语法重要知识点情态动词与虚拟语气.doc

情态动词与完成式连用1. may have done 表示过去的某种可能性，意为“可能或许已经”，有时带有婉转的抱怨或批评之意。The train may have left already. 火车可能已经开走了2. might have done可以有两层意思：一是表示过去可能发生事情的推测，意为“有可能”，其用法与may have done相似；二是虚拟语气用法，表示某事过去有可能发生（但是实际上并没有发生），常用来表示埋怨。They might have been there before. 他们以前可能到过那儿。You might have let me know earlier. 你本可以早点让我知道的。3. cant have done表示否定的推测，即推测过去某件事“一定没有发生，不可能发生，不可能已经”（与must have done相对）。He cant have gone to Peking. I saw him only a while ago.他不可能到北京去了。我刚才还看见他呢。 4. could have done 也可以有两种用法：一是虚拟语气的用法，表示过去有可能做某事而没有做，意为“本来可以会，本能够”（但事实上没有），其否定式couldnt have done意为“本不会，本不能”（但实际上做了）。二是表示对过去或已经发生事情的推测，意为“有可能（已经）”I could have lent you the money. Why didnt you ask me?我本可以把钱借你。你为什么不管我借呢？I didnt see him yesterday. He could have gone to Shanghai.昨天我没看见他。他有可能已经去上海了。5. couldnt have done可以表示对过去或已经发生事情的否定推测，意为“不可能，不会”。6. would have done表示过去会发生而未发生，常用于虚拟语气的主句，表示对过去情况的假设。If Jane had known about the sale, she would have gone. 7. should have doneought to have done也有两种用法：一是虚拟语气的用法，表示过去应该做而没有做，译为“本应该，本应当”（其否定式shouldnt have doneoughtnt to have done表示过去不应该做的事而做了，译为“本不该，本不应当”）；二是表示对过去的推测，译为“应当（已经）”。This ATM has been out of service for a few days. It should have been fixed last week.Ten oclock. She should have arrived in her office by now.8. must have done用于肯定句，表示对过去情况较有把握、肯定性的推测，常译为“一定”，“准是”，“肯定”。其否定式用cantcouldnt have done表示“不可能做过”或“不可能发生”。Jack must have gone awaywe cant find him anywhere in the factory.9. neednt have done表示过去本不必做的事，但事实上做了。（也可以说didnt have to）.They neednt have been punished so severely.虚拟语气1、虚拟语气用于非真实条件句时的构成虚拟语气If从句主句与现在事实相反动词用一般过去式（be用were）Would (should, might, could)动词原形与过去事实相反动词用过去完成式Would (should, might, could)have done与将来事实相反或推测1. should动词原形2. were to动词原形3. 动词的一般过去式Would (should, might, could)动词原形例如：a. If it werent for their support, we would be in a very difficult position.b. The little girl wouldnt have caught cold if she had put on more clothes.c. If they were toshould act like that again, we should criticize them severely.2. 虚拟语气在名词性从句中的用法1）表示要求、建议、决定、命令、假设等动词后面的宾语从句中谓语动词要用虚拟语气，形式为（should）动词原形。在使用“It is / was此类动词的过去分词that从句”结构中，从句中的谓语动词须用“should动词原形”的形式。此类动词有：表示愿望的：desire, prefer等表示建议的：advise, move, propose, suggest, recommend等 表示要求、请求的：ask, beg, insist, maintain, oblige(强迫，迫使),request，require, urge等表示命令的：command, dictate（命令，强制规定）, direct, order等表示决定的：decide, determine, resolve等2）某些名词，特别是上面提到的表示建议、要求、命令等含义的动词相应的名词形式，在其同位语从句或其作为主语的表语从句中，谓语动词要用“（should）动词原形”。这些常用名词包括：advice, command, decision, demand, desire, determination, insistence, motion, necessity, order, preference等。3）在“It is / was形容词that从句”的结构中，常用“（should）动词原形”作从句的谓语。用于这种结构的形容词包括：advisable, appropriate, better，crucial, compulsory, desi