情态动词讲义和专项练习.doc

PAGE PAGE 13 情态动词讲义和专项练习 情态动词有can (could), may (might), must, have to, shall (should), will (would), dare (dared), need (needed),ought to等。 情态动词无人称和数的变化；不能单独使用，必须与其后的动词原形构成谓语 一、 can, could 1) 表示能力（体力、知识、技能）。 e.g. Can you lift this heavy box?（体力） Mary can speak three languages.（知识） Can you skate?（技能） 此时可用be able to代替。can只有一般现在时和一般过去式；而be able to则有更多的时态。 e.g. I’ll not be able to come this afternoon. 当表示“经过努力才得以做成功某事”时应用be able to，不能用can。如： e.g. He was able to go to the party yesterday evening in spite of the heavy rain. Although he can’t swim, yet he was able to cross the river. 2) 表示请求和允许。 e.g. Can I go now? Yes, you can. / No, you can’t. 此时可与may互换。在疑问句中还可用could, might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。 e.g. Could I come to see you tomorrow? Yes, you can. ( No, I’m afraid not. ) 3) 表示客观可能性（客观原因形成的能力）。 e.g. They’ve changed the timetable, so we can go by bus instead. This hall can hold 500 people at least. 4) 表示推测（惊讶、怀疑、不相信的态度），用于疑问句、否定句和感叹句中。 e.g. Can this be true? This can’t be done by him. How can this be true? 5）“can + have done”主要用于否定句和疑问句中，表示对过去发生的行为怀疑或不肯定。 e.g. He cannot have been to that town. Can he have got the book? “could + have done”表示虚拟语气。 e.g. But for your help, we couldn’t have finished the task before the deadline. You could have achieved better results but you wasted the valuable time. 6）习惯用法：cannot …… too…… “再……也不过分” e.g. You cannot be too careful in the choice of your friends.____________________________ 二、 may, might 1) 表示请求和允许。might比 may语气更委婉，而不是过去式。否定回答时可用can’t 或mustn’t，表示“不可以，禁止”。 e.g. Might/ May I smoke in this room? No, you mustn’t. May/Might I take this book out of the room? Yes, you can. (No, you can’t / mustn’t. ) 用May I...？征徇对方许可时比较正式和客气，而用Can I...？在口语中更常见。 2）用于祈使句，表示祝愿。 e.g. May you succeed! 3) 表示推测、可能性（表示此意时，不用于疑问句）。 might不是过去式，它所表示的可能性比may小。 e.g. He may /might be very busy now. Your mother may /might not know the truth. 4）“may / might + have done”表示对过去行为的推测。 e.g. Without the heavy traffic, we