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1、情态动词的用法12009-05-27 09:051.情态动词的用法 :can, could, may, might, must, ought to, shall, should, will, would, need, dare etc.2 情态动词的语法特征：1） 情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。2） 情态动词 除ought 和have 外，后面只能接不带to 的不定式。3） 情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。4） 情态动词没有非谓语形式，即没有不定式，分词等形式3.can &could1)表能力（ability)eg. a. I
2、 can speak English1).can, could 表示能力,可能, 只用于现在式和过去(could). be able to可以用于各种时态。表过去的能力，用was/were able to表将来的能力，用shall/will be able to e.g.a. They will be able to tell you the news soon. 他很快就能告诉你消息了2). 表示成功地做了某事时，只能用was/were able to， 不能用coulde.g. a. He was able to flee Europe before the war broke out.
3、= He managed to flee Europe before the war broke out. e.g. a. The moon cant always be at the full. (3).表请求（request)e.g. a. Can you tell me the way to the post office? e.g. a. Could I come to see you tomorrow?-Yes, you can.-No, you cant.4).表允许（permission)e.g. a. Can I come in?e. g. a. He can not but
4、agree. 5) can not but do =have to 不能不做e. g. a. He can not but agree.6). can not help doing can not help (to) do7).can not (never, hardly) do too 越就越好；无论做都不过分e.g. a. You can not be too careful in the exam. b. You can not praise him too highly. 8).could 加完成式用于肯定句时一般表过去可能完成而却未完成的动作。e.g. a. I could have
5、 passed my examination easily but I made too many stupid mistakes.4. may & might1） 表示允许或请求 当表示请求，允许时，might 比may语气更委婉，否定答语要用must not,表示“不许可”、“不应该”、“不行”。e.g. a.- May I come in?-Yes, you may. -No, you mustnt.2).表示没有把握的推测. “也许”(用于肯定句或否定句中)注意： might 表示推测时，不表示时态,只是可能性比may 小。 e.g. a. He may be playing foot
6、ball.b. He might be at home.3).may 放在句首，表示祝愿e.g. a. May God bless you! b. May you succeed! = Wish you success!4). may/might as well，后面接不带to 的不定式，意为不妨。 e.g. a. If that is the case, we may as well try. 5)may (might) + have +done 表示对过去发生行为的推测，含有“想必”、“也许是”的意思。e.g. a. It may have been true.这事也许是真的。 b. He
7、 might not have settled the question. 他可能尚未解决那个问题。4.will & would1）will表示经常性、习惯性、倾向性，would表示过去的习惯行为。e.g. a. He will sit there hour after hour looking at the traffic go by. b.He would come to see me when he was in Beijing. 2）表示意志，决心或愿望。e.g. a. Surely we will support all the people in the world in thei
8、r struggle for peace. b. He would not let me try it . 3）表示对对方的请求，用于第二人称作主语的疑问句中，would的语气比will委碗,疑问句中一般用some, 而不是any。e.g. a. would/will you kindly tell me the way to the station?b. Would you like some cake?would like = want to 想要 Would like to do e. g. a Would you like to go with me? 5.shall&should s
9、hall的用法1)用于第一,第三人称征求对方的意愿e.g. a. What shall I wear on the journey? b. When shall he be able to leave the hospital? 2)用于第二、三人称时表允诺（现已少见)e.g. a. She shall get her share. 她可以得到她的一份。 b. You shall have it back tomorrow.你明天可以将它拿回。 should 的用法1)用于第一人称疑问句中询问对方的意愿，但语气较委婉温和e.g. a. What should we do now? 我们现在该怎
10、么办？2)表示应该、必须，常与must 换用。e.g. a. We should (must) master a foreign language at least. 3).should 表示劝告，建议，命令，此时也可用ought to. 在疑问句中，通常用should代替 ought to4) should have done 表示过去应该做 而实际没有做should not have done 表示过去不该做而实际做了 6.must表推测1) must用在肯定句中表示较有把握的推测，意为一定。2) must表对现在的状态或现在正发生的事情的推测时， must 后面通常接系动词be 的原形或
11、行为动词的进行式。 e.g. a. You have worked hard all day. You must be tired.（对现在情况的推测判断） b. He must be working in his office. 他一定在办公室工作呢。 比较： e.g. a. He must be staying thereb. He must stay there.他必须呆在那。3) must 表示对已发生的事情的推测时，must 要接完成式。 e.g. a. I didnt hear the phone. I must have been asleep. 4) must表示对过去某时正发
12、生的事情的推测，must 后面要接不定式的完成进行式。 e.g. a. -Why didnt you answer my phone call? -Well, I must have been sleeping, so I didnt hear it.5) 否定推测用cant。e.g. a. If Tom didnt leave here until five oclock, he cant be home yet.have tomust1)两词都是必须的意思，have to 表示客观的需要， must 表示说话人主观上的看法，既主观上的必要。e.g. a. My brother was ve
13、ry ill, so I had to call the doctor in the middle of the night. (客观上需要做这件事) b. He said that they must work hard. （主观上要做） 2)have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务e.g. a. He had to look after his sister yesterday.3） 在否定结构中： dont have to 表示“不必” mustnt表示 “禁止” e.g. a. You dont have to te
14、ll him about it. b. You mustnt tell him about it.8. need&dare这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只能用于疑问句，否定句和条件句。 need 作实义动词时后面的不定式必须带to，而dare作实义动词用时, 后面的to 时常可以被省略。 1) 实义动词:need+ n. / to do sth2) 情态动词： need，只用原形need后加do，否定形式为need not。e.g. a. -Need you go yet? -Yes, I must. -No, I neednt.3) need 的被动含义：ne
15、ed, want, require, worth（形容词）后面接doing也可以表示被动：need doing = need to be done9.情态动词的回答方式问句肯定回答否定回答Need you?Yes, I must.No,I needntMust you?Yes, I must. No, I neednt./dont have to. May I ? Yes, of course. No, you mustnt.Could you? Yes, you can. No, you cant.10.情态动词表猜测must 用于肯定句can 用于否定句或疑问句6 表示推测的用法can, could, may, might, must
