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1、 情态助动词：can (could), may (might), must ,have to (had to), ought to, shall (should), will (would)具有情态动词的特征，又具有实义动词的 某些特征，称为半情态助动词： dare, need, used to, had better, would rather（一）情态助动词1.Can和could的用法 1）表示能力，指有能力做某事，意为“能够” She cancan speak English but she cantcant speak Spanish. Can you finish the work
2、tonight?表示有能力克服困难做成某事，用is/are able toDespite his handicap he is able tois able to drive a car.表示有能力通过努力做成某事还可用manage to或succeed in doingDo you think shell manage tomanage to get a visa?The army succeeded in defeated their enemy. 2)表示请求或允许，意为“可否”，“可以” CanCan I smoke here? You can can have the book wh
3、en I have finished it. 3)表示可能性，含惊讶、怀疑、不相信的语气，常用在否定句、疑 问句或感叹句中，意为“可能” This cannot cannot be done by him. You cantcant sell the cow and drink the milk,as the saying goes.注意：在wh-question中，或与副词only, hardly等连用表 达可能性，用can或could,不用may:Who can/could that be at this time of night?How can you be so careless!I
4、t can/could hardly be the postman, he only comes in the morning.It can/could only be Steve. Hes the only one with a key.在肯定句中，表示现在或将来的可能性，用may, might或could ,不用can:He may/might/could be in the library.What he said may/might/could be true.在肯定句中使用can表示可能性时，其含义是理论上的可能性， 不表示实际的可能性，也就是说，不涉及到是否真会发生：The inv
5、ention can be improved.Even expert drivers can make mistakes.4)Can be用于推测某人或某物一时的情况，意为“有时候会”:SARS can be very dangerous.He can be very friendly at times.The road can be blocked.5)Could 表示轻微的怀疑或委婉地陈述看法： His story could be true, but I hardly think it is. I could do the job today, but Id rather put it
6、off until tomorrow. Im sorry I couldnt lend you the book now. Who could have supposed you were going to do such a thing!6)Could 表示请求，语气较委婉，主要用于疑问句，不用于肯定句 ，答语应用can: Could you lend me some money? Yes, I can.No, Im afraid not.7）couldnt用于一个表示强调语气的结构 “couldnt+动词+比较级”用于对现在行为或感情的强调，意为“非 常”,“再不过了”：-Shall I
7、give you a ride as you live so far away？-It couldnt be better. 再好不过了！-Go for a picnic this weekend, OK?-I couldnt agree more. 我非常同意！2.May和might的用法 1）表示许可 May I interrupt? You may go now.2)表示可能性，用于推测，暗指不确定 She may know Toms address. He may be waiting for you at the station.注意：注意： 表示可能性时，may不用于疑问句当句中出
8、现“Im afraid，Im not sure”等表示不确定 含义时，常用“may”或“might”：I may go, but I dont really want to.He may come, but I am not quite sure. 从语气上判断，may表示的可能性比might大一点， 而might表示较多的怀疑： He may be very busy now. (可能性较大） He might be very busy now. （可能性较小）3）用于表让步状语从句中： However hard you may study, you cannot master Englis
9、h in a month. Come what may, I will never desert you. 无论发生什么，我绝不会背弃你。4）用于祈使句，表示祝愿： May you succeed! May we never forget each other!5) might常用于表示委婉的请求或轻微的责备： You might post this letter for me if you are going near a post box. You might have let me know before!6)用于某些习惯用法中： may well+动词原形，意为“理所当然；有足够的理由
10、” He has changed so much. You may well not recognize him. She may well be proud of her son. may/might (just) as well,意为“最好”=had better,用于提出建议 You may as well give him the letter. You might as well stay at home tonight.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 a
11、way as lend it to him. 你与其借钱给他，不如把钱扔掉。 One may as well not know a thing at all as know it but imperfectly. 与其一知半解，还不如全然不知。3.Must和have to 的用法 1)Must和have to表示义务，意为“必须”、“一定要”： You must arrive in good time. The meeting is very important. Everyone has to register their name and address in order to be ab
12、le to vote. 2)Must表示肯定性或难以避免，意为“必然会”、“肯定会”： All men must die. Dont bet on horse race; you must lose in the long run.3)Must表示有把握的推测，意为“一定是”，“准是”，有3种形式 ： 对现在情况的推测： must+动词原形 That tall fellow must be a basketball player. He must be anxious to know the results. 对现在正在进行中的事的推测： must be+现在分词 You look happy
13、. You must be having a good time. 对过去的推测：must have+过去分词 You must have met him yesterday.4)Must作“偏要”，“硬要”解： 常以第二人称为主语，意指不耐烦或令人不愉快的事 If you must smoke, at least you could use an ashtray. Why must you buy that car? 用于其他人称，表示主语“固执”或“不巧”的意味 The car must break down just when we were starting our holiday.5
14、)Must的否定有如下3种形式，用于 3种不同场合：must表示“合理的推断和可能性”时， 否定含义为“不可能” 肯定：must be 否定：cannot be 肯定：must have done 否定：cannot have done must表示“义务和必要”时，否定含义为“不必”： 肯定：must do 否定：need not do或dont have to do must表示“禁止和批评”时，常用于否定句，其含义为“决不能” ： You mustnt park your car here.6)回答以must提问的句子，用如下肯定或否定形式作答：Must we clean all the
15、 rooms?Yes, you must. No, you dont have to. No, you neednt.7)Must可用作名词，表示“必须有的东西（做的事）”： Warm clothes are a must in the mountains. Dont miss his latest play; its a must.8)Must和have to表示“必须”时，应注意以下几点区别： 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： The play is not interesting, I really must go now. I had to wo
16、rk when I was your age. must一般只表现在，have to则有更多的时态形式。过去式：had to 将来式：shall/will have to现在完成式：have/has had to 过去完成式：had had to二者的否定意义不大相同 A）must not表示禁止，是说话人强有力的劝告，意为“绝 不可以”、“不准”、“不允许”。而dont have to意为“不必” 。You mustnt go. 你决不可以去。 You dont have to go. 你不必去。B）didnt have to do指“过去没有必要做”，至于是否已做，应根 据上下文判断。 It was very kind of you to do the washing-up, but you didnt have to do it. （此事已做） I got up late this morning
