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24 We use modal verbs to express:
PERMISSION You can go to the cinema. In the evenings we could watch TV. You may kiss the bride.
I can swim.
I could swim when I was five.
POSSIBILITY Measles can be quite dangerous. This vase could be very valuable. He may be waiting for us at the airport. John might come to your party. Would John come with us if we asked him? SUGGESTION You could give Mary some flowers. Shall we buy her a hat?
NECESSITY We must buy some more vegetables. Semi-modals (have to/need to) are often preferred. NOT NECESSARY uses don’t have to or don’t need to/ needn’t We don’t need to buy any more vegetables. (It isn’t necessary) ADVICE You should go to the doctor’s tomorrow. . You must go to the doctor’s tomorrow! (emphatic advice) Semi- modals and other forms are often used. However, they sometimes change the level of intensity of the advice given. You ought to/had better/have to/ . . . . . . If I were you I would go to the doctor’s. OBLIGATION You must / have to study harder! I should be studying but I’m too tired. PROHIBITION You mustn’t eat any more chocolate. You should never repeat what you have just said. DEDUCTION-ASSUMPTION It couldn’t have been John because he’s in London. He drives a Ferrari. He must be rich. The plane should be landing any time now. He has studied very hard. He ought to pass. She will have plenty of time to get there. SPECULATION He may have gone to Spain with Mary. Someone might have already told his father. What would I have done without you? Where shall/will we be this time next year? a REQUEST Can I go to the cinema tonight? Could you lend me £5, please? May I leave the room? Would you please close the door?
Using Modal Verbs 