Can and must

Can shows ability. Must shows strong obligation. Must may also show possibility.

In questions and negatives, can is often used to show logical possibility.

Complete the following sentences using can or must.

1. I can’t believe this. You …………….. be joking.

a) can

b) must

2. There is the doorbell. Who …………….. it be?

a) can

b) must

3. She hasn’t arrived yet. She ………………. have missed the train.

a) can

b) must

4. I am a little busy at the moment, but I ……………….. talk to you in the afternoon.

a) can

b) must

5. ‘Who can it be?’ ‘It ………………. be your dad. He is in Amsterdam.’

a) can’t

b) must not

6. ‘Where …………….. she have gone?’

a) can

b) must

7. You …………….. not worry.

a) can

b) must

8. Dogs ………………. be kept on a lead.

a) can

b) must

9. It ……………… have been terrible to live during the war.

a) can

b) must

10. I ………………. find my keys. I ……………… have left them at home.

a) can’t, must

b) must not, can

b) can’t, can

Answers

1. I can’t believe this. You must be joking.

2. There is the doorbell. Who can it be?

3. She hasn’t arrived yet. She must have missed the train.

4. I am a little busy at the moment, but I can talk to you in the afternoon.

5. ‘Who can it be?’ ‘It can’t be your dad. He is in Amsterdam.’

6. ‘Where can she have gone?’

7. You must not worry.

8. Dogs must be kept on a lead.

9. It must have been terrible to live during the war.

10. I can’t find my keys. I must have left them at home.