We can use modal verbs to talk about how sure or
unsure we are about something in the past just as we
use modals in the present with a slight change in the
form.
must have: must
have+ past participle
we use it to make a
deduction about something
that has happened.
might,may,could
might,may,could + past
participle
use them to say that
something was possible in
the past but where are not
sure.
example: I might have been here when I was a child but I can’t really
remember.
example: He must have forgotten
phone at home again. He’s not
answering.
Can’t have + past participle
used
We use ‘can’t have + past participle’ for things that we
are sure did not happen in the past.
example: he can't have liked the show.
She hates musicals