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Thread: deduction

  1. #1
    moniki's Avatar
    moniki is offline Newbie
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    deduction

    Hello, I have a doubt about using the word "can" for deduction, when should I use "can't have" or "couldn't have"? Thanks in advance.

  2. #2
    paul.moss is offline Junior Member
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    Re: deduction

    In this sense and in the negative, no difference. Both are the past negative forms of must: He must have been joking/he can't /couldn't have been joking.

  3. #3
    moniki's Avatar
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    Re: deduction

    Thank you a lot.

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