He mustn't have done it.
(1) He must have done it.
(2) He mustn't have done it.
Is (2) grammatical? If so, does it have the notion of deduction/supposition the way (1) does?
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tkacka15 Is (2) grammatical? If so, does it have the notion of deduction/supposition the way (1) does? Yes and yes.
- tkacka15 Is (2) grammatical?
- If so, does it have the notion of deduction/supposition the way (1) does?
- Yes and yes.
- However.
- This is a big 'however'.
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tkacka15Is (2) grammatical? If so, does it have the notion of deduction/supposition the way (1) does?
Yes and yes.
However. This is a big 'however'.
Almost all the books will tell you that the opposite of 'must' is 'can't' ('cannot') in this circumstance. So in academic settings use those instead of 'mustn't'.
(2) He can't have done it.
0Yes, (2) is understood to express the speaker's deduction/supposition, the same as (1), but it is unusual (much less usual than (1)). Some people may think that it is not quite correct English.
(Cross-posted.)
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