1、情态动词【情态动词】 又叫情态助动词。它们具有以下特点： 它们必须与其他动词连用，即：情态动词动词原形表示说话人对所述动作的看法，如需要、可能、意愿或怀疑等。 绝大多数情态动词没有人称和数的变化，即第三人称单数不加-s（以be和have 开头的情态动词短语除外）。 在意义上，情态动词具有“多义性”。例：can既可表示能力，又可表示可能、允许等意义。【情态动词的基本用法】1. can的基本用法： 表示体力或智力上的能力，即“能够，会”，可与be able to转换。例：He can speak English. = He is able to speak English. Can you pla
2、y basketball? No, I cant. 如果表示将来具备的能力，要用will be able to。例：If I have a good sleep, I will be able to do the problem. 表示许可，主要用于口语，书面语一般用may。例：Can we go home now, please? No, you cant. You can only smoke in this room. You cant keep the library books for more than a month. 表示“可能”，与may同义，但一般用在疑问句中。例：What
3、 can he possibly want? 在否定句中，否定形式cant表示推测“不大可能”。例：Anybody can make mistakes. The news cant be true. 与第一、二人称连用时，还可以就可能的解决问题的方式或可能的行为提出建议。在这里，也可用could使语气婉转。例：Can / Could we meet again next week? 下周我们可以再见面吗？What shall we do? 我们怎么办呢？ We can / could try asking Lucy for help.我们可以请露茜帮忙试试看。You can / could h
4、elp me with the cooking. 你可以帮我做饭。2. may的基本用法: 表示“许可”，用can比较口语化。例：You may / can come if you wish. 如果你想来，你就来。You may not pick flowers in this park. 本公园内不许摘花。（may not表示按规定不许可，如果用mustnt则表示说话人不许可。）May I smoke here? 我可以在这里抽烟吗？No, you mustnt.不行。（mustnt表示明确的禁止。） 肯定句中表示推测，“可能”。例：It may rain tomorrow. 明天可能会下雨
5、。The news may not be true. 这个消息可能不会是真的。注意：如果在疑问句中表示“可能”，通常用can。例：Can it be true? 那会是真的吗？Who can he be? 他究竟是谁呢？ 【注意】：May I/we？Yes, you may./No, you mustnt.3. must的基本用法: 表示必须，强调说话人的主观意志。例：I must go now, or Ill be late. You must be here by ten oclock. 【注意】：表示“必须“时，must的否定式为neednt ，或dont have to ,而不是mus
6、tnt。也就是：Must I/we do it now？Yes, you must . No, you neednt /dont have to .例：Must I go with them?No, you . 表示推测，一般只用于肯定陈述句,表示非常肯定。例：She didnt look at me. She must be angry. 她不朝我看，一定是生气了。He is good at English. He must know the word. 他英语好，准知道这个词。You must be Mr. Jones. 想必您就是琼斯先生吧。4. have to的基本用法：have to
7、可视为情态动词，但它与其他情态动词在用法上稍有不同。其他情态动词没有人称和数的变化，而have to却有人称和数的变化，要视主语的不同而变化。例：I / You / We / They have to. He / She / It has to. You dont have to.Does she have to?have to =have got to，意思是“必须，不得不”。和must不同之处：must强调主观需要have to强调客观需要。例：Sorry, I have to leave now. 对不起，现在我得走了。Ive got to go to a meeting. 我得去参加一
8、个会议。Will he have to work deep into the night? 他将不得不工作到深夜吗？5. need的基本用法：need的基本词义是“需要”，它既可作情态动词，又可作实义动词。 need用作情态动词时，只用于否定句和疑问句。它只有一种形式，后接动词原形。例：I dont believe you need worry. 我相信你没有必要焦急。Need we go so soon?我们需要这么早就去吗？ Yes, we must. / No, we neednt.是的，必须。不，不必。So I neednt tell him, need I? 所以我不需要告诉他，对吧
9、？请比较以下两句话的不同意思：You neednt buy the coat. 你没有必要买那件外衣。（你还没买）You neednt have bought the coat. 你没有必要买这件外衣的。（而你却买了）【注意】：Need I/we？Yes，you must ./No, you neednt / dont have to . need用作实义动词时，有时态、人称和数的变化。如果人作主语，一般后接带to的动词不定式。即need to do sth；如果物作主语，一般后用need to be done 或need doing sth。例如：I need to look up this
10、 word in the dictionary. My watch needs mending/to be mended. 我的手表需要修理了。We dont need to work today. (= We neednt work today.) Does he need to go right now? (= Need he go right now?) 6. had better的基本用法：had better常略作d better。现代语法认为它是一个助动词，因为它后接不带to的动词不定式。had better do sth意思是“最好做某事；还是做某事比较好”。例：Youd bet
11、ter get some sleep. 你最好睡一会儿。Youd better not do that again. 你最好别再做那件事。What had we better do now? 我们现在怎么做才好呢？Hadnt we better tell her the truth? 我们是否最好不告诉她真相?【注意】：Youd better.表示劝告或委婉的命令，对长辈不宜使用。7.could, should, would, might表示推测：. must多用于肯定句中表示把握性极大的推测,意思为“一定、肯定”。如: You have worked hard all day. You mu
12、st be tired. 你已辛苦工作一整天了,一定累了。The book must be his. His name is on the cover. 这本书一定是他的,封面上写着他的名字。【注意】 must不表推测时,在肯定句中意思为“必须(强调内在的职责)”,在否定句中意思为“不许、禁止”,以它开头的疑问句否定回答常用neednt或dont (doesnt) have to。如:We must obey the traffic rules. 我们必须遵守交通规则。Cars mustnt be parked here. 此处严禁停车。Must we hand in the papers t
13、his week? 我们必须本星期交论文吗?No, you neednt. 不,你们不必(本星期交)。 . can / could多用于否定句、疑问句或感叹句中表示推测、怀疑,两者在时间上没有差别。用can时不相信的程度更强一些, cant常常译为“不可能”。如:The man under the tree cant be Tom. Hes gone to England. 这个人不可能是Tom,他已经去英国了。Can it be true that he was fooled by a five-year-old boy? 他被一个五岁的孩子愚弄了,这能是真的吗?Could this be
