Question

1. He cannot have cleaned his room.
2. It is impossible that he cleaned his room.
3. He could not have cleaned his room.
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#1 mean #2, right? Then What is the meaning of #3? Would you write another sentences having similar meaning?

Answer 1

All three mean the same thing.

I can't believe he cleaned his room already.
I'd be surprised if he cleaned his room by now.