1、情态动词和虚拟语气情态动词和虚拟语气一、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、动名词等形式。二、虚拟语气用来表示说话人的主观愿望或假想，所说的是一个条件，多半不是事实，或与事实相反。 高考重点要求：1、情态动词的基本用法2、情态动词表示推测的语义差别3、情态动词后接不定式完成体的不同意义4、虚拟语气中情态动词的用法第一节 知识点概述一、情态动词 （一
2、）情态动词种类1. can表示体力或脑力方面的“能力”、“技能”或根据客观条件能做某种动作的“可能性”, 但表示人的体力或智力的具体动作时须用 be able to .He was able to do that without any help.他不需要任何帮助就能完成这项工作。2. may表示“允许，可以”，相当于be allowed to .may或might可和as well连用，表示“建议”，译为“还是的为好”You may as well keep a certain distance from that mad man. 你们还是离那疯子远点为好。You might as wel
3、l go home now.你还是现在回家为好。3. must表示“必须”或“应当”、“一定”。4. have to 加动词原形，表示“不得不”，“必须”，它比must更强调客观。Tom had to work into the deep night every day to earn a living. 汤姆为生计每天都工作到深夜。5. should 表示“劝告”，“建议”或“义务”时，译作“应当”，或表示“预测”和“可能”。He should take care of his parents as they are old enough not to live on themselves.
4、 由于父母亲老了，不能自理，他应当照顾他们。He should be there now. 他应该在那儿。should have done在虚拟语气中表示“责备或后悔”。6. ought ，只有一种形式，且ought后必须加to，然后跟接动词原形表示“有义务”或“必要”做某事，译为“应当，应该”。7. dare 可以用作情态动词，后面跟不带to的动词不定式，这主要用于否定句中，它本身可有现在时第三人称单数，词尾加s，它还可以有ing分词形式(daring)和过去式及ed分词形式(dared)。（二）情态动词在一般时否定句中的用法cant(cannot) 表示“不可能”， may not 表示“
5、不可以”， mustnt(must not) 表示“一定不要”，“不许可”，neednt (need not) 表示“不必”，dare not 动词原形表示“不敢”。He cant finish his essay by this time. 现在他不可能写完论文。He may not sleep now. 他或许现在没在睡觉。You mustnt criticize her in that way. 你不应那样批评她。You neednt come tomorrow. 你明天没必要来了。He dared not meet his fiance. 他不敢见女朋友。（三）can，may，must
6、三者用法比较can，may，must是三个最重要的情态动词，其基本句型如下：肯定句：主语+can，may，must +动词原形否定句：主语+can，may，must +not +动词原形疑问句：Can，May，Must +主语+动词原形1. can，may，must的肯定句You may eat lunch，but you must wash your hands.你可以吃饭，但是你必须洗手。（1）cana.表示能力；能，会 She can run fast，but I cant. 她很会跑，但是我不会。b.表示可能；能够 I can get there in ten minutes. 我十分
7、钟之后就可以到那儿。c.表示允许；许可 You can use this dictionary. 你可以用这本字典。d. can和be able to比较: can只有现在式和过去式，而be able to可以用于各种时态。can（could）表示能力时，可用be able to代替。I can（=am able to）pay for the book. 我买得起那本书。He will be able to tell you the news soon. 他很快就能告诉你消息了。She has been able to come to school. 她已经能去学校了。（2）maya.表示请求
8、、许可 May I borrow your pen？ 我可以借你的钢笔用一用吗？b.可能、或许 Tomorrow I may go shopping. 明天，我可能（或许）去商店买东西。He might be our new teacher. 他或许是我们的新老师。（3）musta.必须、应该（表示有做某一动作的必要或义务） You must buy a ticket. 你必须买一张票。b.一定、准是（表示有把握的判断或推测，一般只用于肯定句中）He must be our new teacher. 他肯定是我们的新老师。在You must这一句型中，它的意思与祈使句相同。You must g
9、et up early. =Get up early. 你必须早起。You must study hard. =Study hard. 你必须用功读书。2.表示推测的用法 can , could ,may ,might ,must 皆可用来表示推测，其用法如下：acould ,might 表示推测时不表示时态，其推测的程度不如can ,may。bcan ,could 用于否定句和疑问句中。句型：主语+ cant , couldnt +be +动词ing（否定句）Can ,Could +主语 +be +动词 ing（疑问句）They cant be cleaning the room now他们
10、现在不可能在打扫房间。cmay ,might , must 用在肯定句中。句型：主语+ may ,might ,must +be +动词 -ing （表示对现在发生动作的推测）He must be sleeping . 他现在肯定在睡觉。d但如果上述这些词 (must ,cant ) + have +过去分词则指对过去已发生的事进行推测。The road is wet. It must have rained last night . 地是湿的；昨天晚上肯定下雨了。There isnt any water on the road . It (cant ) couldnt have rained
