1、 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。如表示“一定不、肯定不”的意思时，应用cant,如询问某种可能时，应用can。He must know my addr
2、ess.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 finished 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
3、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？You must have learned English for many years,havent you?（完成时）你一定学了好多年英语，是吗？比较：It must have rained last night,didnt i
4、t?（过去）昨晚一定下雨了，是不是？He must have arrived by yesterday morning,hadnt he?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”，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+have done，表示对过去发生的动作进行推测。He cant have gone to Shanghai for I saw him a minute ago.他不可
5、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）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?（4）could have done本能做但未做，表虚拟语气I could have done it well，but I wasnt so careful then.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”H
6、e 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.The boy may/might not be watching TV at home.这个男孩可
7、能没在家看电视These students may/might have seen the film before.（过去）这些学生以前可能看过这部电影。u Choose the best answers:1.I thought you_ like something to read.So I have brought you some books.A.ought B.might C.would D.must 2.That man must be Sarahs husband.-No,he_ be her husband.She is still single.A.cant B.mustnt
8、C.may not D.ought to 3.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 moving.It_ be a car.A.can;cant;must B.can;can;mustC.can;mustnt;must D.must;mustnt;can5.Look,someone is coming.Guess_.-Jack.Hes always on time.A.who can it be
9、B.who he mayC.who he can be D.who it can be6.I saw Mary in the library yesterday.-You_ her.She is still abroad.A.mustnt see B.cant have seen C.mustnt have seen D.couldnt see7.David,you _play with the valuable bottle,you_ break it.A.wont;cant B.mustnt;mayC.shouldnt;must D.cant;shouldnt 8.Susan refuse
10、s to marry Jack now.She _her mind.A.must change B.should have changedC.must have changed D.would have changed9.Sue_ come together with us tonight,but she isntvery 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
11、have missedC.had missed D.might miss 情态动词+have+done”表“本来”使用情形分析一、should have done过去本来应该（而实际上并没有)should not have done 本不应该 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）二、could have done它表示过去本来能够 实际上没能做。如1、I could have run 100 metres in
12、 12 seconds.我本来能用12秒钟完100米的.（实际上没能）2、If you could have finished the task in time，you could have been promoted.如果你当时能如期完成那任务的话，你可能已提升了（实际上没有被提升）三、need not have done它表示过去已做的事，事实上没有必要。如，1、I need not have got up so early.我本来不必要那么早起床的（事实上早已起床）2、I need not have waited for the train for an hour.我本来不必要等一个小时
13、的火车。（事实上已经等了一个小时）问题:would have done在什么情况下使用呢?四、would have done 用在虚拟语气中表示与过去事实相反之假设的结果，常与if 的条件句连用。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 out for a walk.假如昨天没下雨，我们就去散步了。（实际上没有去）。Practice1.Mr White
14、_ at 8:30 for the meeting,but he didnt turn up.A.should have arrived B.should arrive C.should have had arrived D.should be arriving2.If he had been here yesterday,he _ this pop star.A.would meet B.would have metC.met D.must have met3.It is hard for me to imagine what I would be doing today if I_ in love at 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
