情态动词+have done结构

1、nIII. 情态动词情态动词+have+done 结构结构n1. can / could have donen表对过去事态的推测n情态动词can表推测时，用于否定句及疑问句，所以can have done 不用于肯定句中。但could have done 可用在否定句，疑问句以及肯定句中。（见第七小题）nThat cant be Mary-shes in hospital.nCan he still be alive after all these years?nCan/Could he have passed the exam?n他可能通过了考试吗？nI think that he coul

2、dnt/cant have gone abroad. I saw him just now.n我认为他不可能出国了。我刚才还看见他了。nCould have done 用于肯定句：nTom could have taken it; he was here alone yesterday.nDont worry-they could have just forgotten to phone.n（张道真，实用英语语法，2006, 270页）n注意，在虚拟语气中在虚拟语气中：ncould (不能用 can) have done 表示“过去本能够做某事却未做。” n其否定形式 couldnt have

3、 done 没有虚拟语气的用法，couldnt have done 只能表推测，相当于 cant have done，意为：“过去不可能做了某事。”nHe could have passed the exam, but he was too careless. n本来他能够通过考试，但是他太粗心。n（张：271）n2. may / might have done n表示“过去可能做了某事”。may 比 might 表示的可能性在说话人看来稍大些。nmay/might not have done表示“过去可能没有做某事。”nI cant find my keys. I may / might h

4、ave left them at the school yesterday. n我找不到我的钥匙了。我可能昨天把他们落在学校了。nJohn may/might not have passed the exam; he looks very sad.n约翰可能没有通过考试。他看起来很忧伤。n注意：may/might have done表推测一般不用于疑问句中。n在句型使用方面：两者均可用于肯定句和否定句，但用于疑问句时，may通常不用于句首，但可用于疑问句的句中(如特殊疑问句等)，而might尽管可以用于疑问句的句首，但不算普通，通常会改用其他句式(如用could等)： nHe may migh

5、t know the answer. n他可能知道答案。nAnd who may might she be? n那么她会哪一位呢？ nDo you think he may might not be able to pay? n你认为他可能会付不起钱吗？ nMight it be true? 那会是真的吗？ n【注】在很正式的文体中，may 可用于否定疑问句的句首： nMay we not be making a big mistake? n我们难道不可能在犯大错误吗？ n在虚拟语气中：nmight (不能用 may) have done 表示“过去本可以做某事却未做。” n注意：其否定形式

6、might not have done 没有没有虚拟语气的用法，might not have done 只能表推测，相当于 may not have done，意为：“过去可能没有做某事。”nThe pills might have helped him, if hed taken them regularly.n如果这些药片他定时吃，可能对他是有效的。（张：274）n3. must+have+donen表示对过去事情的肯定推测，译成“一定做过某事”n该结构只用于肯定句nIt must have rained last night, for the ground is wet. n昨晚一定下雨

7、了，因为地面还是湿的。nYou must have been mad to speak to the servant. n你和仆人说话，一定是发疯了。n注意：n表推测的must的否定形式用cant,而不是must notnHe cant have been there, for no one has ever seen him.n他一定没去过那里，因为没有人见过他。n（大学教材全解 综合教程3：138）n4. “would+have+done”n虚拟语气n表示对过去事情的假设，意思是“本来会做”n I would have told you all about the boys story, but you didnt ask me. n我本来会告诉你这个小男孩的故事，但是你没有问我。nWithout your help, I wouldnt have achieved so much. n没有你的帮助，我是不会取得如此大的成绩。nI would have done more, if Id had the time.n