'must not/ can't' be home

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MikeLynn

Senior Member
Hi everybody, I have tried to search the previous threads, but I'm afraid I couldn't find the answer to my question ;)
I believed that must not was used only for not to be allowed to and i was a bit surprised when I learned that it can be used for something like "I'm sure it is not true"
Please, what is the difference between "They must not be home." and "They can't be home."? And also, is there a difference between AmE and BrE usage?
Thank you for your help and explanations :)
M&L
 
  • Dimcl

    Senior Member
    Canadian English
    You ring the doorbell and wait. You ring again and wait. There's no answer. You would say "They must not be home".

    You phone them and the phone rings and rings and rings. You would say "They must not be home".

    You argue with a friend about whether they're at home or not. You might say "They can't be home. I saw them driving away 10 minutes ago."

    "must not" is an assumption in this context. "cannot" is a surety.
     

    Loob

    Senior Member
    English UK
    Yes, there is a BrE/AmE difference,

    In BrE we don't use "they mustn't be home" to mean "I deduce they aren't at home". We'd have to say "they can't be at home".

    That said, there may well be BrE variants which parallel the AmE usage.

    There are lots of previous threads:)
     

    MikeLynn

    Senior Member
    Thanks a lot Dimcl for your quick answer, it is a great example :). The reason why I'm a bit confused here is that in my former grammar book it simply didn't seem to exist, but it was dealt with in the new edition of the same book (both of them focus on AmE). The reason it surprised me was that I'd never seen it before. It had always been may not or might not for probably or maybe not and then cannot for definitaey not. Is it recent or they simply forgot to include this option? Thanks
    M&L
     

    Iknownothing

    Member
    British English
    Yes.

    He can't be home gives the meaning "it's not possible"

    He mustn't be home gives the meaning that a series of investigative logical processes have been gone through, and the result is that he's not home ("he mustn't be home")

    They are both very close in meaning really. I usually explain to my students on issues like this that most native speakers wouldn't even notice the modal used, but would understand 100% the situation and wouldn't even think about questioning the modal choice. There's such a small difference in between these examples !
     

    MikeLynn

    Senior Member
    Thank you Loob, that's what I was worried about and I'm sorry I couldn't find the relevant threads. The issue must have been hidden somewhere"deep" inside and the title wouldn't revealt it :)
    M&L
     

    MikeLynn

    Senior Member
    Thank you knownothing for your examples it sure is enlightening. It's really tough to explain something you can't "feel" and for us, non natives, the only things that can help is theory and then a whole bunch of examples that might be deceiving as you can never be sure about the register, dialect etc. etc.
    M&L
     

    johndot

    Senior Member
    English - England
    When used in this context, must and must not reflect a conclusion arrived at by deduction:

    They must be home because I saw the curtains move.

    When used with not, however, the meaning is not so much negative as opposite or contrary:

    They mustn’t be home; the house is in darkness.
     

    Loob

    Senior Member
    English UK
    The conclusion of previous discussions has always, I think, been: "Mustn't" AmE; "can't" [most varieties of] BrE.
     
    Last edited:

    MikeLynn

    Senior Member
    Thank you, johndot, for making it even a bit clearer. Would it be right if I said that must and must not are more about the speaker's personal/subjective feelings while cannot is related to something that is based on logic, research or something of that kind?
     

    MikeLynn

    Senior Member
    Thanks Loob, that was my first impression, but then I got really unsure, and interested in this particular issue even more, when I got some replies from European, understand British, English speakers who say that they use it and there is a difference in meaning, but they didn't label it as "American". But, anyway, hank you for all your answers, guys. This is a great way to learn new things.
    M&L
     

    Cagey

    post mod (English Only / Latin)
    English - US
    For sake of completeness:
    The following searches will find relevant threads:
    mustn't can't
    must not (You will have to sort through a longer list.)
    It isn't always easy to figure out which words will do the trick.
     

    easychen

    Senior Member
    Chinese
    When someone says "They mustn't be home," I would probably take it as "It's not necessary for them to be home."
     

    easychen

    Senior Member
    Chinese
    Why would you take that meaning from that sentence, easychen? I'm not even sure what "It's not necessary for them to be home" means.:confused:
    Oh really, Dimcl? I'm doubly confused!
    That kind of means "They don't have to be home."
     

