We know from earlier Hints
that could has many uses. Several
them are used for present or future time, but could is also
used to show ability in the
Could also has another past form--could have. This form is
followed by the past participle of the main verb:
could have been / could have
gone / could have finished /
could have seen /
could have done / could have taken / etc.
When could is used in this way, it refers to possibility in the
past. It does
not refer to ability or permission in
I don't know
why Bill left early. He could have had
some kind of emergency, I suppose.
(I don't know why Bill left
early. Maybe he had
some kind of emergency.)
I'm not sure where I met her.
It could have been at a party
or it could have been been at a business meeting.
(I don't remember where I
met her. Maybe I met her
at a party or maybe I
met her at a business meeting.)
I know he was at home, but he didn't
answer the phone.
He could have been
asleep or taking a shower, I suppose.
(I know he was at home, but
he didn't answer the phone.
Maybe he was asleep
or taking a shower.)