPP feature (Extended projection principle) and Question Feature play a large role in the movement itself. We have noticed that these two features occur in ex situ questions which allow movement and do not exist in in situ questions that do allow it.
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.