情态动词的推测及虚拟用法历来都是大学英语四级考试的重要内容。情态动词的推测就是指讲话者使用情态动词表示对客观事物的主观看法，而当表示对客观事物的一种主观愿望、假设和建议时，就要用虚拟语气。常用来表示推测和虚拟的情态动词有can,may,could,might,should,ought to,must,need等。

　　下面是情态动词表示推测及虚拟的常见用法：

　　1.情态动词＋动词原形，表示对现在或将来情况的推测。例如：

　　I don't know where she is;she may be in Wuhan.我不知道她在哪儿，可能在武汉。

　　2.情态动词＋动词现在进行时，表示对现在或将来正在进行的情况进行推测。例如：

　　At this moment,our teacher must be correcting our exam papers.这时，想必我们老师正在批改试卷。

　　3.情态动词＋动词完成时，表示对过去情况的推测。它又分以下几种：

　　1)may(might)have＋done sth,can(could)have＋done sth.表示对过去时间里可能发生的事情的推测，表示可能性程度由大到小依次为can,could,may,might。

　　否定句may(might)not have＋done sth., can(could)not have＋done sth.表示推测过去时间里不可能发生的事情。例如：

　　Philip may(might)/can(could)have been hurt seriously in the car accident.菲利普可能在车祸中受了重伤。

　　Mike can't have found his car,for he came to work by bus this morning.迈克不可能找到他的车，因为他今天早上是乘公共汽车来上班的。

　　2)must have + done sth.,对过去时间里可能发生的事情的肯定推测，语气较强，具有"肯定"，"想必"的意思。例如：

　　The road is wet.It must have rained last night.路是湿的，昨晚一定下过雨。

　　3)ought to have＋done sth.,should have

　　done sth.表示本应该做某事，而事实上并没

　　有做。否定句oughtn't to have done sth.,shouldn't have done sth.,表示本不该做某事但却做了。例如：

　　You ought to(should)have been more careful in this experiment.你当时在做试验时应该更仔细点。

　　He ought not to(shouldn't)have thrown the old clothes away.他不该把旧衣服扔了。(事实上已经扔了。)

　　4)needn't have＋done sth.表示本没有必要做某事，但却做了。例如：

　　I dressed very warmly for the trip,but I needn't have done so.The weather was hot.这次旅行，我穿得衣服较多，其实没有必要。那时天很热。

　　4.情态动词＋动词的现在完成进行时，表示对过去一直在做的事情的推测。例如：

　　Your mother must have been looking for you.你妈妈一定一直在找你。

　　下面以分析历年四级考题为实例来学习情态动词的推测及虚拟用法。

　　题1：Mary's score on the test is the highest in her class;she have studied very hard.(1989,1,41)

　　A.may B.should

　　C.must D.ought to

　　正确答案为C。译文：玛丽考试成绩全班第一，她学习一定很刻苦。空格后的动词用的是完成式，表示已经发生的动作。结合选项可知，空格中要填入一个情态动词，表示说话人对玛丽考试能取得好成绩原因的推测。A项表示对过去发生的事的可能性的推测，意思是"玛丽可能学习很刻苦"，B项和D项表示本该做某事但却没做，意思为"玛丽本应该学习很刻苦"。只有C项符合题意。

　　题2：With all this work on hand ,he

　　to the cinema last night.(1989,1,45)

　　A.mustn't go B.oughtn't to go

　　C.wouldn't go D.shouldn't have gone

　　正确答案为D。译文：他手头有这么多工作，昨晚不该去看电影。本句表达的是昨天已经发生但却不该发生的事情，所以应该用情态动词should的否定式，后接动词的完成式。

　　题3：You her in her office last Friday;she's been out of town for two weeks.(1996,1,23)

　　A.needn't have seen　　B.must have seen

　　C.might have seen　　　D.can't have seen

　　正确答案为D。译文：上星期五你不可能在她办公室见到她，她去外地已经两个星期了。选项A表示本没有必要做某事，但却做了，如选A意思是"你已见着她了"；选项B表示对过去发生的事情的肯定推测，如选B意思是"你一定已经看到她了"；选项C表示对过去可能发生的事情的推测，如选C意思是"你可能看到她了"，而根据后半句意思"她已经去外地两个星期了"来推测只有选项D符合题意。

　　题4：You all those calculations! We have a computer to do that sort of thing.(1991,6,53)

　　A.needn't have done

　　B.shouldn't have done

　　C.must not have done

　　D.cannot have done

　　正确答案为A。译文：你没有必要把全部计算都做了，这类计算我们用计算机来做。选项B表示本不该做的事，但却做了，选B意思为"你本不应该做了全部计算"，含有责备的含义。选项C意思为"不许，禁止"。D选项表示对过去发生的事情的可能性的推测，意思是"你不可能做了全部计算"。根据句意，只有A项符合题意。

