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5.10: Trees- Movement

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    • Catherine Anderson, Bronwyn Bjorkman, Derek Denis, Julianne Doner, Margaret Grant, Nathan Sanders, and Ai Taniguchi
    • eCampusOntario

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    X-bar theory: Subject-Aux Inversion as Head Movement

    The first transformation we saw, in Section 6.7, was Subject-Auxiliary Inversion, which reverses the order of the subject and the auxiliary.

    Thinking not in terms of the linear order of the subject and the auxiliary, but instead in terms of our X-Bar structure, could we state this transformation more precisely?

    The tree for [They have left.], an ordinary declarative clause, will be as in Figure 6.28.

    Tree diagram: [TP [NP They] [T have] [VP left]]
    Figure 6.28 Tree diagram for the declarative sentence [They have left.]

    The structural relations in this tree encode the grammatical relations between the subject, the clause as a whole, and the predicate. Those relations should not be fundamentally different in a question. We just want to add a difference in the order of constituents, in order to mark that this is a question.

    The simplest way to change the order of the subject and the auxiliary is to move one of them. We could either move the auxiliary up and to the left, or move the subject down and to the right.

    If we think about embedded questions, which we developed an X-bar theory analysis for in Section 6.18, these had a +Q complementizer above the TP, if or whether. This complementizer is in the same position that the auxiliary appears in in main clause questions: right before the subject. This gives us a way to understand Subject-Auxiliary Inversion as movement of the auxiliary from T up and to the left, to land in C. This is illustrated in Figure 6.29.

    Tree diagram: Pre-movement [CP [C' [C +Q] [TP they [T have] left] ] ] Post-movement [CP [C' [C +Q have ] [TP they [crossed out T crossed out have ] left ] ] ], arrow from T to C
    Figure 6.29 Tree diagrams for the question [ Have they left? ] before and after T-to-C Head Movement

    The movement in Figure 6.29 is an example of Head Movement, which changes a tree by moving a head to the next head above it.

    Head Movement:
    Movement of a head (X) into the next higher head position.

    We can now restate the generalization about how Yes-No Questions are formed in English main clauses. To name an instance of head movement, you can identify the start and end points. So the movement we see in English main clause questions is called T-to-C movement.

    Yes-No Question Formation in English:
    Yes-No Questions are formed by moving the auxiliary in T to C.

    This is a derivational way of representing the relationship between a fronted auxiliary and the position it occupies in statements: we start with one tree structure, and make a change to it in order to arrive at the final structure. There are other ways to represent this dependency, some of which are pursued in non-derivational approaches to syntax.

    Notation for Head Movement

    In the history of generative linguistics, there have been several different notations used for movement. In this textbook we draw a line through the moving head in its base position (

    like this), and draw an arrow to the position it moves to.

    There are other ways of indicating movement, which you might encounter online or in other resources. These include trace notation, where the original position of the moved element has a “trace” (written t) left in it. This can be thought of as a variable, or as the empty space left
    behind by the thing that moved. Trace notation won’t be used in this textbook, but we mention it so that you won’t be confused if you see it elsewhere.

    X-bar theory: Question word fronting as Phrasal Movement

    As we saw in Section 6.8, content questions in English also involve a change in word order from corresponding statements. However, we’ll see in this section that we can’t describe that change just in terms of head movement. Instead, we’re going to introduce a second (and final) type of movement: Phrasal Movement.

    Recall some examples of content questions in English:

    (1) a. What has the squirrel hidden?
    b. Where is it snowing?
    c. When was it snowing?
    d. How do squirrels hide nuts?

    All these questions involve Subject-Aux Inversion, which we analyzed earlier as T-to-C movement when looking at main clause Yes-No questions. We can tell this has applied because the auxiliary is before the subject in all the content questions in (1).

    But we can’t use T-to-C movement to analyze how the content question word gets to the front of the sentence for two reasons:

    1. The auxiliary is already in C. We can’t put two words in one head, so we need to put the WH word somewhere else—and somewhere higher up.
    2. The thing that moves to the front of the sentence in a WH-question isn’t just a head, it’s a whole phrase.

