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1、一、情态动词,1.几组易混情态动词的基本用法(1)can与could的用法在日常会话中表示“许可，容许”时，常用can；当请求得到许可时，经常用could，较为礼貌，而不用can。You can go now.你现在可以走了。Could I borrow your car？我可以借用你的汽车吗？can还可以用于表示做某事的能力；谈论将来有能力做某事时，要用will be able to；could经常地用于表示某人在某时期内拥有的能力。,Ill be able to speak better if I practise more.我如果多练习，就会讲得更好。I could swim when
2、I was eight.我8岁时，就会游泳。can通常用于询问某事是否可能，还通常用来表示某事是不可能的；could表示更多的疑问。That cant be true.那不可能是真的。Could that really be true？那事真的会是那样吗？,(2)may与might的用法may可表示猜测(可能，也许)；表允许(可以)；也可表示祝愿；might也可表示猜测，但可能性比may小；可表示允许；还表示礼貌地询问是否可以干某事等。You may start writing nowthe examination will finish in three hours.你们现在可以开始答题考试
3、将在3小时后结束。May both the bride and groom have long and happy lives.祝新娘新郎幸福长寿。Thinking it might rain，I decided to go in the car.我当时以为会下雨，所以我决定开车去。,(3)shall与should的用法shall用于第一人称时，表示征求对方的意见；当用于第二、三人称时，表示说话人给对方的命令、警告、允诺或威胁，意为“一定要”。should表示“应当，应该”，表示推测等。I said you could go，and so you shall.我说过你能去，所以你一定要去。Yo
4、u should learn to be more polite.你应该学会更有礼貌。,2.情态动词表示建议、推测的用法(1)情态动词表示建议的用法表示“应该做某事”时，常用should，ought to，must(语气逐渐加强)；表示“不应该作某事”时，可用neednt，shouldnt，oughtnt to，mustnt(语气逐渐加强)。You ought to be ashamed of yourself.你应该感到羞愧。You mustnt tell anyone about thisits a secret.你不许跟任何人讲这件事这是个秘密。,(2)情态动词表示推测的用法may，sh
5、ould，must常表示肯定推测，might not，may not，cant，mustnt常用来表示否定推测。It should be a good movieits reviews were very good.这应该是一部好电影各种评论都很赞赏。,3.情态动词不定式的完成式的用法情态动词不定式完成式主要有以下几种构成形式：(1)must不定式完成式此结构常用在肯定句中，表示对过去发生的行为的推测，意为“一定，肯定”。其否定或疑问形式用cant，而不用mustnt。He must have been drunk to say that.他准是喝醉了才那样说的。,(2)should不定式完成
6、式表示本应该做而实际上没有做，其否定式“shouldnt have done”表示某种行为不该发生但却发生了。I think he should have tried to get some more qualifications before applying for the job.我认为他在申请这份工作之前本应努力取得更多的资格证明。(3)can(could)不定式完成式肯定式表示本来可以做而实际上未能做某事，疑问或否定形式表示对过去发生的行为怀疑或不肯定。You could have told me you were going to be late.你应当早告诉我你会晚到的。,(4)
7、may(might)不定式完成式表示对过去(将来)发生的行为的推测，表示可能干了某事。Who knows what will happen？You may even have married by then.谁知道会发生什么呢？到那时你甚至可能已经结婚了。(5)ought to不定式完成式表示过去应做某事而实际未做，其否定式是“ought not to不定式完成时”，此时ought to可与should换用。What you ought to have done is call the police.你早该报警了。(6)neednt不定式完成式表示本来不必做某事而实际上做了某事。Its sun
8、day today，so I need not have got up so early.今天是星期天，因此我本来没必要那么早起床的。,二、虚拟语气,1.虚拟语气用于条件从句中虚拟条件句可以表示假设或不太可能实现的情况，也可以表示与事实完全相反的情况，一般由if引导。,在含有虚拟条件句的复合句中，主句和从句的谓语都要用虚拟语气，主要有以下几种情况：,If she knew English，she wouldnt ask me for help.如果她懂英语的话，她不会找我帮忙的。If I were you，I would go to hospital.如果我是你，我会去医院的。If I had
9、 known her number，I would have called her.如果我知道她的电话号码的话，我就给她打电话了。If it were to snow this evening，they would not go out.如果今晚下雪，他们将不出去了。,(1)在书面语中，如果虚拟条件从句中有were，had或should，可以把if省略，而把这几个词放到主语之前，构成倒装结构。Should they have patience，they could do the work well.如果他们有耐心的话，他们就可能把这项工作做好。Had he worked harder，he w
10、ould have got through the exams.他当时要是学习努力点的话，就会通过这些考试了。Were she to move right now，she would get there on Sunday.她要是马上动身的话，星期天就到那儿了。,(2)当条件状语从句表示的行为和主句表示的行为所发生的时间不一致时，被称为“错综时间条件句”，动词的形式要根据它所表示的时间做出相应的调整。If you had followed my advice just now，you would be better now.如果你刚才接受我的建议，你现在会好些。If you had studi
