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1、情态动词情态动词有can, may, must, ought(to), will shall, dare, need 八个。在众多的英语动词中，情态动词有其独特的用法，概述如下：1. 其中五个有过去形式，分别是：cancould情态动词的过去形式往往表示的是一种语气，而不是时态。（dared 属例外，只表示时态。）maymightwillwould shallshoulddaredarede.g., Can/Could I help you? (后者更加委婉)He may/might come today.（后者表不肯定）Will /Would you please do it again?
2、(后者更加委婉)You shall/ should do it all by yourself. (前者语气极为严厉，后者则只是一种规劝)2. 情态动词不能单独使用，在句子中往往与不加to的不定式一起构成谓语e.g., We must/can/may/will/shall face any difficultyought 后面须跟加to 的不定式e.g. You ought to go out for a rest.3. 情态动词will, shall 还可用作助动词，用于将来时e.g., We shall/will go home next weekend He will come here
3、 again when he is free.Cf. If you will come, he will meet you If you come, he will meet you. 上述两句均为复合句，后半句都是将来时，上句中的will 表示“愿意”为情态动词，不表示将来。下句中的if you come 则是不用助动词的将来时态。4. 情态动词dare, need 通常只用于否定或疑问e.g., Who dare do it?You neednt go now.试看下列的填空：Well try to finish the work in time, but we need_ some mo
4、re workersA. ask for B. to ask for选项A为不加to的不定式，那么此时的need为情态动词，此句为肯定句显然不适，答案为B need to do 中的need为行为动词5. dare, need 还可用作行为动词，后面可跟加to的不定式试比较，A. who dare do it? B.He dares to do it. A.He neednt do it B.he needs to do it 上述句子中A句为含情态动词的句子，B句中dare. need 均为行为动词注意动词 dare 的某些特殊用法。1）在下列句子中只可用情态动词dare，不可用行为动词da
5、reHow dare you say I am unfair?I dare say,. (*I dare to say, X ) e.g., Dont worry, sir. I dare say, nobody will come again.2) 行为动词dare后面跟不定式时，在下述三种情况之一时可省去不定式符号toa. 与助动词连用时（即用于否定，疑问句）e.g., He doesnt dare (to) go to the forest done at night.Do you dare (to) touch the tiger in the case?b. 与never连用时e.g
6、., The man never dares (to) do anything without his owners permission.c. 当dare出现在WH(连接代词)引导的名词从句中时e.g., They wonder why the little boy dares (to) live in such a dangerous place.6. 情态动词不能用作不定式(不与助动词连用)试看下列填空Tomorrow Ill_ go home to see my parents.A. must B. have to (B 为正确答案，助动词will后是省略to的不定式)7. 情态动词的
7、否定式可直接加not 来表示will notwontshall notshantmust notmustntdare not darentneed notneedntmay not maynt (“或许不” “可能不”)（ “不可以要用”cant ,mustnt）can notcant- cannot can+not 并非都可以写成cant, cannote.g., He cannot speak Chinese. He can not only speak Chinese but English.上述两句中第一句可译成“他不会讲英语”（此时可用cant）,第二句可译成“他可以不讲英语”结论：
8、当not否定can时，可写成cant (cannot)，当not否定后面的不定式时，则不能用cant上述第二句中not onlybut(also).则表示“不仅。而且。”此时not与can无关，显然不能用cant。8情态动词的疑问式可通过情态动词前移的方式来表示e.g., - Can/(Must/May/Shall/Will/Dare) he do the dangerous work?Ought he to do the work alone?(1)肯定作答，通常用原情态动词e.g., - Can/(Must/May/Shall/Will/Dare) Mr. Li stay in the l
9、ovely house ?-Yes, he can(must/may /)若是情态动词need引出的问句，则要用must作答e.g., - Need I write an article now?- yes, you _ (A. must B. need)答案只能是A.（2）否定回答，通常用原情态动词的不定式e.g., -Can he go now-No, he cant.若是情态动词may，否定回答用mustnt或cant。若是must则用neednt作答若是need可用neednt或do not have toe.g., -May I go out for a walk?-No you_.