    How can we tell that what moves is a whole phrase? We can tell by looking at a wider range of content questions.

    (2) a. What kind of nuts has the squirrel hidden?
    b. Which city is it snowing in?
    c. Which nuts did the squirrels hide?

    Here instead of the single word what or where, we have larger NPs moving to the front of the question—though these larger NPs still contain content question words. Here what and which are determiners, occurring in the same position that this or the or a would occur.

    So we know that the content question phrase isn’t pronounced in the C head in content questions. Where is it pronounced, then?

    To answer this question, let’s consider again word order for the statement The squirrel has hidden nuts. The auxiliary has is in T, and the object nuts is the complement of the verb hidden. We can represent this in a labelled bracket structure:

    (3) [TP [NP the squirrel] [T’ [T has ] [VP hidden nuts ] ] ]

    In the content question, what changes is that we have what as the object of hidden, instead of nuts. We also have a +Q C head above TP, because that’s where the auxiliary in T moves. We can schematize the structure before we do any movement as in Figure 6.30. (The tree before any movement occurs is called Deep Structure in some theories of syntax, though we won’t focus on that terminology here.)

    Tree diagram: [CP [C' [C +Q] [TP [NP the squirrel] [T' [T has] [VP [V hidden] [NP what] ] ] ] ]
    Figure 6.30 Tree diagram for the question [What has the squirrel hidden?] prior to any movement

    Now we need to transform this clause so that the question phrase appears in initial position, at the beginning of the sentence. This isn’t head movement, it’s Phrasal Movement, also referred to as XP Movement. A phrase can’t go in a head position, but it can move to the empty Specifier position in CP.

    Phrasal Movement:
    Movement of a phrase (XP) into a higher specifier position.

    This type of Phrasal Movement is known as WH-movement; Phrasal Movement is usually named for the type of phrase that moves.

    Move a WH-phrase from its original position into Spec,CP.

    Figure 6.31 shows what the tree structure will look like after both T-to-C Movement and WH-movement have applied.

    Tree diagram: [CP [NP what] [C' [C +Q have] [TP [NP the squirrel] [crossed out T crossed out have] [VP [V hidden] [crossed out NP crossed out what] ] ] ] ] Arrows from T to C and from lower what to higher what
    Figure 6.31 Tree diagram for the question [What has the squirrel hidden?] after both T-to-C and WH-movement

    What does it look like when we have a complex NP moving to Spec,CP? Basically the same, as shown in Figure 6.32. This tree also shows the auxiliary did in C, inserted as a result of Do-Support:

    Tree diagram: [CP [NP [DP what] [N' kind of nuts] ] [C' [C +Q did ] [TP [NP the squirrel] [crossed out T+PAST] [VP [V hide] [crossed out NP what kind of nuts ] ] ] ] ] Arrows from T to C and from lower "what kind of nuts" to "what kind of nuts in Spec,CP
    Figure 6.31 Tree diagram for the question [What kind of nuts did the squirrel hide?] after both T-to-C and WH-movement

    Embedded content questions, which we saw in Section 6.9, have very similar tree structures. They are like main clause content questions in putting the WH-phrase at the front of the CP, but unlike main clause content phrases in that they don’t do Subject-Auxiliary Inversion (T-to-C movement).

    What would this look like in a tree? Consider this embedded content question:

    (4) I know [CP what squirrels hide].

    The tree for this sentence would be as in Figure 6.32.

    Tree diagram: [TP [NP I ] [T' [T -PAST] [VP [V' [V know] [CP [NP [N' [N what] ] ] [C' [C +Q] [TP [NP squirrels] [T' [T -PAST] [VP [V' [V hide] [crossed out NP nuts] ] ] ] ] ] ] ] ] ] ] arrow from lower "what" to "what" in embedded Spec,CP
    Figure 6.31 Tree diagram for embedded content question I know what squirrels hide.

