Choose the correct option for each gap below.
Modal verbs of deduction and speculation
We can use modal verbs to say if we believe something is certain or probable.
But the forms above are used to speculate about the present or future. If we want to talk about the past, we need to use the perfect forms of the modal verbs.
must have done
We use must have + past participle to say that we are quite sure that something was true or happened in the past.
- I can’t find my wallet! I must have dropped it in the taxi.
- You must have had a real scare when you saw the crocodile.
can’t have done
We use can’t/couldn’t have + past participle to say that we are quite sure that something did NOT happen or was NOT true in the past.
- You can’t/couldn’t have seen John last night. He was in hospital.
- She can’t/couldn’t have passed the test. She didn’t even open the books.
Note that for negative deduction we use can’t (NOT
- He can’t be that famous. (NOT
He mustn’t be that famous.)
could/might/may have done
We use might/may have + past participle to say that it’s possible that something was true or happened in the past.
- It’s been three days. They might/may have finished painting the house by now.
- If they left at 9, they might/may have already arrived.
Note that we use might not or may not (NOT
could not) to talk about a negative possibility.
- She might/may not have heard us. Knock again.
should/ought to have done
We use should have/ought to have + past participle to talk about a situation expected to happen in the past. This form is normally used for criticism.
- You should/ought to have already packed your things. We’re going to be late.
- He should/ought to have studied more. Nobody fails if they study.