八.情态动词与助动词
I. 情态动词基本用法:
II. 情态动词must, may, might, could, can表示推测: 以must为例。must + do(be)是推测现在存在的一般状态进行;must + be doing 推测可能正在进行的事情;must +have done是推测可能已经发生过的事情。 1. must“肯定,一定”语气强,只用于肯定句中。 He must be a man from America. / He must be talking with his friend. / He must have already arrived there. 2. may和might“也许”,后者语气弱,更没有把握。可用于肯定句和否定句。 He may not be at home. / They might have finished their task. 3. can和could“可能”,could表示可疑的可能性,不及can’t语气强,用于肯定、否定、疑问句中。 The weather in that city could be cold now. We could have walked there; it was so near.(推测某事本来可能发生,但实际上没有发生) Can he be in the office now? No, he can’t be there, for I saw him in the library just now.(语气很强,常用于疑问句和否定句中)
III. 情态动词注意点: 1. can和be able to: 都可以表示能力。但be able to可以表达“某事终于成功”,而can无法表达此意。Be able to有更多的时态。另外,两者不能重叠使用。 2. used to和would: used to表示过去常常做现在已经不再有的习惯,而would只表示过去的习惯或喜好,不涉及现在。 3. need和dare作情态动词和实义动词的区别: 两者作情态动词时常用于否定句和疑问句。其形式为:needn’t/daren’t do;Need/dare…do…? 做实义动词时可用于肯定句,否定句和疑问句。其形式为:need(needs/needed)/dare(dares/dared) to do, don’t(doesn’t/didn’t) need/dare to do
助动词 助动词有be, have, do, will, shall。它们本身没有词义,只和实义动词的一定形式构成复合谓语,用来表示时态和语态,构成否定、疑问及加强语气等。 1、be (am, is, are, were, been) (l)“be + -ing”构成进行时态;(2)“be + 过去分词”构成被动语态;(3)“be + 动词不定式”构成复合谓语:①表示按计划安排要发生的事。The prime minister is to visit Japan next year. 总理将于明年访问日本。② 用于命令。You're to do your homework before you watch TV.你得做完了作业才能看电视。 2、have (has, had) (1)“have+过去分词”构成完成时态。如:Have you seen the film ? (2)“have been + -ing”构成完成进行时态。如:What have you been doing these days? 这些日子你一直在干什么? 3、do (does, did) (1)“do not + 动词原形”构成行为动词的否定式。如:His brother doesn’t like playing basket.;(2)“Do + 主语 + 动词原形”构成行为动词的一般疑问句。Does he go to school by bike every day? (3)“do + 动词原形”用于祈使句或陈述句中表示加强语气。如:I did go to see him, but he wasn’t in我确实去看望他了,但他不在家。Do do some work. 请一定做点什么;(4)代替前面刚出现的动词以避免重复。My mother told me to go to bed early. So I did. 4.will, shall (would, should) “will (shall+动词原形”构成一般将来时,一般来说shall用于第一人称,will用于第二人称或第三人称,口语中常用will代替shll,如:We will have a meeting to discuss the problem.
|
|