2.  To refer to the PAST.
 To refer to Unreal Situations.
 To show that the activity was different from
what we wanted.
 To say how confident we are that
something has happened.

3. Subject + modal + have + Past participle
•I gone
•We should
can played
•They have
might visited
•The students won
•My son ought to
paid

4.  It expresses deduction, a logical conclusion,
probability:
 It’s very cold; it must have snowed in the mountains.
 I saw him leaving. He must have finished the test.

5.  It expresses past reference about something
that was not carried out.
 She could have called the doctor early in the
morning.
 They could have danced in the party.

6.  It expresses negative deduction, impossibility
or disbelief:
 She can’t have passed the exam. It was too
difficult.
 The boy couldn’t have given a better answer
than this one.
 Bryan can’t have missed the bus.

7.  It expresses the possibility that an action took place
in the past (past possibility).
 The little boy may have lost the key.
 The little boy might have lost the key.
 Our neighbours may have heard some noises when our
car was stolen.
 Our neighbours might have heard some noises when
our car was stolen.
With “may”, action is more probable than with might.

8.  The action was not performed because of
external reasons.
 I would have played football but I had a strong pain
in my leg.
 Past Unreal Conditional.
 I would have gone to Paris if I had had the money
for the plane ticket.

9.  It expresses an unnecessary action, which was
performed.
 I needn’t have knocked at the door in this way. I awoke
the baby.
 You needn’t have bought the flowers for me.
In contrast, “didn’t need to” shows that the
action was not necessary but it wasn’t
performed either.
I didn’t need to knock at the door because it was
open (so I didn’t knock)

10.  It expresses that a past duty or obligation was not
carried out.
 You should have locked the door before leaving the
house (but you didn’t lock it).
 Paul ought to have waited until the lights were green
before he crossed the street (but he didn’t wait).