情态动词与虚拟语气易错点.doc

情态动词与虚拟语气易错点 　　一、情态动词+ have done 1. should/ ought to+have done表示“过去本该做某事”。如： You should/ ought to have come to the conference yesterday. What was the reason for your absence？ 2. must have done 表示对已经发生的事情很肯定的推测，意为“一定/想必做了某事”，只能用于肯定句中。如： The lights were out. They must have been asleep. 3. can/ could have done 用于否定句和疑问句中，表示对过去发生事情的怀疑和不肯定；could have done也可用于肯定句中，表示本来可以做，而实际上没做。如： You cant/ couldn’t have him met at the meeting yesterday. He went abroad two weeks ago. The ground is dry. Can/ Could it have rained last night？ The accident could have been avoided. 4. neednt have done 表示“做了本来不必去做的事”，而didnt need to do 表示“过去没必要做而实际上也没做”。如： You neednt have taken so much cash with you――it nearly got stolen. I didn’t need to clean the windows. My brother did it. 5. may/ might have done 意为“可能做过某事”。此外might have done 还可以表示“本可能做而实际上未做”。如： Sorry I am late. I may/ might have turned off the alarm clock. You might have given him more help， though you were busy. 二、 情态动词的其他用法 1. shall用于二三人称陈述句中，表示命令，威胁，许诺，警告，决心等。如： One of our rules is that every student shall wear school uniform while at school. ――Mum， would you please buy me an MP5 player？ ――If you can help do the dishes the whole vacation， you shall have one as a reward. 2. must用于第二人称，表不满、抱怨等情绪，常译成“偏要、硬要”。如： If you must smoke， please go outside. Why must you be talking so loudly while others are studying？ 3. may作“可以”讲时，其否定式是mustnt，表示“被禁止”；must作“必须”讲时，其否定式是neednt，表示“不必”。如： ――May I use your car？ ――No， you mustnt. （委婉地拒绝可用：Sorry， but I am using it now.或Youd better not.等） ――Must I work out the problem tonight？ ――No， you neednt. 三、 常见的一些虚拟 1. 若条件句中有were， had， should， 可把if省略，而把were， had， should放在主语前，形成倒装结构。否定句中not放在主语后。如： Were I you， I wouldnt do that. Had you come earlier， you would have caught the bus. Had you not come late， you would have caught the bus. Should it rain tomorrow， I would stay at home. Should it not rain tomorrow， I would go o