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would should could have done用法和区别


would/could/might/should have done 等 用法和区别
一、在虚拟语气中的用法(情态动词都是过去时态!) 1. should have done:原本应该做某事,(否)shouldn't have done : 原本不该做某事 2. ought to have done 原本应该做某事,(否) oughtn't to hav

e done :原本不该做某事 注意: ought to do 语气更强,常用于长辈对小辈的用语 或某规则上的要 求(严格的规则应用 must ). should do 可用语平辈朋友间,较为客气与口语化 3. need have done 原有必要做某事 本没必要做某事 注意:做情态动词,need 的过去式仍然是 need;做实意动词,need 的过去式是 needed. 4. could have done 原本能够做某事 注意: couldn't have done 无虚拟语气的用法, 只表推测,相 当于 can't have done:过去不可能做了某事 (否) needn't have done 原

5. might have done 原本可以做某事 注意: might not have done 无虚拟语气的用法, 只表推测, 相当于 may not have done:过去可能没有做某事

6.would have done 原本会做某事 1. I would have told you all about the boy's story, but you didn't ask me. 二、对过去事情表推测的用法(情态动词用原型或过去式都可以,只 是在说话者看来,可能性大小稍微有所不同而已) 1. must have done:过去肯定做了某事。不存在 mustn't have done 的形式。其否定或疑问形式须用 can(could)have done:“不可能做 过某事” 来表示: 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 can't/couldn`t 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/can 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:过去可能做了某事,may 比 might 表示可 能性稍大些。 may/might not have done 过去可能没有做某事: I can't 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,疑问句中表 推测,一般用 can/could have done sth.很可能做过某事 3. can/could have done 常用于(否定句)和(疑问句),间或(肯定句) Can/Could he have passed the exam ? 他可能通过了考试吗 ?

I think that he couldn’t/can't 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: “He must / could / may / might have heard of it from Mary.” “他肯定/很可能/可能/兴许 (没准儿) 已从玛丽那儿听说此事了。 ” 4.would have done:想必会/肯定会做某事 President Obama has canceled plans to set stronger air qualit y rules in the United States.The president said these plans wo uld have forced(想必会/肯定会迫使) businesses to take action at a time when the country's econo my is weak. On Friday, president Obama ordered environment officials to halt a plan that would have affected (想必会/肯定会 影响) companies, states and cities. All three would have requi red to reduce the amount of chemicals that case smog. Failure to do so, would have led to(肯定会/想必会导致) feder

al action.


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