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1、情态动词的语法特征,情态动词除ought和have外，后面只能接不带to的不定式。情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。情态动词没有非谓语形式，即没有不定式，分词等形式。,表示能力: can, could, be able to *be able to 能用于各种时态。 can / could 只能表示现在或过去的能力。 *只能用be able toa.位于助动词、情态动词后，b.was / were able to : “设法做成某事” 相当于 managed to do sth.,1. 表示能力、许可的情态动词的用法。,表示许可: may / might, can /
2、 could * might, could 比较委婉, 一般多用于疑问句.* can, may 表达的语言比较随便.* 在以could, might 表示征询对方意见 或表示请求时，回答应相应使用can, may.,例1：-Could I borrow your dictionary? -Yes, of course you_.A. might B. will C. canD. should,析：选C。该句用can的委婉表达式could 来征求对方意见，could 和might通用，但回答时必须要用can或may，因此该题不选A.,例1：-Must I start at once? -No,
3、you_.A. needntB. mustnt C. cantD. wont,析：A。由语境可知该答句表示“不必”，而mustnt表示“不准、禁止”，不符合语境，显然应使用neednt表示“不必”，但肯定句回答继续用must。,例2：-Need I hand in my exercise book at once?-Yes, you_.A. must B. need C. can D. will,析：选A。根据规定need用于一般疑问句作肯定回答应换成must,而作否定回答时，使用need的否定式neednt。,7. shall和should的用法,Shall shall用于构成将来时是助动词
4、，shall用于征求对方的意见，表示“决心”是情态动词。Perhaps I shall pay a visit to England this winter.I shall be there.(1)用于一三人称，征求意见或提议。 Shall we go out for lunch? (2)用于第二、三人称，表一种强烈的感情，如“命令，禁止，威胁，允诺”等. If you dare do that, you shall be punished.(3)在条约、规章、法令等文件中表义务或规定，一般用于第三人称。应，必须 指示，预言等。 The new regulation shall take ef
5、fect on June 1st,“The interest _be divided into five parts, according to the agreement made by both sides.A. may B. should C. must D. shall The room is so dirty. _ we clean it? Of course. (2003北京春) A. Will B. Shall C. Would D. Do 上述两题均考查 shall的非常用含义，当shall 用于一、三人称疑问句中时，表示征求对方意见；用于二、三人称陈述句中，表示说话人给对方的
6、命令、警告、允诺或威胁等。,should,should should用于构成将来时是助动词。should用于表示“应当”“猜测”是情态动词。 (1) 表示义务，责任，意为“应当” 。 You should pay for your taxes.（2） 表示推测，可能性。意为“可能，应该”。 Its mid-night, he should be home.（3） 表示惊讶和难以置信,表示说话人的感情(惊奇、愤怒、失望等)“竟然” 。 Why should he do such a thing?,2. 表示否定的情态动词的用法: 部分情态动词的否定式是情态动词中的考点之一。,mustnt 不准,
7、 禁止 neednt 没必要 ( = dont have to )cant 不能; 不可能may not 不可以; 可能不shouldnt 不应该 ( = ought not to ),可兼做行为动词的情态动词：need 、 dare,情态动词 (+动词原形),行为动词,.,need,dare,2.尤其用于：,*否定句及疑问句中;,3.常以neednt 和darent 的形式出现;,4.dare有其过去时dared.,多用于肯定句; (sb.) need to do dare to do(sth.) need to be done (sth.) need doing,判断正误:,How dar
8、e you say such a thing? How dare you to say such a thing?,He darent to speak English before such a crowd, did he?He darent speak English before such a crowd, dare he?,Nobody need to be afraid of catching the disease.Nobody need be afraid of catching the disease.,need 的被动含义：need，want, require, worth
9、(adj.)后面接doing 也可表示被动 need doing =need to be done,表示推测的用法can, could, may, might, must 皆可表示推测,情态动词+动词原形 表示对现在或将来的情况推测,不同的“肯定”程度可按下列层次排列： He is at home. (事实) He must be at home.（非常肯定的推断） He could be at home.（很可能） He ought to be at home.（很可能） He may be at home.（仅仅可能而已） He might be at home.（或许, 非常不确定） H
10、e might not be at home.（也许不在家）He may not be at home. （比might可能） He couldnt be at home.（很可能不在家） He cant be at home.（一定不在家）He isnt at home.（事实）,二、情态动词+have done表示对过去情况的推测,（一）should /ought to have done本来应做而未做，表达遗憾感情色彩,例1：I told Sally how to get there, but perhaps I _for her.(NMET94) had to write it out
11、 must have written it outC. should have written it outD. ought to write it out,析：选C。分析语境可知，口头上告知Sally如何去那里是不够的，所以我本应书面告知，却有没书面告知之，显得应使用should /ought to have written表示遗憾之情。,（二）may/might have done可能已做 / must have done 一定已做/cant have done不可能做,例1：-Where is my pen? - I _it.(NMET88)A. might lose B. wouldn
12、t have lost C. should have lost D. must have lost,D,（三）could have done指本来能做而实际未做，表达遗憾的感情色彩,You could at least have sent five cards.你本来可以至少寄去5张明信片的。（说明没有寄那么多）,He must be reading, _ he?You must do it yourself, _ you?He must have gone over the article, _he?It must have rained last night, _ it?,表猜测语气的反意疑问句的构成,isnt,dont,hasnt,didnt,
