Which question tag should follow He must have overslept ?

He must have overslept, mustn't he ?


He must have overslept, hasn't he ?

or even

He must have overslept, didn't he ?

What motivates my question is that adding not to modal must usually changes its meaning from the logical deduction that something is/was the case to prohibition, doesn't it?

  • 1
    I'd not consider the first tag question jarring; the context dictates the sense of the tag. The other two tags would be appropriate with 'he's overslept, ... Notice that this essentially makes 'He's overslept' into something modally somewhere along the continuum towards a declarative question rather than a pure assertion. – Edwin Ashworth Nov 13 '15 at 13:10
  • Yeah, frankly they all sound terrible. Using "must have" with a clause that reiterates as a question like that (except perhaps with "dontcha think") is basically not workable. Rephrase. – Hot Licks Nov 13 '15 at 13:11

About 313,000 results on a Google search for "mustn't he" would perhaps indicate that people saying the usage is terrible (1) haven't checked and (2) are speaking subjectively.

UsingEnglish.com has an article addressing this debate:

He must have seen it, mustn't he?

This is the first time I have seen such a question tag as with 'must have done'. In China's English tests or examinations, such a tag is thought to be absolutely wrong. They say we must use 'hasn't he?'. They also say we must say 'He must have seen it yesterday, didn't he?'

I thought 'mustn't he?' was fine, but I had never found any proof. Now that I've got this sentence, I'd like to know how authoritative it is and whether we can use this sentence at all.

Might I ask native English teachers to help me clarify this puzzle of mine?


And after checking, as well as being familiar with the usage, I can agree with the reply [bolding mine]:

There's nothing wrong with this. Any other tag question implies an ellipsis such as 'He must have done it. [Tell me I'm not wrong. (Beginning to be unsure) He did...] Didn't he?'. In that case, it's not really a tag question at all, as it's not asking for routine confirmation of a certainty.


The modal tag-question is very common:

I can go out tonight, can't I?

They could go via Vail, couldn't they?

It would be a disaster, wouldn't it?

He must use the lift, mustn't he?

I shall die, shan't I? [formal]

He'll tell his dad, won't he?

'Mightn't' may sound a little awkward, but 'mustn't' is in regular use, at least in some areas. ODO includes the contraction and a tag-question usage:

So I thought, if it's man made, there must be someone driving it, mustn't there?

  • I understand your annoyance at people from different dialects denying the existence of a construction found in your dialect; but I don't think it's productive to just flip that around and do the same thing in reverse. You could take this opportunity to step up and write an answer that speaks directly to the dialect difference, instead of just promoting your dialect instead of theirs. (Or failing that, you could at least indicate upfront which dialect you're writing about.) – ruakh Aug 11 '18 at 14:46
  • @ruakh Whatever do you mean? Modal tags cohere with the modal used, except for (in this day and age), the use of mightn't. Mighn't is still used as the main clause modal in BrE but one doesn't hear it much in AmE. – Lambie May 29 '19 at 17:14
  • @ruakh I hadn't seen the comment. Are you contesting my 'There's nothing wrong with this.'? Are you saying that 'my dialect' (I always thought 'BrE' was the closest descriptor) should bow to say that used in China? Are you saying that ODO (now Lexico) isn't a valid reference? ... And I can't see that your 'your annoyance' was justified, can you? Note that I haven't claimed in this answer that different tag questions are incorrect, merely that these aren't incorrect. – Edwin Ashworth Dec 9 '19 at 16:49
  • @EdwinAshworth: I'm saying that in American English, "mustn't he?" sounds hopelessly quaint. That's not because Americans "haven't checked" Google or "are speaking subjectively", but rather, simply because American English is different from British English in many respects, and this is apparently one of them. If you weren't actually annoyed at the claims you were reacting to, then what, were you being a jerk about them for no reason? – ruakh Dec 9 '19 at 18:27

All three are awful and beg to be rephrased:

  • He overslept, didn't he?
  • He must have overslept, don't you think?

Must have done something = I am sure someone did something.

The true meaning of the sentence is the assumption that someone did do something with must have done being just a mask to it or a periphrasis. The tag question refers to the true meaning of an utterence, therefore must have done, didn't they.

However, challenging your own assumption with a tag question doesn't make much sense, therefore don't you think is the logical thing.

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