【英语】2018届二轮复习：情态动词学案（10页） 11页

‎2018届二轮复习情态动词 一. 情态动词的类型和特征 ‎1. 类型 只作情态动词用的有：can（could），may（might），must，ought to。‎ 可作情态动词也作实义动词的有：need，dare。‎ 可作情态动词也作助动词的有：shall（should），will（would）。‎ 具有情态动词某些特征的有：have（had）to，used to。‎ ‎2. 特征 ‎ 情态动词有一定的词义，但不能单独作谓语，须和实义动词或系动词连用，构成谓语；且适用于主语的各种人称和数（have to例外），主语是第三人称单数时，要用has to。‎ 二. 情态动词的基本用法 ‎1. can与could 表示能力或客观可能性，还可表示请求和允许，她存在以下几种形式：‎ 肯定式 否定式 缩略否定式 现在式 can cannot can’t 过去式 could could not couldn’t ‎ 如Children can be troublesome sometimes.‎ 表示惊异、推测、怀疑、不相信的态度（主要用于否定句、疑问句中）。‎ ‎ 如This can’t be done by him.‎ can的习惯用法 A. can but的用法 ‎ can but“只好，至多不过”，如We can but do our best.‎ B. cannot help but，cannot help的用法 ‎ 二者都表示“不得不；不能避免；不禁”；但前者后加动词原形，后者加代词或动名词等。‎ ‎ 如The girl couldn’t help but live on herself.‎ ‎ When I try to speak, I can’t help making mistakes.‎ C. cannot … too“无论怎样……都不过分；越……越好”‎ ‎ 如We can’t thank you too much for what you have done for us。‎ ‎ We can not be too careful to cross the road.‎ ‎ 温馨提示： can与be able to：can表示有能力做某事，be able to表示通过努力、克服困难做成某事。如Although his leg was hurt, he was able to swim to the bank.‎ ‎ I believe I can work it out all by myself. could与be able to：could表示过去一般的能力，即不表示做与未做某事，而was / were able to表示有能力做并且成功地做了某事，相当于managed to do sth / succeeded in doing sth。如She could sing like an angel when she was a child. The fire spread through the hotel very quickly but everyone was able to get out.‎ ‎2. may与might 表示许可：may / might可以表示允许别人做某事，也可征求对方的许可，还可表示“法律、条文”等的许可。如May / Might I trouble you to pass the book?‎ ‎ Father said that I might play football before supper.‎ ‎ Cars may not be parked in front of the hall.‎ 表示可能性：may / might表示可能性时，可以对现在、过去或将来进行推测，might表示的可能性比may所表示的可能性要小一些。‎ A. 对现在或未来的可能性的推测：如I must go home at once; Tom might visit me.‎ B. 对可能正在发生的事情的推测：如Let’s speed up. They may / might be waiting for us now.‎ C. 对过去发生的事情的可能性进行推测：如You know the story very well. You may / might have read it before.‎ 其他用法 A. may放在句首，表示祝愿。如May God bless you!‎ B. may / might as well，后面接不带to的不定式，意为“不妨，还是……好”。‎ ‎ 如You may (just) as well tell me the truth.‎ ‎3. must与have to ‎ 表示必须，必要，但have to表客观，而must表说话人主观上的看法。‎ 如This film is not interesting. I really must go now.‎ ‎ My brother was very ill, so I had to call the doctor in the middle of the night.‎ 二者的否定意义不相同，mustn’t带有很强的语气，表示“禁止、不允许”；而don’t have to表示“不必”。如You mustn’t tell him about it. You don’t have to tell him about it.‎ must只有一种形式；而have to有人称、数和时态的变化。‎ ‎ 如She had to look after her brother yesterday.‎ must表示不服从，译为“非得；偏要”。如Why must you make so much noise?‎ must表示“猜测”，可以对现在、过去和将来进行猜测。其否定形式为can’t / couldn’t，而不是mustn’t。如You must be ill. I can see it from your face.‎ ‎ You must have gone to bed late last night. Your eyes are red.‎ ‎ He must be leaving tomorrow.‎ ‎4. shall，should与ought to shall用于第一人称，表示征求对方的意见。如What shall we do next?‎ shall用于第二、第三人称陈述句中，表示说话人给对方的命令、警告、允诺或威胁等。‎ ‎ 如You shall fail if you don’t work harder.‎ ‎ He shall have the book when I finish reading.‎ should用于第一人称时，可以表示说话人的一种谦逊、客气、委婉的语气。‎ ‎ 如I should think it would be better to try it again.‎ should表推测时，接按常理和常规所作的推测，译为（按道理）“理应，应该”。‎ ‎ 如It’s 8 o’clock now. He should be at work.‎ “Why / How + should”结构，表示说话人对某事不能理解，感到意外、惊异等意，译为“竟会”。如Why should you be so late today?‎ ought to表义务，用于各种句式。如You ought to go to see the doctor.