情态动词讲义和专项练习情态动词有 can (could), may (might), must, have to, shall (should), will (would), dare (dared),need (needed),ought to 等。 情态动词无人称和数的变化；不能单独使用，必须与其后的动词原形构成谓语一、can, could1) 表示水平(体力、知识、技能)。e.g. Can you lift this heavy box?(体力)Mary can speak three languages.(知识)Can you skate?(技能)此时可用be able to代替。can只有一般现在时和一般过去式；而be able to则有更多的 时态。e.g. Ill not be able to come this afternoon.当表示“经过努力才得以做成功某事”时应用be able to,不能用can。如：e.g. He was able to go to the party yesterday evening in spite of the heavy rain.Although he cant swim, yet he was able to cross the river.2) 表示请求和允许。e.g. Can I go now?Yes, you can. / No, youcant.此时可与may互换。在疑问句中还可用could, might代替，不是过去式，仅仅语气更委 婉,不能用于肯定句和答语中。e.g. Could I come to see you tomorrow? Yes, you can. ( No, Im afraid not. )3) 表示客观可能性(客观原因形成的水平)。e.g. Theyve changed the timetable, so we can go by bus instead.Even experienced teachers can make mistakes.4) 表示推测(惊讶、怀疑、不相信的态度)，用于疑问句、否定句和感叹句中。e.g. Can this be true?This cant be done by him.How can this be true?5) “can + have done”主要用于否定句和疑问句中，表示对过去发生的行为怀疑或不肯 定。e.g. He cannot have been to that town.Can he have got the book?“could + have done ”表示虚拟语气。e.g. But for your help, we couldnt have finished the task before the deadline.You could have achieved better results but you wasted the valuable time.6) 习惯用法：cannottoo “再也不过度”e.g. You cannot be too careful in the choice of your friends.二、may, might1) 表示请求和允许。 might 比 may 语气更委婉，而不是过去式。否定回答时可用 cant 或mustnt，表示“不能够，禁止”。e.g. Might/ May I smoke in this room? No, you mustnt. May/Might I take this book out of the room? Yes, you can. (No, youcant / mustnt. )用May I.?征徇对方许可时比较正式和客气，而用Can I.?在口语中更常见。2) 用于祈使句，表示祝愿。e.g. May you succeed!3) 表示推测、可能性(表示此意时，不用于疑问句)。 might 不是过去式，它所表示的可能性比 may 小。e.g. He may /might be very busy now.Your mother may /might not know the truth.4) “may / might + have done”表示对过去行为的推测。e.g. Without the heavy traffic, we might have caught the train.5) 习惯用法：may / might as well + do “不妨”e.g. You might as well have an another try.三、must, have to1) 表示必须、必要。e.g. You must come in time.在回答引出的问句时，如果是否定的，不能用mustnt (禁止，不准)，而用neednt,dont have to (不必).e.g. Must we hand in our exercise books today? Yes, you must. No, you dont have to / you neednt.2) must是说话人的主观看法，而have to则强调客观需要。must只有一般现在时，have to 有更多的时态形式。e.g. The play isnt interesting, I really must go now.I had to work when I was your age.3) 表示推测、可能性(只用于肯定的陈述句)e.g. Youre Toms good friend, so you must know what he likes best.Your mother must be waiting for you now. 表示肯定推测的否定句，用 cannot e.g. This cannot be your pen.4) “must + have done”对过去行为的肯定推测，否定句用cannot have done.e.g. It must have been rainy yesterday,wasnt it?It must have rained yesterday, didnt it?5) have got to 是 have to 的口语形式。e.g. Youhavent got to go to school today, have you?6) must “偏偏”e.g. Why must it rain on Sunday?We were going to see a movie, but it must rain yesterday.四、dare, need1) dare 作情态动词用时, 常用于疑问句、否定句和条件从句中, 过去式形式为 dared。 e.g. How dare you say Im unfair?He darent speak English before such a crowd, dare he?If we dared not go there that day, we couldnt get the beautiful flowers.2) need 作情态动词用时, 常用于疑问句、否定句。在肯定句中一般用 must, have to, ought to, should 代替。e.g. You neednt come so early. Need I finish the work today? Yes, you must. / No, youneednt.3) dare和need作实义动词用时，有人称、时态和数的变化。在肯定句中，dare后面 常接带to的不定式。在疑问句和否定句中，dare后面可接带to或不带to的不定式。而 need 后面只能接带 to 的不定式。e.g. I dare to swim across this river.He doesnt dare (to) answer.He needs to finish his homework today.4) “neednt + have done”表示虚拟语气，本不必做某事而事实上却做了。e.g. Youneednt have waited for me.5) need doing = need to be done.e.g. The washing machine needs repairing. = The washing machine needs to be repaired.6)“I dare say”意为“我猜测”e.g. I dare say he will come.五、shall, should, ought to1) shall 用于第一人称，征求对方的意见。e.g. What shall we do this evening?2) shall 用于第二、三人称的肯定句，表示说话人给对方的命令、警告、允诺或威胁。e.g. You shall fail if you dont work hard.警告)He shall have the book when I finish it.(允诺) He shall be punished.(威 胁)3) 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。e.g. Shall we begin our lesson?When shall we be able to leave the hospital?4) should, ought to 表示“应该”， ought to 表示义务或责任，比 should 语气重。e.g. I should help her because she is in trouble.You ought to take care of the baby.5) 表示劝告、建议和命令。should, ought to可通用，但在疑问句中常用should。e.g. You should / ought to go to class right away.Should I open the window?6) should 表示主观推测，“估计”“按道理应该”e.g. He ought to/should be home by now.They should finish it by now.7) should + have done”用于虚拟语气，本应该做某事而实际上并未做某事。Shouldnt have done 本不该做而做了e.g. You should have arrived here 5 minutes earlier.8) 特殊用法：“竟然”“居然”表示说话人感到意外，赞叹，愤怒，惊异等感情。e.g. You cant imagine the gentleman should be a thief.e.g. I dont know why you should think I did it. “倒是”，用于第一人称时表示说话人的一种谦逊，客气，委婉的语气。e.g. I should think it