高三英语 一轮复习 情态动词

情态动词（一）学习目标：在以往知识的基础上进一步全面掌握情态动词的相关知识。

一、【知识要点】情态动词就是表示说话的语气或情态的动词。

常见的情态动词有can, may, must, need, dare, shall, will, should, ought to, have to, used to, had better, would rather等。

情态动词具有以下3个特点：(1)情态动词后面接动词原形并与动词原形一起构成谓语。

(2)情态动词虽有时态的变化，但却没有人称和数的变化，即情态动词不会因为主语的人称或单复数的不同而用不同的形式。

(3)变为疑问句或否定句时不需要助动词，而是将情态动词移至主语前变为疑问句，直接在情态动词后加not，构成否定句。

can和could■ 表示能力：能，能够，会He could swim when he was five.Can you drive a car? —Yes, I can. —No, I can’t.■ 表示推测：可能，会。

I think the work can be completed ahead of time.What can he mean?Today is Sunday. He can’t/couldn’t be at school.注意：表示推测时，could不是过去式，只是语气更委婉；若是推测已发生的事或过去的情况，用can/could have加过去分词。

Mike can’t have found his car, for he came to work by bus this morning.You could have started a little earlier.You needn’t have cooked it. We could have eaten it raw.could后接动词的完成式，除表示对过去的推测外，还有以下用法(不用can)：①表示过去没有实现的可能性(即某事本来可以发生，却没发生)：He could have told her, but he didn’t choose to.I could have lent you the money. Why didn’t you ask me?②用来委婉地责备某人过去应该做某事而没有去做：You could have been a little more considerate.You could ask me before you use my phone.You could have helped me why did you just sit and watch?■ 表示允许：可以(口语中常代替may)You can first lend me one book this time.You can’t take the book out of the room.注意：1. 表示允许别人做某事只能用can，不能用could。

2. can’t 和mustn’t 一样，都可表示“不准，不允许”。

■ 表示请求：可以Can I go swimming today, please, mum?Could you tell me how I can get to the railway station?注意：could不是过去式，只是语气较can更委婉，注意在回答中不可用could。

—Could I have the television on?—Yes, you can. / No, you can’t.【典型例题】1 . -Could I borrow your dictionary?-Yes, of course you___c______A. mightB. willC. canD. should2. A left-luggage office is a place where bags __b____ be left for a short time,especially in a railway station.A. shouldB. canC. mustD. will3. Two eyes _a___see more than one.A.canB.mayC.willD. should4.—Isn’t that Ann’s husband over there?—No, it ___a____ be him I’m sure he doesn’t wear glasses.A. can’tB. must notC. won’tD. may notCan、could与be able to(1) be able to比can有更多的时态。

如：In the past 50 years or so, scientists have been able to “see” farther and farther into the sky.(2) 在表示过去具体某次能够成功做成某事时，只能用was/were able to。

如：He worked very hard and was able to pass that examination.(3)表示将来的能力，通常不用can或could，而用be able to的将来时态：I’ll be able to speak French in another few months.One day people will be able to go to the moon on holiday.但是，若表示现在决定将来是否有能力做某事，则可用can：Can you come to the party tomorrow?【注】could 不用来表示过去特定能力通常只限于肯定句，否定句或疑问句中，它则可以表示过去特定的能力：I managed to find the street, but I couldn’t find her house. (前句为肯定句用managed to，不用could，后句为否定句，可用could)另外，could还可与表示感知的动词(如see, hear, smell, taste, feel, understand 等)连用表示的特定能力：Looking down from the plane, we could see lights on the runway.还有在间接引语中，could也可表示过去特定的能力：He said he could see me next week.【典型例题】1.You should bear in mind that he is not so strong as he__b__.A.was used to beB. used to beC.was used toe to2. An Englishman who _b___not speak Italian was once traveling in Italy.A.mustB.couldC.mayD.mightmay与might■表示请求允许：可以—May/Might/Can I come in?—Yes, please.He said I might borrow his car.注意：前例中的might不是过去式，只是更婉转；但在后例这样主句动词是过去式的句子里，might可看作是may的过去式。

