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    #1

    must not or cannot

    Both UNDERSTANDING AND USING ENGLISH GRAMMAR and FUNDERMENTALS OF ENGLISH GRAMMAR (both published by America's Simon and Schuster) say that mustn't can be used to mean cannot as follows:

    Eric ate everything on his plate except the pickle. He must not like pickles.

    Sally looks tired. She's been coughing and sneezing. She must not feel well.

    But the question is: Why don't we see the use of mustn't in any dictionary? And in all examination papers this use of mustn't is treated as incorrect?

    Thank you in advance.




































































































    7say

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    #2

    Re: must not or cannot

    I've been wondering why we can't use mustn't to mean can't when sth seems very unlikely. Though the teacher tells us again and again about that, many of us Chinese students will still choose mustn't rather than can't in exams.

    Could anyone please tell me how Americans or other people choose between these two words?


    • Join Date: Jan 2007
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    #3

    Re: must not or cannot

    To be able to as in i can or you cannot describes your ability to do something. It says whether or not it is possible.

    To have to as in I must or they musn't describes whether or not you feel an obligation to do something.

    In the sense that you mentioned, he must not like pickles, mustn't seems to mean doesn't (rather than cannot as you suggested). This use of must not seems quite colloquial, and as much as it isn't wrong, its not very formal at all.

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    #4

    Re: must not or cannot

    Quote Originally Posted by Niall View Post
    To be able to as in i can or you cannot describes your ability to do something. It says whether or not it is possible.

    To have to as in I must or they musn't describes whether or not you feel an obligation to do something.

    In the sense that you mentioned, he must not like pickles, mustn't seems to mean doesn't (rather than cannot as you suggested). This use of must not seems quite colloquial, and as much as it isn't wrong, its not very formal at all.

    sir, you mean we can't say He can't like pickles? Since mustn't is not very formal, then what is the formal way to express this idea? Is it that can seems not to go well with like?

    Thank you very much.


    • Join Date: Nov 2007
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    #5

    Re: must not or cannot

    The sentences could also be written like this:

    Since Eric ate everything on his plate except the pickle, I think he doesn't like pickles.

    Maybe that is less colloquial. However, I use that form of "must" all the time. It indicates a conclusion.

    He must like pickles = (for some reason) I think he likes pickles.
    He must not like pickles = (for some reason) I think he doesn't like pickles.

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    #6

    Re: must not or cannot

    How I'd like to know why this use of mustn't can't be seen in any dictionary, since many people are using it, and since the grammar books mentioned above have treated it in the UNIT OF MODAL VERBS. And why in exam papers we aren't allowed to use it in this way?:

    That can't be Mary--she's in New York. (Why not mustn't?)
    He can't have slept through all that noise. (Why not mustn't?)

    ps: these two sentences are taken from OXFORD ADVANCED LEARNER'S DICTIONARY 6th edition, can.

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