Modals for deduction (present & past)

 
We can use modal verbs to say how certain we are about things in the present  and also  to speculate about the past.



DEDUCTIONS ABOUT THE PRESENT

 must

We use must + infinitive without to when we feel sure that something is true because there’s very strong evidence.

       She must live near here because she comes to work on foot. [We don’t know where she lives but we’re sure it’s not far away].

 might, may, could

We use might, may or could+ infinitive without to 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].

 can’t

We use can’t + infinitive without to when we feel sure something is not true.

          It can’t be a burglar. All the doors and windows are locked. [He doesn’t know it’s not a burglar but he feels sure it’s not.]

DEDUCTIONS ABOUT THE PAST

 must + have+ participle/ been+ -ing

We use must + have+ participle when we feel sure about something in the past.

·                                 You must have been delighted when you heard you’d won the lottery.

·                                 Oh no! Where’s my car? Someone must have stolen it!

·                                 He must have been working all day- he looks exhausted.

might/may/could + have+ participle/ been+ -ing

We use might, may or could with the have+ participle 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…

can’t + have+ participle/ been+ -ing

We use can’t+ have+ participle 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.

    Source The British Council

Click HERE to practice

Present and Past Modals of Deduction with Sherlock Holmes from David Mainwood