    Notice that the embedded C is empty! In many varieties of English, when you get a phrase in embedded Spec,CP, it’s impossible to also have an overt complementizer. So sentences like (5) are always ungrammatical in my English, even though if is a +Q complementizer.

    (5) *I know [CP what if squirrels hide].

    This isn’t true in all languages! In many languages WH-movement is totally compatible with an overt complementizer. Tlingit is a Na-Dené language spoken by members of the Tlingit Nation, whose territory includes parts of Southeast Alaska in the United States, and parts of the Yukon territory and Northern British Columbia in Canada. In Tlingit content questions, the content question word must appear in the left edge of the sentence, but must also be followed by a question particle , as shown in (6). The Tlingit examples here are drawn from Cable (2007). “Ergative” is a case that appears on transitive subjects; the symbol <g̲> represents a voiced uvular stop, an acute accent on a vowel indicates high tone, and the symbol <x’> represents a glottalized velar fricative.

    (6) a. Daa kéet axá?
    what +Q killerwhale
    “What do killerwhales eat?”
    b. Aadóoch kg̲watóow x’úx’?
    who.ERGATIVE +Q this book
    “Who will read this book?”

    Other phrases can appear before the content question word, but only when they are the topic of the sentence. One way to understand the word order in (6) is that the content question word has moved to the specifier of CP, while the head of CP is also filled by a +Q complementizer sá. So the restriction we see in English isn’t a universal one, it’s just one type of syntactic pattern.

    Movement gives us another tool for understanding the variation in word order that we see across different languages. In this section we’ve focused on how we can use movement to analyze the word order difference between statements and questions in English. This can be applied to any other type of construction or to any other language: if there is a difference in word order in a language that can’t be explained by X-bar structure, one possibility is that the difference results from either a head or a phrase moving in some contexts but not others.

    Check your understanding

    Coming soon!

    If you are following the alternative path through this chapter that interleaves core concepts with tree structures, the previous section was 6.9 Embedded content questions, and the next section is 6.10 Arguments and thematic roles.

    6.20: Trees- Movement beyond questions

    Head Movement outside questions: V-to-T movement of auxiliaries

    Based on the discussion so far, you might think of movement as something that we only find in questions. But that isn’t the case! It happens that questions are one of the places that we clearly see movement in English, but both Head Movement and Phrasal Movement can be found in other contexts as well.

    In this section we’ll see evidence that auxiliaries like be and have start out lower than T and move to it via Head Movement, then evidence that the same is true for all verbs in a language like French.


    The following sentences all have one auxiliary in them:

    (1) a. The leaves will fall.
    b. The leaves have fallen.
    c. The leaves are falling.

    We saw in Section 6.5 that auxiliaries all have the same distribution in English sentences, a distribution that is different from main verbs: they appear before negation and participate in Subject-Auxiliary Inversion (T-to-C movement). They also appear before adverbs like always, as in (2):

    (2) a. The leaves will always fall.
    b. The leaves have always fallen.
    c. The leaves are always falling.

    We explained this similarity in distribution—and the way the auxiliaries are all different from main verbs—by analyzing all the auxiliaries as belonging to a single syntactic category: T.

    But it turns out that the picture is a bit more complex. There’s a difference between modals (and nonfinite to) on the one hand, and all the other auxiliaries on the other.

    First, for many speakers of English, modals (and to) cannot stack—you always get exactly one of them.

    (3) a. *The leaves will might fall. (cf. will maybe fall)
    b. *The leaves must can fall. (cf. must be able to fall)

    By contrast, have and be can stack, with a modal or with each other. And the order is always the same: the modal must be the highest auxiliary, the one that shows the distribution that we associated with the head T.

