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1、Unit13 Grammar,情态动词must, can, could, may, might表推测的用法：,情态动词中的must, can, could, may, might都表推测。其中must的可能性最大，can / could次之，may / might最小。具体用法如下： 1. must的用法 （1）表示推测“可能性”时，意思是“一定、准是”，语气较肯定，较有把握。 He must be American. = It is certain that he is American. 他准是个美国人。,（2）must表推测只能用于肯定句。如果要表示“一定不、肯定不”的意思时，应用can
2、t,如询问某种可能时，应用can。 He must know my address. 他肯定知道我的地址。（一定） He cant know my address. 他肯定不知道我的地址。（一定不） Can he know my address? 他知道我的地址吗？（询问可能性）,3）must表示推测时，可以推测现在/正在发生的动作/过去发生的动作。 He must have a car now. （现在）他一定有辆小汽车。 He must be doing his exercises in the classroom.（正在进行）他一定在教室里做练习。 He must have finish
3、ed the work.（过去发生）他一定已完成了工作。 注：must表示推测时很少用于将来的情况。一般不用He must come tomorrow.可用Its certain / Im sure that he will come tomorrow.,（4）在反意疑问句中，当附属部分含有表示推测意义的must时，疑问部分的助动词应与must后面的动词在非推测情况下的用法保持一致。 He must be a worker, isnt he? （现在）他准时个工人，是吗？ It must have rained last night, didnt it? （过去）昨晚一定下雨了，是不是？ Yo
4、u must have learned English for many years, havent you? （完成时）你一定学了好多年英语，是吗？,2. can / could的用法 （1）can表示推测“可能性”时，往往用于否定句或疑问句。Cant“一定不”，语气很肯定。can在疑问句中意思是“会、可能”。 He cant be at home. = It is impossible that he is at home. 他一定不在家。 （2）can /cant后可接进行时/完成时，表示对现在发生的动作或过去发生的动作进行推测。 They cant be reading in the
5、library. 他们一定不在图书馆读书。 He cant have gone to Shanghai for I saw him a minute ago. 他不可能去了上海，我刚才还看见他。 Its so late. Where can she have gone? 天晚了，她可能去哪儿了呢？,（3）在反意疑问句中，当陈述部分含有表示推测意义的cant时，疑问部分的助动词应与cant后面的动词在非推测情况下的用法保持一致. He cant be a teacher, is he? 他不是教师，是吗？ She cant have finished her homework, has she?
6、 她一定没有完成家庭作业，是不是？ （4）could可用于表示某事有可能发生或可能是事实。 Dont eat it. It could be poisonous. 不要吃它，可能有毒。 The plane could be delayed by fog. 飞机可能会因为雾晚点。,5）could 还可以用于表示客气、委婉、礼貌的请求语气。 Excuse me, could you tell me the way to the bus station? Could you help me? （6）couldnt表示否定推测，表示某事不可能真实，或由于特定事实或环境某事肯定不会发生。 It coul
7、dnt possibly be poison. 这不可能是毒药。 注：有时与形容词的比较级连用强调某人或某物不可能再更多地具有某种属性。 You couldnt be more wrong. 你真是大错特错。 I couldnt be happier. 我简直是幸福极了。,3. may和might的用法 （1） may, might表示推测“可能性”时，意思是“可能”、“也许”，语气没有 must肯定。 He may / might be American. = It is possible that he is American. 他可能是个美国人。 注：might不表示过去时态，只是语气上
8、比may更委婉，表示的可能性更小。 （2）may, might表推测时，可以用于否定句，意思是“可能不、也许不”，但不用于疑问句。 He may / might not be at home. 他也许不在家。,（3）may, might可以推测现在正在发生的动作或过去发生的动作。 He may / might be sleeping now. （现在）他可能正在睡觉。 The boy may / might not be watching TV at home. （现在） 这个男孩可能没在家看电视 These students may / might have seen the film be
9、fore.（过去） 这些学生以前可能看过这部电影。 （4）may, might还可以推测将来的情况。 I think we should take raincoat with us, it may rain. 我想我们应该带上雨衣，可能要下雨了。 She might not come this afternoon. 她今天下午可能不来了。,一. Choose the best answers to complete the following sentences: 1. I thought you_ like something to read. So I have brought you s
10、ome books. A. ought B. might C. could D. must 2. That man must be Sarahs husband. -No, he_ be her husband. She is still single. A. cant B. mustnt C. may not D. ought to3. Peter _come with us tonight, but he isnt very sure. A. must B. may C. can D. will,4. What_ it be? -It_ be a mail box, for it is m
11、oving. It_ be a car. A. can; cant; must B. can; can; must C. can; mustnt; must D. must; mustnt; can 5. Look, someone is coming. Guess_ . -Jack. Hes always on time. A. who can it be B. who he may C. who he can be D. who it can be,6. I saw Mary in the library yesterday. -You_ her. She is still abroad.
12、 A. mustnt see B. cant have seen C. mustnt have seen D. couldnt see 7. David, you _play with the valuable bottle, you_ break it. A. wont; cant B. mustnt; may C. shouldnt; must D. cant; shouldnt,8. Susan refuses to marry Jack now. She _her mind. A. must change B. should have changed C. must have chan
13、ged D. would have changed 9. Sue_ come together with us tonight, but she isnt very sure yet. A. must B. may C. need D. will 10. Aunt Margaret_ the train, otherwise she would have arrived here by now. A. must have missed B. should have missed C. had missed D. might miss,情态动词+have+done”的使用情形分析,一、shoul
14、d have done/ should not have done 它们分别表示“过去本来应该（已经）（而实际上并没有）”/“过去本不应该（已经）而实际上却已经” 如：1、We should have studied last night, but we went to the concert instead . 我们昨晚本应学习的，但我们却去看音乐会了。（实际上没有学习） 2、If he had joined us , we should have had a more enjoyable time . 如果他加入我们的活动，我们就可以玩得更开心了。（实际上没那么开心，由于他没加入我们的活动
15、）,3、I should have thought of that 这一点我应该想到的。（但实际上没想到） 4、They shouldnt have left so soon . 他们不应当走得那么早。（但实际上还是走了） 5、He shouldnt have said such a thing .他当时不应该说那种话。（但已经说了） 在表示推测时，它表示的是“大概已经，或许已经”的意思。 如，1、The train should have already left.火车大概已经开走了。 2、Time is up , you should have finished your exercise
16、s . 时间已到，你们可能已经做完作业了。,二、would have done 它表示的是与过去事实相反之假设的结果，意思是“当时就会了”而实际上没有 如，1、 I would have helped you if I had known of your difficulties . 要是我当时知道你们的窘境，我就会帮助你了（而实际上没有帮助你） 2、If it hadnt rained yesterday, we would have gone on excursion .假如昨天没下雨，我们就去远足了。（实际上没有去）。 在表示推测时，它表示“过去大概是，似乎、可能”如 1、I suppose the writer would have been about thirty when he published his first work . 我想这位作家出版第一部作品时，大概是30岁左右。,
