情态动词讲解 ppt课件.ppt

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1、-Modal Verbs,语法 ：情态动词,I 情态动词的定义 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。 情态动词数量不多，但用途广泛，主要有： can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would) .,情态动词 Modal Verbs,II 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， 情态动词放在主语之前。 I can see you. Co

2、me here. 我能看见你，过来吧。 He must have been away. 他一定走了。 What can I do for you? 你要什么？ How dare you treat us like that! 你怎么敢那样对待我们!, 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，后面只能接动词原形。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。, 情态动词的用法,can和could,表示能力,表示请求和允许。

3、表示请求，口语中常用could代替can，使语气更委婉。,表示惊异、怀疑、不相信等态度，主要用在否定句、疑问句和感叹句中。,在肯定句中，表示客观可能性，常用来说明人或事物的特征（译为“有时会”）。要表达具体某事实际发生的可能性时，不用can，需用could，may，might。,表示对现在的动作或状态进行主观的猜测，主要用在否定句和疑问句中。,特别说明：1.could用来表示请求时，语气委婉，主要用于疑问句，不能用于肯定句，答语应用can（即：could不能用于现在时态的简略答语中）。如：Could I use your dictionary?Yes, you can.(否定回答可用：No,

4、Im afraid not.或者是you cant)2.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 done,3.can和be able to辨析can(could)和be able to都可以表示能力，意思上没有区别。但can只有现在式和过去式，而be able to则有更多的形式。如： Ive always wanted to be able to speak fluent English. Those bags look really heavy, are you sure youll be able to carry

5、 them on your own?但是，表示在过去某时的某一场合经过一番努力，终于做成了某事，通常不用could，而用was/were able to来表示。这时，was/were able to相当于managed to do或succeed in doing。如： After the accident it was a long time before she was able to walk again. The fire was very big, but most people were able to escape from the building.,4 惯用形式“cannot

6、 too”表示“无论怎么也不（过分）”。如：You cannot be too careful.你越小 心越好。 惯用形式“cannot but+ 不定式（不带to）”表示“不得不，只好”。如：I cannot but admire her determination. 我不得不钦佩你的决心。,二may和 might,表示允许、许可。否定回答一般用must not/mustnt,表示“禁止、阻止”之意，但也可以用had better not (最好别)或may not（不可以），语气较为委婉。,在表示请求、允许时，might比may语气更委婉些。用May I征询对方许可在文体上比较正式，在日常

7、用语中，用Can I征询对方意见更为常见。,表示可能性的推测，通常用在肯定句和否定句中，含有“或许”“大概”“可能”之意；用might代替may时，则语气显得更加不肯定。,may用于祈使句表示祝愿,惯用句式：“may as well或might(just)as well+动词原形”意为“最好，满可以，倒不如”，相当于“had better.,1.A computer _ think for itself; it must be told what to do. A. cant B. couldnt C. may not D. might not,I thought you _ like som

8、ething to read, so I have brought you some books. A. mayB. mightC. couldD. must,may, might, can, could,1. They (can/might) _be away for the weekend but Im not sure.2. You (may/might) _leave now if you wish.3. (could/may) _you open the window a bit, please?4. He (can/could) _be from America, judging

9、by his accent.5. (may/can) _you swim?6. Listen, please. You (may not/might not) _ speak during this exam.,might,表示猜测,may,表示许可,could,表示请求,could,表示猜测,can,表示能力,may not,表示不允许,may, might, can, could,7. They (can not/may not) _ still be out, the light is on in the house.8. You (couldnt/might not) _ smoke

10、on the bus.9. With luck, tomorrow (can/could) _be a cooler day.10. You (can/might) _ be right, but Im going back to check it.,表示许可,couldnt,could,表示猜测,can not,表示猜测(不可能),might,表示猜测,三must和have to,表示“必须，应该”之意，语气比should，ought to强烈。其否定形式mustnt表示“不准，不应该，禁止”等意,在回答带有must的问句时，否定回答常用neednt或dont have to，表示“不必”，

