2015英语语法情态动词讲解及练习PPT.ppt

3) 在lest, for fear that, in case引起的状语从句中， 谓语动词用(should + do) He clears the glass with care for fear that he should break it. Be quiet in case you should wake the baby. They spoke in whispers lest they should be heard. 4) should + have done表示过去应该做某事却没做。含有“责备，内疚”之意。 She should have helped you a lot. You should have told him about it. They should / ought to have come back yesterday. ought to ought to 用于表示“想必会，最好(语气较must 弱)： 他们想必已到那儿了。 They ought to be there by now. 2.　他最好不要抽烟了。 He ought to stop smoking.　 多数情况下，ought to可与should互换使用。 Ought to的反意疑问句用shouldn’t替代。 比较had better, should ought to 三者均表示建议，意为“应该”，“应当”或“最好做…”. 三者的语气程度为渐强。 Had better指一般性的建议，最弱。 Shouldought to含义相近，常可互换。区别在于，ought to常指特殊情况下的“应当”。Should则指一般情况。见下页例句。 You ought to help him because he is in trouble now.(语气强，有命令意味。) You should have a rest after finishing your sports.（一般性建议） You ought to call the police when you find something wrong in your house. He should take care of the babies tonight. shall用于第一，三人称疑问句， 　　　　征求意见或请求 shall 第二，三人称　 　　　陈述句,命令,警告,允诺,威胁 should 表劝告，建议，命令，顺理成章的 　＝ought to 疑问句中常用should代替ought to ought to 表应该，语气＞should 美语中，ought to用于否，疑句时to 可省 shall , should ought to --- Excuse me, but I want to use your computer to type a report. --- You ______ have my computer if you don’t take care of it. 2) --- We need a person badly to think up such an idea. --- ______ the new comer have a try? 3) I can’t believe that he _______ be so rude to me. 4)---What does the sign over there read? --- “No person ______ smoke or carry a lighted cigarette, cigar or pipe in this area.” 三、shall/ should shan’t Shall should shall 六. dare的用法 1）dare 用作情态动词常表示现在或将来时间，有时也可表示过去，可用于肯定句，否定句，疑问句或if,unless等引导的从句 He dare go deep into the mountains alone. She dare say what she thinks. He dare not criticize her. She never dare speak in public. No one dare go there. How dare you do such a thing? Dare you go home alone?