What tense is this

Question

If I say It can't have been a dog . is this past tense?

Mister Micawber · Accepted Answer

panickingIs this past tense?

Yes. Here is one grammarian's viewpoint:

Can't have and couldn't have share a similar degree of probability. They are equal in meaning when they express the impossibility of something.

The differences:

- "Can't have been" suggests that it happened more recently. It expresses a judgment about a recent action or situation, a context in which the issues are still fresh and relevant to the present.
  (e.g. Can you check my homework? I'm quite sure I can't have found every bug.)
- "Couldn't have been" suggests that it was further in the past.
  (e.g. As a young woman who had never given birth before, she couldn't have known what the experience of childbirth would be like.)

BillJ · Answer

It can't [have been a dog].

This sentence consists of two clause: the matrix clause (the sentence as a whole) and an embedded subordinate clause have been a dog.

Syntactically the matrix clause is present tense, since the modal auxiliary verb can is a present tense form, while the subordinate clause is the perfect infinitival have been a dog which is past tense.

Semantically, can't is like mustn't (though few people would say ^%It mustn't have been a dog). And some speakers would have used the past tense couldn't instead of can't.

What tense is this

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