He [can't/mustn't] have lost his way.

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peptidoglycan

Senior Member
Turkish
He --------- have lost his way. He knows the city so well!

A) wouldn't
B) might
C) mustn't
D) can't

The question is from a book published in Turkey. The correct answer is D according to key. I wonder whether C) is correct as well. Thanks.
 
  • Gavril

    Senior Member
    English, USA
    He --------- have lost his way. He knows the city so well!

    A) wouldn't
    B) might
    C) mustn't
    D) can't

    The question is from a book published in Turkey. The correct answer is D according to key. I wonder whether C) is correct as well. Thanks.
    To me, "He mustn't have lost his way" means "He is not allowed to lose his way", which doesn't make sense in this context.

    "mustn't" is used in sentences like

    "You mustn't smoke indoors!" = smoking indoors is not permitted

    "You mustn't forget to buy some milk!" = it's important for you to remember to buy milk

    and so on.
     

    Thomas Tompion

    Senior Member
    English - England
    I agree that mustn't doesn't work here, but not that it has to do with obligation or permission.

    I mustn't have said that
    - it's very unlikely that I said that.

    We can use must to weaken a statement:

    I mustn't have said that is a weakened form of I didn't say that.

    He must have lost his way is, similarly, a weakened form of He has lost his way, and we are using the weakened form because we are inferring an explanation for his non-appearance. We aren't certain, so we use a weak form of assertion.

    However, if we say He mustn't have lost his way, we are inferring an explanation for his appearance. And granted that he has appeared we can use the strong form with confidence - he didn't lose his way. This is why we don't use the weakened form in such circumstances.
     

    Gavril

    Senior Member
    English, USA
    Thanks, Thomas T. -- the form mustn't is not used very often in US English compared to British so I'm not hugely familiar with its nuances.
     

    peptidoglycan

    Senior Member
    Turkish
    Thanks. Are the following suppositions correct?

    He can't have lost his way. = It is impossible that he has lost his way.

    He mustn't have lost his way. = It is unlikely that he has lost his way.
     

    Keith Bradford

    Senior Member
    English (Midlands UK)
    Can I put a word in for (A) as a possibility?

    A) He wouldn't have lost his way = It is unlikely that he has lost his way.
    C) He mustn't have lost his way = Please God let him not have lost his way!
    D) He can't have lost his way = It is impossible that he has lost his way.

    Once again, though (D) is the obvious answer, it isn't the only correct one.

    (I hate these badly-conceived multiple choices. Did I mention that?)
     
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