常用情态动词与助动词用法总结 助动词本身无意义，在句中帮助主要动词构成一定的时态，语态、语气，或是帮助构成 否定句和疑问句，常用的助动词有be, do, have, shall(should), will(would)。 情态动词表一定的词义，本身并不表示动作或状态，而仅仅表达说话人的态度，它在句中须和主要动 词一起构成谓语， 主要的情态动词有can(could), may (might),  must, have to, oug ht to, need, dare, shall, should, will, would。   1.can   能，可以，表说话人同意，许可还可表客观条件许可，如:You can go now.   提建议或请求时可用can I, can you表客气，如Can I buy you a drink?   2.may   （1）、可以，表说话人同意，许可或请求对方许可。You may go.   （2）、（现在和将来）可能，也许，只用于肯定句和否定句中，如He may not be right. 高中英语必修二单词 七年级下册英语单词表朗读 八年级下册英语单词朗读   3.must, have to   must表主观上的必须，have to表客观上的必须，如: It's getting late. I have to go. -Must I go now. -Yes, you mus t. (No, you needn't./ No, you don't have to.)   4.need, dare   这二词有实意动词和情态动词两种词性，如用作实意 动词后接动词不定式to do，如用作情态动词后接动词原形。Need I go now? --Yes, you must./N o, you needn't.)   5.shall   用于第一人称疑问句中表说话人征求对方的意见或向对方请求 ，如，Shall we begin our  lesson?   用于二、三人称陈述句，表说话人命令、警告、允诺、威胁等 口吻，如: You shall fail if you don't work harder.   6.should   表应该，意为有责任，有义务。如:W e should try our best to make our country more beautiful.   7.will   表有做某事的意志、意愿、安心、打算，如 "Will you lend me your boo k?" "Yes, I will."   8.should have  done表应该做而未做   must have done表对过去事实的肯定推测   could have done表本可以做某事   9.判断句：   肯定句用must, 否定句用can't, 不太肯定用may, might   He must be in the office now.   He must have gone to bed, for the light is out.   He can't be in the office. He is at home.   He couldn't have cleaned the classroom, because he didn't come here today.   He might be in the office, I am not sure.   He might have cleaned the room, I suppose.  参考范文：         With more and more cars coming into our families, we are happy that it has greatly improved our life. But unluckily, it has also brought many problems, such as heavy traffic and traffic accidents.    Traffic safety is everybody's busines s. We must obey the rules. For example, we must walk on walk side, when we cross zebra-crossing, stop, look right and left, and then go across fast. Don’t play football on the road. we can tell our parents not to drink before they drive, not to run through red lights, not to talk and laugh while driving.   We can say cars are coming into our life, but only when everybody thinks traffic safety is everybody's business can we be safely driving on roads and walking  on sidewalks.