1、专题三情态动词 知 识 梳 理 情态动词本身有一定的词义，但需和其他动词一起构成谓语。除ought, used外，情态动词后面接动词原形。情态动词中have to可以用have got to代替；need, dare也可用作实义动词；used to有两种否定形式：used not to和did not use to。can，could表示具有某种能力，指有能力做某事He could swim when he was five.By the age of seven he could write beautifully.表示请求和允许，和may相近；口语中可用could表示委婉语气，但回答时仍用
2、canCould /Can I use your pen?Yes, of course you can.Could I ask for your reaction to this policy？表示推测，常用于否定句和疑问句中Mike cant have found his car, for he came to work by bus this morning. I think the work can be completed ahead of time.表示“有时也会”It can be quite windy there, especially in spring.cannot but
3、 do sth.表示“只好，不得不”Father cannot but agree with his daughters opinion.cant help doing sth.表示“禁不住做某事”I cant help feeling sorry for the poor man.The film is so impressive that we cant help crying.be able tobe able to可以有多种时态，如：将来时(will be able to)，完成时(have /has /had been able to)I will be able to speak
4、French in another few months.I have been able to swim since I was 5.be able to侧重通过努力成功做成某事的能力He said he could swim across the river. (指本身具有这种能力)At last he was able to swim across the river. (指通过努力做到了)may, might表示允许、许可或征求允许，否定回答时要用mustnt; might比may语气委婉Might /May I smoke in this room? No, you mustnt.M
5、ay /Might I take this book out of the room? Yes, you can. (No, you mustnt.)表示可能性，might比may可能性更小I think the trip may give me time to calm down.An active volcano may explode at any time.Dont go too far afield or we might lose you.may /might as well do sth.“不妨做某事，还是做某事为好”Everything is ready. We might a
6、s well start now.will，would表示意志、决心或愿望We will do our best to save the child.I told her to stop crying, but she just wouldnt listen.用于第二人称，表示请求、建议等Will /Would you please post the letter for me?Wont you take off your coat？will表示“总是，惯于”； would表示过去的习惯，意为“过去常常”When he was a child, he would often go skiing
7、.He would sit there for hours sometimes doing nothing at all.表示推测或猜想This will be the house youre looking for.I think he would accept the invitation.shall用于第一、三人称的疑问句中，表示征求对方的意见或请示Shall I clean the desks one by one？用于第二、三人称的陈述句，表示说话者的命令、警告、许诺等语气He shall return that book tomorrow. (命令)I shall think it
8、 over and let you know my idea. (许诺)You shall fail if you dont work harder. (警告)用于第三人称，在条约、规定、法令等文件中表示义务或规定，意为“应该，必须”Candidates shall remain in their seats until all the papers have been collected.Persons under 18 shall not be employed in night work.should, ought to表示“应该”，常用于表示现在或将来的责任或义务；还可表示推测，指有一
9、定依据的推测We should /ought to help each other and learn from each other in our work.We ought to go and see Mary tomorrow, but I dont think we will.It ought to be a fine day tomorrow morning.should还可表示惊讶，意为“竟会，居然”Its strange that he should be absent.It seems unfair that this should happen to me.must, hav
10、e tomust强调主观看法，表示“必须”，have to强调客观需要，意为“不得不”Yesterday morning I told my father that I must call on a friend. You have to wear uniform on duty, dont you？must表示“偏要，非得”等含义，这种用法常用于疑问句、条件句中Must you waste so much time?Must you make so much noise? Why must you always interrupt me? We were ready to leave, bu
11、t the baby must catch cold.mustnt意为“不许，禁止”；若表示“没有必要，不必”时，用neednt或dont have toThat car is my property; you mustnt use it without my permission.You mustnt drive into a street with a “No Entry” sign.You neednt talk to anyone if you dont want to.You dont have to worry about me. Im a good swimmer.must表示推
12、测时，仅用于肯定句，但在反意疑问句中，其后面反问部分取决于must后面的动词形式You must be a newcomer, arent you? She must have been very young when she got married.It must be your mother who you are thinking of.need表示“需要，必须”，常用于疑问句和否定句中； 肯定回答用must，否定回答用needntYou neednt have the bike repaired right away.Need I go back to Xiamen after I v
13、isited Fuzhou? Yes, you must. /No, you neednt.dare主要用于否定句、疑问句以及条件句中，有过去式形式daredDare she tell him what she thinks about him? She darent say anything. He will only shout at her. “How dare you speak to me like that？” he will say.used to“过去常常”，含有今昔对比的意味，表示过去习惯的动作或状态现在已结束，而would表示过去反复发生的动作，但不含对比意味He used
14、 to get up at six every morning. (现在不这样了) He would get up at six every morning and had a walk in the forest then. (现在是否还这样不得而知) had better，would betterhad better /would better表示“最好”(但一般都用had better)；would better还可表示“宁愿，宁可”You had better go to the factory and have a look. I would better die before as
15、king him for help.情态动词havedonemust have done用在肯定句中，表示对过去情况的肯定推测，语气坚定It must have rained last night, for the road is wet. Tom must have taken your dictionary by mistake.cant have done表示对过去情况表示否定的推测，是must have done的否定形式Mr.Smith cant have gone to Beijing, for I saw him in the library just now.Mary cant
16、 have stolen your money. She has gone home.could have done用于肯定句，表示过去本能完成某事但事实上并没有完成，意为“本来能够做”He could have passed the exam, but he was too careless.He could have bought the car, but soon his company went bankrupt.may /might have done表示过去可能发生某事，意为“可能，或许”；might have done还可表示“本可能做某事”What has happened t
17、o George?I dont know. He may have got lost.She might have achieved greater progress, if you had given her more chances.should have done表示“过去本应该做某事而没有做”Tom, you are too lazy. The work should have been finished yesterday.If I knew she was short of money, I should have lent her some.shouldnt have done
18、sth.表示“过去本不该做某事而实际上做了”Look, Tom is crying. I shouldnt have been so harsh on him.I dont think you have changed at all! Xiao Li shouldnt have failed to recognize you.neednt have done表示“过去本没有必要做某事而实际上做了”I neednt have bought so much wineonly five people came.As you worked late yesterday, you neednt have come this morning.
