B2 Grammar: Modal verbs to express certainty and possibility

Modal verbs to express certainty and possibility

To express certainty about the present	·        Use must: She’s been in over 15 films, so she must be very well known. Note: we usually have a good reason for expressing this certainty, e.g. She’s been in over 15 films. ·        Use can’t or couldn’t for the negative (not mustn’t). You can’t be tired. You’ve just got out of bed! Mark couldn’t be coming to the party – he’s on holiday in America at the moment.
To express certainty about the past	·        Use must have + past participle: You have a very big part in the play. It must have taken you ages to learn all the lines. ·        Use can’t have and couldn’t have + past participle for the negative: She can’t have left her glasses at home – I saw her wearing them on the bus. She couldn’t have stolen the money because she’s far too honest!
To express possibility about the present or future	·        Use may, might or could: I may come and visit you next summer. We might go to the cinema this evening if we finish all our work in time. We’d better go out for a walk now because it could rain later. ·        Use may not and might not (not mayn’t or mightn’t) for the negative (not can’t or couldn’t which express certainty): Frankie is looking very pale. He may not be very well. Don’t cook any dinner for me because I might not be back in time.
To express possibility about the past	·        Use may have, might have, could have, may not have, might not have + past participle: It’s unlike Sally to be late. She may have overslept, or she might not have remembered the appointment.