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情态动词 助动词(auxiliary)主要有两类:基本助动词(primary auxiliary)和情态助动词(modal auxiliary)。情态助动词有十三个:may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to. 上述两类助动词的共同特征是,在协助主动词构成限定动词词组时,具有作用词的功能:情态助动词的特征情态助动词有自己的词义,但是必须和实义动词连用,能表示说话人对有关动作或状态的看法,或表示主观设想。我个人认为可以把情态二字理解为感情(讨厌或是喜欢)和态度(赞成或是反对,还有推测)1) 情态助动词在限定动词词组总是位居第一:They need not have been punished so severely.2) 情态助动词用于第三人称单数现在时的时候,没有词形变化,即其词尾无-s形式:She dare not say what she thinks.3) 情态动词没有非限定形式,即没有不定式、-ing分词和-ed分词形式:Still, she neednt have run away.4) 情态助动词的“时”的形式并不是时间区别的主要标志而是语气强弱的区别。在不少场合,情态助动词的现在时和过去时形式都可以表示现在、过去或将来时间:Would you mind if I ask you to do something?She told him he ought not to have done it.Can you help me?Could you help me?后者就比前者的语气委婉的多。情态助动词的意义和用法情态助动词从最普通的意义上来说,是修饰分句意义的一种方式,它可以反映说话者对其表述是否真实和可能的程度作出判断。但不同的情态助动词本身所包含的意义和用法又不同,下面我们就例举几个常见的情态动词1) can和could的用法1 表示能力或客观可能性,还可以表示请求和允许。如:I can speak English.Man cannot live without air. Can I go now? Yes, you can.注意:could也可表示请求,预期委婉,主要用于疑问句,不可用于肯定句,答语应用can(即could不能用于现在时态的简略答语中)。如: Could I come to see you tomorrow? Yes, you can. (否定答语可用No, Im afraid not.) can表示能力时,还可用be able to代替。 同时我们过去的某种能力我们不采用can的过去式,而是用这个短语对应的过去,如: Ill not be able to come this afternoon.I was able to swim across the river when I was 5 years old.2 表示惊异、怀疑、不相信的态度。(主要用在否定句、疑问句或惊叹句中)Can this be true?How can you be so careless!This cannot be done by him.3 “can(could) + have + 过去分词”的疑问或否定形式表示对过去发生的行为怀疑或不肯定。如:He cannot have been to that town.Can he have got the book?2) may和might的用法1 表示许可。表示请求、允许时,might比many的语气更委婉一些,否定回答时要用mustnt表示“不可以”、“禁止”、“阻止”之意。如:You may drive the car. Might I use your pen? No, you mustnt.用May I . 征询对方许可在文体上比较正式,在口气上比较客气。在日常口语中,用Can I . 征询对方意见在现代口语中更为常见。2 用于祈使句中表示祝愿。如:May you succeed!3 表示推测、可能(疑问句不能用于此意)。He may be very busy now.4 “may(might) + have + 过去分词”表示对过去发生的行为的推测。如:He may not have finished the work.3) must和have to的用法1 表示必须、必要。如:You must come in time.回答must引出的问句时,如果是否定的回答,不能用mustnt,而要用neednt或dont have to。 Must we hand in our exercise books today? Yes, you must. (No, you dont have to.)2 “must be + 表语”的结构表示推测,它的否定或疑问式用can代替must。 This must be your pen.3 “must + have + 过去分词”的结构常用在肯定句中,表示对过去发生的行为的推测。它的否定或疑问式用can代替must。He must have been to Shanghai.4 have to的含义与must相似,两者往往可以互换使用,但have to有各种形式,随have的变化而定。must与have to有下列几点不同: must表示的是说话人的主观看法,而have to则往往强调客观需要。如:The play is not interesting. I really must go now.I had to work when I was your age.5.must 表示固执,偏偏Why must you be talking so loudly while others are studying?为什么在别人学习的时候,你非得这么大声地说话?4) shall和should的用法1 Shall用于第一人称,表示征求对方的意愿。如:What shall we do this evening?2 Shall用于第一、第三人称疑问句中,表示说话人征求对方的意见或向对方请示。如:Shall we begin our lesson?When shall he be able to leave the hospital?3 Shall用于第二、第三人称,表示说话人给对方命令、警告、允诺或威胁。如:You shall fail if you dont work harder. (警告)You shall get the bike if you get full marks in the exam.(允诺)4 Should表示劝告、建议、命令,其同义词是ought to;在疑问句中,通常用should代替ought to。如:You should go to class right away.Should I open the window?5) will和would的用法1 表示请求、建议等,would比will委婉客气。如:Would you pass me the book?2 表示意志、愿望和决心。如:I will never do that again.They asked if we would do that again.3.will可以表示一种习惯性的动作,总是或总要之意Every morning he will have a walk along the river.4.Would可表示过去反复发生的动作或某中倾向。Would表过去习惯时比used to正式,并没有“现已无此习惯”的含义。如:The wound would not heal.During the vacation he would visit me every week.6) ought to的用法1 Ought to表示应该。如:You ought to take care of him.2 表示推测。注意与must表示推测时的区别:He must be at home by now. (断定他已到家)He ought to be home by now. (不十分肯定)This is where the oil must be. (比较直率)This is where the oil ought to be. (比较含蓄)3 “ought to + have + 过去分词”表示过去应做某事而实际未做。如:You ought to have asked him (but you didnt).这时,ought to和should可以互相换用。注意:在美国英语中,ought to用于否定句和疑问句时,to可以省略。如:Ought you smoke so much?You oughtnt smoke so much.情态动词+have done”的用法1 Must + have done表示对过去事情的肯定推测,译成“一定做过某事”,该结构只用于肯定句。 1. It must have rained last night, for the ground is wet. 昨晚一定下雨了,因为地面还是湿的。2. You must have been mad to speak to the servant. 你和仆人说话,一定是发疯了。2 should + have done表示“本来应该做某事而实际上未做”,而shouldnt have done则表示“本不应该做某事而实际上做了”。如:You should have told me about it earlier.You shouldnt have said such words to your parents.3 ought to have done也表示“本应该”而ought not to have done则意为“本不应该”。如:You ought to have told me about it earlier.You ought not to have said such words to your parents.4 neednt have done表示“本无必要做某事而实际上做了”。如:You neednt have walked so quickly since time was enough.5 could have done表示“本来有可能而事实上未做到”。如:I could have come on time, but my car broke on the way.6 may/might +have done 表示对过去行为的推测,可能做过。Might 表示的可能性更小语气更委婉。Might have done可表示本可能做而实际没有做。I can not find my purse anywhere.You may have lost it while shopping.
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