    (4) a. The leaves will have fallen. (Future + Perfect)
    b. The leaves will be falling. (Future + Progressive)
    c. The leaves will have been falling. (Future + Perfect + Progressive)
    d. The leaves have been falling. (Perfect + Progressive)
    Some varieties of English, including Southern American English, and also some varieties of Scots do allow more than one modal in a clause—for speakers of these varieties, the equivalent of (3a) or (3b) might be grammatical (though there are restrictions on which modals can stack, and these restrictions are different in different varieties). When analyzing the syntax of these varieties, we might need a different hypothesis about where modal auxiliaries start out, and whether any of them also move to T in declarative clauses. Even in varieties where modals can co-occur with one another, though, it’s still the case that all modals come before have and be auxiliaries.

    If we check all these sentences for the distributional properties that we’ve associated with being in T—being before negation + adverbs like always, undergoing Subject-Auxiliary Inversion—it turns out that only the first auxiliary passes those tests. All the subsequent auxiliaries suddenly have the same distribution of main verbs. Let’s see this for the Future + Perfect:

    • will is in T:
      • Before negation: The leaves will not have fallen.
      • Before always: The leaves will always have fallen.
      • Subject-Aux inversion: Will the leaves have fallen?
    • have is not in T:
      • Not before negation: *The leaves will haven’t fallen.
      • Not before always (maybe not totally ungrammatical, but not totally acceptable): *The leaves will have always fallen.
      • Can’t invert, alone or with will: *Have the leaves will fallen? *Will have the leaves fallen?

    So where is the second auxiliary—or in the Future + Perfect + Passive, where is the third auxiliary?

    Proposal (for English)
    Only tense features, the modals, and nonfinite to start out in T—that is, only these morphemes truly belong to the functional category T. All other auxiliaries move to T, but they only do so if that T isn’t already filled by a modal or to.

    So when there’s a modal in T, the lower auxiliary will appear in an extra VP layer—sometimes called a VP “shell”. (We could instead label this phrase AuxP, or even PerfectP or ProgressiveP—if you read more about syntax you might encounter those labels, but for simplicity we’ll call it VP here.) This is illustrated in Figure 6.34.

    Tree diagram: [TP [NP the leaves] [T' [T will] [VP_prog [V' [V be] [VP falling ] ] ] ] ]
    Figure 6.34 Tree diagram for [The leaves will be falling.], showing a progressive VP shell

    But if there’s nothing in T—or rather, if all that’s in T is a tense feature—the auxiliary verb will move from V to T, as illustrated in Figure 6.35.

    Tree diagram: [TP [NP the leaves] [T' [T are] [VP_prog [V' [crossed out V are] [VP falling ] ] ] ] ], arrow from [V are] to [T are]
    Figure 6.35 Tree diagram for [The leaves are falling.], showing a progressive VP shell and movement of auxiliary are to T

    Very few verbs move in most contemporary varieties of Modern English. Only be (as an auxiliary and as a main verb copula), and have (only as an auxiliary) show evidence of moving to T.

    The same isn’t true in other languages, necessarily. For example in French (and in earlier stages of English), we have reason to think that all verbs move to T.


    In contemporary English it’s only auxiliaries that ever appear in T—main verbs always show a different distributions. But in French—and in earlier stages of English—when there’s no auxiliary the main verb also appears in the T position.

    French auxiliaries, like English auxiliaries, show up before negation, before auxiliaries like toujours (“always”), and can undergo Subject-Aux inversion (though only with pronominal subjects, and even then it isn’t very natural in casual speech for most speakers).

    (5)   Les feuilles ont tombé.
        the leaves have fallen
        “The leaves fell/have fallen.”
    (6)   Les feuilles (n’)ont pas tombé.
        the leaves (NEG)have NEG fallen
        “The leaves have fallen.”
    (7)   Les feuilles ont toujours tombé.
        the leaves have always fallen
        “The leaves always fell / have always fallen.”
    (8)   Ont-ils tombé?
        Have-they fallen
        “Have they fallen?.”
    Negation in French is traditionally described as involving a ne before the tensed verb, and a pas after the verb—kind of like a circumfix. But in spoken French in both Quebec and France, the ne is almost never pronounced, and so it’s marked as optional in all examples in this section.

