1、情态动词讲解,can和could (could为can的过去式) 的基本用法,(1)表示能力，如： He can speak English better than you. can和be able to都可表示能力，两者在意思上没有什么区别。但是can只能有现在式和过去式，而be able to则有更多的形式，可位于情态动词之后或表达过去成功地做了某事。如： He will be able to do the work better. He was able to finish the work on time.,(2) 表示客观的可能性 Accidents can happen to an
2、y drunken driver. According to the radio, it could rain this afternoon. (3)表示“许可”时can可以和may换用，如： You can (may) go home now.如果要表示语气婉转，可用could代替can，这时could不再是can的过去式，注意回答时不能用could。 如： Could you come again tomorrow?Yes, I can./ No, I cant.,(3) 在疑问句和否定句中表示怀疑、惊奇、不相信的态度。如： Can this green bike be Liu Dongs
3、? How can you believe such a liar like him? (4) 用于肯定句，表示一时的情况，意为：有时候会。如： It can be very hot here in summer. Tom is a clever boy, but he can be dull sometimes.,may和might (might为may的过去式)的基本用法,(1)表示允许或许可，否定用mustnt, 表禁止。如： - May we swim in this lake? - No, you mustnt. Its too dangerous. 肯定可以用比较婉转的说法进行回答
4、。如： - May I use this dictionary? - Yes, please. /- Certainly. / Yes, you can.(2)在表示请求、许可时，用might比may 语气更婉转些, 如： May I have a look at your new computer? May I?在文体上较正式，较客气，日常口语中常用Can I?,(3)may或 might都可以表示可能性，表示“或许“、“可能“之意，如果用might表示可能性，则语气更加不肯定，如：They may (might) be in the library now .He is absent. H
5、e may/ might be ill.,must的基本用法,(1)must表示“必须”、“应该”之意，语气比should, ought to强烈， 其否定式 must not，缩写形式为 mustnt，表示 “不准”、或“禁止”之意，如： We must study hard and make progress every day. You mustnt touch the fire.,(2)对以must提出的疑问句，如作否定回答时，要用neednt或用dont (doesnt) have to (不 必)来回答，而不用mustnt，因为mustnt表示的是“禁止”或“不许可”之意，如：-
6、Must we finish the work tomorrow?- No, you neednt (dont have to), but you must finish it in three days.,(3) must可以表示推测，表示“一定”或“必定”之意，只用于肯定句中。如： - Whose new bike can it be? - It must be Liu Dongs. I know his father has just bought him a new one. You must be ill. I can see it from your face.,have to 的
7、基本用法,1.have to和must的意义相近，只是 must侧重表示说话人的主观看法，而have to 则表示客观需要，如： I must study hard. You have to hand in your compositions before next Monday.2.have to 有人称、数和时态的变化,否定式要用助动词，dont have to如： They had to speed up, for the weather turned terrible. He has to stay at home because of illness,should的基本用法,(1)s
8、hould表示“建议”或“劝告”，有“应该”之意，可与ought to 互换。如： You should learn from each other. You should/ ought to go and see Mary some time. (2）表示推测，译作：很可能，该，是说话人对客观事物的真实性做出较大可能性的判断。如： Its already 10. She promised to come by 10. She should be here at any moment. (3) why/how + should 表示“竟然”，含意外、惊异等语气。 Why should you
9、be so late today? I dont understand why you should think that I did it.,(4)should后接完成式表示过去没有做到本来应该做的事情，或是做了本来不应该做的事情。如： You should have given him more help. You shouldnt have left home without saying a word. (5) 表示万一，用于if 从句 Ask Tom to ring me up if you should see him.,will的基本用法,(1) 可以表示“意志”或“决心”，如：
10、 I have told him again and again to stop smoking, but he will not listen. Can someone help me? I will. (2) 请求或询问对方的意愿，如： Will you please tell me how to get to the Capital Gymnasium? Will you open the window? (3)表示一种习惯性的动作，有“总是”或“惯于”之意，will 指现在，would 指过去。如：Every morning he will have a walk along this
11、 river.,would的基本用法,(1)would作为will的过去式，可用于各人称，表示过去时间的“意志“或“决心“，如：He promised he would never smoke again. (2)在疑问句中，用于第二人称，表示说话人向对方提出请求或许问对方的意愿时，比用will的气更加婉转，如：Would you like some more coffee? (3)在日常生活中，学用“I would like to“表示“我想要“或“我愿意“之意，以使语气婉转，如：I would like to do Ex.2 first.,(4)would可以表示过去的习惯动作，比used
12、 to正式，并没有“现已无此习惯“的含义。如：Last year our English teacher would sometimes tell us stories in English after class. / During the vacation he would visit me every week. (5)表料想或猜想，如：It would be about ten when he left home./ What would she be doing there?/ I thought he would have told you about it.,shall的基本用法
13、,(1)在疑问句中，shall用于第一人称，表示说话人的征询对方意见或请求指示，如：Shall I open the door?,need的基本用法,(1)need作情态动词用时，主要用于否定句和疑问句中，如：He neednt worry about us now. (2)need也可作为行为动词用，可用于肯定句，否定句和疑问句中，其后可接名词、代词、动名词或带 to 的动词不定式为其宾语。如：You need to practise reading aloud every day. (3)neednt后接完成式可以表示过去做了一件本来不必要做的事情，如：- Did you answer t
14、he letter yesterday? - Yes, I did. - But you neednt have answered it.,dare的基本用法,(l)dare (dared为其过去式) 作情态动词用时，主要用于否定句，疑问句和条件从句中，如：Dare he break the traffic regulations again?You will be punished if you dare do such a thing. (2)在现代英语中dare常用作行为动词，其变化与一般行为动词相同，如：She dares to stay at home alone at night.,
