can和could的用法.doc

can和could的用法1.表示能力：能，能够，会 He could swim when he was five. Can you drive a car? Yes, I can. No, I cant.2. 表示推测：可能，会 I think the work can be completed ahead of time. What can he mean? 注：表示推测时，could不是过去式，只是语气更委婉；若是推测已发生的事或过去的情况，用can/could have done Today is Sunday. He cant/couldnt be at school. Mike cant have found his car, for he came to work by bus this morning. 3. 表示“有时也会” It can be quite windy there, especially in spring. 4. 表示允许：可以 (口语中常代替may) You can first lend me one book this time. You cant take the book out of the room. 注意：1. 表示允许别人做某事只能用can，不能用could。 2. cant和mustnt一样，都可表示“不准，不允许”。5. 表示请求,可以Could you tell me how I can get to the railway station? 注意：could不是过去式，只是语气较can更委婉，注意在回答中不可用could。Could I have the television on?Yes, you can. / No, you cant.6. 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。 Can this be true? This cant be done by him. How can this be true?7. can与be able to的比较 1) can表示能力(体力知识技) 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。2) 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。 Ill 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。He was able to go to the party yesterday evening in spite of the heavy rain.may与might的用法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cant 或mustnt，表示“不可以，禁止”。 -Might/ May I smoke in this room? - No, you mustnt. - May/Might I take this book out of the room? - Yes, you can. (No, you cant / mustnt.) 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. 表示请求允许：可以May/Might/Can I come in? Yes, please. He said I might borrow his car. 注意：前例中的might不是过去式，只是更婉转；但在后例这样主句动词是过去式的句子里，might可看作是may的过去式。3. 表示祝愿May you succeed! May you live happily!4. 表示推测、可能性（不用于疑问句）。 He may /might be very busy now. Your mother may /might not know the truth.It may/might rain this afternoon. He may come, or he may not. She may still be waiting for us. 1). 作此种用法时，也可用might(不是过去式) 语气更委婉；若是对过去情况的推测，用may/might have done (本来可以做某事)You may/might have helped me when I asked you. 2). 表示推测时，may not意为“可能不”，cant意为