Why put "auxiliary verb" in front of the sentence in English interrogative sentence?

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Senior Member
Hello, :)

- Mary is a student.
- Is Mary a student?

- She has a bag.
- Does she have a bag?

- I have finished my homework
- Have you finished your homework?

- Tom can speak English
- Can Tom speak English?

- When did you go to school?

Why can this form constitute an interrogative sentence?
How did this form evolve?
How should we understand it correctly?

Thank you:thank you::thank you:
Last edited:
  • berndf

    German (Germany)
    First of all, it is not always an auxiliary verb. In the first of your examples, is is the main (copula) verb and in the last example, can is a modal verb. Do-support (examples 2 and 5) was originally an emphatic construction (which it still is in some cases) but is now regularly used to avoid putting verbs other than be, have and modal verbs in front of the subject. But this is a more recent development. In early Modern English the 5th sentence would be When wentest thou to school?

    The real question should therefore be: Why is the finite (=conjugated) verb put in front of the subject.

    There are two parts to the answer:

    1. Question sentences beginning with a question particle.
    These are sentences like your 5th example. Here it is a remnant of the old Germanic word where the finite verb is always in 2nd position. This is called V2 word order. I.e. when you start a sentence with something else then the subject then the subject has to move after the verb to ensure that the verb remains in 2nd position. E.g. the sentence Yesterday, he came late to school is in German (where V2 word order is still largely obeyed) Gestern kam er zu spät in die Schule. English has gradually lost this word order over the centuries in favour of SVO word order but a few remnants remain.

    2. Sentences without a question particle.
    Sentences like Is Mary a student have the finite verb in 1st and not 2nd position. How is this to be explained? This cannot be completely explained by attested language but needs a bit of reconstruction. Older texts suggest that the participle whether (more precisely its corresponding forms in various Germanic languages, like hwæþer in Old English, wedar in Old High German or hvaðarr in Old Norse) was originally a question particle with the meaning which of the two? and this particle was originally used to introduce yes/no-question, i.e. if this use had survived, we would today say Whether (=which of the two? yes or no?) is Mary a student. The assumption is that this particle was later dropped but the associated word order remained making the word order itself a question marker.
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