内 容 提 要
情态动词有can（能），may（可以），must（必须），have to（不得不），ought to（应该），dare（敢），used to（过去经常），had better（最好），would rather（宁愿）。在肯定句中它们后边都要接 动词原形 .在否定句中，can，may，must和dare后边加not；have to和ought to分别在have和ought后加not；used to的否定式可用used not to，也可用didn't use to，但后者用得较多；had better和would rather的否定式分别是had better not和would rather not.这些情态动词与现在完成时连用在某种意义上有一定的虚拟性。
情态动词与完成时的使用
一、must+have+ED分词：用于肯定句，表示对过去情况的一种肯定推测，表示“肯定，一定”
1） It around nine o'clock when I drove back home because it was already dark.
［A］ had to be ［B］ must have been ［C］ was to be ［D］ must be
2） John's score on the test is the highest in the class；
［A］ he should study last night
［B］ he should have studied last night
［C］ he must have studied last night
［D］ he must had to study last night
3） After searching ［A］ for evidence in the house，the police concluded ［B］ that the thief must have come in ［C］ through the window and stole ［D］ the silver while the family was asleep.
二、may （might）+have+ED分词：用于肯定句和否定句，表示对已发生事情的不肯定的推测，相当于“可能，大概，”其中might较may 语气更弱，把握更小
She might have gone to see her doctor last week， but I am not sure.
上星期或许她去看医生了，但我不敢肯定。
Don't worry， your husband may not have been hurt seriously.
别急，你丈夫也许伤得不厉害。
三、should（ought to）+have+ED分词：肯定句表示过去本应发生的事却没有发生；否定句表示已发生了本不该发生的事。前者可译为“本应，”后者为“本不该”
You should have apologized to her for not soon replying to the letter. 你本应向她道歉，说明为什么没能及时回信。（可你没这么做）
4） You yesterday if you were really serious about your work.
［A］ ought to come［B］ ought to be coming［C］ ought to have come［D］ ought have come
四、can（not） +have+ED分词
He is an hour late —— He can have been delayed by fog. Of course，that's a possibility.他迟到了1小时，可能因为大雾而耽搁了。当然这只是可能性问题。
The poem can not have been written by her since she was only five years old then.这诗不可能是她写的，因为她那时才5岁。
五、“could+have+ED分词”有时用于表示过去的时间，说明某事可能或不可能已发生；有时可表示过去本来可以做某事，但却未做
I simply can't understand how he could have made such a mistake. 我简直不明白他怎么会犯那样的错误。
He walked there，but he could have taken a taxi. 他走着去了，可当时完全可以坐出租。
“couldn't+have+ED分词”还表示无论如何也不可能或没有做到
I couldn't have called you. I wasn't near a telephone. 反正我也不可能给你打电话，我附近没有电话。
5） “We didn't see him at the lecture yesterday.”“He it.”
［A］ mustn't attended［B］ couldn't have attended［C］ would have not attended［D］ needn't have attended
六、needn't+have+ED分词：表示对过去不必做的事情却做了，可译为“其实不必”
6） You all these parcels yourself.The shop would have delivered them if you had asked a shop assistant.
［A］ didn't need to carry［B］ needn't have carried［C］ needn't carry［D］ didn't need carry
七、used to 表示过去的习惯动作或状态，现在已不存在，在否定陈述句中，一般用didn't use to，也可用used not to；在疑问句中用“Did…use to”。used to还可never，often，always等连用。注意used to与be used to的不同，后者表示be accustomed to “习惯于某种状态”，而且跟接名词或ING形式，而used to后接动词原形，试比较
He used to drink. 表示“他过去经常喝酒”而现在不喝了。
He is used to wine （He is used to drinking wine） at each meal.
表示“他现在已养成习惯，每顿饭喝点葡萄酒。”
八、had better表示“最好……”，后接动词原形，其否定式为had better not＋动词原形
You had better not follow his behavior. 你最好不要学他。
九、would rather 意思是“宁愿”，表示选择。它有两种用法，一是在肯定句中后边直接跟动词原形，其否定句是在would rather 后加not，即 would rather not＋动词原形；二是它后边可以跟接从句，该从句的谓语动词用一般过去式表示虚拟语气。由于would rather表示选择，它后边可跟接than
She would rather sleep than talk rubbish. 她宁愿睡不愿闲聊。
7） “Did you criticize him for his mistakes？”——“Yes，but it.”
［A］ I'd rather not do［B］ I'd rather not doing［C］ I'd rather not have done［D］ I'd rather not did
［注］ would rather和had rather都表示“宁愿”，在用法上也没有区别。但如果说would rather与had rather完全一样（Longman Dictionary of Comtemporary English 如是说），这一说法有争议。其实had rather在现代标准英语中几乎已经不用了。这对我们考试来说是比较重要的，因为一般考题作为标准英语是不用had rather的。
十、例题解析
1） B为正确答案。2） C为正确答案。
3） D错。改为stolen.这里C处和D处是并列的谓语，D处相当于must have stolen.
4） C为正确答案。5） B为正确答案。6） B为正确答案。7） C为正确答案。
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