Unit 19: Modals | Grammar | B1
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Unit 19: Modals | Grammar | B1

‘Must’ for deduction

We can use must + be to express conclusions and assumptions from known facts (deductions). To make such conclusions/assumptions negative, we use can’t + be.
E.G. “She must be Mr Maxwell’s daughter.” “She can’t be. He hasn’t got a daughter.”

Must sometimes combines with verbs other than be:
E.G. He must earn a lot. He’s got three expensive cars.

We can combine must and can’t/couldn’t with have been and other perfect infinitives to draw conclusions about the past:
E.G. The thief must have been a professional burglar - he left no clues.
When I last saw Michael, he had long hair and a beard. He can’t/couldn’t have been the bald man you saw.


Study the examples in the box above and use must/can't/couldn't to complete the following sentences:

1. There's a letter for John. It _________ be the exam results he's been expecting.

2. I walked straight past him but he didn't say 'Hello'. He _________ have seen me.

3. Your daughter _________ have been studying in the library this morning. I saw her having coffee with a young man.

4. Mrs Perkins _________ have felt very proud when she saw her son on TV.

5. The little boy _________ like ice cream; that's the sixth one he's eaten today.

6. That _________ be the man who stole your wallet - he's a police inspector!

7. Barry is in Jamaica so you _________ have seen him this morning.

8. You _________ have been out of your mind when you married that man!

Using modals to express possibility

We use be or any other main verb when we are sure of our facts:
E.G. Tigers are wild animals. Tigers live in the jungle.

We use may/might/could + be/have been when we are referring to possibility:
E.G. There may/might/could be a hotel in the next village.
We may/might/could be running out of water.


Complete the following sentences with an appropriate main verb or may/might/could:

1. My father ____________ give you the job but I doubt it.

2. Is it true there ____________ life on Mars?

3. The police don't trust your uncle. They say he ____________ be lying.

4. Some people don't ____________ in ghosts; I'm not certain, but I think they ____________

5. He's been reading the map upside-down and now he says we ____________ be lost!

6. “____________ there any biscuits left?”

“Have a look in the cupboard; there ____________ be some there.”

7. Don't ever drive so fast again. We ____________ have been killed!


Rewrite the following sentences using may/might/could and retaining the original meaning:

e.g. Perhaps there's hope of finding the stolen jewellery after all.

There may be hope of finding the stolen jewellery after all.

1. It is possible that people will live on other planets in the future.

People ________________________________________________.

2. Maybe scientists will find a cure for AIDS by the turn of the next century.

Scientists ________________________________________________.

3. I'm not sure, but perhaps you're right after all.

You ________________________________________________.

4. The engine's making strange noises. It probably needs fixing.

If the engine's making strange noises, it ___________________.