专题04 情态动词-备战2021年高考英语语法精讲PPT

语法专题四　情态动词 考试考点聚焦 考点一　can, could (1)表示能力和客观可能性。 Some of us can use the computer now, but we couldn't last year. It will be sunny in the daytime, but it could rain later on this evening. (2)表示请求和允许。 If you keep still, you can sit on either side of the boat. —Can I come in? —Yes, you can. (3)表示请求，口语中常用could代替can，使语气更委婉。但主要用于疑问句。此类问句的答语不能用could，应该用can。 —Could I use your bike tomorrow morning? —Yes, you can.(否定回答可用：No, I'm afraid not.) (4)表示惊异、怀疑(不相信)等态度，主要用于否定句、疑问句和感叹句。 How can you be so foolish? They can't be working at this time of day. (5)can和be able to都表示能力，在意义上没有区别。但can只有现在时和过去时，而be able to则有更多的时态形式。如果表示过去某时做成了某事，常用was/were able to，而不用could。 The fire was very big but everyone was able to escape from the building. 考点二　may, might (1)表示请求或允许。否定回答时，一般要用mustn't表示“禁止、阻止”之意。 —May I smoke here? —Yes, please./Certainly./Yes, you may./No, you mustn't. (2)表示可能性的推测，含有“或许”“可能”之意，用might代替may时，则语气显得更加不肯定。 The news may not be true. He might have some fever. (3)may可用来表示祝愿。 May you be happy! May you succeed! (4)may as well表示“还是……的好”。 You may as well tell me the truth. We may as well stay where we are. 考点三　must, have to (1)表示必须，其肯定回答用must，否定回答用needn't或don't have to。 —Must I finish the work today? —Yes, you must./No, you needn't./You don't have to. (2)must可表示肯定性的推测，意为“一定，准是”，只用于肯定句中。其否定形式为can't，表示不可能。 You must be hungry after a long walk. There must be a hole in the wall. (3)must表示的是说话人的主观看法，而have to则往往强调客观需要。 I must go now. I have to go now, because my mother is in hospital. (4)mustn't表示禁止、不许。 You mustn't leave the room. 考点四　shall, should (1)shall与第一、三人称连用时，表示征求对方的意见。 When shall he come to meet you? Shall we begin our class? (2)shall用于第二、三人称的陈述句中时，表示命令、警告、允诺等。 He shall be punished if he breaks the school rules.(警告) You shall stick to your post.(命令) You shall have the bike if you win the game.(允诺) (3)should用于表示劝告和建议，作“应该”讲。 You should keep your promise. (4)should用于表示推测，表示“可能”或“该”。 They should be prepared now. (5)should可用