Modals –
deduction (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.
Have + past participle (‘have done’,
‘have been’ have stolen’ etc.) is called the perfect
infinitive. When we use modal verbs to talk about the present they are
followed by an infinitive without ‘to’. When we use modal verbs to talk about
the past they are followed by a perfect infinitive.
must + perfect infinitive
We use must + perfect infinitive when we
feel sure about something in the past.
•
You must have been delighted when you heard you’d won the lottery.
•
The thieves must have come in through the window. Look – it’s still open.
•
Oh no! Where’s my car? Someone must have stolen it!
might/may/could
+ perfect infinitive
We use might, may or could with
the perfect infinitive to say that we think something was
possible but we aren’t sure.
•
The thieves might have escaped by car but we can’t be sure.
•
He should be hour by now. He may have been delayed by a traffic jam or
something.
•
I can’t find my purse. I could have left it in the supermarket but I just
don’t know.
can’t +
perfect infinitive
We use can’t + perfect infinitive when
we feel sure something didn’t happen in the past.
•
I thought I saw John in town this morning but it can’t have been him – he’s
in Greece this week.
•
I can’t have left it in the supermarket – I had it on the bus on the way
home.
You can’t have
read the instructions properly. They’re perfectly clear.
practice