按说应该 / / can / 不可能 有可能吗? could 微弱的可能 不可能 语气比can弱 may 或许,也许,也未 可知,也说不定 可能不 / might 比may还弱 比may not 还弱 / (2)表示具体事情实际发生的可能性时,may,must常用于肯定句中,一般不用于否定句和疑问句中(may not表示“可能不”);can常用于否定句、疑问句或感叹句中,表示疑惑、惊讶或不相信等意思;could既可用于肯定句中,又可用于否定句、疑问句中。如: This can’t/couldn’t be done by him. 这不可能是他干的。(表不相信) This may not be done by him. 这可能不是他干的。(表不确定) He could be on his way home now. 他现在可能在回家的路上。(could不如may/might常用) Can this be done by him? 这可能是他干的吗?(表示疑惑、惊讶) I didn’t hear the phone.I must have been asleep. 我没听见电话铃响。当时我一定睡着了。(表肯定) —Are you going to Jeff’s party? ——你要去参加杰弗的聚会吗? —I’m not sure.I might go to the concert instead. ——我不确定。我可能去听音乐会。(表不确定)
(3)would, could, should, might并不一定与过去时间有关,而表示可能性弱于它们相应的现在时形式。如: This may/might be done by him. 这件事有可能是他干的。(语气依次递减) (4)should用来表示推测时意为“应该”,即含有“按道理来说应当如此”的意思。 (5)表示对现在正在发生的事情进行推测要用“情态动词+be+现在分词”这种结构。这种结构在高考题中出现的次数不太多,但也要引起注意。如: My mother must be watering the flowers in the garden now. 我妈妈现在肯定正在花园里浇花。 The students may be climbing the mountain at the moment. 此刻学生们可能正在登山。 3.情态动词后跟完成式表示对过去事情的推测参见考点三。 考点二 情态动词表示必要性 must常用来表示必要性,意为“必须”。表示现在或将来必须做某事用“must+动词原形”;表示现在或将来不必做某事时,用don’t have to do sth.或don't need to do sth.或needn’t do sth.;表示过去没必要做某事时,分为以下情况:①表示过去没必要做某事,但事实上却做了,用needn't have done sth.②表示过去没必要做某事,而不涉及是否做,可用didn't have to do sth.或didn’t need to do sth.或It was not necessary to do sth.等。如: You needn’t have worked that late last night.It was harmful to your health. 你昨晚不必工作到那么晚。那对你的身体没好处。 —Did you work very late last night? ——你昨天晚上工作到很晚吗? —No, I didn't. I didn't need to work very late. ——不是很晚。我没必要工作到很晚。 should也可以表示必要性,意为“(义务上)应该”。should表示必要性时,在语气上比must(必须)弱。“should+动词原形”,表示现在或将来应该做某事(的必要性);“should+have+过去分词”,表示过去本该做某事(的必要性)。如: I should go and visit him this afternoon, but I wonder if I will be free. 今天下午我应该去看望他,但我不知道我是否有空。(表示将来的必要性) You should have come to the conference yesterday. What was the reason for your absence? 你昨天应该参加那个会议。你缺席的原因是什么?(表示过去的必要性) 考点三 “情态动词+完成式”表示推测、必要性等用法一览 情态动词 +完成式 用法 例句 must have done 表示对过去已经发生的行为进行推测,意为“想必/准是/一定做了某事”。 The lights were out. They must have been asleep. can/could have done 表示对过去发生的行为的怀疑和不肯定,通常用在否定句和疑问句中。 ①I saw Mr.Wang just now. He couldn't have gone to Beijing. ②Can he have gone to his uncle's? 情态动词 +完成式 用法 例句 could have done 可用于肯定句中,表示对过去没有实现的事情的遗憾或责备,意为“本来可以,本能够……”。 You could have done better, but you were too careless. may/might (not)have done 表示对过去已发生行为的推测,用于肯定句中,表示“也许已经……”;在否定句中表示“可能不”,不用于疑问句中。用might则表示语气更加不肯定。 ①It's too late. I think he may have gone to bed. ②He may not have finished the work. ③She might have caught a cold. 情态动词 +完成式 用法 例句 should/ought (not)to have done 用于肯定句中,表示“本该做某事,而实际上却未做”;用于否定句中,则表示“不该做的事反而做了”。 ①You should have come to the meeting earlier. ②He ought not to have treated his parents like that. need/needn't have done 肯定式表示“本来有必要做某事”;否定式表示“做了本来不必去做的事”。 You needn't have taken a taxi, for it was very near. 情态动词 +完成式 用法 例句 had better have done 用于事后的建议,含轻微责备的口吻,意为“当时最好做了某事”,其否定式had better not have done表达相反的含义。 You'd better not have scolded her. would rather have done 表示“当时宁愿做了某事”;其否定式表达相反含义。两者都表示“后悔”之意。 I would rather have taken her advice. 如:I am starving to death. I can eat two bowls of rice now. 我快饿死了,现在我能吃两碗米饭。(现在的能力) If you have a good sleep, you will be able to work out this problem. 如果你好好睡一觉,你将能够解出这道题。(将来的能力) The fire spread through the hotel very quickly but everyone was able to get out. 尽管这场大火迅速蔓延到了整个宾馆,但是每个人都能够逃出去。(过去有能力做并且成功地做了某事) I could have worked out the problem,but l didn’t. 我本来可以解决这个问题,但没有解决。(过去有能力做但却未做) 2.表示请求、允许、允诺 当对方是决策者时,你代表你(们)自己(I,we),或代表第三者(he,she,they)向对方(you)请示或提出建议时用(shall常用于一、三人称,will/would常用于第二人称):①Shall/May(Might)/Can(Could)I/we...?②Shall he/she/they...?③Would/Will you...?如: Shall we begin our class? 我们可以开始上课吗? Shall the driver wait outside? 司机在外边等着可以吗? When shall my father be able to leave hospital? 我父亲什么时候可以出院? Would you do me a favor?请帮我一下,好吗? could/might/would/should表委婉的语气。如: —Could/Might I use your bike tomorrow morning? ——明天上午我能用一下你的自行车吗? —Yes,you can/may.(No,I'm afraid not.) ——行,你可以用。(不,恐怕不行。) 不可说:Yes,you could/might.回答允许时,用could/might表委婉是不恰当的。如: —Could I borrow your dictionary? ——我能借你的词典吗? —Yes,of course you can. ——是的,当然可以。 当你自己(Ⅰ)是决策者,给对方(you)或第三者(he,she,they)以命令、警告、允诺或威胁时,要用shall。此外,当颁布法律、规定时,也要用shall。如: You shall leave the room at once,and he also shall.(=I order you and him to leave the room at once.) 你马上滚出去,他也一样。(说话者的命令) It has been announced that candidates shall remain in their seats until all the papers have been collected. 在所有试卷收上来之前,应试者必须留在座位那里。(规则或规定) 3.其他用法 (1)“can not but+动词原形”表示“不得不,只好”。如: I can not but choose to go. 我只好去。 (2)may well和may/might as well结构 ①“may well+动词原形”是一种常用结构,意为“完全能,很可能”,相当于be very likely to。如: Her appearance has changed so much that you may well not recognize her. 她的模样变化太大,你很可能认不出她了。 ②“may/might as well+动词原形”意为“最好,满可以,不如”。如: You may as well do it at once. 你最好马上就做这件事。 cannot(或never等否定词)与enough连用表示“再……也不为过”。如: You cannot be careful enough to cross the road. 过马路时你怎么小心都不为过。 may可以用于祈使句中,表示祝愿。如: May you return in safety. 愿你平安归来。
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