情态动词语法讲解

1、学习必备欢迎下载Modal Verbs情态动词有 can (could), may (might), must (must), have to, shall (should), will (would), need (need), dare (dared), ought to等。情态动词 无人称和数的变化。它不能单独使 用，必须跟其后的动词原形构成谓 语。情态动词的具体用法如下：一、can, could1、表示能力。a. Can you speak English?b. Can you finish this work tonight?c. Man cannot live without ai

2、r.Note:(1) can表示能力时,可用be able to 代替。a. I ll not be able to come this afternoon.(2)当我们要表示“某件事情已经 成功”时，应用 was/ were able to , 不能用coulda. He saw well and he was able to swim to the river when the flood happened.b. He was able to go to the party yesterday evening and he enjoyed himself very much.2、表示客观可

3、能性a. People who live near airports can have their hearing harmed.b. The boy can sometimes be very naughty.（表示某人或某物一时 的情况，“有时会。”）c. The invention can be improved.d. Even experts can make mistakes.e. He cant be in Beijing now because I saw him a moment ago.f. He had a lot of work to do last night, so

4、he couldnt have gone to see a film.Note:在肯定句中用can表示可能性时， 其含义是理论上的可能性，不表示实际的可能性，也就是说，不涉及 到是否真会发生。3、表示惊异、怀疑、不相信的态 度（主要用与否定句、疑问句或感 叹句中）a. Can this be true?b. How can you be so careless!c. This cannot be done by him.4、表示请求和允许。a. 一 Can I go now?一 Yes, you can.b. You can smoke if you want to.c. You can,t

5、pick flowers in this park.Note:could也可以表示请求）语气较委 婉，主要用于疑问句，不用于肯定 句，回答应用can一 Could I come to see you tomorrow?-Yes, you can. / No, Im afraid not.5、can的一些其他惯用法.cannot but, cannot help but, cannot choose but 初词原形， 意思为“不得不，只得。a. I cannot help but tell her the truth.2. cannot help doing stha. I cannot he

6、lp laughing.3. cannot too / enough, can never tooa. You cannot be too careful when you cross the street.b. I cannot thank you too much for your kindness; I owe my progress to you.二、may, might1、表示许可。a. You may go now.b. We may keep the books for two weeks.c. 一 May I smoke here?一 Yes, you may. / No, y

7、ou may not. / No, you mustnt.2、表示可能性a. He may be waiting for you at the station.b. They may have got lost.Note:表示可能性时，may不用于疑问 句。在疑问句中表示“可能”时， 通常用 “be likely to ” 或 “Do you think”这一结构。3、用于让步状语从句中a. However hard you may study, you cannot master English in a month.b. Dont give up whatever difficulties

8、 you may meet with.4、用于祈使句，表示祝愿。a. May you succeed!b. May we never forget each other!5、might常用于表示委婉的请求或 轻微的责备。a. You might post this letter for me if you are going near a post box.b. You might have let me know before!6、用于某些习惯用法中 may /might as well= had bettera. Its getting darker and darker. You may

9、/might as well go home.(2) may well +动词原形,向、思为“理所当然，有足够的理由”。a. He has grown up tall. You may well not recognize him.三、must, have to1、表示义务和强烈的劝告。意思为“必须”、“一定要”。a. You must finish your task ahead of time.b. You must talk to your daughter about her future.2、表示有把握的推测，意思为“一定是，“准是”。a. I failed in the exam.

10、 You must think I am stupid.He must be a college student, isnt he?b. You look happy. You must be having a good time.c. He looks tired. He must have stayed uplate last night, didnt he?d. You speak English so fluently. You must have learnedit for many years, havent you?3、表示肯定性或难以避免，意思为“必然会、” “肯定会”。a.

11、All men must die.b. Dont bet o horse races; you must lose in the long run.4、作“偏要”、“硬要”解。(1)常以第二人称为主语，意思指不耐烦过令人不愉快的事情。a. If you must smoke, at least you should do it outside.b. If you must know, Im going to help him look for an apartment.c. Why must you buy that car?(2)用于其它人称，表示主语“固执”或“不巧”的意思。a. The

12、car must break down just as we were starting our holiday.b. Jane was never a pleasant young girl. After you gave her your advice, she must go and do the opposite.5、must的否定有如下三种形式, 用于三种不同的场合。(1)当must表示“推测”时，其否 定含义为“不可能”。将mustbe 改为 cannot be;斗容 must have done 改为 cannot have done。a. It must be eleven 0

13、 clock now.It cannot be eleven 0 clock.b. You must have met him before.You cannot have met him before.(2)当must表示“必须”时，其否定含义为“不必”。将must do改为 need not do 或 dont have to do。a. You must get up at six tomorrow morning.You need not get up at six tomorrow morning. / You dont have to get up at six tomorrow

14、morning.(3)回答以must提问的句子，可 以如下形式进行肯定或否定形式作答。Yes, you must.a. Must we clean all the rooms?No, you dont have to.No, you neednY6、must和have to的区别四、ought to1、表示“应该（与should同义， 只是语气稍重一些，ought to强调 责任、义务），无人称和时态变化。a. You are his father. You ought to take care of him.b. You ought not to smoke here.c. Ought yo

15、u to smoke so much?五、shall, should1、在疑问句中，用于第一、第三 人称，表示征求对方的意见。a. Shall we do this evening?b. Shall I do it for you?c. Shall he come in or wait outside?=Do you want him to ？2、用于第二、第三人称，表不说 话人给对方的命令、警告、允诺或 威胁。a. You shall fail if you dont work harder.b. He shall be punished.c. You shall have the book

