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1、情态动词专题讲解一情态动词(Model Verbs)的语法特征情态动词主要有can, may, must, could, might, shall , should, will, would, ought to, need, dare等。1） 情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。2） 情态动词 除ought 和have 外，后面只能接不带to 的不定式,即动词原形。3） 情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。4） 情态动词没有非谓语形式，即没有不定式，分词等形式。二. 情态动词的基本用法1) can、could和be able to ca
2、n和be able to都表示能力(Ability)，意思上没多大区别。但can只有现在和过去时，而be able to则有更多的形式。但当成功地完成某一具体动作时，通常不用could而用was/were able to来表示。这时was/were able to表示经过一番努力，终于能够完成某事, 在许多情况下又可以交替使用。如： Can you use chopsticks?I cant do it now, but I can do it later.Is there anything I can do for you. The wounded man still was able to
3、 get to the village and was saved in the end.As I have got enough money, I can / am able to help her.can和couldcan和could都可以表示能力、技能、许可、建议或请求和可能性。但比较委婉客气地提出问题或陈述看法，一般用could，回答时则用can。但在肯定句中， could 所表示的“能力”仅是泛指过去的一般能力。如：Could you help me carry the bag?She could play the piano when she was only six.Can I
4、help you?在疑问句表示“可能”， 须用can 而不用may。如：Where can he be? He may be in the office.Can they have missed the bus? Yes, they may have.2) must 和 have to must 和 have to 都可以表示“必须”，但有几点区别： must 强调“内在的职责”、“义务”，而have to 强调“外界压力”、“不得已而为之”。 have to可用于多种时态，而must一般用于现在时，其过去时与将来时分别由had to与shall / will have to代替。 在回答mu
5、st引起的问题时，如果是否定的答复，不能用mustnt，而要用neednt或dont have to，因为mustnt是“一定不要”、“一定不能”的意思。如： You must come to the classroom before eight. It is raining hard outside, but I have to leave now. “Must we do it now?” “No, you neednt.” 3） shallshall作为情态动词用于第二、三人称，表示说话人的意愿，有“命令”、“警告、威胁、强制”和“允许”等意思。如： We shall do as our
6、 teacher says. You shall have the book as soon as I finish it.在疑问句中，shall用于征求对方的意见或请求指示，常用于第一、第三人称。如： Where shall he wait for us? / Shall we go out for a walk? 4) need的用法 need既可用作情态动词，也可用作行为动词，作“必须”、“需要”讲。作为情态动词，need也只用于否定句和疑问句。如：He neednt worry about it.Need I collect the books myself?作为行为动词，其后接的不定
7、式要加to。如: I want to go to the dentist, but you need not go with me. 我要去看牙科医生，但你不必跟我一起去。( need作情态动词) He needs to buy a new pair of shoes. 他需要买一双新鞋子。(need作实义动词)以need作情态动词提问，其答语如果是肯定的，须用must; 如果答语是否定的，则用neednt。如：Need we work late today? No, but we must tomorrow.Need I tell Tome at once? No, you neednt t
8、ell her just yet.三. 情态动词表示推测或判断的用法1） 情态动词+动词原形: 表示对现在或将来的情况的推测，此时动词通常为系动词。如: At this moment, our teacher must be correcting our exam papers.You must be hungry after a long walk.She may not be at home. = It is possible that she is not at home.She cant be at home. = It is impossible that she is at hom
9、e.They should be there right now.2） 情态动词+动词完成时, 即“情态动词+ have + done分词”:表示对过去行为或动作进行推测、评论或判断。 must have done 表示对过去某事的肯定猜测（只用于肯定句）“一定已做 ” cant /couldnt have done 表示对过去的否定推测.“不可能已做” (can/could have done 表推测通常只用于否定句和疑问句)may /might have done 表示对过去的可能推测 “可能已做 ”（may 比 might 表示的可能性在说话人看来稍大些。） 如: Since the r
10、oad is wet, it must have rained last night. He cant have missed the way. I drew him a map. “The dictionary has disappeared. Who could have taken it?” I cant find my keys. I may / might have left them at the school yesterday.四、情态动词在虚拟语气中的用法情态动词用于虚拟语气中表示责备的感情色彩，用法如下：1）should have done表示“本来应该做某事而实际上未做”
11、，而shouldnt have done则表示“本不应该做某事而实际上做了”。如： You should have told me about it earlier. You shouldnt have said such words to your parents.2) ought to have done也表示“本应该”而ought not to have done则意为“本不应该”。如： You ought to have told me about it earlier.You ought not to have said such words to your parents.3）ne
12、ednt have done表示“本无必要做某事而实际上做了”。如： You neednt have walked so quickly since time was enough.4）could have done表示“本来有可能而事实上未做到”。如： I could have come on time, but my car broke on the way.情1 May I stop my car here?No, you_.A. cant B. mustnt C. neednt D. dont have to2. Must we clean the house now?No, you
13、_.A. neednt B. may not C. mustnt D. cant3. John his father about his failure in the exam.A. dares not tell B. dares not telling C. dare not tell D. dares not to tell4. You return the book now. You can keep it next week if you like.A. cant B. mustnt C. neednt D. may not5. Johnny, you play with the kn
14、ife, you hurt yourself.A. wont.cant B. mustnt.may C. shouldnt, must D. cant.shouldnt6. The fire spread through the hotel very quickly but everyone get out.A. had to B. would C. could D. was able to7. Would you go out for a walk with me?No, I ._ My girl friend is coming.A. wouldnt B. shall not C. won
15、t D. shouldnt8. Man die without water.A. will B. can C. need D. shall9. If he started at 9 0clock, he be there by now.A. need B. shall C. ought to D. must10. I mailed the letter two weeks ago. She_it.A. must receive B. cant receive C. might receive D. must have received11.The professor gave orders that the experiment before 5:30p.m.A. be finished
