1、第二册第四单元 情态动词情态动词表示说话人对某种动作或状态的看法，不能单独作谓语，必须和实意动词或连系动词的原形一起构成谓语。情态动词没有人称和数的变化。1 can /could 表示“能力”（可用于肯定句、疑问句或否定句）。- Can you use chopsticks ? I can lift this stone. 注意can和be able to 的区别：can有现在时、过去时；可用于被动语态。be able to有各种时态；不可用于被动语态。You will be able to speak fluent English by the end of this term.I was
2、able to help you yesterday.在表达过去某个时间有能力干某事时，could表示虽有能力，但不一定做了；而was/were able to=succeed in doing/manage to do指“不但有能力，而且实际做了” 。Thefirespreadthroughthehotel,buteveryonewasabletogetout. 表示“允许”(=may),用于 疑问句中表示征询对方意见。You may/can borrow my bike. Can you lend me a hand? could用于一般疑问句时，肯定答语只能用can/may，而不能用co
3、uld。- Could you lend me a hand? - Yes, I can. 表示“可能性/推测”（一般用于疑问句/否定句）What you said cant be true. -Who can it be? -It cant be Dr. Smith. He has gone abroad.can有时用在肯定句中，表示“一时的可能性”，译作“有时候可能会”, 按照经验来说。 Babies are lovely, but sometimes they can be tiresome. “ could（不用can）+ have done ” 译为“过去本来能够”；cannot h
4、ave done表示“不可能已经做过了”，是must have done的反义。I could have lent you the money. Why didnt you ask me?The boy cant have finished reading the book so soon because it is difficult even to an adult. cant but do/cant help/ choose but do 不得不，只好。 I could not but admit that something was wrong. cannot too/ enough
5、“再也不为过”。 You cannot be too careful when you drive a car.2 may/might 表示“允许”(=can) ,可用于肯定句，疑问句或否定句。 You may smoke in here. - May I come round in the morning? - Yes, please./ Certainly. - No, you cant/mustnt. 表示“可能性/推测” 可用于肯定句或否定句。He may be on her way home at this moment. She may not believe your story
6、. might (不用 may) have done 表示“过去本可以做某事却未做；may/might+ have done表示对过去事情的推测，译为“过去可能”。You may have read some account of the matter. may+主语+动词原形，表示祝愿 May you have a long and happy life! May our friendship live long. may/might as well do最好/不妨 Perhaps I might as well stay at home tonight. may well do很可能；充分
7、理由；有充分理由可以 She has changed so much that I may well not recognize her.3 must 表示 “必须/应当”。 I must be off now. Must we hand in our composition now? Yes, you must./ No, you neednt/dont have to. must和 have to用法比较 must 更强调说话人的主观看法；而have to强调客观要求，且有更多的时态。 You will have to go back to receive continuing educa
8、tion. You dont have to /neednt tell them about it. 否定句中表示“禁止/不许”(mustnt 不能来表示推测) The teacher mustnt favor some children than others. if you must do sth.如果你非要/偏要/硬要；I must admit/say我得承认 Must you make so much noise while others are sleeping? 表示推测，语气比may肯定，只用在肯定句中。 He must be ill. Her face looks pale.
