Grammar Modal verbs（情态动词）,How many modal verbs do you know?,1 can / could / be able to,2 may/might,3 must / have to,4 shall / should,5 will / would,6 need / dare,7 ought to,modal verbs,表示推测,不表示推测,情态动词的特点：,1.没有人称和数的变化 2.不能直接跟宾语，必须搭配实义动词或be动词的原形 3.情态动词的过去式往往不表示时态,can 与could 1.表示能力：会 在表示过去的能力时用could I can swim. 我会游泳 I could not read such a easy book when I was 7 years old. 我七岁时连如此简单的书都看不懂 2.表示允许，许可。常用在口语中 此时could不表示时态，而是表示比can语气上客气些 -Could I use your dictionary?我可以用一下你的字典吗？ -Yes, go ahead.可以，用吧（或Yes, you can.但不能说Yes, you could.) Can/Could you tell me the way to the zoo?你能告诉我怎么去动物园吗？,3.表示推测，用于肯定句（can罕见），否定句或疑问句。 但更常见于疑问句与否定句，在此种用法中，can 与could没有时态的区别，只有可能性大小的区别。can表示推测的可能性比could大。 Can he be ill at home?(他会是生病在家吗？) He cannot be at home.(他不可能在家) You mustnt smoke when you walk in the woods. You could start a fire.那样可能会引起火灾。 could/ can have done 表示对过去事情的推测 She cant have gone to school. Its Sunday. 4.表示理论上的可能性，指常有的行为或情形，意为有时会。 Peter can be really annoying . Peter 有时候会很讨厌 Accidents can happen to any drunken driver.醉酒的司机都有可能发生交通事故。,can的习惯用法 1.表示惊异，怀疑，不相信等态度，主要用于否定句和疑问词 How can you be so careless? 你怎么这么粗心？ 2.can but只好，最多不过 We can but do our best. 我们只好尽力而为 3.cannot too to 无论怎么样都不过分 You cannot be too careful to cross the road. 过马路时 你再小心也不过分,can 与be able to的区别 1.can 表示“能力“时，和be able to相当，许多场合都可以互相替换。但当叙述过去经过一番努力才能完成的事情或前面有特殊说明，你有能力，只能用be able to. Can you speak any foreign languages?你会说外语吗？（正） Are you able to speak any foreign languages?（正） The fire spread the building quickly but everybody could escape.(误) The fire spread the building quickly but everybody was able to escape.（正） 大火迅速蔓延到整栋大楼，但大家都逃出来了。 can表示又能力做，但不一定做。be able to在这里=manage to,2.be able to比can有更多的形式 No one could answer the question.没人能回答这个问题。 =No one was able to answer the question. When he grows up, he will be able to support his family. 当他长大了，他将可以养家糊口。 Frank is ill. He hasnt been able to go to school for one week. Frank 生病了，一星期没能去上学了 Im sorry for not being able to help you in time. 对不起，不能及时帮你的忙,may 和might,1.表示请求，许可，常译为“可以” 在口语中可以用can和could代替may，但在正式场合用may.表示允许时，可以用might，might不表示过去时，而表示语气婉转。 You may take this seat if you like.如果你喜欢你可以做在这。 May/Can/Could/Might I have a talk with you ? -May/Might I come into the room yo see my mother? -No, you musnt. She needs to have a good rest. may I 问句常见的肯定回答与否定回答,肯定回答，Yes, please. Certainly. Yes, of course. Sure Go ahead, please. 否定回答 No, you cant.(最常见) No, you mustnt(表示强烈禁止的意思) Please dont. Youd better not. I dont think you can. Im sorry its not allowed. 2.表示推测，可译为“可能，也许” Your Math teacher may/might be in his office. (一般情况下，might表示的可能性极小) The light isnt on. It may/ might be broken. 注意：用may表推测，一般不用于疑问句，在疑问句中通常用can来代替 Can he be at home? -Can it be true? -It may be, or it may not be.,3.用在目的状语从句中，构成谓语。 He wants to take a taxi so that he may get there in time. I arrivved at the airport earlier in order that I might meet him 4. 有时可用于祈使句，表示祝愿。 May you succeed. May you be happy. May that day come soon. 5.在机关，学校等的文书，公告里的“不得，禁止”，在正式场合下不用cannot表示，而用may not 或mustnt表示 Any book may not be taken out of the library.,6.may/might as well 这种结构表示有礼貌的劝告，常译为“还是.的好，不妨” Its too late. You might as well not go. There is nothing to do, so I may as well go to bed.,must 和 have to,1. must 表示有做某一动作的必要或义务，强调主观看法，可译为“必须，应该” Everyone must obey the rule. We must do everything step by step. 2. have to因客观使主语不得不做某事 You cant turn left here. You have to turn right. My eyesight is very poor, so I have to wear glasses for reading. tips: 在口语中 经常会用 have got to替代 have to Ive got to work on Sunday. 3.must 与have to 的区别,must和have to 在表示必须时，意思相近，但用法不同。 a.must表示主观看法，have to 表示客观的必要 I must study hard.(发自内心的决定) I have to study hard.(外界因素逼迫) b . msut 只有一种形式，而have to 有多种时态 They had to put off the sports meeting due to the bad weather. These two days he has had to take a rest at home. c. must 否定式和have to 否定式 意思完全不同 You must keep this secret. You mustnt tell anyone. mustnt表示禁止 You dont have to tell me the secret. dont have to= dont need to,4.must 用于表示推测，它的肯定程度比may,might,could 大的多，一般只用于肯定句。 a. must+do（这里的do通常是状态动词或系动词），表示对现在状态的推测。 He must be very lazy for his desk is untidy. b. must + be doing 表示对现在动作的肯定推测 Put on your clothes, you must be feeling very cold with only a shirt on. c. must have done 是对过去或状态的肯定推测 The ground is wet. It must have rained yesterday. 5.must 表示根据逻辑推理必然要发生的事情，可译为“必然会，总是会” We all must die.我们都会死。,6.must 有时可以用来表示“偏偏” Why must it rain today? When I was taking a nap, a student must knock at my door. will 和 would 1. will 和would 可用于第二人称疑问句，表示请求和建议等。would比will婉转 Will you have some tea? Would you pass this book to the student in the last row? 必背： Will/Would you?表示请求和建议的答复 肯定回答Yes, please. 是的，请。Certainly.当然可以 Sure.当然了。 All right. 好啊,否定回答：Im sorry, I cant.对不起，不行。 No, thank you. No , I wont. 2. will和would 可表示意志，愿望和决心，用于各种人称陈述句 I will do anything for you. They would not let him in because he was poorly dressed. 3.will 和would 可表示某种倾向或习惯性动作。will表示现在的习惯性动作，would表示过去习惯性动作。 He will surf the Internet every night. He woul