Modals Deduction Past 50515

Modals Deduction Past We can use modal verbs to talk about how sure or unsure we are about something in the past just as we use modals in the present with a slight change in the form. He must be really happy about his promotion. (present deduction) He must have been very happy when he was told about his promotion. (past deduction) When we use a modal verb to talk about a situation where we are not expressing a fact but we are using deduction the form is MODAL + have + past participle (verb 3) 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. He’s not answering. I must have left my keys in the car. I can’t find them. 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 . I wasn’t listening. I might have been here when I was a child but I can’t really . Can’t have + past participle We use ‘can’t have + past participle’ for things that we are sure did not happen in the past. I can’t have left my phone at work. You phoned me when I was walking to my car. That’s it. It must be in the car. 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.

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.

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The thieves must have come in through the window. Look – it’s still open.

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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.

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The thieves might have escaped by car but we can’t be sure.

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He should be hour by now. He may have been delayed by a traffic jam or something.

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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.

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I thought I saw John in town this morning but it can’t have been him – he’s in Greece this week.

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I can’t have left it in the supermarket – I had it on the bus on the way home.

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You can’t have read the instructions properly. They’re perfectly clear.

- See more at: http://learnenglish.britishcouncil.org/en/quick-grammar/modals-deductionpast#sthash.Fvrc8mQa.dpuf