情态动词用法详解,情 态 动 词 的 定 义,情态动词是一种本身有一定的词义，表示说话人的情绪、态度或语气的动词，但不能单独作谓语，只能和其他动词原形构成谓语。 We can be there on time tomorrow. May I have your name? Shall we begin now? You must obey the school rules.,can / could,may / might,must,shall / should,will / would,need,dare,ought to,had better,cannot / could not,cant / couldnt, + not,maynt / mightnt, + not,mustnt, + not,shant / shouldnt, + not,wont / wouldnt, + not,neednt, + not,darent,ought not to,oughtnt to,Had better not,d better not,情 态 动 词 的 位 置,情态动词在句中放在谓语动词之前，谓语动词前若有助动词，则在助动词之前，疑问句中， 情态动词放在主语之前。 I can see you. Come here. 我能看见你，过来吧。 He must have been away. 他一定走了。 What can I do for you? 你要什么？ How dare you treat us like that! 你怎么敢那样对待我们!,情 态 动 词 的 特 点,情态动词无人称和数的变化，情态动词后面跟的动词需用原形，否定式构成是在情态动词后面加“not”。个别情态动词有现在式和过去式两种形式，过去式可以用来表达更加客气、委婉的语气，时态性不强，可用于过去，现在或将来。 He could be here soon. 他很快就来。 We cant carry the heavy box. Im sorry I cant help you. 对不起，我帮不上你。,情 态 动 词 的 用 法,、表能力 （can, could, be able to, were / was able to, could have done） 1. 表现在的或一般的能力：表示现在的或一般的能力用can 或 be able to. 一般的能力是指你无论什么时候做什么事情就能做到的能力。表示现在的能力或一般的能力时，can比be able to 更普遍。,、表能力 ：表现在的或一般的能力：表示现在的或一般的能力用can 或 be able to. 一般的能力是指你无论什么时候做什么事情就能做到的能力。表示现在的能力或一般的能力时，can比be able to 更普遍。 A computer cant think for itself; it must be told what to do. （表示一般的能力） I am starving to death. I can eat two bowls of rice now. （表示现在的能力）,2. 表示将来的能力 表示将来的能力用 will be able to. If you have a good sleep, you will be able to work out this problem. 3. 表示过去的能力 （1）could , was/ were able to 表示过去一般的能力，即不表示做与未做某事。 She could / was able to sing like an angel when she was a child.,3. 表示过去的能力 （1）could , was/ were able to 表示过去一般的能力，即不表示做与未做某事。 She could / was able to sing like an angel when she was a child. (2) was/ were able to 表示过去有能力并且成功地做了某事，相当于managed to do something / succeeded in doing sth. The fire spread through the hotel very quickly but everyone was able to get out. (过去有能力并成功地做了某事),(3) could have + 过去分词，表示过去有能力做但未做。 I could have worked out the problem, but I didnt.,二、表推测 。 可能性可分为客观的可能性和具体事情实际发生的可能性两种。 所谓客观的（理论的）可能性即不涉及具体某事是否发生，此种用法常常可以说明人或事物的特征。 情态动词 can 可用于肯定句中表示客观的 / 理论的可能性， 而表示具体事情发生的可能性时，can 一般不用于肯定句。 Accident can happen on such rainy days. （客观的可能性）,二、表推测 。 1. 可能性可分为客观的可能性和具体事情实际发生的可能性两种。所谓客观的（理论的）可能性即不涉及具体某事是否发生，此种用法常常可以说明人或事物的特征。情态动词 can 可用于肯定句中表示客观的 / 理论的可能性，而表示具体事情发生的可能性时，can 一般不用于肯定句。 Accident can happen on such rainy days. （客观的可能性） Peter may come with us tonight, but he isnt sure yet. （实际的可能性，不用 can,而用 may.,2. 表示具体事情实际发生的可能性 （1）表示具体事情实际发生的可能性的层次比较 （见下表） （2）表示具体事情实际发生的可能性时， may, must 常用于肯定句，一般不用于否定句和疑问句（may not表示“可能不”）； I didnt hear the phone. I must have been asleep.(表示肯定) This may not be done by him.（表示不确定）,表示具体事情实际发生的可能性时， can 常用于否定句、疑问句或感叹句中，表示疑惑、惊讶或不相信等意思；could 既可疑用于肯定句，又可以用于否定句、疑问句中。 This cant / couldnt be done by him. (表示不相信) He could be on his way home now. （could 不如 may / might常用） Can this be done by him? （表示一种疑惑、惊讶）,（3）would, could, should, might 并不一定与过去的时间有关，而是表示可能性弱于他们相应的现在形式。如： This may / might be done by him. （语气一次递减） 4）should 表示推测时，表示确定或可能有的未来或期望，即合乎理想的情况或结果。 He should be around sixty years old. 他可能60岁上下。 Its nearly seven oclock. Jack should be here at any moment. （表示确定或期待）,4）should 表示推测时，表示确定或可能有的未来或期望，即合乎理想的情况或结果。 He should be around sixty years old. 他可能60岁上下。 Its nearly seven oclock. Jack should be here at any moment. （表示确定或期待） - When can I come for the photos? I need them tomorrow afternoon. - They should be ready by 12:00. （表示期待）,三、 “情态动词 + have done “ 用法一览表 1. must have done 表示对过去已经发生的行为进行推测，意为“想必 / 准是/ 一定做了某事 It must have rained last night, for the road was quite muddy. The lights were out. They must have been asleep.,2. can have done cannot have done表示对过去发生的行为的怀疑和不肯定，通常用于否定句和疑问句中。 He cannot have forgotten it. Can he have gone to his aunts? 3. Could have done 可用于肯定句中，表示“可能已经”之意，此外，还可以表示过去免于是想的可能性，意为“本应该”.,3. Could have done 可用于肯定句中，表示“可能已经”之意，此外，还可以表示过去没有实现的可能性，意为“本应该”. I saw Mr. Wang just now. He couldnt have gone to Beijing. You could have been here earlier, but you didnt.,4. May /might have done 表示对过去已经发生的行为的推测，意为“也许 / 或许已经（没有） ”. 一般只用于肯定句或否定句中(在否定句中表示“可能不”)，不用于疑问句。用 might 语气更加不肯定。 Its too late. I think he may have gone to bed. He may not have finished the work. He might have caught a cold.,5. Might have done 表示“本来可能”，但实际上没有发生的事。 另外，还可以表示“本应该或可以做某事，”,含有轻微的责备语气。 You should not have swum in that sea. You might have been eaten by fish. You might have given him more help, though you were busy.,6. Should / ought to have done 用于肯定句时，表示“本应该做某事，而实际上未做”；用于否定句时，则表示 “不应该做的事情反而做了”。You should have come to the meeting earlier. You ought to have done this exercise more carefully. You shouldnt have told her the truth. He ought not to have treated his parents like that.,7. Neednt have done 表示“做了本来不必去做的事情”， 注意：didnt need to do 表示“没有必要做而实际也免于做某事”。 You neednt have taken a taxi here, for it was very near to my house. I didnt need to clean the windows. My brother did it.,8. Had better have done 用于事后的建议，含有轻微的责备语气，意为“当时做好做了某事”，其否定形式是 had better not have done 表示相反的意思。 You had better have started earlier. You had better not h