　　题5：It was very kind of you to do the washing-up ,but you it.(1998,6,44)

　　A.mustn't have done

　　B.wouldn't have done

　　C.mightn't have done

　　D.needn't have done

　　正确答案为D。译文：你把这些东西都洗了，真是太好了，但你是没有必要洗的。选项A中must not意思为"不许，不允，禁止"，其否定推测用can't或couldn't。选项B主要用于条件从句的虚拟语气。选项C是推测过去的某种可能性，意思为"你不可能洗的"。A，B，C都不符合题意，只有D项符合，表示过去本不必要做的事，但实际上却做了。

　　题6：Research finding shows we spend about two hours dreaming every night,no matter what we during the day.(1999,4, 54)

　　A.should have done

　　B.would have done

　　C.may have done D.must have done

　　正确答案为C。译文：研究结果表明，我们每晚有两个小时在做梦，不管白天做了什么。根据句意，空白处应填上可能发生的事，而A项表示本应该做而没有做的事，B项用于if条件句，D项表示"一定已经做了"，表示对过去发生的事情的肯定推测，只有C项表明可能做了某事，是对过去可能发生的事情的一种推测。故C项为正确答案。

　　题7：Investigators agreed that passengers on the airliner at the very moment of the crash.(2002,6,67)

　　A.should have died B.must be dying

　　C.must have died D.ought to die

　　正确答案为C。译文：调查人员一致认为

　　客机上的乘客肯定是在坠毁的那一刻丧身的。通过"agreed"可以知道这是对过去发生事件的猜测。B，D项都不是虚拟语气，只能在A，C项中选择。A项表示"本该丧身而没丧身"。只有C项表示对过去发生的事情的肯定推测，意为"一定已经丧身了"，符合题意。

　　题8：The careless man received a ticket for speeding.He have driven so fast.(2002,12,33)

　　A.can't B.wouldn't

　　C.shouldn't D.mustn't

　　正确答案为C。译文：这个粗心的人因为超速而收到一张罚单，他不应该开得那么快。A项表示对过去不可能发生的事情的推测；B项主要用于非真实条件从句中，主句表示对过去的假设；D项意思为"不许"，"禁止"；C项表示本不该做的事但却做了，选C意思为"他本不该开得那么快"，正好符合题意。

　　练习：从A、B、C、D中选择最佳答案。

　　1.-What has happened to Mary?

　　-I don't know,she lost.

　　A.should have got B.may have got

　　C.might get D.could get

　　2.You should have told us about it.We

　　you.

　　A.could have helped

　　B.must have helped

　　C.should have helped

　　D.will have helped

　　3.You to the meeting to discuss that

　　matter if you were really serious about your

　　work.

　　A.ought to come

　　B.ought to have come

　　C.must come D.must have come

　　4.He is an hour late.He by fog,of

　　course,that's only a possibility.

　　A.may have been delayed

　　B.should have been delayed

　　C.can have delayed

　　D.must have been delayed

　　5.Mary the bus,otherwise she would

　　have arrived here by now.

　　A.missed B.had missed

　　C.should have missed

　　D.must have missed

　　6.The dentist said that my tooth had become

　　worse and I it pulled out.

　　A.should have had B.might have had

　　C.needn't have had

　　D.mustn't have had

　　7.You that car with the brakes out of

　　order.You might have had a serious accident.

　　A.ought to drive B.oughtn't do drive

　　C.ought not to have driven

　　D.ought not have driven

　　8.She was thankful that she'd had her baby in

　　hospital;otherwise ,she thought the baby

　　.

　　A.died B.had died

　　C.might have died D.might die

　　9.He in London by eleven o'clock,

　　but he started too late.

　　A.should be B.ought to have been

　　C.must have been D.might have been

　　10.They out because the light's on!

　　A.mustn't have gone

　　B.may not have gone

　　C.should not have gone

　　D.needn't have gone

　　11.When we got to the theatre,the play hadn't

　　started yet,so we .

　　A.needn't hurry B.didn't need to hurry

　　C.needn't to hurry

　　D.needn't have hurried

　　12.It was really very dangerous;you

　　him seriously.

　　A.might have injured B.could injure

　　C.should have injured D.must injure

　　答案：1.B2.A3.B.4.A5.D6.A7.C8.C9.B.10.B.11.D12.A

　　(文/河北工程学院徐运红;英语通大学英语四级考试版03~04学年第10期;版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)