We use MUST when we feel sure
that something is true because
there’s very strong evidence.
He must live near here
because he comes to
work on foot. We don’t
know where he lives but
we’re sure it’s not far
away.
We use might, may or could to say
that we think something is possible
but we’re not sure.
Did you hear that? I think there might be a
burglar downstairs. She’s not sure there’s a
burglar but she thinks it’s possible. We’ll try
to get there early but we may arrive late if
there’s a lot of traffic.
We use can’t when we feel
sure something is not true.
It can’t be far away now. We’ve been driving
for hours. Where’s the map? Really? He has
to work on Christmas Day? He can’t feel very
happy about that.
in Past
In the same way that we use modal
verbs to say how certain we are about
things in the present we can also use
them to speculate about the past.
we use deduction the
form is MODAL +
have + past participle
Must have +
past participle
We use ‘must have + past
participle’ when we are
quite sure about
something.
You must have been very pleased when
you received the results of your exams.
He must have forgotten his phone at
home again.
Might have/may
have/could have + past
participle
We use ‘might have/may
have/could have + past
participle’ when we are not sure
about something but we think
it was possible.
He was supposed to be here an
hour ago but he could have been
stuck in a traffic jam. He may have
said he was coming but I can’t
really remember. I wasn’t listening.
I might have been here when I was
a child but I can’t really remember.
Can’t have + past participle
We use ‘can’t have +
past participle’ for
things that we are sure
did not happen in the
past.
You can’t have seen him this morning. He was
with me all the time. She can’t have liked the
show. She hates musicals.
We use modal verbs to say how sure
we are about something.