11、 last night .地面上一个水滴都没有，昨天不可能下雨了。（四） have to的用法1. have（has）to +动词原形have（has）to后面要用动词原形。当主语为第三人称单数时用has to，当句子是过去时用had to。We have to leave now. 我们不得不现在就离开。He has to work on Sunday. 他不得不在周日工作。I had to do my homework last Sunday. 上周日，我不得不做作业。2. have to的否定句句型：主语+dont（doesnt, didnt, will not）have to+动词原形
12、You dont have to walk so fast. 你不必走那么快。He will not have to buy a new coat next year. 明年，他没必要买新外衣了。3. have to的疑问句句型：Do（Does, Did, Will）+主语+have to +动词原形？-Do you have to study maths now？ 你现在必须学数字吗？-Yes，I do.是的，必须学。/ No，I dont（have to）。不，不必学。-Did he have to ask the question？ 他非要问那个问题吗？-Yes，he did.是的。/
13、No，he didnt（have to）.不。4. must与have to比较must侧重于个人意志和主观上的必要，have to侧重于客观上的必要。如果用于过去时态或将来时态时，则要用have to的相应时态来代替must。但must可用于间接引语中表示过去的必要或义务。My brother was very ill，so I had to call for the doctor in the middle of the night.我弟弟病得很厉害，我只得半夜里把医生请来。（一般过去时）I havent got any money with me，so Ill have to borro
14、w some from my friend.我身上没有钱，只好向朋友借点了。（一般将来时）He said that they must work hard.他说他们必须努力工作。补充总结：I. 情态动词基本用法：情态动词用法否定式疑问式与简答can能力（体力，智力，技能）允许或许可（口语中常用）可能性（表猜测，用于否定句或疑问句中）can not / cannot /cant doCando?Yes,can.No,cant.couldcouldnt domay可以（问句中表示请求）可能，或许（表推测）祝愿（用于倒装句中）may not do Maydo? Yes,may.No,mustnt/c
15、ant.mightmight not doMightdo? Yes,mightNo,might not.must必须，应该（表主观要求）肯定，想必（肯定句中表推测）must not/mustnt doMustdo? Yes,must.No,neednt/dont have to.have to只好，不得不（客观的必须，有时态人称变化）dont have to doDohave to do?Yes,do. No,dont.ought to应当（表示义务责任，口语中多用shouldought not to/oughtnt to doOughtto do?Yes,ought. No,oughtnt.
16、shall将要，会用于一三人称征求对方意见用于二三人称表示许诺、命令、警告、威胁等shall not/shant doShalldo?Yes,shall. No,shant.should应当，应该（表义务责任）本该（含有责备意味）should not/shouldnt doShoulddo?will意愿，决心请求，建议，用在问句中would比较委婉will not/wont doWilldo?Yes,will. No,wont.wouldwould not/wouldnt dodare敢（常用于否定句和疑问句中）dare not/darent doDaredo?Yes,dare. No,dar
17、ent.need需要必须（常用于否定句和疑问句中）need not/neednt doNeeddo?Yes,must. No,neednt.used to过去常常（现在已不再）used not/usednt/usent to dodidnt use to doUsedto do?Yes,used. No,use(d)nt.Diduse to do?Yes,did. No,didnt.II. 情态动词must, may, might, could, can表示推测：以must为例。must + do(be)是推测现在存在的一般状态进行；must + be doing 推测可能正在进行的事情；mu
18、st +have done是推测可能已经发生过的事情。1. must“肯定，一定”语气强，只用于肯定句中。He must be a man from America. / He must be talking with his friend. / He must have already arrived there.2. may和might“也许”，后者语气弱，更没有把握。可用于肯定句和否定句。He may not be at home. / They might have finished their task. 3. can和could“可能”，could表示可疑的可能性，不及cant语气
19、强，用于肯定、否定、疑问句中。The weather in that city could be cold now.We could have walked there; it was so near.（推测某事本来可能发生，但实际上没有发生）Can he be in the office now? No, he cant be there, for I saw him in the library just now.(语气很强，常用于疑问句和否定句中)III. 情态动词注意点：1. can和be able to: 都可以表示能力。但be able to可以表达“某事终于成功”，而can无法表
20、达此意。Be able to有更多的时态。另外，两者不能重叠使用。2. used to和would: used to表示过去常常做现在已经不再有的习惯，而would只表示过去的习惯或喜好，不涉及现在。3. need和dare作情态动词和实义动词的区别：两者作情态动词时常用于否定句和疑问句。其形式为：neednt/darent do；Need/daredo?做实义动词时可用于肯定句，否定句和疑问句。其形式为：need(needs/needed)/dare(dares/dared) to do, dont(doesnt/didnt) need/dare to do二、虚拟语气 虚拟语气表示说话人的
21、意愿、假设、猜测或建议。虚拟语气不表示客观存在的事实，谓语动词用特殊的形式表示虚拟语气。1 表示与现在事实相反时的谓语形式。从句主句过去式 (be和were)would (should、could)+ 动词原形例如：If Tom were hungry, he would eat the bread. (In fact, Tom isnt hungry.)2 表示与过去事实相反的谓语形式。从句主句had + 过去分词would (should、could) + have +过去分词例如：If I had left a little earlier, I would have caught th