10、A. may not B. must not C. cant D. dont 答案为B或C-Must we do it now?- No, you _A. dont B. mustnt C. cant D. neednt答案为D-Need I do the work again?-No, you_A. neednt B. dont C. mustnt D. cant答案为A9. 情态动词用法分述1) willI. 表现在经常发生的情况e.g., The man will go to work every day.(= The man goes to work every day 后者更常用)T
11、he door wont open. (=The door isnt easy to open.)II.表示“决心”“意愿”“可能”等e.g., Hes full of faith and he will beat all his matches.If you will come tonight, hell meet you, I think. This will be the book you are looking for.Will you come in ? (=Will you please come in?)III. 若表示过去，则用woulde.g., He would take
12、a walk after supper when he lived in the country.He said he would help.表示“过去常常”除了用would，还可以用used to，不过后者常常含有“现在不”之意。e.g., When young, he would go out for a trip on Sundays.(Now maybe still does)When young, he used to go out for a trip.(But now he doesnt)此外，would表示“过去常常”时后面动词须是某种行为或动作，不能是静态动词 。e.g.,
13、Near the village, there _ be a stream.A. would B. used to(答案是B)Would更多的用来表示语气而不是时态e.g., Would /Will you please take a seat?Would/ Will you mind opening the windows?I would / will do anything for you , sir.有时甚至只能用would而不用wille.g., I would like. Would you like.?They would love. He would rather 2) shal
14、lI. 表示“询问”用于一、三人称e.g., Shall I open the door?要我开门吗？Shall he stay here for the night? 让他留下过夜吗？II.表示允诺，用于二、三人称e.g., If you /they work well ,you /they shall be well paidIII. 表示“强制”“威吓”等，用于二、三人称e.g., He says he wont come, but I say he shall.If you go there again, you shall lose what youve got.Should 是sh
15、all的过去式，它本身的词义为“应当”（ought to）Shall的上述三种用法中，I、II两种不可用should，否则句意变了。在III中若用should则语势较弱。Should在虚拟语气中的用法这里暂不介绍。3) mayI. 用于肯定句,表示 “可能”, “允许”II. 用于否定句,表示 “或许不”III. 用于问句,表示 “请求许可” 或”惊讶”e.g., You may do it.It may be a new house.Mr. Li may not be in his office.How old may she be?She looks so young while her
16、husband loods so old.May I make a suggestion?Might是may的过去式,但用于现在时中则表示更不确定e.g., She might stay at home now.Might I take this seat ?4) must表示 “必须” “一定”等eg,You must come next week. He must be in trouble.must与have to 的用法前者侧重于主观意念,后者则用于表示客观条件或义务,译为”只好” “不得不”e.g., He must work to make his living. He has t
17、o beg for a living.Must没有过去式,在单句中若是过去时,须用had to e.g., He begged from door to door, for he had to do so to live若在从句中,则可用must来表示过去e.g., He said he must manage to own a new house for Easter.5) canI. 表示“可以” “可能” “会”e.g., You can do what you want to do.Who can be the old man sitting over there ?The mothe
18、r can be very brave when her children are in dangerCould是can的过去式,常用来表示语气的婉转e.g., Could I help you?II. 表示能力e.g., He can speak English不过can在此句中还可表示”可以”. 要说”他会说英语”, 常用的译句是He speaks English. III. can 与be able tobe able to 虽然也可以译作“能”, 但更强调“能力”e.g., Will you be able to come? Im able to do the work all by
19、myself.两者的用法区别在于can不能作不定式,而be able to 则能e.g., He will _do the work better.A. canB. be able to答案为Bcan不用于完成时e.g., Now he has been able to work alone. They have been able to use the computer since they came here.can可用于将来时,但句中须有时间状语e.g., You can use this machine next week.(can意为”可以”不表能力)当然,不可以同时使用表示将来的助
