1、情态动词的用法情态动词的用法 情态动词表示说话人对某一动作或状态的情感和态度。情态动词没有人称和数的变化。但不能单独作谓语动词用，必须动词原形一起构成谓语动词。将情态动词置于主语之前即构成其疑问式，在情态动词之后加not既构成其否定式。1.can和could(could为can的过去式)(1)表示能力，eg：He can speak English better than you.(2)在疑问句和否定句中表示“怀疑”、“猜测”或“可能性”，eg：Can this green bike be Liu Dongs?(3)表示“许可”时can可以和may换用 eg:You can(may)go ho
2、me now.(4)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 eg:Could you come again tomorrow?(5)can和be able to都可表示能力。但是can只能有现在式和过去式，而be able to则有更多的形式，如：eg:He will be able to do the work better.2、may和might(1)表示允许或征询对方许可意为“可以”You may use my dictionary.在回答对方说“可以做或不可以做某事”时，一般多不用may或 may not，以避免语气生硬或不容气。而用比较婉转的
3、说法进行回答。eg：-May I use this dictionary?-Yes,please.-Certainly.在请求对方许可时，如果Might I?就比用May I?语气更婉转些，如：May I have a look at your new computer?但是表示“阻止”或“禁止”对方做某事时，要用must not代替may not，-May we swim in this lake?-No,you mustnt.Its too dangerous.(2)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，eg：The
4、y may(might)be in the library now.3、must的基本用法(1)must表示“必须”，其否定式must not，缩写形式为 mustnt，表“不准”、“不许可”或“禁止”之意，eg: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 eg：-Must we finish the work tomorrow?-No,you nee
5、dnt(dont have to),but you must finish it in three days.(3)在肯定句中must可以表示推测，表示“一定”或“必定”之意，eg：-Whose new bike can it be?-It must be Liu Dongs.I know his father has just bought him a new one.4、can,could,may,must后接完成式的用法(1)can,could后接完成式的用法：在否定句或疑问句中表示对过去发生过的事情的“怀疑”或“不肯定”的态度，Could he have said so?在肯定句中，可
6、以表示过去可能做到而实际并没做到的事情，有“劝告”或“责备”的语气。如：-When did you answer her letter?-Only yesterday.-Its too late.You could have answered it earlier,I am sure.(2)may,might后接完成式的用法 表示对过去某事的推测，认为某一件事情在过去可能发生了。eg：Mary might have learned some Chinese before.可以表示过去本来可以做到而实际没有做到的事情，有“劝告”或“责备”的语气eg：You didnt do the work w
7、ell that day.You might have done it better.(3)must后接完成式的用法：表示对过去某事的推测，认为某事在过去一定做到 了。如：Liu Dong isnt in the classroom.He must have gone to the library.5、have to 的基本用法：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，eg：I must study hard.I had to give it up because of illness.6、ought to的基本用法(l)表示根据某种义务或必要“应当
8、”做某事，语气比should强，eg：Everyone ought to obey the traffic regulations.(2)表示推测，注意与must表示推测时的区别：He must be 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+have+过去分词”表示过去应做某事而 实际未做。eg：You ought to have helped him.
9、这时，ought与 should可以互相换用。注意，在美国英语中ought to 用于否定和疑问句时to可以省略。例如：Ought you smoke so much?You oughtnt smoke so much.7、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。eg：Dared he break the traffic rules again?(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，eg：She dares to stay at home alone at night.8、need的基本用法(1)
10、need作情态动词用时，主要用于否定句和疑问句中，eg：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。eg：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，eg:-Did you answer the letter yesterday?-Yes,I did.-But you neednt have answered it.9、shall的基本用法(1
11、)shall用作情态动词时，用于第二、三人称，表示说活人的意愿，可表示“命令”、“警告”、“强制”、“威胁”或“允诺”等意。eg：He shall go first,whether he wants to or not.(2)在疑问句中，shall用于第一、三人称，表示说话人的征询对方意见或请求指示。eg：Shall I open the door?10、should的基本用法(1)should作为情态动词可以表示“建议”或“劝告”，有“应该”之意，eg：You should learn from each other.(2)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
12、不应该做的事情。eg：You should have given him more help.11、will的基本用法(1)用于各种人称，可以表示“意志”或“决心”，eg：I have told him again and again to stop smoking,but he will not listen.(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询问对方的意愿 eg：Will you please tell me how to get to the Capital Gymnasium?(3)will可以表示一种习惯性的动作，有“总是”或“会要”之意，eg：Every mo
13、rning he will have a walk along this river.12.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”。eg：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可对方的意愿时，比用will的气更婉转eg：Would you like some more coffee?(3)在日常生活中，用“I would like to”表示“我想要”或“我愿意”之意，以使语气婉转。eg：I would like to do Ex
14、.2 first.(4)would可以表示过去的习惯动作，比used to正式，并没有“现已无此习惯”的含义。如：Last year our English teacher wouldsometimes 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
15、 you about it.13.used to,had better,would rather(1)used to表示过去的习惯动作或状态，现在已不存在，在间接引语中，其形式可不变，例如：He told us he used to play foot ball when he was young.否定疑问句：Usednt you to？Didnt you use to be interested in the theatre?强调句：I certainly used to/did use to smoke,but it was a long time ago.其反意疑问句或简略回答中，也有两
16、种形式：Used you to get up early in the morning?Yes,I did./used to.Did you use to play chess?Yes,I did.Used you to get up early in the morning?Yes,I did./used to.(2)had better意为“最好”，后接不带to的不定式。eg:-We had better go now.-Yes,we had(wed better/we had better).Hadnt we better stop now?Had we better not stop
17、now?I think Id better be going.(用于进行时态，表“最好立即”)You had better have done that(用于完成时态，表未完成动作)注：had better用于同辈或小辈，对长辈不可用(3)would rather意为“宁愿”。Id rather not say anything.Would you rather work on a farm?-Wouldnt you rather stay here?-No,I would not.Id rather go there.由于would rather表选择，因 而后可接than。eg:I would rather work on a farm than in a factory.I would rather watch TV than go to see the film.I would rather lose a dozen cherry trees than that you should tell me one lie.
