情态动词情态动词是一种本身有一定的词义，但要与动词原形及其被动语态一起使用，给谓语动词增添情态色彩，表示说话人对有关行为或事物的态度和看法，认为其可能、应该或必要等。

情态动词后面加动词原形。

情态动词有四类：①只做情态动词：must,can(could),may(might)……②可做情态动词又可做实义动词：need，will③具有情态动词特征：have(had,has) to,used to，ought to④情态动词表猜测：一肯一否三不定（must一肯，can not一否，may，might，could，三不定。

）注：mustn't代表强烈禁止 must表示主观，have to表示客观。

常用的有：can may could must have use .情态动词无人称和数的变化，情态动词后面跟的动词须用原形，否定式构成是在情态动词后面加"not"。

个别情态动词有现在式和过去式两种形式，过去式用来表达更加客气，委婉的语气，时态性不强，可用于过去，现在或将来。

情态动词属非及物动词，故没有被动语态。

情态动词表推测的用法小结（一）情态动词表推测的三种句式1．在肯定句中一般用must （一定），can,could（可能），might /may（也许，或许）。

e.g:(1)He must/can/may,might know the answer to this question.他一定/可能/也许知道这个问题的答案。

(2)It is cold in the room. They must have turned off the heating.屋里很冷，他们肯定把暖气关了。

2．否定句中用can’t / couldn’t（不可能），may not/might not（可能不）。

e.g:(1)It can’t/couldn’t be the headmaster. He has gone to America.这不可能是校长，他去美国了。

(2)He may not/might not know the scientist.他也许不认识那位科学家。

3．疑问句中用can/could （能……?）。

e.g:(1)．Could he have finished the task?他可能把任务完成了吗？注：以上三种句式中情态动词的语气按程度都是依次递减的。

Might,could并非may,can的过去式，而表示语气较为委婉或可能性较小。

（二）情态动词表推测的三种时态1．对将来情况的推测，用“情态动词 + 动词原形”。

e.g:(1)．She must / may / might / could arrive before 5.5:00前她一定/可能/也许到。

2．对现在或一般情况的推测，用“情态动词+ be”，“情态动词+be doing”或“情态动词 + 动词原形”。

e.g:(1)．He must / may / might / could be listening to the radio now.他一定/可能/也许正在听收音机。

(2)．He can’t ( couldn’t ) / may ( might ) not be at home at t his time.这个时候他不可能/可能不在家。

3．对过去情况的推测，用“情态动词 + have +过去分词”。

e.g:(1)．It must / may / might / could have rained last night .The ground is wet.地湿了，昨晚肯定/可能/也许下雨了。

(2)．The door was locked. He can ( could ) not / may ( might ) not have been at home . 门锁着，他不可能/可能不在家。

注：情态动词 should /ought to表推测时，意为“想必会，理应……”但与“have +过去分词”连用时，则又可构成虚拟语气意为“本应该做某事却没做”。

例如：(4)．It’s seven o’clock. Jack sh ould/ought to be here at any moment.现在七点钟了，杰克理应随时到达。

（推测）（5）．Tom should not /ought not to have told me your secret,but he meant no harm. （虚拟）汤姆本不该告诉我你的秘密，可是他并无恶意。

can 和could 表示推测的用法对现在或将来的推测，两者均可用，但can 通常只用于否定句或疑问句中，一般不用于肯定句，而could则可用于肯定句、否定句和疑问句；对过去的推测，应在 can,could 之后接动词的完成式，且此时can仍只用于否定句或疑问句，不用于肯定句；而could 则可用于各种句型。

如：Can [Could] this be true? 这能是真的吗Where can [could] he have gone? 他能到哪里去了呢She can’t [couldn’t] have left so soon. 她不可能走得这么早。

注：could后接动词的完成式，除表示对过去的推测外，还可表示过去没有实现的可能性（即某事本来可以发生，却没发生），或委婉地责备某人过去应该做某事而没有去做（此时不用can）。

如：You could have started a little earlier. 你本可早点动身的。

You needn’t have cooked it. We could have eaten it raw. 你其实可以不煮熟（它），我们（本来）可以生吃。

can 和could 表示允许的用法表示现在的允许时，若是请求别人允许自己做某事，两者均可用，但用could 语气更委婉；若是自己允许别人做某事，一般只用 can，而不用 could。

如：Can [Could] I come in? 我可以进来吗“Could [Can] I use your pen? ” “Yes,of course you can.” “我可以借用你的钢笔吗?”“当然可以。

”（不能说Yes,you could.)表示过去的允许时，若表示过去一般性允许（即表示某人随时都可以做某事），用could；若表示在过去某一特定情况下允许进行某一特定的活动，则不用 could。

如：When I lived at home,I could watch TV whenever I wanted to. 我住在家里时，想什么时候看电影就可以什么时候看。

（一般性允许）I was allowed to see the film yesterday evening. 昨天晚上允许我去看了电影。

（特定的允许，不能用 could)can 和could 表示能力的用法can 表示现在的能力，could 表示过去的能力，要表示将来具备的能力通常 be able to 的将来时态。

