情态动词理论知识.doc

情态动词一 情态动词是一种本身有一定的词义,表示说话人的情绪,态度或语气的动词,但不能单独作谓语, 只能和其他动词原形构成谓语。 二情态动词的位置: 情态动词在句中放在谓语动词之前, 谓语动词前若有助动词,则在助动词之前,疑问句中, 情态动词则在主语之前。 三情态动词的特点: 情态动词无人称和数的变化, 情态动词后面跟的动词需用原形,否定式构成是在情态动词后面加 not。 个别情态动词有现在式和过去式两种形式, 过去式用来表达更加客气, 委婉的语气, 时态性不强, 可用于过去，现在或将来四下面分组介绍情态动词的一般用法1. can/could(1)表示能力。 Could 为can的过去式，could表示过去的能力。We can use computers now, but we couldnt ten years ago.(2) 表示许可或征求对方许可Can 和could 都可以，could更委婉，这时也可用may, 需要注意的是回答时不用could-could I borrow your book?-yes, you can.也可以说成：can/may I borrow your book?(3) 表示客观的可能性Dont play with the dog, for it can be dangerous sometimes.(4) 表示推测，这时can多用在否定句或疑问句中，肯定句多用could, may, might.What he said could/may/might be true.It cant be true. / Can it be true? can 和be able to 两者都可以表示能力，只是be able to 强调经过一番努力而能够。2. may/ might(1) 表示允许或征求对方许可，“可以”的意思，可以与can 互换You may go now.He said that I might use his computer.-may I borrow your pen?-yes, you may.-no, you may not/you mustnt/ youd better not.(2)表示可能性由“或许，可能”的意思He may be at home.-where is Lilei?- Im not sure, he may be in the library.3. must/ have to(1) must表示“必须，应该”强调说话人的主观看法have to “不得不，必须“强调客观需要must的否定形式mustnt 表示不允许，禁止(2)注意在回答must 的问句时，否定形式用neednt或you dont have to The work must be finished as soon as possible.-Must I finish the work before seven oclock?-Yes, you must.-No, you neednt/you dont have to.(3) 表推测”一定，肯定“只用于肯定句中， 否定句和疑问句中用can.He must be a teacher.He cant be a teacher. / Can he be a teacher?(4)表“一定要，坚持要“表主张if you must go, at least wait till the storm is over.(5) “偏要，偏偏“Why you must keep on troubling me with such question while I am busy?4.shall/ should(1) shall用于一，三人称的疑问句中用来征求对方的意见或请求指示时，多用于第一三人称。Shall I open the window?Shall he come in?(2) shall 用于二三人称的陈述句中表示说话人的命令，警告，威胁，允诺等语气。You shall be punished if you insist on doing it in this way.(3) 用于第一人称表将来I shall go to work after I finished school.Should(1) 表劝告建议译为“应当“You should stay at home because of the bad weather.(2) 表示说话人的感情，惊奇，愤怒，失望等“竟然“Can you imagine that he should speak to his mother like that?(3) 表示有很大可能性的推测He should be there now.5. will/ would(1) 表示意志，意愿，可用于各种人称。would 为will的过去式,表示过去的意愿I will go with you.He said that he would tell me the truth.(2) will用于第二人称的疑问句中，表示向对方征求意见或向对方提出请求。这时would和will的用法一样都表示现在时间，只是would 比will 语气更加委婉。Would you like to join the basketball club?Will you go with me?(3) 表示某种倾向性Fish wont live without water.6. ought to 应该，应当表示责任或义务7. dare/ need(1) need表示“需要”“必须”作情态动词时， 仅用于否定句或疑问句中，在肯定句中一般用must, have to, ought或should代替You neednt come so early.-Need I finish the work today?-Yes, you must / - No, you neednt.(2) need作实义动词时有时态，人称和数的变化后接to He needs to go there himself.He has grown up, so we dont need to worry about him.(3) dare 表示敢，敢于做情态动词时主要用于疑问句否定句条件句中，一般不用于肯定句中。He dare not go out alone at night.I darent walk through the forest at night.Dare you walk through the forest at night?(4) dare作实义动词，后面通常带to在否定句和疑问句中，dare后的to可带可不带I dare to swim across the river.He does not dare (to) go there alone.五情态动词表推测的重要用法1. 情态动词 对将来 对现在 对过去肯定的推测 +v must +v +be doing +have done 可能的推测may/might 同上 同上 同上 否定的推测 cant /couldnt 同上 同上 同上疑问的推测can/ could 同上 同上 同上2. 情态动词+have done1) must have done 表示对过去放生的行为进行推测意为“想必，一定做了某事”He was late yesterday, he must have got up late.He must have gone to Beijing.2) can/could have done表示对过去的行为的怀疑和不肯定，通常用在否定句和疑问句中。在否定句中表示“不可能已经做了某事”，在疑问句中表示“可能已经做了某事了吗”The window was broken, who could have done that?It couldnt have been Mr. Green, he has gone to NewYork.I didnt see her at the party, she cant have been there.3) may/might have done 表示对过去放生事情的推测，意为“可能已经做了某事”He might have gone abroad, but Im still not sure about it.4) could have done(不能用can)表示本能做某事而没做（强调能力）用于肯定句中。You could have told me earlier.5) might (不用may) have done 表示本可以做某事却没做You might not have told her.6) should/ought to have done用于肯定句表示本应该做某事却没做，用于否定句表示本不应该做却做了You should have told him the