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How often do you use "can('t) have done" structure? I have read and watched relatively enough but my eye and ear are not accustomed to it.

He can't have been at the meeting, he's on a business trip this week.

They can't have bought it today because the shops are closed.

I don't think I can have been listening to the same debate.

How our usage can have gone from under 2Gb monthly to over 15Gb.

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  • You should use couldn't have, not can't have.
    – WendiKidd
    Jun 23, 2013 at 16:12
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    The editors of the Merriam-Webster Learner's Dictionary obviously don't know what they should and shouldn't use. They included an example there: He can't really have meant that.
    – stillenat
    Jun 23, 2013 at 17:21
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    @WendiKidd - In He can't have been at the meeting I think the present tense is normal when you are concerned with the current consequences or conditions of his being at the meeting - as here, where his being on a business trip is still current, or in He can't have been at the meeting, or he'd know his project is about to be cancelled. Jun 23, 2013 at 19:05

2 Answers 2

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He must have been at the meeting.

We use this modal to express logical deduction in an affirmative sense.

I am quite certain that he was at the meeting

He can't have been at the meeting.

This modal expresses logical deduction in a negative sense.

I am quite certain that he was not at the meeting.

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I looked at a corpus of my own online communications from over the last three years; out of about 400,000 lines, I found 9 instances of this construction. That works out to an average of 3 times per year. So the answer is "not all that often, but often enough".

To put that another way: this construction may not be used every day, but as an English Language Learner, it's something you need to recognize.

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