20、动词will或shall(be able to 可以)can与be able to 用法区别常与句子时态有关现在时比较1) 表示”能力”时,be able to 不用于第二人称,e.g., You are able to do the work, I think. (X) 当改用can2) can与感官动词feel, hear, see, smell, taste连用时, can显得可有可无,因而失去了情态动词的意义,这种情况下can不能用be able to 代替e.g., We can see beautiful flowers and green trees here and there
21、.Anyone can see it is of no use.3) can与某些表示意念的动词如：understand, remember, forget, hope, imagine, believe, suppose等连用时，同样没有情态动词的意义，因而也不可用be able to取代。e.g., I cant believe there are so many tall buildings now in my home town.过去时比较was/were able to 意含”经过努力” “凭借才能” 获得的”能力”常与”manage to ”相通e.g., He started e
22、arly, and he was able to arrived the earliest.They worked hard, so they were able to do more for the company.They were short of modern machines, but they were able to complete the project in time.could 可表示具备能延续长时间的能力e.g., He could write beautiful prose when he was only 5.could 只表有能力，be able to 还可以表示
23、结果c.f., He could cure the old mans illness.(他能治好这老人的病)He was able to cure the old mans illness(他治好了这老人的病)将来时的比较can表示”能力”时,只有具备两个条件时才可用于将来时,那就是一, 句子中有时间状语二, 句子主语只能是第一人称e.g., I can do the work better next time. You can use this machine next week.（此句can表示“可以”，不表示“能力”）6) ought to用法同should7) need与dare 详见
24、4-510. 情态动词+ have done1) must have done, may/might have done 表示猜测can与have done 连用时, 为否定句或疑问句,表示猜测2) neednt have done 表示”本来不必做(却做了)”Some of the eggs have gone bad. You neednt have bought so many.而neednt do 则表示”不必做(也没做)”We still have enough eggs. You needt buy any more.3) ought to /should have done 表示
25、”本来应当做的却未做”e.g., Youre late again . You should (ought to) have started earlier. Why tell her the bad news? You shouldnt have let her know it.4) would/could/might/should + have done 用来表示与过去事实相反的虚拟句e.g., If I had been free that day, I would have gone with you.11. 表示猜测的情态动词许多情态动词可用来表示猜测,常用的有以下几个:1) mus
26、t “肯定” “一定”e.g., Man must die. He must be at home now. must 表猜测时,仅用于肯定句.2) may “或许” “会”e.g., Mr.Smith may/ might be in the office now.might 用于现在时,表示语气更不肯定.通常,may 用于肯定猜测,若用may not,则表示”或许不”e.g., - Is Li Ping in?- He may not be in , but Im not sure.3) can”会” “可能”can表示猜测时,用于否定或疑问e.g., - Who can be the m
27、an in the office with light on?- It cant be Mr. Li. He has been out on business.could 为can的过去式,但用于一般现在时却可用来表示肯定猜测e.g., - Where can the thief hide in the house?- It could be in the bathroom, I think.此时,could 的语势介于must与may之间注意点:I. 若跟动词原形,表示对现在(或目前)情况之猜测, 如上述各例若后面跟have done 则表示a) 对到目前为止情况的猜测(相当于完成时)e.g
28、., She looks worried . She must have met with some trouble.b) 对过去情况之猜测(相当于过去时)e.g., He must have done something wrong yesterday.究竟属于何种猜测往往要从句子本身或上下文联系来判断,如上例有一现在时句子,可判为对现在情况的猜测,而下面句子中有表示过去的时间状语,显然是对过去情况的猜测了.II. 当表猜测的情态动词出现在反意疑问句的陈述部分时,反意疑问句的疑问部分的动词从情态动词后面的不定式.e.g., He must be ill, isnt he ?They cant know the news, do they?She must have been to Beijing before, hasnt she?(相当于现在完成时)She must have been in that day, wasnt she?(相当于过去时)He loods sad. He must have failed the test, hasnt he ?He must have failed the exam in maths yesterday, didnt he?