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情态动词
（一）情态动词的定义
    情态动词表示说话人对某一动作或状态的态度。
（二）情态动词的特点
1. 情态动词有一定的词义。
2. 情态动词不能单独做谓语，它必须和其他动词的原形一起构成谓语。
3. 情态动词没有人称，数的变化。
（三）情态动词的结构和意义
1.情态动词的基本句型
 肯定句： 主语+情态动词+动词原形+......
 否定句： 主语+情态动词+not+动词原形+......
 疑问句： 情态动词+主语+动词原形+......
2. 情态动词的意义
 must“必须” ； can/could“能，会” ； may/might “可以”； should“应该”；  would“愿，要” ； have to“不得不” ； need“需要”
（四）情态动词的基本用法
1.can (could主要指过去时间 )
1） 表示人或物本身所具有的能力，意为“能，能够，会” :   
  Two eyes can see more than one.   两只眼比一只眼看得清。
2） 表示可能（理论上或是逻辑判断上）    
  He can’t (couldn’t) have enough money for a new car.   他不可能有足够的钱买新车。
3） 表示允许：
   Can I have a look at your new pen? 我可以看一看你的新钢笔吗？
He asked whether he could take the book out of the reading-room.他问他可不可以把书带出阅览室。
4） 表示对现在动作或状态的猜测，主要用于否定句和疑问句中或感叹句中:
He can’t (couldn’t) be over sixty.   他不可能超过六十岁。
5） could表示比can更委婉客气的提出问题或陈述看法，指的是现在时间。
   Can (Could) you lend me a hand?  帮我一把好吗？
2. may (might)
1）表允许，询问或说明一件事可不可以做，might指过去时间；但在疑问句中might也可指现在时间，语气比may更委婉。
May (Might) I ask for a photo of your baby?   我可以要一张你宝宝的照片吗？
在回答以may引起的问句时，肯定回答是一般可仍用may,或Yes, please. / Certainly./Sure./Of course. ；否定回答根据说话人的语气由强到弱分别选用must not(mustn’t)（禁止）/ had better not（最好别）/ may not（不行）
2) may表可能,但所表示的可能性不如can所表示的那样肯定。might可以指过去时间，也可以指现在时间，但语气更加不肯定。
He may be at home.   他可能在家。
They might be having a meeting, but I’m not sure.   他们有可能在开会，不过我不肯定。
3. must（have to表示客观需要）
1）表示 “必须”（主观看法）时，用于肯定句或疑问句；用于否定句时表示“禁止”。
We must do everything step by step.   我们一切都必须循序渐进地做。
2）表示揣测。意为“想必、准是、一定”等，只用于肯定句。
He must be ill. He looks so pale.   他准是病了。他的脸色苍白。
3)must的疑问句，肯定回答用must， 否定回答用needn’t或don’t have to。
4. should
1）表责任或义务，意为“应该”，用于各种人称。
You should be polite to your teachers.   你对老师应该有礼貌。
2）表推测，意为“想必一定、照说应该、估计”等。
The film should be very good as it is starring first-class actors.  
这部新电影是一流演员主演的，估计拍得很好。
5.will
1）表意愿,用于各种人称。
I will do anything for you.   我愿为你做任何事。
2)will在疑问句中用于第二人称，表示询问对方的意愿或向对方提出请求
Will you close the window?  请你把窗户关上好吗？
6.would
1）will的过去式，表示过去时间的“意志、意愿”。
They would not let him in because he was poorly dressed.   他们不让他进去因为他衣着破旧。
I said I would do anything for you.   我说过我愿意为你做任何事。
2）would用于现在时间，表示比较委婉地提出请求、建议或看法。
Would you like another glass of beer?   再来杯啤酒好吗？
7.need
1)need作为情态动词，主要用于否定句，疑问句；作为实义动词可用于肯定句，否定句或疑问句中。
You needn’t telephone him now.   你现在不必打电话给他。
2)回答由need引起的问句时，肯定回答一般用must，否定回答是用needn’t
--Need I come?  --Yes, you must.  --我需要来吗？  --需要。
情态动词练习题
(一) 单项选择
1. "__________ I take it out?"   "I'm sorry, you __________."
  A. Could ...couldn't   B. Might...might not    C. Could...can   D. May...can't
2. You were stupid to climb the tree. You __________ hurt yourself.
  A. may   B. might   C. will   D. might have
3. You __________ those letters. Why didn't you ?
  A. should post   B. should have posted   C. must have posted   D. would post.
4. All the lights are on, the Smiths __________ up.
  A. must get   B. is getting   C. must be getting   D. would get
5. He __________ lead a horse to the water but he __________ not make it drink.
  A. will...can   B. may...can   C. may...dares   D. dare...can
6. "Need we do this job now?"    "Yes, __________."
  A. you need   B. you should   C. you must   D. you can
7. __________ to have lunch with us today?
  A. Do you likes   B. Would you like   C. Will you liked   D. Have you liked
8. He said that you __________ watch TV all the evening if you wished.
  A. may   B. must   C. can   D. might
9. -Is John coming by train?     --He should, but he __________ not. He likes driving his car.
  A. must   B. can   C. need   D. may
10. Peter __________ come with us tonight, but he isn't very sure yet.
  A. must   B. can   C. may   D. will
11. Michael __________ be a policeman, for he's much too short.
  A. needn't    B. can't   C. shouldn't   D. won't
12. I thought you __________ be hungry, so I have brought you some cakes.
  A. may   B. might   C. can   D. could
13. Come on! We __________ hurry because there isn't much time left.
  A. may   B. must   C. can   D. need
14. Amy did best in the English test. She __________ hard last week.
  A. must have working   B. should have worked   C. should work   D. must work
15. ---I stayed at a hotel while in New York.   
  ---Oh, did you? You  __________ with Barbara.
  A. could have stayed   B. could stay   C. would stay   D. must have stayed
16. It's nearly seven o'clock. Jack  __________ be here at any moment.
   A. must   B. need   C. should   D. can
17.—Would you like to drink some juice?
  — Thanks._________,but I have drunk a lot if tea.
A. I’d love to  B.I think so  C.I’m afraid not  D. I don’t think so.
18.—May I smoke here?
—No, you______! Look, there is a “NO SMOKING”sign here.
A.may   B.may not   C.needn’t   D.mustn’t
19.—Listen!Helen is singing in the next room.
   —It_____be Helen. She has gone to Beijing.
A.can’t   B.mustn’t   C.may   D.should
20.—What do drivers do when the traffic lights turn red?
   —They______stop and wait till the green light.
A.must    B.can     C.may    D.need
(二)根据语境用适当的情态动词填空：
1.“________I leave school now?”“No, you_______clean the classroom.”
2.It’s time for class. You________stop plalying football, or you_______be late for school.
3.“_______they answer the queation in Russion?”“No, they________.”
4.—________I hand in my paper now.
—No, you _______.But you________hand it in tomorrow.
5.“________you skate?”“No, I________.But my brother_________”
6.We_________cross the street carefully.
7.He is very clever. He_________know the answer.