14、an excuse? 这会不会是个借口?How can you be so careless! 你怎么这样粗心!.may / might多用来表示把握性不大的推测,意思为“也许、可能”, might比may的把握性更小一些。may not在否定句中常常译为“可能不”。(注意区分“不可能”与“可能不”在把握性大小上的差异。)如:Mr. Wang may know Professor Lis telephone number.王先生也许知道李教授的电话号码。This might be the key Tom has been looking for.这可能就是汤姆一直在找的钥匙。She may n
15、ot be there today. 今天她可能不在那儿。一、 典型例题 【中考链接】（ ）1Who is the man over there? Is it Mr. Li? No, it _ be him. Mr. Li is much taller.A. mustnt B. may no C. cant D. neednt（ ）2Must I go with them tomorrow？ No，you _. A. mustnt B. shouldnt C. neednt D. cant（ ）3_ I take some photos in the hall? No, you _.A. Ca
16、n, neednt B. Must, mustnt C. Could, wont D. May, mustnt（ ）4Dad, must I finish my homework today?No, you _. You may do it tomorrow.A. neednt B. mustnt C. dont D. wont（ ）5The lake is said to be dry. Is that true? It _.Look, some kids are swimming in it.A. must be true B. cant be true C. may not be tru
17、e（ ）6What is your mother going to do this Saturday? Im not sure. She _ go to see my grandmother. A. canB. mustC. may（ ）7Susan has bought a large house with a swimming pool.It _ be very expensive. I never even dream about it.A. must B. might C. cant D. shouldnt （ ）8Listen! Is Professor Johnson giving
18、 a report in the hall?No, it be him. He has gone to Japan.A. needntB. may not C. mustnt D. cant（ ）9Lets go to the West Hill Park by taxi.Oh, it is not far away from here. We _take a taxi.A. couldnt B. mustnt C. neednt D. cant（ ）10Can you play the piano?Yes, I _. I often practice it on weekends.A. ne
19、ednt B. need C. cant D. can 三、课后练习 一、用can, may, must, need, have to, had better的适当形式填空：1. You _ return the library book on time.2. I _ (not) find the way to the hospital. _ you show me the way?3. _ I finish the work right now? No, you _ (not). You _ do it later.4. He said he _ (not) come tonight.5.
20、Her mother was ill. She _ stay at home and look after her.6. Its time for class. You _ stop playing football or you _be late for class.7. We _ start right now, or they would get there first.8. The cloud is lifting, so it _ (not) be a rainy day tomorrow.二、选择填空（ ）1.Do we have to finish our homework th
21、is afternoon?Yes, you _.A. must B. can C. may D. need（ ）2. Must I be in hospital for a week， Doctor? No， you . You can go back home tomorrow. A. mustnt B. neednt C. must （ ）3. The desk is not dirty. You _clean it.A. mustntB. shouldntC. neednt C. cant（ ）4. May I watch TV for a while？No, you _. You ha
22、ve to finish your homework first. A. shouldnt B. neednt C. mustnt D. wont（ ）5.Is Jessica giving us a speech this evening? No, it _be her. She_ to Japan.A. mustnt; has gone B. mustnt ;has been C. cant ;has gone D. cant ;has been（ ）6. Its the library! So you_ know shouting is not allowed here.A. canB.
23、 mustC. needD. may（ ）7. Boys and girls, dont forget your report . It _ today. A. cant finish B. cant be finished C. should finish D. should be finished（ ）8.Mr Smith must have been to your home this morning. No, he _ ,because he didnt know my address.A. couldntB. cantC. mustntD. may not（ ）9. Must I m
24、op up the window now? No, you_.A. needntB. cantC. shouldntD. mustnt（ ）10. Is Lucy knocking at the door?No. It _ be Lucy. She is in Japan now.A. neednt B. must C. cant（ ）11. Another cup of coffee?No, thanks. I _ be off. Mary is waiting for me.A. can B. may C. must D. might（ ）12. Im a little tired. Le
25、ts go to the zoo by taxi.We take a taxi. Its not far from here. A. cant B. mustnt C. couldnt D. neednt（ ）13. If the traffic light is red, you _ cross the road. Its very dangerous.A. dont B. mustnt C. neednt D. wouldnt（ ）14. Must I finish watering the flowers now?No, you_.A. must B. wont C. neednt D. cant（ ）15. I cant give up smoking, doctor.For your health, Im afraid you _.A. may B. can C. have to D. must5
