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1、情态助动词的推测性用法能做推测性用法的情态动词：共九个情态动词非推测性用法推测性用法might / may表示许可表示可能could / can表示能力许可表示可能should/ ought to表示义务： “应该”表示必然：“应该”would/will表示意志表示推测：“估 计一定” must表示义务: “必须”表示必然: “一定”表推测时各个情态动词的程 度might May Could Can Should Ought to Would Will mustUncertainCertainThat might be George.That must be George.l按可能性的程度的高
2、低这九个情态动词 可分为三档 l一，表“可能”： might / may/could / can l二，表“很有可能”: should/ ought to / would/will l三，表“最有可能”:mustl 3.说话人推测的事情所发生的时间要根据情态 动词后的动词形式来定，可以是现在，过去， 将来，一般动词是非完成体形式则表示现在或 将来，动词是完成体形式则表示过去时间，但 完成进行体有两种可能一是相当于现在完成进 行体，一是相当于过去进行体 l He must be there.：现在 l Our team might win the race.：将来 l He must be wo
3、rking late at the office.：现在 （进行） l He must be calling tonight.：将来 l He may have come last year.：过去 l They cant have been waiting so long:表现在 完成进行 l He must have been dozing.：过去 “进行”l 2. 能做推测性用法的情态助动词的句法特征 l A. 其后的不定式可以采取完成体形式 l Eg. You must have thought about that. l B.其后的不定式可以采取进行体形式 l Eg. He must
4、 be working late at the office. l C.可以用于there存在句 l Eg. There must be some mistake. l D.其后的不定式为一般形式时通常是静态动词 。 l Eg. He must be there. l E.主语可以使表示无生命的名词词组。 l Eg. It must be George.例1： Are you coming to Jeffs party? Im not sure. I _go to the concert instead.A. mustB. wouldC. shouldD. might 析：选D。Im not
5、sure.的语境表明把握 性不大，当然我去参加音乐演奏会的可 能性就比较小了，故不用must应用 might例 2： -_the news be true? No, it_be true. A. Can, cant B. May, cant C. May, may not D. Must, mustnt l析： 选A。Cancant vs Must mustntlCan表示具有某种能力，表示推测意为“不可 能”，多用于否定句和疑问句中 l eg. 1.Where can he have gone？他可能会 去 l 2.It cant be true.这不可能是真的。 l 哪儿呢？ lmust表
6、“义务”或“强制”，表示主观的必要；表 推测意为“一定”,用在肯定句中。 l mustnt：表“禁止” l eg.1.We must clean the room.（表示我 们认为房间太脏了。） l 2.He must be at home before supper. （他晚饭前一定在家。） l 即表推测的must的否定形式是cant而不是 mustnt情态动词的完成式用法 （一）should /ought to have done本来应 做而未做，表达遗憾感情色彩should /ought not to have done本来 不应做而做了，表达遗憾感情色彩例1：I told Sally
7、how to get there,but perhaps I _for her. A. had to write it out B. must have written it out C. should have written it out D. ought to write it out析： 选C。分析语境可知，口头上告知 Sally如何去那里是不够的，所以我 本应书面告知，却有没书面告知之 ，显得应使用should /ought to have written表示遗憾之情。例2： I was really anxious about you, you_home without a wor
8、d.A. mustnt leaveB. shouldnt have leftC. couldnt have leftD. neednt leave 析: 选B。由语境可知，我真的为你担心， 所以你不应该一句话不说就离开 家，但实际上你确实这么做了， 显然应填shouldnt/ought to have left，表示责备。 （二） may/might have done可能已做 must have done 一定已做 cant have done不可能已做例1：-Where is my pen?- I _it. A. might lose B. wouldnt have lostC. shou
9、ld have lost D. must have lost答案： D D例2： The light in his room is still on, so he _ to bed. A. mustnt have gone B. must have gone C. shouldnt have goneD. cant have gone析：选D。由于他房间里的灯还亮 着推测，他不可能已经上床睡觉 了，应填cant have gone 。（三）might/could have done指本来可能/能做而实 际未做，表达遗憾的感情色 彩 You might have killed yourself本
10、可能送 命 I could have reported you本可以告发你 I could have passed the exam, but I failed. You could at least have sent five cards. 你本至少可以寄5张明信片的。（四）neednt have done表过 去本来不必做某事却做了l didnt need to do表示： 过去不必做某事, 事实上也没做。. l neednt have done表示： 过去不必做某事, 但事实上做了。 l John went to the station with the car to meet Mar
11、y, so she didnt need to walk back home. 约翰开车去车站接玛丽，所以她 不必步行回家了。 l John went to the station with the car to meet Mary, so she neednt have walked back home. 约翰开车去车站接玛丽，所以 她本不必步行回家了。 (Mary步行回家，没有遇上John的车。)l Eg1.You neednt have bought that house l Eg2.I neednt have gone to the station l 比较 l Eg3.I didnt
12、 need to go to the station因为没有必要不曾前往l 典型例题 l There was plenty of time. She _. l A. mustnt have hurried B. couldnt have hurried l C. must not hurry D. neednt have hurried l 答案D。neednt have done. 意为“本不必“， 即已经做了某事，而时实际上不必要。 l Mustnt have done 用法不正确，对过去发 生的事情进行否定性推断应为couldnt have done, “不可能已经“。 must not
13、 do 不可以（用 于一般现在时）。 情态动词的异化现象有些情态用于疑问句进行回答时 ，出现了异化现象，此时回答在 某 个角度不能继续使用该情态动词 ， 而改用别的动词。 例1：-Must I start at once?No, you_. A. needntB. mustntC. cantD. wont析：A。由语境可知该答句表示“不必 ”，而mustnt表示“不准、禁止”， 不符合语境，显然应使用neednt表 示“不必”，但肯定句回答继续用 must。例2：-Need I hand in my exercise book at once?Yes, you_. A. mustB. need
14、C. canD. will析：选A。根据规定need用于一般疑 问句作肯定回答应换成must,而作否 定回答时，使用need的否定式 neednt。exercisel There were already five people in the car but they managed to take me as well. It _ a comfortable journey. A.cant be l B.shouldnt be l C.mustnt have been l D.couldnt have been l Dl 1. You _Jim anything about. It was
15、none of his business.a. neednt have told b. neednt tell c. mustnt have told d. mustnt tell 2000 l 2. He _unwisely, but he was at least trying to do something helpful.a. may have acted b. must have acted c. should act d. would act 1999 l 3. Much as _, I couldnt lend him the money because I simply didnt have that much spare cash.a. I would have liked to b. I would like to have c. I should have to like d. I should have liked to l 4. As it turned out to be a small house party, we _so formally.a. need not have dressed up b. must not have dressed upc. did not need to dress up d. must not dress