11、而不用mustnt,表示有把握的推测，意为“一定、准是、相必”，只用于肯定句中,“必须，不得不”，意义与must相近。但must表示的是说话人的主观看法，而have to则往往强调客观需要。,must只有一种形式，即现在式与过去式都是一种形式，而have to则涉及各种人称、时态等方面的变化形式。,两者的否定意义不同，mustnt表示“禁止，不许”，dont have to表示不必。,注意：表示”偏要，硬要做某事-how old are you, madam?-if you must know, Im twice my sons age.,如果你非得知道，是我儿子年龄的两倍,四shall和sh

12、ould,用于第一、三人称构成的疑问句，表示征求对方意见或请求指示,其意为“要不要”、“好吗”：,1 用于第二、三人称陈述句中，表示说话人给对方的命令、警告、允诺、威胁、命令、规定、必然性等,2表示强制，用于法令、条约、规章中，意为“必须，应该”。,.(允诺),警告）,(命令),(威胁),(表规定),(表必然性),表示劝告或建议，意为“应该”,表示推测，用在肯定句中，对现在的情况或可能发生的事的主观推测或期待。意为“想必，理应” 大概。【注】should表示推断时，语气较肯定，通常是指非常可能的事(因为暗示有一定的事实依据或合乎常理)，,还可以用在if引导的条件句中，表示一件事听起来可能性很小

13、，但也不是完全不可能，相当于“万一”的意思。从句谓语用should+动词原形构成，主句都一定用虚拟语气,1should表示意外或惊讶2用于疑问句或感叹句中，表示意外、惊异的情绪，意为“竟会”，与why，what，how，who连用，如果是疑问句，则不需要回答。,1. Its nearly seven oclock. Jack _ be here at any moment. A. must B. need C. should D. can,2. Johnny, you _ play with the knife, you _ hurt yourself. A. wont; cant B. mu

14、stnt; may C. shouldnt; must D. cant; shouldnt,3.Our house is on the top of the hill, so in summer the wind _ be pretty cold. A. mustB. can C. ought toD. need,4. Professor Smith, many students want to see you. _ they wait here or outside? A. Do B. Shall C. Will D. Would,五will和would,用于表示意志或意愿或决心。will指

15、现在，would指过去。,表示请求、建议等和you连用，用would比用will委婉、客气。,表示习惯或倾向，意为“总是，惯于”。will至现在，would指过去。,表示推测，意为“很可能，大概”。will表示推测比should把握大，比must把握小。,表示功能，意为“能，行”。惯用形式：will do/would do表示“解决问题”、“就行”。,用于否定句中，意为“不肯”、“不乐意”,特别说明：would与used to辨析1 He _ be a naughty boy and cause trouble. 2 I _get up at six in the morning. 3 Som

16、etimes she _take a walk in the neighboring woods. 4 In those days, whenever I had difficulties, I _go to Mr. Chen for help.,used to,used to,would,would,would可用来表示过去反复出现的动作，但不能表示过去存在的状态.另外，would强调过去某种特定情况下的活动，是完全过去的事情，同现在没有联系。而used to则着眼于过去和现在的对比，隐含现在已不存在，动作或状态都可表示。Would可以表示不规则的习惯，used to则不可。,1. We _

17、 smoke here, because the worker is carrying some petrol.2. It is dangerous. You _ leave the room immediately.3. He _ go hiking with friends at weekends when young.4. Write to me when you get home.-I _.5. -Need I hand in my exercise book at once?-Yes, you_.6. You have been working all day. You _ be v

18、ery tired.7. It is a long time since we met last time. You _ come and see us more often.8. Why dont you try on this dress? It _ look nice on you.,will, would, shall, should, must:,mustnt,should,would,will,must,must,should,will,表示禁止,不许可,表示建议,命令,表示过去习惯,表示意愿,表示必须,表示肯定猜测,表示建议,表示将会,一定会,六need和dare,用于表示“需要