    Zsuzsu

    Senior Member
    Hungarian
    Oh really, Dimcl? I'm doubly confused!
    That kind of means "They don't have to be home."
    Easychen, didn't you want to write: "They are not allowed to be home"? For me, this is what "they mustn't be home" means. I mean, of course, this is what I had thought before having read the thread.:D
     

    Cagey

    post mod (English Only / Latin)
    English - US
    It is true that "they must be home [to great their guests]" can* mean:
    It is necessary for them to be home.
    So it seems reasonable to think that
    They must not be home.
    would mean that it is not necessary for them to be home, but it doesn't. It has the meaning discussed above: "We have reason to think that they are probably not home."

    (*Remember, that "They must be home" by itself can also mean: "We have reason to think that they are probably home.")
     

    JulianStuart

    Senior Member
    English (UK then US)
    My $.02.
    The use of must in "they must(n't) be home" has the same sense as "It must be the case, logically speaking, that they are(n't) home. In other words they are not "musting" at all, it is the case that "musts", very idiomatic.

    It occurs to me (and perhaps it's buried in one of the many prior threads) to suggest that must does not have a negative form. Any negative in a "must not X" construction applies only to the X and not to the "must". Therefore we have
    "They must be home" and "They must not be home". In each case they must, in a positive sense.

    I know this is an English only forum but to make the point clear of the English meaning of what I'm saying, I'll add the following. This must be confusing for German-speaking English learners because the German form does have a normal negative "I don't must X" which translates into the English form "I don't have to X"
     

    BAS24

    Senior Member
    USA English
    As a side note, I very rarely hear Americans use the contraction "mustn't", though it could just be my region of the country. I do like it though. Maybe I'll try it out today and see what kind of strange looks I get.
     

    desert_fox

    Senior Member
    English
    Can't means that it is impossible for then to be home.
    Must not means that you came to this conclusion by knocking on the door, calling the house, etc.
     

    JayGatz

    New Member
    English - US
    There is a third usage that while the rarest, hasn't been discussed, which uses "must not be" as a requirement.

    Example:

    Painter to Man:
    We will start painting on Monday, but the paint we use is toxic, so you must not be at home for us to begin.

    In this sense there isn't any deduction, but rather a command or precondition to not be home. The usage is similar to that of "can't" in this instance.

    Just wanted to make sure we didn't leave an interpretation unturned!
     

    JulianStuart

    Senior Member
    English (UK then US)
    There is a third usage that while the rarest, hasn't been discussed, which uses "must not be" as a requirement.

    Example:

    Painter to Man:
    We will start painting on Monday, but the paint we use is toxic, so you must not be at home for us to begin.

    In this sense there isn't any deduction, but rather a command or precondition to not be home. The usage is similar to that of "can't" in this instance.

    Just wanted to make sure we didn't leave an interpretation unturned!
    I would say that that is an example of "You must (not X)"; the must is positive and the command is to not do something. "You must be absent" would be an adequate substitute for "You must not be at home"
     

    MikeLynn

    Senior Member
    Just a quick explanation and apology. I'm afraid that the reason I couldn't find any usable previous threads was that I didn't use the contracted form in the search ;) M&L
    Thanks a lot for all for all your contributions
     

    easychen

    Senior Member
    Chinese
    It occurs to me (and perhaps it's buried in one of the many prior threads) to suggest that must does not have a negative form. Any negative in a "must not X" construction applies only to the X and not to the "must". Therefore we have
    "They must be home" and "They must not be home". In each case they must, in a positive sense.
    Yeah, this seems to me to be more reasonable for understanding.:)

    But, is that why a guy would cry "Oh no, buddy, you mustn't die" ?
     
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