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1、Unit 5 Discovering Useful StructuresModal verbs DefinitionA modal verb is a type of verb that is used to indicate modality that is, likelihood, ability, permission, and obligation. Some commonly used modal verbs: can, could, may, might, must, ought to, shall, should, will, would Grammatical Features
2、 在形式上，情态动词没有实义动词的各种变化，只有could, would, had to, might 等几个过去式，其他情态动词如must, ought to等的过去式皆与现在式同形。 在意义上，大多数情态动词有多个意义，如can 可以表达“能力”“可能”“许可”等。 在用法上，情态动词须后接 ，构成谓语动词。无 和 。Functions can / could1. 表示 ，相当于be able to, 常译为“会，能”。can表示 ，could表示 He can ride a bike now, but he couldnt a few weeks ago.2. 表示 。can多用于 和
3、中，但也可用在肯定句中；could表示过去的可能，多用于 中。 That cant be Mary - she has gone to school. I told the boss that I couldnt finish the work in such a short time.3. 表示请求或允许，译为“可以”。表示此意时，用could语气更委婉。 - Can/Could I borrow your bike? - Sure. may / might1.表示 。might比may语气更委婉。用“May I.?”征询对方许可时比较正式和客气,而用“Can I.?”在口语中更常见。 -
4、May I open the window? - Certainly. 注意：答语避免使用may，以免显得太严肃或太不客气2. may用于祈使句,表示 。 May you succeed! May you have a good journey! 3. 固定搭配: may/might as well表示“还是为好,不妨” You may as well stay longer. must / have to1. must表示“ ”。在回答以must开头的一般疑问句时,如果是否定回答,不能用mustnt (禁止,不准),而应用 或 (不必)。 Must we hand in our exerci
5、se books today? Yes, you must. / No, you dont have to. / No, you neednt.2. must是说话人的主观看法, 而have to则强调客观需要。 The play isnt interesting. I really must go now. I had to work when I was your age. shall, should / ought to1. shall用于第一、三人称的疑问句中,表示 。 What shall we do this evening?2. shall用于第二、三人称,表示说话人给对方的 、
6、 、允诺、威胁或决心。 You shall fail if you dont work hard.3. shall还可用于正式文件、法律、规章制度等,表示 。 The president shall hold office for five years.4. should常与what、how、why等词连用,表示意外、惊讶等情绪,意为“ ”。 I dont know why you should think that I did it.5. should与ought to表示 ,意为“应该”,也可以表示可能性,意思相当于will probably。 We should / ought to a
7、ll work together to draw a new and better blueprint for the sake of succeeding generations. will, would / used to1. will、would表示 等,would语气更 。 Will/Would you pass me the ball, please?2. will、would可表示意愿。 He will donate money to the poor although he is not wealthy.3. will还可表示“ ”,表示一般规律或真理。 Fish will di
8、e without water.4. would表示过去 的动作或某种倾向。 During the vacation, he would visit me every other day.5. used to表示 ，现在不再这样。 He used to be late, but now he is the first one to arrive at school every day. dare / need1. dare和need作为情态动词时,常用于 句和 句中。 Need I tell her the news at once? He dare not go to school alon
9、e.2. 这两个词也可以用作 动词。 Jack needs to help her because she is in trouble. She didnt dare to stay at home alone. had better / would rather1. had better“ ”，缩写为 d better，否定为had better not , 表示提出 、 等，含有“应该做某事，有义务做某事”之意，一般适用于对晚辈、平辈。 Itshalfpasttwo.Wehadbettergohome.2. would rather “ ， ”缩写为 d rather，否定为would r
10、ather not. He would rather starve than beg for food. 情态动词表推测注意： 可能性可分为 可能性和具体事情 可能性两种。 客观的可能性并不表示具体某事是否会发生,而用来说明 。 情态动词can可用于肯定句中表示 的(或理论的)可能性,而表示具体事情实际发生的可能性时,can 一般不用于肯定句。如： Accidents can happen on such rainy days.在这样的多雨天气里可能会发生事故。(客观的可能性) We may go to the cinema tonight, but we are not sure yet.今
11、晚我们可能去看电影,但还没确定。(实际可能性,不用can)表示具体事情实际发生的可能性的层次(由强及弱)比较Examples V情+have done 情态动词原形+have done 表示 。 情态动词过去式+have done 还可以表示 意义。试比较： They may have just graduated from university. They might have just graduated from university. He cannot have forgotten it. He couldnt have forgotten it.Exercises1. With s
12、o much work on hand, you _ to see the game last night. A. mustnt go B. could have goneC. shouldnt go D. shouldnt have gone2. - I saw Mary in the library yesterday.- You_ her. She is still abroad.A. mustnt see B. cant have seen C. mustnt have seen D. couldnt see3. Aunt Mary _ the train; otherwise she
13、 would have arrived here by now.A. must have missed B. should have missedC. missed D. might miss 4. Jim says we _ stay in his house as long as we leave it clean and tidy. A. must B. can C. need D. should5. In todays information age, the loss of data _ cause serious problems for a company. A. needB.
14、should C. can D. must6. I cant find my purse. I _ it in the supermarket yesterday, but Im not sure. A. should leaveB. must have leftC. might leave D. could have leftTranslate the sentences into English1. The phone is ringing, but nobody answers. . (他一定不在家）2. I cant find my coat. . (我可能昨天落在店了)3. Its
15、a pity. . (你本应该邀请她来参加你的毕业典礼的)4. 办公室不能抽烟。 .5. - 他一定要去吗？ - 不，不需要。 .The past future tense 过去将来时意义：表示从 某一时间来看 的动作或存在的状态,表示一种倾向或推测。 基本结构：主语 + would (not) + V原形 常用于 从句和 中。 They said the letter inside would explain what it was all about. Tim thought that the problem would soon be solved.可以用于表示“过去将来”的其他结构 w
16、as/were (not) going to do表示说话者过去 做某事,或 表明过去即将发生某事(但不一定发生)。 They said they were going to attend a meeting. The dark clouds suggested that it was going to rain. was/were (not) to do表示过去计划中 的或按职责、义务和要求必须去做的事。 The press conference was to be held the next week. was/were (not) about to do表示过去 的事,不强调主观,一般不
17、能与具体的时间状语连用。这种结构后面常与并列连词 连用。 I was about to leave when it suddenly began to rain. was/were (not) + doing一些表示 的动词, 如go、come、leave、arrive等可以用过去进行时表示过去将来。 She told me she was coming to see me.Exercises1. Albert Einstein was born in 1879. As a child, few people guessed that he _ a famous scientist whose theories would change the world. A. has been B. had beenC. was going to be D. was2. At college, Barack Obama didnt know that he _ the first black president of the United States of America. A. was to becomeB. becomesC. is to becomeD. became5学科网（北京）股份有限公司