19、，必要”之意。做情态动词时，仅用于否定句和疑问句，只有现在时，过去式要用neednt have，疑问式用need+人称?,否定式用need not(即neednt），,做实义动词时，其变化与一般的实义动词相同，后接带to的不定式（need doing = need to be done ）, 疑问式，否定式要在前面加do的相应形式,用于表示“敢于”之意。做情态动词，没有人称和数的变化，主要用于否定句、疑问句和条件状语从句中,用作实义动词时，其变化与一般的实义动词相同。在肯定句中，dare后接带to的不定式；否定句中，dare后既可接带to的不定式，也可接不带to的不定式。,七ought的用法：

20、,说明：should与ought to 表示“应该”时的区别You_ help them with their work. You are his father. You _get him to receive good education.,表示“应该”之意,表示推测。注意与must表示推测是的区别,should,ought to,should 表示自己的主观看法，而ought to的语气中，含有“按道理应该”之意。若要反映客观情况或涉及法律义务和规定，一般用ought to。,Shall I go and buy more fruit for the party? No, I have a

21、lready bought 3 baskets. That _ be enough.A. can B. ought to C. may D. mightHe used to teach in that university and I _ ride past it on my way to work.A. would B. could C. should D. mightWould you be here to attend the English party this evening? Yes, we _. A. shall B. would C. will D. must,八“情态动词+h

22、ave done”用法,表示对过去已经发生的行为进行肯定推测，意为“想必，准是，一定做了某事”只用于肯定句,表示对过去已发生行为的可能推测，意为“也许/或许已经（没有）“。一般用于肯定句或否定句中，不用于疑问句。用might则表示语气更加不肯定。,表示对过去发生的行为的怀疑和不肯定，通常用在否定句和疑问句中。（can换成could时语气委婉）,可用于肯定句中，表示“可能已经”之意，此外，还可以表示过去能做而没做的事，有一种对过去为付诸实施的事情的惋惜。,表示“本来可能，但实际上没有发生的事情”。另外，还可以表示“本来应该或可以做某事”之意，含有轻微的责备语气。,用于肯定句时，表示本该做某事，而

23、实际上未做；用于否定句时，则表示不该做的事反而做了。,表示做了本来不必去做的事。,用于事后的建议，含轻微责备的口吻，意为“当时最好做了某事”，其否定式had better not have done表示相反的含义。,表示“当时宁愿做了某事”，其否定式would rather not have done表示相反的含义，两者都表示“后悔”之意。,1The thief _ in from the kitchen window as the door was closed. A. may climb B. must have climbed C. could have climbedD. should

24、 have climbed2I posted the letter a week ago. Then they _ the letter by now. It usually takes four days. A. can have received B. must receive C. should receiveD. ought to have receive3.There were already five people in the car, but they managed to take me as well. It _ a comfortable journey. A. cant

25、 B. shouldnt be C. must have been D. couldnt have been,1.-There were already five people in the car but they managed to take me as well. -It _a comfortable journey. ( ) A. cant be B. mustnt have been C. shouldnt be D. couldnt have been,D,2.The fire spread through the hotel very quickly but everyone

26、_ get out. ( ) A. had to B. would C. could D. was able to,D,EXERCISES,3. Peter _ come with us tonight, but he isnt very sure. must B. can C. may D. will,C,4. - Could I call you by your first name? - Yes, you_. A. will B. could C. may D. might,C,5. Sorry, I m late. I _ have turned off the alarm clock

27、 and gone back to sleep again. might B. should C. can D. will,A,6.-Excuse me, but I want to use your computer to type a report.-You _ have my computer if you dont take care of it.A. shant B. might not C. neednt D. shouldnt,A,7. -When can I come for the photos ? I need them tomorrow afternoon. -They

28、_be ready by 12 : 00 . A. can B. should C. might D. need,B,8. With so much work on hand, you _to see the game last night. A. mustnt go B. could have goneC. shouldnt go D. shouldnt have gone,D,9.Johnny, you _play with the knife, you _hurt yourself. ( )A. wont ; cant B. mustnt ; mayC. shouldnt ; must D. cant ; wouldnt,B,10. I missed the bus, so I _ go home on foot. A. must B. may C. can D. had to,D,