其中要注意的是，could 表示过去的能力，通常只用于表示过去一般性能力，而不表示过去具体某次特定情形下能够做某事的能力。

如：他学习很努力，所以考试能及格。

误：He studied hard and could pass the exam.正：He studied hard and was able to pass the exam.注：若在否定句中没有以上限制，即couldn’t 可表示过去特定情况下的能力，如可说 He studied hard but still couldn’t pass the exam.口诀：情态动词两特点动词原形接后面，说话语气较委婉。

can "能力"may"许可"，must"责任"或"义务"。

否定回答needn’t 换，"需要"need, dare"敢"。

should"应该"，would"愿"，have to"被迫"表客观。

情态动词专项练习题1. --- Where is Mary? --- She ____ in the library.A. should beB. must beC. can beD. must have been2. His room is dark. He must ____ to bed.A. goB. be goingC. have goneD. have been gone3. “Will your father stay home tonight?”“I’m not sure, He ____to work.”A. must goB. can goC. may be goneD. may be going4. “Where is Tom?”“He isn’t here I think he ____ have gone home.”A. mayB. mustC. mightD. A or B or C5. “I think Helen is at home.”“No, she ____ be at home, for she phoned me from the airport just five minutes ago.”A. mustn’tB. needn’tC. can’tD. daren’t6. He’s late. What ____ have happened to him?A. canB. mayC. should D, must7. “ _____ he be watching TV now?”Yes, he _____ be watching TV now.”No, he _____ be watching TV now.”A. Must; can; mustn’tB. Can; must; can’tC. Must; must; can’tD. Can; can; mustn’t8. “____. He have left yesterday?”Yes, he ____ yesterday.”No, he ____ yesterday.”A. Must; must have left; can’t have leftB. Can; can have left; can’t have leftC. Can; must h ave left; can’t have leftD. May; must have left; shouldn’t have left9. You must be a writer, ____ you?A. mustn’tB. areC. mustD. aren’t10. You must have seen her yesterday, ____ you?A. mustn’tB. haven’tC. didn’tD. don’t11. You must have seen her, ____ you?A. haven’tB. didn’tC. don’tD. A or B12. There was plenty of time. She ____ worried or hurried.A. mustn’t haveB. shouldn’t haveC. must beD. needn’t have13. I got up early, but I ____ so because I had no work to do that morning.A. mustn’t have doneB. didn’t need to doC. needn’t have doneD. can’t have done14. I ____ up early this morning. So I stayed in bed till 9 a. m.A. needn’t have gotB. didn’t need to getC. shouldn’t have gotD. can’t have got15. The flower is dead. I ____ it more water.A. will giveB. would have givenC. must giveD. should have given16. He ____ have come here yesterday, but he didn’t.A. couldB. shouldC. ought toD. A or B or C17. “Must he do it?”“No, he ____.”A. mustn’tB. needn’tC. doesn’t have toD. B or C18. “Need you go now?”“Yes, I ____.” “No, I ____.”A. need; needn’tB. must; needn’tC. may; mustn’tD. can; needn’t19. “May I borrow your bike?”“No, you ____.”A. mustn’tB. may notC. had better notD. can’t20. “Can I do it?”“No, you ____.”or “No, please ____.”A. can’t; doesn’tB. can’t; don’tC. can’t; can’tD. can’t; you don’t21. I missed the last bus, so I ____ go home on foot.A. mustB. have toC. mayD. had to22. We ____ hurry if we want to arrive in time.A. mustB. needC. mayD. have to23. He ought to have won the first prize, ____ he?A. oughtn’tB. shouldn’tC. mustn’tD. oughtn’t to24. He ____ get up early when he lived in the countryside.A. wouldB. used toC. mustn’tD. can’t25. My brother ____ be very naughty, and my sister ____ like reading.A. used to; wouldB. would; used toC. used to; used toD. would; would26. ____ you please pass on a message to him?A. DoB. ShallC. MayD. Will27. ____ we set off now?A. ShallB. WillC. WouldD. ought28. “____ he open the window?”Yes, please.”A. DoesB. willC. ShallD. Would29. I’ve told him many times, but he ____ listen to my advice.A. shall notB. won’tC. will notD. wouldn’t30. “Will you lend me a hand?”“Yes, I ____.”A. willB. shallC. canD. may31. Everyone ____ do his best for the modernization of China.A. will youB. don’t weC. shall weD. do you32. Let’s clean our room, ____?A. will youB. don’t weC. shall weD. do you33. Let us watch TV, ____?A. will youB. don’t weC. shall weD. do you34. Close the door after you, ____ you?A. don’tB. doC. shallD. will35. Every time he meets me, he ____ to me.A. smiledB. would smileC. will smileD. is smiling答案1-5 BCCDC 6-10 ABCDC 11-15 DDCBD 16-20 DDBDB 21-25 DDDDC 26-30 DACDA 31-35 CCADC。