9、must+ have done表示对过去事情的推测，过去一定做过了。It must have rained last night, for the ground is still wet.4. need /dare用作情态动词时，主要用于疑问句和否定句中。 She neednt come at present. Need I do it again? Yes, you must./No, you neednt. Dare she go out camping herself? need/dare也可用作实意动词，可用在肯定句、否定句或疑问句中。 She doesnt need (to) com
10、e here again. The flowers need watering/to be watered. After a period of practice, you will dare to speak English in public. dared 是情态动词dare的过去式。 I dare say 我想，我认为 How dare you do? 你竟敢/怎么敢? neednt have done 表过去做了一件本没有必要做的事情。4 ought to/should 表示义务（应该/应当）。You should/ought to do it for your own good. s
11、hould用在某些表示“建议、命令、要求、必要性、渴望”等含义的词后面的从句中。suggest/insist/demand/require/urge /desirethat (should) do 用在if从句中，表示“万一” 。 If it should rain tomorrow, dont expect me. 用来表示一种估计的情况，“按理应当/估计”。They should be here by now, I think. should用来表示惊讶、意外，难以置信，意为“怎么会、居然、竟然”。 I didnt expect you should have finished the w
12、ork so soon. How should I know? should/ought to have done表示“本应该做某事，但事实上却没有做”；shouldnt/oughtnt to have done表示“本不该做某事，但事实上却做了”。You should have got up earlier. You shouldnt have told him about it. 5 shall 用于二、三人称的陈述句，表示命令 、警告、允诺 、威胁必然结果。 She shall do as she is told. You shall hear everything directly y
13、ou come. 用于第一、三人称的疑问句，表示说话人征求对方意见。 Shall I turn on the light, Mom? Shall the boy wait? 用于法律法规等文件中表示的义务或规定等。 It is announced that candidates shall remain in their seats until all the papers have been collected.6 will/would 用于第二人称的疑问句，表示征求意见或提出请求，would此时不表过去，而是语气更加委婉。Bring the fruit up to the dining r
14、oom, will you? Would Sunday night suit you? 用于各种人称的肯定句,表示说话人的愿望和决心,可译作表“愿意/肯/会”, 此时will可用于条件句中。If you will allow me, Ill see you home. 表示“习惯”或“倾向性”,常译作“老是/总是”；would表示过去习惯性动作 （可译成“会”）Oil will float on water. A drowning man will catch at a straw. The window wont open. (不用被动) He would sit there for hou
15、rs sometimes, doing nothing at all. 表示 决心/诺言/命令We will never talk about that subject again. I wont let him down in any way. 表推测，没有must的把握大。This will be the house youre looking for.情态动词表示推测意义时语气由弱到强为： might may could can ought to should would will must8. would /used to would用在某些含有虚拟语气的句子中。 would /use
16、d to两者均可表过去习惯性动作，但used to可用来强调或暗示今昔不同的对比，而would无此含义。He is an honest man, but when he was young, he used to tell lies. 注意以下固定用法would rather do sth. prefer to do sth.would rather do A than do Bprefer to do A rather than do Bwould do A rather than do Bprefer doing A to doing Bwould rather sb did sth (对
17、现在/将来的虚拟) would rather sb had done sth (对过去的虚拟)情态动词have done1. should （ought to） have done表示过去应该做而（实际）没有做的事情，含有责备或遗憾的语气，意为“本应该”；其否定形式为“should notought not to have done”，表示某种行为不该发生但却发生了。2. neednt have done表示过去没有必要做某事， 但实际上做了某事。3. must have done用于肯定句，表示“过去一定做过某事”，表示一种很有把握的推测。4. maymight have done表示对过去
18、情况的一种不太有把握的可能性推测，表示“过去可能大概已做了某事”；否定句表示“过去可能还没有做某事”。5. can/ could have done表示“过去本来可以做某事，但实际上没有做”、“过去可能有能力做”；用于疑问句中，表示“可能也许已做了某事吗？”。6. can/ could not have done表示“过去不可能做了”、“过去没有能力做”。7. would have done表示“过去本来做了某事，但实际上没有做成” ，用于虚拟语气中。巩固练习一、判断正误 (将错误之处找出并改正)1. I would rather stay at home than to go to the
19、cinema.2. You might not have laughed at his mistakes.3. You must have seen the film last week, mustnt you?4. My dictionary is left in the room; this one must not be mine.5. You must not hand in your exercises today.6. The child dared not to go into the dark room.7. He was a good runner, so he could
20、escape from the police.8. It was too dark here, and you might tell me earlier.9. We couldnt have walked to the station, it was so near. Yes. A taxi hadnt been at all necessary.10. The construction of the laboratory must have been completed by the end of next month.二、填入适当的词。1. Jenny_ have kept her wo
21、rd. I wonder why she changed her mind.2. Its nearly seven oclock. Jack_ be here at any moment.3. The boss has given everyone a special holiday, so we go to work tomorrow.4.When we got to the cinema, the film hasnt started yet, so we _ have hurried.5. Mr.White should _ (arrive) at 8:30 for the meetin
22、g, but he didnt show up.6. As far as I know, he is the last one to help others. He _ be prepared to give you a hand, though.7. As he had heart attack, he was told that he _ continue the work.8. The thief _ have climbed in from the kitchen window as all the other windows and doors were closed.9. John
23、ny, you _ play with the knife; you_ hurt yourself10. Nobody knows how people first came to these islands. They might _ (sail) from South America on rafts.参考答案：一、1.去掉第一个to 2. mightshould 3. mustntdidnt 4. mustcan5. 去掉not 6. dared not todidnt dare to 或dared not 7. couldwas able to8. might tellshould have told 9. couldnt neednt 10. mustwill二、1. should 2. should 3. neednt 4. neednt 5. have arrived 6. may/might 7. might not 8. must 9. mustnt; may 10. have sailed
