第8章 情态动词 情态动词是表示表示说话人的情绪，态度或语气等的动词，不能单独做谓语，只能和其他动词原形构成谓语。 can只能用于一般现在时和一般过去式 (could) ，没有人称和数的变化。be able to可用于各种时态，有人称和数的变化。 can可以表示①能力；②请求，许可；③可能性或推测 Jane can drive car. Can I borrow your umbrella That can’t be Mary. She has gone abroad. Could I use your cell phone for a while (语气委婉) may可以表示①请求许可；②允许；③推测 (可能性较小) might比may的语气更加委婉一些。也可做may的过去式。 May I use your name and address You may go now. It may rain the day after tomorrow. He asked if he might go home. must可以表示①必须；②推测；have to表示“，必须，不得不”强调客观，must多强调主观 All passengers must wear seat belts. This book mustn’t be removed from the library. (禁止） It must be John’s. It has his name on it. （推测）） need可以表示①作情态动词; ②作实义动词 There’s enough time for you to go to the airport. You needn’t hurry up. (安徽中考) I don’t need to buy a new backpack. = I needn’t buy a new backpack. --Need I answer the question --Yes, you must/have to. --No, you needn’t. should可以表示①应该；②推测； We should protect the environment. She left hours ago. She should be home now. 表示最好，缩写为 ’d better You’d better eat these bananas before they go bad.
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