English Grammar in Use

1. 情景语法 3：情态动词 could (do) & could have (done) ; must & can’t ; might as well needn't do & needn't have done; should; can & could; if I do & if I did; I wish I did; I wish ...would English Grammar in Use

2. Sometimes “could” is the past of “can”. Sometimes “could” isusedin the future (especially to make a suggestion) could (do) & could have (done) • A: What shall we do this evening? • B: We could go to the cinema.

3. Compare vs could (do) could have done I'm so tired. I could sleep for a week. (now) I was so tired. I could have slept for a week. (past)

4. note could have done Most often, we use could have (done) for things which were possible but did not happen: but he didn't hurt himself you had opportunity to stay with her but you didn't  Jack fell off a ladder yesterday but he's all right. He's lucky - he could have hurt himself badly.  Why did you stay at a hotel when to New York? You could have stayed with Barbara.

5. must & can’t • My house is very near the motorway. • It must be very noisy.

6. note We use “must” to say that we feel sure something is true: must Traveling is tiring and you've been traveling all day, so you must be tired.)  You've been traveling all day. You must be tired.  'Jim is a hard worker.' 'Jim? A hard worker? You mustbe joking. He's very lazy.'  Carol mustget very bored in her job. She does the same thing every day.

7. note Can’t We use “can't” to say that we feel sure something is not possible: (People are not normally hungry just after eating a meal. You've just eaten, so you can't be hungry.)  You've just had lunch. You can't be hungry already.  Brian said he would definitely be here before 9.30. It's 10 o'clock now and he's never late. He can't be coming.  They haven't lived here for very long. They can't know many people.

8. (Helen and Clare have just missed the bus. The buses run every hour.) might as well Helen: What shall we do? Shall we walk? Clare: We might as well. It's a nice day and I don't want to wait here for an hour.

9. note might as well '(We) might as well do something'= (We) should do something because there is nothing better to do and there is no reason not to do it. You can also say 'may as well'. = taxis are just as good, no more expensive or ... I may as well go now  A: What time are you going? B: Well, I'm ready, so I might as well go now.  The buses are so expensive these days, you might as well get a taxi.

10. Compare vs must do mustn't do You mustn't do something' = it is necessary that you do not do it (so don't do it) You must do something' = it is necessary that you do it

11. Compare vs must do mustn't do Don't tell anybody what I said. You must keep it a secret. We haven't got much time. We must hurry. It's essential that nobody hears us. We mustn't make any noise. You must keep it a secret. You mustn't tell anybody else. (= don't tell anybody else)

12. (George had to go out. He thought it was going to rain, so he decided to take the umbrella.) needn't do & needn't have done • I think it's going to rain. I'll take the umbrella.

13. (But it didn't rain, so the umbrella was not necessary. ) needn't do & needn't have done • I needn't have brought the umbrella.

14. Compare vs needn't do needn't have done That shirt isn't dirty. You needn't wash it. Why did you wash that shirt? It wasn't dirty. You needn't have washed it.

15. Compare vs didn’t needn't do needn't have done I didn't need to ... = it was not necessary for me to... (and I knew this at the time): 'I needn't have (done) something' = I did something but now I know that it was not necessary

16. Compare vs didn’t needn't do needn't have done I didn't need to get up early, so I didn't. I didn't need to get up early, but it was a lovely morning, so I did. I got up very early because I had to get ready to go away. But in fact it didn't take me long to get ready. So, I needn't have got up so early. I could have stayed in bed longer.

17. should He should be wearing a helmet.

18. note should We use should when something is not right or what we expect. For example: (= she isn't here yet, and this is not normal  The price on this packet is wrong. It should be L1.20, not L1.50.  I wonder where Liz is. She should be here by now.  Those boys shouldn't be playing football at this time. They should be at school.

19. can & could Could you open the door, please?

20. note can & could We often use can or could to ask people to do things:  Can you wait a moment, please? Could you wait a moment, please?  Liz, can you do me a favor?  Excuse me, could you tell me how to get to the airport?  I wonder if you could help me.

21. If I do & if I did If I won a million pounds…

22. note If I do Sue has lost her watch. She thinks it may be at Ann's house. Ann feels there is a real possibility that she will find the watch.  SUE: I think I left my watch at your house. Have you seen it?  ANN: No, but I'll have a look when I get home. If I find it, I'll tell you.

23. note if I did Here, Ann is not thinking about a real possibility; she is imagining the situation and doesn't expect to find a wallet in the street.  Ann says: If I found a wallet in the street, I'd take it to the police.

24. She is imagining the situation. The real situation is that she doesn't know his number. If I did & I wish I did If I knew his number.

25. We use “wish” to say that we regret something, that something is not as we would like it to be. If I did & I wish I did I wish I had an umbrella.

26. Jill is complaining about the rain and wants it to stop. I wish ...would I wish it would stop raining.

27. note I wish ...would We use I wish ... would... when we want something to happen or when we want somebody to do something. The speaker is not happy with the present situation.  The phone has been ringing for five minutes. I wish somebody would answer it.  I wish you would do something instead of just sitting and doing nothing.