语法情态动词n.docVIP

情态动词也叫语气动词，表示说话人对所说动作的看法，认为它可能、应当、必要等。情态动词不能单独作谓语动词，只能和动词原形一起构成谓语动词。英语里的情态动词主要有：can (could), may (might), must, shall, will, would, need, dare, should, ought to。情态动词在任何主语后没有人称和数的变化。 1. can 和could ⑴ 表示能力 Whales cannot live on land. A computer cant think for itself. 计算机不会独立思考。 He hurt his foot and couldnt play football. ◆be able to 可用于多种时态，can和could只用于现在时和过去时。 He will be able to go with us this afternoon. I havent been able to see the difference yet. ◆如果表示做到，设法干成了某事，常用be able to …来表达（相当于managed to do sth. 或succeeded in doing sth. ）,而不用can /could。 With the firemen, they were able to escape from the burning house. We were able to get there before the meeting began. ⑵ 表示可能性 can表示可能性时，常用于疑问句和否定句中。 Can it be Mr. Black? He cant be at home. 他不可能在家。He may not be at home. 他可能不在家。 ◆can间或可用于肯定句，表示理论上的可能性，表示笼统的时间，事物的特征Anybody who wants to try can be successful. 只要想试，任何人都可能成功。 Scotland can be very warm in September. ⑶ 表示许可和请求 在日常生活中，can可以代替may, 表示允许；could 可以代替can，但语气较为婉转。Can/Could I use your pen?　　　　Yes, of course you can. (不能用could?) ’m afraid not. ⑷ 习惯短语： cannot…too…　　越…越好 You cannot be too careful. cannot but 　　　不得不 I cannot but do so. 我不得不这样做。 ⑸ can 和could 后面接动词的完成式，表示对过去情况的猜测或判断。 can常用于疑问句和否定句，could用于肯定句，表示一个非事实的或不可能实现的可能性。 Where can he have gone? He cant have gone to school. ----Its Sunday. You were stupid to go skiing there. You could have broken your leg. ⑹ could have done 本来能做而实际未做，表达遗憾的感情色彩 ----I stayed at a hotel while in New York. ----Oh, did you? You could have stayed with Jane. 2. may 和might ⑴ 表示允许 might 比may 语气更客气、更委婉 You may take a rest now. May/Might I take the book out of the room? No, you mustnt / may not/ cannot. Sure / Certainly/ Of course 否定用于拒绝给予许可，或禁止做某事。通常在官方公告中。 Students may not stay out after midnight. 学生午夜后不得在外逗留。 ⑵ 表示可能性 常用于肯定句和否定句，指说话人的猜测。might指把握性不大， He may/might come. Youd better stay here for a moment. I may/might not be back for dinner. (Im not sure whether Ill be back. ） may 强调逻辑上的可能。can 强调事实