16、 after I finish reading it.3、用在法律、条约、规章、预言 等文件中，无论主语人称如何，一 律用shall,表示义务、规定。a. Each citizen shall carry his identification card when travelling.b. Death is certain to all; all shall die.4、should表示劝告、建议、命令， 其同义词是ought td在疑问句中， 通常用should代替ought tda. You should go to class right away. b. Should I open t

17、he window?c. The book is good and you should buy one.5、should表示义务，意指应该做，且有一种道义上的责任。a. You should help him because he is in trouble.6、should表示期待，用于表示合理的推断（“应该”）或明显的结果（“可能”）。切所期待的事儿几乎是事实，因此不是虚拟语气。a. It is three oclock. The football game should begin soon.b. You have prepared for the exam for several d

18、ays. It shouldnt be difficult for you.7、should表示惊讶、忧虑、惋惜等情绪，意思为“竟会，竟然。常用在 Im surprised; It worries me; Its a pity / shame; You cant imagine; It s unbelievable; You cant believe 等结构中。a. I find it astonishing that he should be so rude to you.b. It is a pity that you should be so careless.8、在疑问句中，常与how

19、, why, who 等连用，表示不合理难以相信或不 应该之事。a. How should I know?b. Why should I clean the blackboard again?六、will, would1、will表示意志、愿望和决心。a. I will never do that again.b. I will do all I can to help you.c. I wont let you down.d. will表示自然规律。a. Oil and water will not mix.b. If pure water is heated to 100 degrees

20、centigrade, it will boil.3、will表示习惯、倾向，多用于第三人称。a. He will sit there hour after hour doing nothing.b. Boys will be boys. 男孩终究是男孩。4、用在条件句中(1)表示意志，意思为insist on a. If you will go out without a coat, you will catch a cold.(2)表示有礼貌的请求或劝阻。a. If you will allow me, I will see you home.b. If you wont stop smo

21、king, you can only expect to have a bad cough.5、would可表示过去反复发生的动作或某种倾向。表示过去习惯时比used to正式，且没有“现在无此习惯” 的含义。常与 every day, often, frequently 等连用。a. During the vacation, he would visit me every week.b. When he lived in the country, he would take a walk after supper every day.6、would表示估计或猜想。a. It would be

22、 about ten when he left home.b. What would she be doing there?7、would表示谦恭的请求，常用于疑问句。a. Would you tell me the way to thestation?b. I would like to have a try.半情态动词：一、dare1、做情态动词时，主要用于疑问 句、否定句和条件句，以及含否定 或不肯定意义的语境。a. He dared t go out alone at night.b. Dare you go out alone at night?c. If the enemy dar

23、e come, we will drive them out.d. He dared not tell his father the result of the exam.2、How dare you /he？不是真正意义的疑问句，而是对所做的事表小 贝怒、阳贝 之息。a. How dare you open my drawer without my permission?b. How dare you say Im unfair?3、惯用语I dare say意思为“我以为；我想”。a. He is not here yet, but I dare say he will come late

24、r.二、need1、need作情态动词时，主要用于疑问句和否定句，没有过去时形式。a. You neednt come so early.B Need I finish the work today?一 Yes, you must. / No, you neednt. / No, you dont have to.三、used to1、used to表示过去的习惯动作或状态。（现在已不复如此）。a. He told us he used to play football when he was young.2、在疑问句、否定句有两种形式。a. Did you use to go there t

25、o see your brother? Yes, I did. No, I didnt.Used you to go there to see your brother? Yes, I used to. No, I usednt.四、had bettera. We had better go now.b. You had better not tell him the news.五、would rathera. Id rather do it right now.b. Id rather not tell him the news.情态动词+不定式的完成式1. could +不定式的完成式“c

26、ould have +过去分词”表示 “过去可以做而实际上未能做某事” （can的完成式仅用于否定句 和疑问句中）。否定式 “cant / couldnt have+过 去分”表示“过去不可能发生的事 情”。疑问形式和否定形式表示对过 去发生的行为怀疑或不肯定。用“can” 语气较强烈，“could”语 气较委婉。a. The boy could have finished his homework. ( But he didnt.)b. He could have done better, but he didnt try his best.c. We could have finished

27、 the task, but it was always raining.d. Where could Mary have gone?e. Can he have written the book alone?f. Uncle cant have arrived in Paris this morning.g. They cant have gone out because the light is on!2. may / might + 不定式的完成式“may / might +过去分词”表示对过去发生的行为的推测。might所表示的可能性比may小，语气较委婉。a. Alice might

28、 have gone to bed because there is no light in her room. b. The visitors might have taken a later tram.c. He may have finished the exercises, but he didnt hand in.d. He might not have finished his homework.3. must +不定式的完成式“must +过去分词”的结构常用在肯定句中，表示对过去发生的行为的推测，意为“一定，想必”。 它的否定或疑问形式用 can代替must。a. The sp

29、y must have taken the other way.b. Mr. Smith must have studies Chinese before,hasnt he?c. It must have rained last night, didnt it?4. neednt +不定式的完成式“ neednt +过去分词”表示本 来不必做某事而实际上做了某事。a. You neednt have bought thedictionary.b. The parents neednt have given the boy so much money.Note:1) didnt need to do指“没有必要做而实际上也没有做某事。”a. I didnt need to clean the windows.My sister did it.b. I got up very late this morning as I didnt have / need to go to work.5. should /