I noticed that in English, it is incorrect to say "Who did eat the apples?" but it is correct to say "who ate the apples?" It would be very helpful if you can give me some clues based on syntax. Thanks very much!

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    This is definitely not a language-specific grammar & usage question, it is about Wh-movement, do-support, and feature checking. That is why the question asks about clues based on syntax. No need to close this one.
    – Keelan
    Oct 26, 2021 at 7:26
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    @Keelan How are wh-movement and do support not language-specific grammar? They apply exclusively to English, unless you want to compare how they work across languages, which isn’t what this is about. This is a perfectly good question for ELL, or even ELU, but if the community has decided that questions about language-specific grammar are off-topic here (I don’t think they should be, but I’m not the whole community), then this definitely is too. Oct 26, 2021 at 7:43
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    @Keelan In my view, simply tacking on ‘based on syntax’ does not make a question primarily concerned with linguistics if it wasn’t already (and if it’s even possible to speak of a question of grammar that isn’t primarily concerned with linguistics to begin with). In this case, the fact that the asker seemingly does not know that “Who did eat the apples?” is a perfectly grammatical and normal sentence strongly supports this being a not-very-linguistic grammar question. But I didn’t vote to close, as I don’t believe such questions should be off-topic here. Oct 26, 2021 at 8:31
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    @Keelan As the question is asked right now, it is a plain question on English language and usage, and it seems that a linguistic answer to this question will overwhelm the original poster. It should be moved to English Language & Usage or English Language Learners Oct 26, 2021 at 9:04
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    The question is good; it's pointing at a core phenomenon in the syntax of the English language, namely: what necessitates that subject-auxiliary inversion occur? I for one am quite interested to see what sort of answer is produced. Surely it's possible to answer the question without overwhelming the poster. Oct 26, 2021 at 9:16

1 Answer 1


I don't know how much background in syntax you (or later readers) have, so I'm going to start with some basics (the complementizer layer, do-support, and object Wh-questions) before going into subject Wh-questions. Also, fair warning: syntax is not really my field, so things may be incomplete or incorrect, and anyone is invited to add or correct things.

The complementizer layer for yes/no questions

This is based on Carnie (2013, §7.3).

A sentence like You have seen Louis is analyzed with have in T(ense) and you moved from Spec,VP to Spec,TP, the default for subjects:

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To account for the word order in the corresponding yes-no question, Have you seen Louis?, it is argued that have moves from T to a higher layer C:

enter image description here

The reason behind this is that the C head has a [+Q] ("question") feature, which needs to be phonologically realized, i.e. it must contain something / cannot be null. Support for this comes from languages like Irish, which have an overt [+Q] complementizer (rather than T-to-C movement), Ar:

(1) Ar thit Seán?
    Q fall John
    "Did John fall?"

Further support comes from the fact that T-to-C is blocked when there is an overt complementizer, which is the case in embedded questions in English:

(2) a. Fabio asked if Claus had run a marathon. (overt C; no T-to-C)
    b. *Fabio asked if had Claus run a marathon. (overt C and T-to-C)
    c. *Fabio asked had if Claus run a marathon. (T-to-C and overt C)


This is based on Carnie (2013, §10.2–3).

This poses a problem for sentences without auxiliary verb. The T head cannot move into C to give it phonological content, because it is null itself! As a last resort, a dummy do is inserted in T so that it can move to C:

(3) a. You eat apples.
    b. Do you eat apples?

enter image description here enter image description here

Object Wh-questions

This is based on Carnie (2013, §12.1).

We now come to Wh-questions. We first need to look at questions where the Wh-element is the object. In this case, the object moves from its position in the VP layer to Spec,CP:

enter image description here

Recall that above we argued that T-to-C was triggered by a [+Q] feature on the C head. We now say that there is a [+Wh] feature on the C head as well. The Wh-phrase whom moves to Spec,CP to check this [+Wh] feature.

(The existence of the [+Wh] feature is again supported by Irish, which has at least three complementizers in main clauses: go [-Q, -Wh]; an [+Q, -Wh]; aL [+Q, +Wh].)

Note that do-support is still needed because whom cannot check [+Q].

Subject Wh-questions

What you observe is called the T-to-C asymmetry (Koopman 1983): we do have T-to-C in object Wh-questions (and hence require do-support), but we do not have T-to-C in subject Wh-questions:

(4) a. What did Mary buy?
    b. *What Mary bought?
    c. *Who did buy the book?
    d. Who bought the book?

(Example (4c) is possible when did is focused, but this is not a case of do-support because it is not required for [+Q] feature checking. It also occurs in Mary did buy the book!)