22、e early bus. (In fact, I didnt catch the bus.)3 表示与将来事实相反的谓语形式。 从句主句动词过去式should + 动词原形were to + 动词原形would (should、could) + 动词原形例如：If they came tomorrow, we would told them about it. (In fact, they wont come tomorrow。)4 动词wish后的宾语从句中，谓语动词可用过去式、过去完成式或would、might加原形。例如： I wish I were as strong as you.H
23、e wished I would stay with us.She wished I had attended the meeting yesterday.5 在有些动词如：suggest、insist、order等动词后，从句谓语动词用“should + 动词原形”，should可以省略。例如：He suggested that we (should) discuss the problem right now.6 在有些句型中如：It is important (necessary、natural、strange等) + that从句中的谓语动词用should + 动词原形，should可
24、以省略。例如：It is necessary that the doctor (should) be sent there at once.7 在It is time that, I would rather that句式中从句谓语动词用过去式。例如：It is time we went to bed.I would rather he came next week.第二节 实战演练一、复习时需注意的要点（一）情态动词1、情态动词在句中没有人称和数的变化。2、含有情态动词的句子改为否定句或疑问句不必加助动词，只需要将情态动词置于主语前，或在情态动词后加上not。例如： Must I write
25、 a letter to cheer him up?You neednt wait for me.3、 情态动词的过去式，例如cancould，maymight。但是少数情态动词只有过去式，例如used to表示过去常常。must的过去式往往用had to代替。4、 情态动词后还可接不定式的进行式、完成式和被动式。例如： He cant be doing his homework now. 他现在不可能在做功课。He must have attended the meeting last night. 昨晚他一定参加了会议。（二）虚拟语气1、 在if条件句中，如果含有were , should
26、或had等助动词，if可以省去，句子用倒装。例如： Were I you , I would buy this reference book.2、 should与would都可以用于if条件句的主句中，但should一般只用于第一人称，would用于所有人称。例如： If you were here , I would tell you the news .3、 某些条件可以用介词短语without , but for 等来表示 。例如： Without your help , I could not have succeeded in passing the exam .4、 有时句子通过b
27、ut或otherwise等词来表示真实与虚拟的转换，在这种情况下，只有不真实的部分用虚拟式。例如： I was ill yesterday；otherwise I would have played football with you . But for the heavy rain , we would have gone to the concert .5、 有suggest等词的相应的名词组成的同位语从句及表语从句用虚拟式。例如： I accepted my mothers suggestion that I should eat an apple every day . 二、历届高考试
28、题分析例1、There _ be any difficulty about passing the road test since you have practised a lot in the driving school. A. mustnt B. shant C. shouldnt D. neednt 答案：C【解析】 根据经验或惯例对某一情况进行推测，用should或ought to，常译成“按理应该”或“可能会”。shouldnt是其否定形式。例2、Is John coming by train? He should, but he _ not. He likes driving h
29、is car.A. must B. can C. need D. may答案为D。【解析】 come, go, leave, start等趋向动词的进行时表示将来时，所以答语是对这一将来动作做出的推断。may not“可能不；不一定”，根据he likes driving his car可以看出John可能乘火车来，也可能自己开车来。may not正好符合这一语境。must not“不准”；cannot“不可能”；need not“不必”。 例3、It is hard for me to imagine what I would be doing today if I _ in love, a
30、t the age of seven, with the Melinda Cox Library in my hometown.A. wouldnt have fallen B. had not fallenC. should fall D. were to fall答案为B。【解析】 根据句意和I would be doing可以判断这是虚拟语气。at the age of seven 是表示过去的时间状语，if从句中的谓语要用had not fallen，表示对过去情况的假设。由于主句中的谓语表示对现在的虚拟，条件句中的谓语表示对过去情况的虚拟，增加了试题的难题，但是，使用排除法可以容易地做出该题：should fall 和were to fall都可以用于条件句中表示对将来的虚拟；wouldnt have fallen不用于条件句中，所以都不能作为答案。译文：如果我不在七岁时就迷恋上了我们家乡的Melinda Cox图书馆，我真不能想象我今天会做什么。 例4、You cant imagine that a well-behaved gentleman _
