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情态动词

（一）情态动词的含义：

情态动词表示说话人对某一动作或状态的的态度，认为“可能”，“应当”，“必要”等。

情态动词不能单独作谓语，必须和不带to的动词不定式连用。情态动词没有人称和数的变化。

（二）几种主要的情态动词：

1. 表示可能的情态动词: may, might, could , can, must,

（1）may , might, could 都可以用来表示可能性，意思是“可能”，“也许”，它既表示现在的可能性，也表示将来的可能性： They may be waiting at the station.

You’d better take an umbrella. It might rain tonight. The phone is ringing. It could be Tim.

I haven’t decided where to spend my holidays. I may go to Ireland. The bus doesn’t always come on time. We might have to wait a few minutes.

它们的否定形式是:

may not, might not 意思是 “可能不”

I’m not sure whether I can lend you any money. I may not have enough money.

It might not be true.

Ann may not come to the party tonight. She isn’t well.

（2）may, might, could 后面接 have done 的形式，表示一种过去的可能性，是对过去动作的推测。 He may have left yesterday.

——I wonder why he was in such a bad mood yesterday. ——He may not have been feeling well. He might have known about it.

Tom could have taken it; he was here along yesterday.

（3）must 也表示比较有把握的推测, 是有一定事实基础之上的判断: The police are stopping all cars. They must be looking for the escaped prisoner.

The light is on. They must be at home.

You have been traveling all day. You must be very tired.

（4） can 一般用在否定和疑问句中表示可能性.

You have just had lunch. You can’t be hungry already.

They haven’t lived here for very long. They can’t know many people. That couldn’t be John. I know he’s still out of town. There is someone outside.——- Who can it be. Can he still be alive after all these years?

（5）must, can’t , couldn’t 后面可以接 have done 表示对过去的判断.

The phone rang but I didn’t hear it. I must have been asleep.

Jane walked past me without speaking. She can’t have seen me. You couldn’t have forgotten my name. Exercise：

1. The restaurant ________ be very good. It’s always full of people. 2. The restaurant _____ be very good. It’s always empty. 3. ——Where is Bob?

——I’m not sure. He _____________ be having lunch.

4. Ted wasn’t at work last week. He ____________ （ be ） ill. 5. I left my bike outside the house last night and this morning it isn’t there any more. somebody __________ （ take ） it.

6. It rained every day during their holiday, so they _________ （ have ） a very nice time.

7. ——I was surprised that Sarah wasn’t at the meeting. ——She ____________ （ know ） about it. 8. ——I wonder why Kay didn’t answer the phone. ——She ___________ （be） asleep. 答案：

1. must 2. can’t 3. may/ might/ could 4. must have been 5. must have taken 6. can’t have had 7. might not have known 8. may have been 2. must , have to

（1）must 表示义务，或强制。

If you can’t finish the book by then, you must come and renew it. I must remember to write home.

Passengers must cross the road by the footbridge. （2）mustn’t 意思是不许可，不应该

You mustn’t take photographs in here. It’s forbidden. ——May I borrow this magazine?

——No, you mustn’t.

（3）needn’t 用来表示没有做?事的必要.

You can come with me if you like but you needn’t come if you don’t want to.

We’ve got plenty of time. We needn’t hurry.

I can manage the shopping alone. You don’t need to come with me.

（4）have to 也可以表示应该、必须，但 must 多表示主观意志， have to 往往强调客观需要。而且 have to 可以用在各种不同的时态。 You can’t turn right here. You have to turn left.

My eyesight isn’t very good. I have to wear glasses for reading. George can’t come out with us this evening. He has to work. We had to return home at 4 o’clock yesterday. You will have to come tomorrow. She doesn’t have to work on Sundays. What do I have to do to get a licence? Exercise：

1. We have enough food at home so we ____________ go shopping today. 2. There’s plenty of time for you to make up your mind. You __________ decide now.

3. You really ______ work harder if you want to pass the examination. 4. We couldn’t repair the car ourselves. We ____________ take it to a garage.

5. This is a valuable book. You ______________ look after it carefully and you ___________ lose it.

6. Julia wears glasses. She ______ wear glasses since she was very young. 答案：

1. don’t have to 2. needn’t/ don’t have to 3. had to 4.had to 5. must , mustn’t 6. had to

3. 表示能力的情态动词can, could, be able to

（1）can , could 表示能力，通常指由体力、知识、技能等所产生的能力，也可以表示由于客观原因而形成的能力。

We can see the lake from our bedroom window. Can you speak any foreign languages?

I’m afraid I can’t come to the party on Friday.

We can’t afford to pay the bill.

（2）could 为 can 的过去式

When we went into the room, we could smell something burning. She could speak three languages before she was eighteen.

（3）be able to 也可以用来替代 can

Helen is able to read well even though she is only three.

I had some free time yesterday, so I was able to write a few letters.

（4）如果表示特定的能力时，应该用 be able to，而不用 can/could。 The fire spread through the building quickly but everybody was able to escape.

They didn’t want to come with us at first but we managed to persuade them.

Exercise：Fill in the blanks：L

1. My grandfather was a very clever man. He _________________ speak five languages.

2. They didn’t want to come with us at first but we ________ persuade them.

3.. Laura had hurt her leg and ______ walk very well.

4. A girl fell into the river but fortunately we _______ rescue her. 5. I used to _________ stand on my head but I can’t do it now. 6. I looked very carefully and I _________ see a figure in the distance. 答案：

1. could 2. were able to 3. couldn’t 4. were able to 5. be able to 6. could

4. should , ought to 表示应该, 有责任, 义务做某事. （1）should用来提出建议，劝告。 You look tired. You should go to bed.

The government should do more to help homeless people. You shouldn’t believe everything that he said.

Margaret should pass the exam. She’s been studying very hard.

（2）should 可以用来表示推测，表示某事不太对头或像我们想象的那样： I enjoyed her first novel, so the new one should be good.

The boys shouldn’t be playing football at this time. They should be at school.

（3）ought to 可以用来替代，表示建议，劝告，应该做某事，或推测。