2011高考英语二轮复习课件：情态动词和虚拟语气

专题五 情态动词和虚拟语气,一、几组情态动词的区别 1can 和 be able to can 与 be able to 都可以表示能力，但两者在用法上有点差异：can(could) 表示主观能力，不表示意愿；be able to 表示主观意愿，强调要克服困难去做某事。它的将来时用will be able to。例如： My grandma is over seventy，but she can still read without glasses. He is able to give up his bad habits.,2must 和 have to must 和 have to 都可以表示“必须”，但有几点区别： (1)must 强调“内在的职责”、“义务”，而 have to 强调“外界压力”、“不得已而为之”。 (2)have to 可用于多种时态，而 must 一般用于现在时，其过去时与将来时分别由 had to 与 shall/will have to 代替。,(3)在回答 must 引起的问题时，如果是否定的答复，不能用 mustn't，而要用 needn't 或 don't have to，因为 mustn't 是“一定不要”、“一定不能”、“禁止”的意思。例如： 1)You must come to the classroom before eight. 2)It is raining hard outside，but I have to leave now. 3)“Must we do it now？”“No，you needn't.”,3used todo，be used todoing 和 be used todo (1)used todo意为“过去常常做某事”，“过去一直做某事”；be used tov. ing/n.意为“习惯于”；be used todo 意为“被用来做某事”。 (2)used to 只表示过去，而 be used tov. ing/n.可表示现在、过去或将来。例如： 1)He used to smoke.Now he doesn't. 2)He's quite used to hard work/working hard. 3)The knife is used to cut bread.,4can't 与 mustn't can't 表示“不能”，是指无能力；mustn't 表示“不能”，指的是“禁止，不允许”。在口语里，can't 也可表示“禁止，不允许”，但语气不如 mustn't 强。例如： He is so young that he can't go to school. There's a meeting inside.You mustn't make any noise.,5can 和 may 考试中主要测试 can，may 或 could，might，表示可能性的区别及对 may 构成的疑问句的回答。 (1)can，could，may，might 都可以表示可能性。can，could 表示潜在的可能性或理论上或逻辑判断上存在的可能性；而 may，might，则表示事实上的可能性。此外，can，could 还有“有能力”的意思，而may与 might 不具有此意。例如： According to the weather forecast，it may rain tomorrow. Any man with a little sense can see that he is wrong.,(2)May I/we.？这一类疑问句的肯定回答为 Yes，please.或 Certainly；否定回答为 Please don't.或 No，you mustn't.例如： “May we leave now？”“No，you mustn't.You haven't finished your homework yet.”,6情态动词动词完成式 情态动词动词完成式即“情态动词havedone”，表示对过去的行为或动作进行推测、评论或判断。 (1)must have done must have done 表示对过去某事的肯定猜测。其否定或疑问形式都用 can(could)来表示。例如： Since the road is wet，it must have rained last night. He can't have missed the way.I drew him a map.,The dictionary has disappeared.Who could have taken it? 当然对现在发生或将来发生的事情，要用 must do 表示猜测，否定式为 can't do。 He must understand that we mean business. You must be hungry after a long walk.,(2)may/might have done may/might have done 表示推测过去某事“也许”发生了，may 比 might 表示的可能性在说话人看来稍大些。例如： I can't find my keys.I may/might have left them at the school yesterday. (3)could have done 在肯定句型中，往往表示委婉的批评。本可以做什么而没做；有时也用作猜测。 You could have told us earlier. Tom could have taken the dictionary.,(4)ought to/should have done和ought not to/shouldn't have done ought to/should have done和ought not to/shouldn't have done用于对已发生的情况表示“责备”、“不满”，分别表示“本应该”和“本不应该”。例如： 1)With all the work finished，I should have gone to the party last night. 2)You ought not to have made fun of him.He is not the one you laugh at but learn from.,(5)needn't have done needn't have done 表示过去做了某事，但没有做的必要，意为“本没必要”。例如： Yon needn't have waken me up; I don't have to go to work today. 注：表示推测过去某动作发生的可能性时，就表示的可能性程度而言，must 最大，could 其次，may 更次之，might 最小。例如： I wonder how Tom knew about your past. He must/could/may/might have heard of it from Mary.,7情态动词动词进行式 情态动词行为动词进行式(即情态动词bedoing)，表示推测或评论某动作现在是否正在进行。例如： (1)He must be playing basketball in the room. (2)She may be staying at home.,二、几个情态动词使用的特定范围 1表示推测时，can 不能用在肯定句中(但 could 可以)；may 和 might 不能用在疑问句中。例如： Peter may come with us tonight，but he isnt very sure yet. Can it be a sunny day tomorrow? 2作为情态动词，need 和 dare 不能用在肯定句中(条件状语从句除外)。肯定句中，须把它们用作实义动词，后接带 to 的不定式。例如：,【误】We need hold a meeting to discuss the matter. 【正】We need to hold a meeting to discuss the matter. 【正】If you need hold a meeting to discuss the matter, I'll give you a help. 3在回答由 could 和 might 引起的表示请示的一般疑问句时，不能用 could 和 might (应分别用 can 和 may)回答。例如： Could I borrow your dictionary? Yes，of course you can.,三、一些“形义不一致”的现象 1过去式 could 或 might 后接动词原形可以表示对现在或将来(不是对过去)的推测。例如： I'm afraid it might snow tonight. 2may (not) 和 can't 后接完成时态，表示对过去(不是对现在或将来)的推测。例如： There were already five people in the car but they managed to take me as well. It can't have been a comfortable journey.,四、情态动词的常用形式的特殊使用 1should 和 ought to 后接动词原形，常表示“应该”；但也可用来表示推测，意为“想必会”。例如： (1)It's nearly seven o'clock.Jack should be here at any moment. (2)When can I come for the photos? I need them tomorrow afternoon. They should be ready by 12：00.,2could 后接完成式常表示“(过去)可能”，但也可用来表示责备语气，意为“过去本来能够，而实际上却未”。例如： We could have walked to the station；it was so near. Yes.A taxi wasn't at all necessary.,五、虚拟语气在条件句中的应用,1虚拟条件句中谓语动词的形式,(1)主句中的 should，could，might 具有情态意义。 (2)与将来事实相反时，条件句中谓语可由“should动词原形”构成，但要注意这里的 should 不能被 would，could，might 等替代。 (3)从句中单数 be 动词的过去式一般用 were，在口语中有时也可用 was。 2有时候，从句与主句所指时间并不一致，这时谓语动词应分别用其相应的形式。这时便称为错综时态虚拟条件句。例如： If he had studied hard, he would pass the exam tomorrow.,3条件句中的if省略时，从句应倒装。例如： Had they got enough boats，they would have succeeded in crossing the river. 但条件句的谓语是实义动词的过去式，即谓语部分没有 had，were 或 should 时，if 不能省略，从句也不能倒装。,4含蓄条件句 非真实条件有时不用条件句而用短语，或通过上下文含蓄地表达出来，但在意义上它们仍相当于条件句。例如： Without your help，we couldn't have finished it on time. 要不是你帮忙，我们不可能按时完成它。 But for the storm，we would have ar