1、情态动词,Modal verbs,一、概述,情态动词是一种本身有一定的词义,表示说话人的情绪、态度或语情气的动词,但不能单独作谓语, 只能和其他动词原形构成谓语。 He does the job. He can do the job. He may do the job. He must do the job. He has to do the job. He ought to do the job.,1. can/could 的用法,can (could) 表能力，许可，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），或表示 推测(从理论上或逻辑上判断的可能性）。could指过
2、去或表示语气委婉。,表示能力： The boy can speak three languages. I could swim when I was eight.,表示许可： You can go out if you have finished your work. -Could I use your book?-Yes, you can.,表示惊异,怀疑,不相信等. How can you treat your mother like that!,can (could)表示推测. 多用于否定句(cant不可能)和疑问句中,1)表示对现在的推测：-Someone is knocking th
3、e door, who can it be? -It must be Tom. -It cant be Tom. Tom is in Beijing now.2)表示对过去的推测：常用句型cant have done 或 couldnt have done 意为不可能发生过有时也可以用could have done 结构，意为本来能够 She cant have left school, for her bike is still here. He could have done it better.,注意点,can/could 表示推测时，也可用于肯定句，表示客观可能性，常译为可能会,Any
4、body can make mistakes. 任何人都可能会犯错误。 Driving on the snowy roads can be very dangerous. 在积雪的路上开车可能会有危险。,2. must 的用法： 表命令、推测（现在或过去的推测）、偏偏,偏要,硬要等含义。,表示命令 You must do it like this. 偏偏，偏要，硬要 -Can I have a word with you? -ok, if you must. 表示推测 1）表示对现在的推测 You look pale, you must be ill. 2)表示对过去的推测（只能用于肯定句）m
5、ust have done 一定发生过 （没有mustnt have done 这一用法） The road is so wet. It must have rained last night.,注意点： 1）must not (mustnt) 只表示禁止 不准，不许 Children mustnt play with fire. 2）用must 提问时，否定回答要用neednt或dont have to -Must I leave now? -Yes, you must/ No, you neednt (dont have to),3. have to 的用法,表示客观的必要，“不得不”，且
6、have to 有更多的时态形式。 Toms mother was ill, so he had to stay at home to look after his mother.,注意点： have to 的否定式为dont have to, 而不是直接加not,4. should的用法,1）应该(表示主观看法，建议，劝说) You should study hard.,2)用来表示说话人对某事不能理解、感到意外、惊异等意思，译为 竟然，竟会 You cant imagine that a well-behaved gentleman should be so rude to a lady.
7、,3)表示预测或可能。 This kind of reference book should be in the reading-room.,4）在虚拟条件句中用以加强假设语气，表示“与将来事实相反的假设”，用 If+主语+ should +动词原形,意为 万一 If you should be fired, your health care and other benefits will not be immediately cut off.,注意点 should have done 本来应该做 shouldnt have done 本来不应该做 I should have finished
8、 the work on time. You shouldnt have left home without a word.,5. ought to 表示客观情况（因责任、义务等应该 做） ought to 的口气比 should稍重You are his father, so you ought to take care of him.注意点:1）ought to 的否定式为ought not to /疑问形式把 ought 提前2) ought to have done=should have done (本来应该做)3）反意疑问句里，下面两种形式都可以： He ought to be h
9、ere, shouldnt he? He ought to be here, oughtnt he?,二、常用情态动词的用法比较,1. can与be able to,can表示“能力”时，与be able to相当，许多场合可以互相替换。但当叙述过去经过一番努力才能完成的事情，只能用was (were) able to. He could (= was able to) swim when he was six years old. 他六岁时就会游泳了。（叙述一般的能力）Even though I had my leg hurt, I was able to finish the whole
10、distance.,2. must与have to,must多表示说话人主观意志，have to多强调客观条件。You must go to bed early every night.你每晚必须早点睡觉。I have to go now. My friend is waiting for me downstairs. 现在我得走了，朋友在楼下等我。,三. 随堂练,1. You _be tired-youve only been working for an hour.A. must not B. wont C. cant D. may not,C,2. John, look at the t
11、ime. _ you play the piano at such a late hour?A. Must B. Can C. May D. Need,A,3. He _ have completed his work; otherwise, he wouldnt be enjoying himself by the seaside.A. should B. must C. wouldnt D. cant,B,4. - Do you know where David is ? I couldnt find him anywhere.- Well. He _have gone far his coat is still here.A. shouldnt B. mustnt C. cant D. wouldnt,C,5. I was really anxious about you. You _ home without a word. A. mustnt leave B. shouldnt have left C. couldnt have left D. neednt leave,B,Thank you,
