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A co-worker of mine took an ELL test for her job and she had to compose a question.
She wrote:

"Does she plays?"


I know that in a statement rather than a question, the third person singular subject is in effect necessitating the 's' on the end of play.

But what is the rule in questions that makes the 's' not needed? I don't know how to explain why we don't do this in a question.

4

Typically, only the first verb in each clause can be finite:

I play.
I played.
She plays.
She played.

As you can see, this verb changes form. It shows tense (present or past) and agrees with the subject (adding -s if the subject is third person singular present). This must be our finite verb.

Our example is a declarative clause. To make it into a question, we should turn it into an interrogative clause. And for this sort of sentence, we do that by swapping the subject and auxiliary verb, like this:

She was safe.  →  Was she safe?

This is called Subject-Auxiliary Inversion (SAI). We use SAI to mark these sentences as questions. And in this case, SAI is possible because we have the auxiliary be.

But what if our example doesn't have an auxiliary verb? Let's look at our example from earlier:

I play.
I played.
She plays.
She played.

We can't swap the subject and auxiliary verb if we don't have one! Let's solve that problem by adding the meaningless ("dummy") auxiliary do:

I do play.
I did play.
She does play.
She did play.

Now we've got two verbs! And only the first can be finite. In this case, that means do! And as you can see, do now changes form, but play doesn't! That's because play is no longer finite.

Now we can make it into a question. So, let's do Subject-Auxiliary Inversion again, moving the auxiliary before the subject I:

Do I play?
Did I play?
Does she play?
Did she play?

These questions are formed correctly. But what about your example?

*Does she plays?

It doesn't work! Why not? Because we'd have two finite verbs.


In this answer, the * symbol marks a sentence as ungrammatical, and bold in examples marks a verb as finite.

2

Because the "adjusting to the subject" is done in two ways:

  1. Without auxillary verb (aka open-ended questions):
    Adjust the main verb.

    He plays the piano. <-> Who plays the piano?

  2. With auxillary verb (aka yes-no questions or closed-ended questions):
    Adjust the auxillary verb, the main verb stays in the infinitive.

    He plays the piano. <-> Does he play the piano?

Note that native speakers tend to "forget" that irregular verbs - and auxillary verbs are irregular - switch their forms instead of adding the 's'. So yes, there is an adjustment, but not via the '+s'.


Edit for the sake of completeness:
as @pazzo noted, there is the unchanged "He plays the piano?" question as well - same rules apply: No auxillary -> adjust main verb.

  • Also: He plays the piano?, a common word order for questions (unchanged from non-question form. Distinguishable by the tone of the speaker). But I can't help thinking that this question is a duplicate of a previous question. – user6951 May 13 '15 at 16:55
  • @pazzo: true. But not what I would suggest for a learner - can only be recognized in spoken language by intonation. (or the '?' obviously for written tests) – Stephie May 13 '15 at 16:57
  • As you like, but I teach ESL, and we teach this from rather early on, as it is similar to other languages, and also as a way of showing the importance of tone in English... – user6951 May 13 '15 at 17:00
  • @pazzo - and I have worked with international collegues (english as 3rd language and a h**l of an accent...) who obviously never got the memo on the importance of intonation. Add to this a crackling phone line and you have a recipe for disaster. Will add this type for the sake of completeness. Did you find the duplicate? – Stephie May 13 '15 at 17:42
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    @Araucaria Because it has an auxillary -> adjust the auxillary. Wil try to phrase it better later, am on the run. – Stephie May 13 '15 at 17:56

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