    What’s different about French is that main verbs show exactly the same distribution—whereas English verbs are after negation and adverbs, and can’t do Subject-Aux inversion (instead they require the support auxiliary do):

    (9) Les feuilles (ne) tombaient pas.
    the leaves (NEG)fell NEG
    “The leaves didn’t fall/weren’t falling.”
    (10) Les feuilles tombaient toujours.
    the leaves fell always
    “The leaves always fell / were always falling.”
    (11) Tombaient-ils?
    “Did they fall? / Were they falling?.”

    English verbs do not have the same distribution as auxiliaries—though they did in Early Modern English, ca. 1600s).

    (12) *The leaves fell not.
    (13) *The leaves fell always.
    (14) *Fell the leaves?

    We can analyze this difference in word order between English and French by saying that while in English only be and auxiliary have move to T, in French all verbs undergo V-to-T movement. This is illustrated for (10) in Figure 6.36.

    Tree diagram: [TP [NP les feuilles] [T' [T tombaient] [VP [AdvP toujours] [crossed out V tombaient] ] ] ] arrow from V to T
    Figure 6.36 Tree diagram for [Les feuilles tombaient toujours.], showing a movement of the main V to T

    We’ve now introduced two types of movement in our theory:

    • Head movement: movement of a head to the next head position up in the tree.
    • Phrasal movement: movement of a phrase to a higher specifier position.

    Though we find them both in English questions (as T-to-C and WH-movement, respectively), what we see in English auxiliaries and with all French verbs is that these movement types can be found in other
    contexts as well—and that languages can differ in what types of movement they exhibit.

    Head movement and phrasal movement in passives

    So far we’ve talked about how to identify passives—but what is their syntax like? Remember the pair of active and passive sentences we saw in Section 6.11:

    (15) a. The pirates sank the ship. (active)
    b. The ship was sunk (by the pirates). (passive)

    In a theory of syntax that employs movement, the natural way to think about the passive is to say that its syntax (e.g. the presence of the passive be) prevents the subject from being introduced in the first place, leaving an empty position (indicated by an underscore).

    (16) [TP _ was sunk [the ship] ]

    Then because English is a language that always requires a subject, in Spec,TP, something needs to be done to fill that empty position. This is done by moving the object NP into the subject position:

    the ship ]
    (16) [TP [the ship] was sunk

    This is a new case of phrasal movement: movement of an NP into subject position.

    NP movement:
    Move an NP into Spec,TP, to fill an otherwise-empty subject position.

    We start with the theme argument the ship as the complement of the verb, and the passive auxiliary be in a VP shell. To get the correct output, we apply two instances of movement:

    1. The passive auxiliary moves to T: V-to-T movement
    2. The object NP [the ship] moves to the subject-position in Spec,TP: NP-movement

    The result of these two steps of movement is illustrated in Figure 6.37.

    Tree diagram: [TP [NP the ship] [T' [T was] [VP_pass [crossed out V was] [VP sunk [crossed out NP the ship] ] ] ] ] arrow from [V was] to T, and from lower [the ship] to Spec,TP
    Figure 6.35 Tree diagram for [The ship was sunk.], showing a passive VP shell, movement of auxiliary was to T, and NP movement of the passive subject

    This section has illustrated our final tool in accounting for word-order differences across languages: not just the parameters of head-initial vs. head-final ordering, but also what types of movement arise in what contexts.

    Check your understanding

    Coming soon!

    If you are following the alternative path through this chapter that interleaves core concepts with tree structures, the previous section was 6.11 Changing argument structure: Causatives and passives, and the next section is 6.21 Trees: Summary.

    This page titled 5.10: Trees- Movement is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Catherine Anderson, Bronwyn Bjorkman, Derek Denis, Julianne Doner, Margaret Grant, Nathan Sanders, and Ai Taniguchi (eCampusOntario) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.