■表示给予允许：可以You may bring it back tomorrow.You may not go there.注意：1. 表示给予允许，不能用might；2. 常用来回答表示不允许。

—Might I go now?—Yes, you may. —No, you mustn’t/can’t. —You’d better not.■表示祝愿May you be happy! May you succeed!!May God bless you! May you live happily.■表示推测：可能It may/might rain this afternoon.He may come, or he may not.2、might 后接动词的完成式，表示过去某事可能发生而实际上却并没发生或表示委婉的批评或责备(此时不用may)。

如：You might have let me know before!A lot of men died who might have been saved．【典型例题】1. Sorry I'm late. I _a_____ have turned off the alarm clock and gone back to sleepagain.A. mightB. shouldC. canD. will2. --- __d___ I go out to play now, Mum?--- No, you _____. You should do your homework first.A. Must; mustn’tB. Must; wouldn’tC. May; needn’tD. May; had better not3.—Is John coming by train?---He should, but he ___d_ not. He likes driving his car.A. mustB. canC. needD. maymay和cancan和may均可表示推测，can用于否定句和疑问句，may用于肯定句和否定式。

两者均可用于否定句，但是含义不同：cannot=不可能，may not=可能不。

比较：It can’t be true. 这不可能是真的。

It may not be true. 这可能不是真的。

若要加强推测的语气，表示较大的可能性，可在may, might后加副词well：You may well be right. 你很可能是对的。

That may well have been their intention．这很可能是他们的意图。

【典型例题】1. He ______ you more help, even though he was very busy.A. might have givenB. might giveC. may have givenD. may give2. A hardworking man ___d__ become a great scientist, but a great scientist _____be a hardworking man.A. can’t; canB. may not; canC. can’t; mustD. may not; must3. You know he is not going to let us leave early if we ____a___ get the work done.A. can'tB. may notC. shouldn't D mustn't4. I can't find the recorder in the room. It _a___ by somebody.A.may have been taken awayB. may leaveC.may take awayD.must have taken awaymust一、must表示“必须”、“一定要”(1)可用于肯定句、否定句或疑问句；用于否定句时，mustn’t 的意思是“一定不要”、“不能”，而不是“不必”：You must finish it today. Must you go so soon?We mustn’t think only of ourselves.(2)对于must 开头一般疑问句，若要作否定回答，可用needn’t，不用mustn’t："Must I come over tonight?" "No, you needn’t."(3)其后可接被动结构或进行形式：Something must be done to stop it.I think I must be going.二、must表示推测其意为“准是”、“一定是”，注意以下几点：(1)通常只用于肯定句，在否定句或疑问句用can 代之：It must be true. 比较：Can it be true? It can’t be true.(2)后接动词原形，表示对现在情况的推测：He must be wrong. The man must have a lot of money. (3)后接完成式，用来谈论已发生的情况：He must have arrived already．I didn’t hear the phone. I must have been asleep.三、must表示“应当”相当于should, ought to的意思：You must say hello to her．We must go and have a weekend there．四、must 与have to 的区别(1)强调重点不同：两者都表示“必须”，但must 侧重于说话者的主观看法，认为有必要或有义务去做某事；have to则重于客观需要，含有“不得不”或“被迫”之意：We must go at once.If I buy that car, I’ll have to borrow some money.(2)时态形式不同：must 只有现在时一种形式(在宾语从句中可以表示过去)，而have to则有多种时态形式：He said (that) she must go with me. She had to go there on foot yesterday.(3)否定式的意义不同：must 的否定式mustn’t 意为“一定不要”、“不允许”；而have to 的否定式don’t have to 意为“不必”(=needn’t)。