‎ ‎ You ought’t to smoke so much.‎ ought to亦可用于完成式表推测，在肯定句中表未完成的动作，意为“该做而没有做”，而在否定句中则表示完成的动作，意为“不该做而做了”。‎ ‎ 如You ought to have done something to help him.‎ ‎ You ought’t to have married her, David. It was a great mistake.‎ ‎ 温馨提示：should表示劝告、建议、命令时也可用ought to代替。但ought ‎ to语气重，含有“按道理应该……”之意，用should时表示自己的主观看法，如要反映客观情况或涉及法律、义务和规定时，一般用ought to。在疑问句中，通常用should代替ought to。‎ ‎ 如You should go to class right away. Should I open the window?‎ ‎5. will与would 表示请求、建议等，would比will委婉客气。如Would you pass me the book?‎ 表示意志、意愿和决心。如I will never do that again.‎ 表示一种习惯、倾向或趋势。如Without water, fish will die.‎ would表示过去反复发生的动作或某种倾向。used to也表示“过去常常”，但它暗含“现在不了”之意。如During the vacation he would visit me every week.‎ There used to be an old temple in front of our village. (现在没了)‎ ‎6. need与dare ‎ need，dare既可用作情态动词，也可用作实义动词。用作情态动词时，它们只有一种形式，后跟不带to的动词不定式，主要用于否定句和疑问句。用作实义动词时，它们有动词的全部形式，即现在时第三人称单数needs，dares，现在分词needing，daring以及过去式和过去分词needed，dared，后跟带to的不定式，可用于一切句 式。‎ 情态动词 实义动词 肯定式 He needed / dared to escape.‎ 否定式 He needn’t / daren’t escape.‎ He doesn’t need / dare to escape.‎ 肯定疑问式 Need / Dare we escape?‎ Do we need / dare to escape?‎ 否定疑问式 Needn’t / Daren’t he escape after all?‎ Doesn’t he need / dare to escape after all?‎ ‎ 如He daren’t speal English before such a crowd, dare he?‎ ‎ You needn’t buy the book.‎ ‎ ---Need I finish the work today?---Yes, you must.‎ ‎ I dare to swim across this river.‎ ‎ I wondered how he dared (to) say that.‎ ‎ I need to have a long holiday.‎ ‎ You don’t need to worry about your son. He’s no longer a small child.‎ 三. 易混情态动词辨析 ‎1. may，can，must与should表“推测”‎ may（might）表示主观的推测，“也许，可能”，一般用于肯定句，其否定式may not，表示“可能不”。如He may be right. He may not come tonight.‎ can（could）表示主观的推测，常用于否定句（can’t“不可能”）和疑问句；用于肯定句时，can表示一时的、客观的可能性。‎ 如He can’t be at home, since I met him in the street just now.‎ ‎ Can he tell you all that he knows?‎ must表示主观的推测“一定”，语气十分肯定。其否定式为“can’t，不用mustn’t。‎ ‎ 如He must be in the classroom now. You can’t have known the truth.‎ should表示根据常规、事理、经验作出的判断，“想必、应该“。‎ ‎ 如Today is Sunday. Our teacher should be at home.‎ ‎2. can’t与mustn’t ‎ can’t多表示“没能力”或否定的推测“不可能”，也可表示“不可以，不允许”等含义；而mustn’t表达“禁止，不允许”含义时更常用，而且语气更强。‎ ‎ 如He can’t be that foolish. Students mustn’t smoke.‎ ‎3. “情态动词 + have done”用法区别 情态动词 ‎+ 完成式 用法 例句 must have done 表示对过去已经发生的行为进行推测，意为“想必 / 准是 / 一定做了某事”。‎ The lights were out. They must have been asleep.‎ can have done cannot have done 表示对过去发生的的行为的怀疑和不肯定，通常用在否定句和疑问句中。‎ He cannot have forgotten it.‎ could have done 用于肯定句，表示“可能已经……”，还表示过去没有实现的可能性“本来可以……”。‎ You could have done better, but you were too careless.‎ may / might have done 表示对过去已发生行为的推测，“也许已经……”；也表示“本来可能……”，但实际上没有发生的事；还表示“本来应该或可以做某事”。‎ She might have caught a cold.‎ You might have given him more help, though you were ‎ busy.‎ should / ought to have done 用于肯定句时，表示“本该做某事”，而实际上未做；用于否定句时，表示“不该做的事反而做了”。‎ You should have come to the meeting earlier.‎ You shouldn’t have told her the truth.‎ need / needn’t have done 肯定式表示“本来有必要做某事”，否定式表示“做了本来不必去做的事”。didn’t need to do表示“没必要做某事”。‎ You needn’t have taken a taxi here, for it was very near to my house.‎ had better have done 意为“当时最好做了某时”，否定式表示相反的含义。‎ You’d better not have scolded her.‎ would rather have done 表示“当时宁愿做了某事”，否定式表示相反的含义，两者都表示“后悔”之意。‎ I would rather have taken her advice.‎