Why this happens is a bit of an open question, so good job on noticing the asymmetry.

Below are two possible solutions. There may be more, this is not really my field.

Pesetsky & Torrego (2001): nominative DPs have a tense feature

Pesetsky & Torrego (2001) argue that in main interrogative clauses, C bears an uninterpretable T feature uT. This means that something must be done to delete this feature. This is done by moving T to C. This is as before, but the terminology has been updated: we now talk about a uT feature that must be deleted instead of a [+Q] feature that must be checked.

Next, they propose that nominative DPs have a uT feature on the D head. This is the key proposal of their paper.

Within this framework, when a feature is deleted it remains somehow available, and it can itself delete features of the same type. So once the subject has moved into Spec,TP, it bears a deleted feature uT. By moving it further into Spec,CP, it can delete uT on C. When this is done, there is no need any more to also move T to C.

A question that may arise is: why in this situation must Spec,TP move to Spec,CP to delete uT on C; why can T not move to C instead? This would give Did who buy the book?, which is clearly ungrammatical. The answer here is twofold. First, Spec,TP really must move to Spec,CP because we still have the [+Wh] feature to check (or, rather, the uWh feature to delete). Second, by assumption, we only allow as many movements as are necessary to delete all uninterpretable features. After Wh-movement there is no uT feature left on C, so there is no need for T-to-C.

Of course one needs to explain why a nominative DP has a uT feature. Pesetsky and Torrego argue that this is not entirely unexpected because the reverse is true: T holds uD features like person and number for which it needs a subject DP.

Adger (2003): uclause-type on T

Adger (2003, §9.3–4) gives a slightly different account for do-support, from which the lack of do-support in subject Wh-questions follows.

In his theory, T has a uninterpreted uclause-type feature that can be deleted by C[+Q]. This explains T-to-C movement in yes/no questions and object Wh-questions. As above, the requirement of T-to-C leads to do-support.

In subject Wh-questions, there is at some point a [+Wh] DP in Spec,TP. Adger suggests that the [+Wh] feature in this position deletes uclause-type on T. Afterwards, the subject goes on to Spec,CP to delete uWh over there.

The difference is that Pesetsky and Torrego have a uT feature on C that is deleted by T-to-C or Wh-movement into Spec,CP, whereas Adger has a uclause-type feature on T that is deleted by T-to-C or Spec,TP.


  • Adger, David. 2003. Core Syntax: A Minimalist Approach. Oxford University Press.
  • Carnie, Andrew. 2013. Syntax: A Generative Introduction. 3rd ed. Wiley-Blackwell.
  • Koopman, Hilda. 1983. ECP effects in main clauses. Linguistic Inquiry 14: 346-350.
  • Pesetsky, David, and Esther Torrego. 2001. T-to-C Movement: Causes and Consequences. In Michael Kenstowicz (ed.), Ken Hale: A Life in Language. MIT Press.
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    While the trees help, the answer itself is convoluted and difficult to follow, bringing in too much additional and unnecessary information. Why not simply point to the fact that the subject is the one constituent that naturally precedes the finite verb in English and so there is no need for subject-auxiliary inversion to occur if the subject is questioned. The answer is actually a good illustration of how misguided mainstream phrase structure syntax has become, it's theoretical apparatus having become too complex and hence opaque long ago. Oct 27, 2021 at 1:01
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    Although I don't get the last part of your answer, it is still very helpful for me to understand the question. Thanks for your hard work on it!@Keelan
    – Yili Xia
    Oct 27, 2021 at 2:32
  • I am a complete beginner in syntax, and I lost you half way through. I understand that “Ate you apples?” is “wrong” but I didn’t understand your explanation as to why it isn’t possible in English but it is in other languages such as French. Oct 27, 2021 at 4:19
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    @Xia.Yili please be careful not to mix up different approaches. In traditional generative syntax, subject-auxiliary inversion is a symptom of T-to-C movement (since the subject is in Spec, T). That the Wh-element is already to the left of T in a subject Wh-question does not matter, since T-to-C movement is still necessary to check/delete [+Q]. So you still need to explain why we do not get do-support in this situation.
    – Keelan
    Oct 28, 2021 at 8:27
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    When either of the other two major constituents is questioned, however, the necessity that the wh-expression appear at the front of the sentence has them appearing in a position that is not natural for them. The grammar therefore marks their non-natural position in terms of subject-auxiliary inversion., e.g. What did Frank eat yesterday?, When did Frank eat the apples?. Oct 28, 2021 at 8:44

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