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.
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.
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.