11、ed hard before，you would be a college student now.如果你从前努力学习，你现在会是一名大学生。,2.虚拟语气用于主语从句中(1)在句型Itbe形容词that.(should).中。常见的形容词有：necessary，good，important，right，wrong，better，natural，proper，funny，strange，surprising，unthinkable等。Its necessary that we(should)have a walk now.我们有必要出去散散步。Its natural that she(shou
12、ld)do so.她这样做是很自然的。,(2)在句型Itbe过去分词that.(should).中。常见的过去分词有：desired，decided，suggested，requested，ordered，proposed等。It is suggested that the meeting(should)be put off.有人建议会议应推迟。(3)在句型Itbea pity/no wonder that.(should).中。It is a pity that you(should)lose the chance.很遗憾你失去了这个机会。,3.虚拟语气用于宾语从句中(1)wish后面的宾语
13、从句一般用虚拟语气，表示一种不可能实现的愿望。其谓语动词构成形式为：宾语从句动作与wish同时，用过去时。宾语从句动作先于wish时，用过去完成时。宾语从句动作后于wish时，用could/would/might动词原形，即过去将来时。I wish(that)I were a bird and could fly freely in the sky.I wish(that)I had met that film star yesterday.I wish they would stop fighting.,(2)表示“要求、建议、命令”等动词后的从句，用“should动词原形”，should常
14、可省略。常见的动词有：advise，direct，demand，decide，desire，insist，order，prefer，propose，request，suggest等。The teacher suggested that we(should)clean the blackboard after class.老师建议我们课后把黑板擦了。He ordered that the students wash the clothes every week by themselves.他要求学生每周都要自己洗衣服。,4.虚拟语气用于表语从句和同位语从句中与表示决定、主张、要求、建议、命令的动
15、词相对应的名词advice，demand，order，insistence，desire，requirement，request，proposal，suggestion，command，decision等构成的表语从句和同位语从句中常用“(should)动词原形”结构。He made a suggestion that he(should)stay there.他建议他留在那儿。My advice is that we should think it over before accepting it.我的建议是三思而后行。,5.虚拟语气在其他句型中的应用(1)虚拟语气用于It is(high/
16、about)time(that).句型中(定语从句)在此句型中，从句中的谓语动词一般用过去时或should动词原形，should不可省。It is high time you went home.你该回家了。,(2)在as if(as though)引导的从句中，常用虚拟语气，其动词形式的判断要通过与主句动词的比较而定。Alan talked about Rome as if he were a Roman.艾伦谈起罗马来好像他是个罗马人一样。(从句中的动作与主句的动作同时进行)He talks as if he had been to the moon.他说得就好像去过月球似的。(从句动作发
17、生在主句动作之前)He talks as if he would go to the moon.他说得就好像要去月球似的。(从句动作发生在主句动作之后),(3)would rather后面接从句，用虚拟语气若表示现在或将来要做某事，从句谓语动词需用一般过去时；表示过去已经做的事，从句谓语动词用过去完成时。Frankly speaking，Id rather you didnt do anything about it for the time being.坦白地说，我宁愿你现在对于此事什么也不要做。I would rather you had returned the book yesterd
18、ay.我真希望你昨天把这本书还了。,(4)用介词短语代替条件状语从句常用的介词有with，without，but for。What would you do with a million dollars(if you had a million dollars)？如果你有百万美元，你会怎么做？We couldnt have finished the work ahead of time without your help.(if we hadnt got your help)Without your help，we couldnt have finished the work ahead of
19、 time.But for your help，.If it had not been for your help，.Had it not been for your help，.要不是你的帮助，我们无法提前完成工作。,(5)含蓄条件句有时为了表达的需要，在虚拟语气中并不总是出现if引导的条件句，而通过其他手段来代替条件句。I was ill that day.Otherwise，I would have taken part in the sports meet.(副词)He telephoned to inform me of your birthday，or I would have known nothing about it.(连词)A man who stopped drinking water would be dead in about seven days.(定语从句)I might have given you more help，but I was too busy.(连词)Everything taken into consideration，they would have raised their output quickly.(独立主格结构),
