语法专项训练之情态动词.doc

语法专项训练之情态动词情态动词（modal verbs）：无人称和数的变化，只能与行为动词或状态动词构成谓语。既有情态助动词特征又具有实义动词特征的称为半情态助动词。情态助动词：can(could),may(might),must,have to(had to),ought to,shall(should),will(would);半情态助动词:dare ,need,used to,had better,would rather;(1) 情态助动词1、 can的用法1） 表示能力(ability)，意为“能够” Can you finish the work tonight?2) 表示请求或允许（permission）,意为“可否”，“可以” Can I smoke here?3) *表示可能性（possibility），常用在否定句，疑问句或感叹句（含惊讶、怀疑、不相信的语气），意为“可能” Jack cantt have arrived yet, otherwise he would have telephoned me. Can it be true? How can you be so careless!4) can be 用于推测某人或某物一时的情况，意为“有时候会” Drinks in restaurants can be very expensive.5) 惯用语 cannottoo 意为“无论怎样也不为过；越越好” I cannot thank you too much. You cannot be too careful in doing exercises. cannot help doing 意为“禁不住”2、may和might的用法1）表示请求允许(即请求别人允许自己做某事) MayIsithere?2）表示推测两者都可用，只是might比may语气更不确定，表示的可能性更小。 Hemayknowtheanswer.(可能性较大) Hemight knowtheanswer.（可能性较小）3）might 常用于表示委婉的请求或者轻微的责备 You might have let me known before!4) 惯用语 may/might (just)as well 意为“最好”（= ）,用于提出建议 You may as well give him the letter. May/might as well +do A + as +do B 意为“与其做B不如做A” You might as well throw the money as lend it to him.3、 must 和have to 的用法1)*must表示有把握的推测：（否定：cannot be）对现在情况的推测：must +动词原形The lecture hall is so crowded. There must be over 600 people in it.表示对过去事情的推测: must+完成时You must have left your umbrella in the theatre.你一定把雨伞丢在剧院里了。His car is still here. He must have gone by bus.他的车还在这里，他一定乘公共汽车走了。对现在正在进行中的事的推测：must be +现在分词You look happy .You must be having a good time.2) have to表示“必须”，“不得不”，在这个意义上与must很接近，但must表示的是说话人的主观看法，而have to 表示的却是客观需要。I have to go now.我得走了。（客观需要）I must go now.我必须走。（主观看法）You have to work hard to make a living.为了谋生你就得努力工作。（客观需要）You must do what I tell you.你必须按照我告诉你的去做。（主观要求）（5）have to 有更多的时态形式：现在时，过去时，将来时等，而must只有现在时形式。We had to be there at 8.我们得8点到那里。I shall have to go to school tomorrow.明天我得去上学了。（6）have to 不能代替表推测的must，但在虚拟条件句中用had had to+动词原形表示与过去相反的情况。You must be joking.你一定是在开玩笑。（不能用have to）If I had had to do the work, I should have done it in a different way.如果我不得不做这项工作，我会以不同的方式去做。（不能用must）(二)半情态动词既有情态助动词特征又具有实义动词特征情态动词实义动词肯定式He dares to escape.He needs to escape.否定式He darent escape.He neednt escape.He doesndare(to) escape.He doesnt need (to)escape.疑问式Dare he escape?Need he escape?Does he dare to escape?Does he need to escape?(3) 情态助动词+不定式的完成式结构含义例句1、could have done本可以，差点就要The accident could have been prevented.2、must have done一定已做He must have been to shanghai.3、may/might have done或许已经，可能做He may have finished the exercises.4、should have done本来应该做而实际没做“本应该做”You should have started earlier,but you didn t.5、neednt have done本来不必做而实际上已经做了“本不必做”You neednt have watered the flowers,for it is going to rain.(四)总结 事实上的 may must 可能性 必然性 can have toYou may lead a horse to the water,but you cannot make it drink. 说话人为权威 may must允许 责任义务 can have to （五）练习 权威方非说话人（客观规定） 1.They _have arrived at lunchtime but their fight was delayed. IA. will B. can C. must D. Should2.No one _be compared with Yao Ming in playing basketball. A. can B. need C. must D. Might3.I left my handbag on the train, but luckily someone gave it to a railway official. How unbelievable to get it back! I mean, someone _it.A. will have stolen B. might have stolen C. should have stolen D. must have stolen4.It _be the postman at the door. Its only six oclock. A. mustnt B. cant C. wont D. neednt5.If you _go, at least wait until the storm is over. A. can B. may C. must D. Will6. I _worry about my weekendI always have my plans ready before it comes. A. cant B. mustnt C. darent D. neednt7. The police still havent found the lost child, but theyre doing all they _. A. can B. may C. must D. Should8. You _ buy a gift, but you can if you want to. A. must B. mustnt C. have to D. dont have to9.Just be patient .You _