情态动词用法

1、 在虚拟语气中的用法1. should have done 过去本应该做某事却未做shouldnt have done 过去本不该做某事却做了2. ought to have done 过去本应该做某事却未做oughtnt to have done 过去本不该做某事却做了3. need have done 过去本有必要做某事却未做neednt have done 过去本没必要做某事却做了4. could (不能用 can) have done 过去本能够做某事却未做。注意：其否定形式 couldnt have 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。”5. might (不能用 may) have done 过去本可以做某事却未做注意：其否定形式 might not have done 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。”二、表推测的用法1. must have done表示对过去某事的肯定猜测，译为：过去肯定做了某事。不存在 mustnt have done 的形式。其否定或疑问形式须用 can(could) 来表示. 例如：Since the road is wet, it must have rained last night. 既然路是湿的，那昨天晚上肯定下雨了。He cant have missed the way. I drew him a map. 他不可能迷路。我（当时）给他画了张图。“The dictionary has disappeared. Who could have taken it?” 词典不见了，（过去）谁可能把它拿走了？2. may / might have done may / might have done 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。may/might not have done表示“过去可能没有做某事。”例如： I cant find my keys. I may / might have left them at the school yesterday. 我找不到我的钥匙了。我可能昨天把他们落在学校了。John may/might not have passed the exam; he looks very sad.约翰可能没有通过考试。他看起来很忧伤。注意：may/might have done表推测不能用于疑问句中。3. can/could have done 表推测一般用在否定句和疑问句中，表示不相信或怀疑的态度。Can/Could he have passed the exam?他可能通过了考试吗？I think that he couldnt/cant have gone abroad. I saw him just now.我认为他不可能出国了。我刚才还看见他了。注：表示推测过去某动作发生的可能性时，就表示的可能性程度而言，must 最大，could 其次，may 更次之，might 最小。例如： 英语里形容词的比较级有三个等级,原级（positive degree）as+原级+as.如：Im as tall as my twin brother.我和我的双胞胎哥哥一样高.比较级（comparative degree)比较级+than. 如：My father is younger than my uncle.我的父亲比我的伯父年轻.最高级（superlative degree）The+ 最高级1. Sorry Im late. I _ have turned off the alarm clock and gone back to sleep again. （2000 北京春季）A. might B. should C. can D. will 答案为 A。表推测的用法。句意：对不起，我迟到了。我（当时）兴许是关了闹钟又回去睡觉了。might 相当于 may, 但语气更加不肯定。2. I was really anxious about you. You_ home without a word. （01 全国）A. mustnt leave B. shouldnt have left C. couldnt have left D. neednt leave答案为 B。虚拟语气用法。句意：我（那时）真地很担心你。你本不应该不留个话就离开家。3. Ill tell Mary about her new job tomorrow. You_ her last week. （04 福建）Aought to tell Bwould have told Cmust tell Dshould have told答案为 D。虚拟语气用法。句意：-我明天要告诉她我的新工作的情况。 -你本应该上周告诉她。4. Tom graduated from college at a very young age. Oh, he _ have been a very smart boy then. （04 全国IV） A. could B. should C. might D. must答案为 D。表推测的用法。句意：汤姆很年轻的时候就大学毕业了。哦，他肯定是一个很聪明的男孩儿。5. He _ have completed his work; otherwise, he wouldnt be enjoying himself by the seaside. (05 北京卷) A. should B. must C. wouldnt D. cant答案为 B。用法同4题。句意：他肯定做完了工作，不然他就不会在海边痛快地玩儿了。6. Do you know where David is? I couldnt find him anywhere. Well. He have gone farhis coats still here. （05湖北卷）Ashouldnt Bmustnt Ccant Dwouldnt答案为 C。表推测的用法。句意：你知道大卫在哪儿吗？我哪儿也找不到他。瞧，他不可能走远他的上衣还在这儿呢。cant 相当与 couldnt，但后者语气更加委婉。 四、练习1. The woman biologist stayed in Africa studying wild animals for 13 years before she returned. Oh, dear! She _ a lot of difficulties! (05 江苏卷) A. may go through B. might go throughC. ought to have gone through D. must have gone through2. I have lost one of my gloves. I _ it somewhere. （05 北京春季）A. must drop B. must have dropped C. must be dropping D. must have been dropped 3. Mr. White _ at 8:30 for the meeting, but he didnt show up. （04 广西） A. should have arrived B. should arriveC. should have had arrived D. should be arriving4. He paid for a seat, when he _ have entered free. （05 山东卷）A. could B. would C. must D. need5. Tom is never late for work. Why is he absent today? Something _ to him. (05 江西卷) Amust happen Bshould have happened Ccould have happened Dmust have happened6. I _ have been more than six years old when the accident happene