情态动词1、can(could)1）表示能力、could主要指过去时间。 Two eyes can see more than one. Could the girl read before she went to school?2）表示可能（理论上或是逻辑判断上） The temperature can fall to -60. You mustnt smoke while youre walking around in the wood. You could start a fire. He cant(couldnt) have enough money for a new car.3）表示允许 Can I have a look at your new pen? He asked whether he could take the book out of the reading-room.4）表示惊异、怀疑、不相信等态度。主要用于否定句、疑问句或感叹句中。 Where can (coould) they have gone to? He cant (couldnt) be over sixty. How can you be so careless?5）比较委婉客气地提出问题或陈述看法。 Can(Could) you lend me a hand? Im afraid we couldnt give me an answer today?2、may（might）1）表示允许，might可以指过去时间，也可指现在时间，语气更委婉。 You may take whatever you like. He told me that I might smoke in the room. May(Might) I ask for a photo of your baby? 在回答以may 引起的问句时，多避免用这个词，而用其它方式。Yes, please/Certainly. Please dont/Youd better not./No, you mustnt.(显得太严肃或不客气)2）表示可能（事实上）。可以指过去时间，也可以指现在时间，但语气更加不肯定。 He may be at home. She may not know about it. He was afraid they might not agree with him. They might be having a meeting,but Im not sure.3、must 1）表示义务。意为“必须”（主观意志） We must do everything step by step. You mustnt talk to her like that. -Must we hand in our exercise-books now? -No, you neednt./No, you dont have to.2）表示揣测。意为“想必、准是、一定“等，只用于肯定句。 He must be ill. He looks so pale. Shes wearing a diamond necklace. She must have a lot of money.4、should1）表示义务。意思是“应该“（在某件事情适宜做），用于各种人称。 You should be polite to your teachers. You shouldnt waste any time.2）表示揣测，意思是“想必、一定、照说、应该、估计”等。 The film should be very good as it is starring first class actors. They should be home by now.5、would1）表示意愿 They would not let him in because he was poorly dressed. I said I would do anything for you.2）表示委婉地提出请求、建议或看法。 Would you like another glass of beer? Would you mind cleaning the window? They wouldnt have anything agaist it.3）表示过去反复发生的饿动作或过去的一种倾向。 Every time she was in trouble, she would go to him for help.6、used to 表示过去的习惯动作或状态，现在不复存在或发生。疑问式和否定式有两种。 He used to live in the countryside,but now he lives in the city. There used to be a building at the street corner,but it has been pulled down. I usednt (didnt use) to smoke. Used you( Did you use) to go to school on foot?7、几组词的差异1）can 和be able to （1）情态动词can只有两种时态形式，现在式can和过去式could，而be able to有多种时态形式。 Mary can play the piano.She has been able to play it since she was 5.（2）用在过去时中，could经常表示能够做某事，事实上不一定去做。而was/were able to则表示“过去做成了某事”。在否定句中两者可通用。 He couldnt across the English Channael. But he didnt feel like it that day. Yesterday I was able to get home before the heavy rain.2) must和 have tomust 表示主观意愿，而have to 表示由于客观因素不得不做某事。专项练习:( ) 1. The little girl is only four, but she _swim very well.A. can B. must C. will( ) 2. May I take the newspaper away? -No, you mustnt. You _read it only here.A. will B. can C. must D. need( ) 3. _I have your name, please?-Yes, Smith.S-M-I-T-H.A. Must B. May C. Will D. Need( ) 4. You _wash your hands before meals.A. need B. must C. can D. may( ) 5. The traffic_stop when the lights are red.A. must B. may C. cant D. mustnt( ) 6. Must I hand in the weather reports this morning? -No, you_. A. mustnt B. neednt C. may not D. must( ) 7. -_I take some photos in the hall? -No, you _. A. Can; neednt B. Must; mustnt C. Could; wont D. May; mustnt( ) 8. The restaurant _be very good. It is always full of people. A. may B. can C. must D. should( ) 9. Li Lei cant go hiking today, because he _take care of his sick mother. A. have to B. may C. has to D. mustnt( ) 10. Where is mon now? -Im not sure. She _be in the kichen. A. shall B. may C. need D. must( ) 11. You_ play with fire,Tom. Its dangerous. A. neednt B. may not C. mustnt D. wouldnt( ) 12. That tall boy_ be John. John is medium height. A. mustnt B. must C. cant D. might( ) 13. Yesterday it rained heavily when school was over. We _stay in our classroom. A. should B. must C. have to D. had to ( ) 14.I hear youve got some new Australian coins _I have a look? A. Do B. May C. Shall D. Should( ) 15. Shall I tell Sally about it?-No, you_. Ive told her already. A. shouldnt B. mustnt C. neednt D. cant( ) 16. Mom, _ I play computer games? -Yes, you can. But you have to finish your homework first. A. must B. may C. will D. need( ) 17. -_ your friend play the guitar?-Yes,he can, but he cant play it well. A. Must B. Can C. Should D. Need( ) 18. Phone me as soon as you get to Shanghai. -I _. A. can B. should C. must D. will( ) 19. “Where