英语语法-情态动词

1、情态动词情态动词1.表示能力时，只能用can (现在) could do (过去能做) was/were able to do ： （1）过去能做 (2) 过去设法成功完成某一具体动作 =manage to do =succeed in doingEg. 1.A blind man can not judge colors. 2.He could/was able to swim like a fish when he was young. 3.Though he was tired , he was able to swim across the river. 4.Because he wa

2、s tired, he couldnt /wasnt able to swim across the river.(在否定结构中无区别)2.表推测时：may/might( 语气最不肯定，多用于肯，否定句) 可能can （语气肯定，一般不用于肯定句）可能could (较can不确定，也可用于肯定句) 可能 must (语气最肯定，只用肯定句)一定should(表可能性，推论，推测，期待等)按理该；估计ought to (表可能性，揣测，猜测，期望等)照说应该，理应may/might have +ed (语气不肯定) 过去可能cant/couldnt have +ed (语气肯定)过去不可能mus

3、t have +ed (语气肯定) 过去一定should have +ed 过去按理应该ought to have +ed过去按理应该 Eg. 1.A: Look, someone is coming. Who can it be? B: It may be the headmaster. A:It can not be him.He has gone to Shanghai. B: It must be Mr Zhang. He looks like the headmaster. 2.I dont know his age. He could be thirty or thirty-fiv

4、e. 3. The report is written after careful investigation, so it should be reliable. 4.-I didnt see Mary at the meeting yesterday. -She might have been ill, I guess. 5.The street are all dry. It couldnt have rained during the night. 3. 表责备时： may/might have +ed（语气委婉）过去本可能 can/could have +ed (语气委婉) 过去本能

5、 should have +ed (语气强烈) 过去本应该，而未 ought to have +ed (语气强烈) 过去本应该，而未 neednt have +ed 过去本不必，却做了Eg. 1.He might have given you more help, even though he was very busy. 2.-Did you listen to the speech? -No, we could have attended it.But we had a lot of traffic on our way. 3.The plant is dead. Maybe I shou

6、ld have given more water. 4.Your brothers failed in English again. You ought to have given him more help. 5. -Mr Smith didnt come last night, did he? - No. We neednt have waited for him. A whole night was wasted.4.表未曾实现：was/were to have +ed 过去本打算/本想should like /love to have +ed 过去本想 而没=would like/lo

7、ve to have +ed=should have liked /loved to do=would have liked/loved to dohad better have +ed 当初最好would rather have +ed 当初真该Eg. 1. He was to have come here yesterday, but he had an important meeting to attend. 2. We would like to have gone to see the film, but we had no time. 3. I would love to have

8、 gone to the cinema to see the film that day, but the tickets were all sold out. 4. I should have liked to stay another week, but I had to go back to work. 5.We had better have bought (当时真该买) the book. 6.She would rather have stayed (当初真该呆) at home than go to see the dull film.5. 委婉的请求 肯定的答语 could c

9、an might may would willEg. 1. -Could you lend me your book? -Certainly, I can. 2. -Might I ask you a question? -Surely, you may. 3. -Would you do me a favor? -Of course, I will. 4. -Would you like to do it for me? -Yes, Id like to. ( 特殊)7. Shall : 可 用于一、三人称表示征询对方意见或请求指示Eg. Shall he wait for you at t

10、he gate? Shall we begin our lesson?Shall 用于第二、第三人称， 表示说话人对对方的命令、警告、允诺或威胁。He shall be punished. ( 威胁)You shall have the book when I finish reading.（允诺）You shall fail if you dont work harder. (警告)8.dare :作情态动词时，主要用于疑问句、否定句和条件从句中，一般不用于肯定句。Eg. How dare you say Im unfair! He darent speak English before s

11、uch a crowd, dare he?dare作实义动词时，在肯定句中，其后通常接带to的不定式；在否定和疑问句中，其后可接带to或不带to的不定式。 Eg.I dare to swim across this river. He does not dare (to) answer.9. Need 表示“需要”或“必须”，作情态动词时，仅用于否定句或疑问句中。在肯定句中一般用 must,have to, ought to 或should 代替。Eg.You neednt come so early. - Need I finish the work today? -Yes, you mus

12、t. 10.used to 表示过去的习惯动作或状态（现在已不复存在），在间接引语中，其形式可不变。Eg.He told us he used to play football when he was young.在疑问句、否定句、否定疑问句或强调句中，可有两种形式：疑问句 Did you use to go to the same school as your brother? Used you to go to the same school as your brother?否定句：I usednt to go there. I didnt use to go there.Usednt 亦

13、可拼作usent否定疑问句：Usent you to be interested in the theatre?Didnt you use to be interested in the theatre? 其反意疑问句或简略回答中，也有两种形式：She used to be very fat, didnt she? 或use(d)nt she?11.will 和would 的用法：（1）表示请求，建议等，would 比will 委婉客气。Eg. Would you pass me the book?(2) 表示意志、愿望和决心。They asked us if we would do that

14、 again.(3)would可表示过去反复发生的动作或某种倾向。Would表过去习惯时比used to 正式，且没有“现已无此习惯”的含义。 During the vacation he would visit me every week.(4) 表示估计或猜想。 I thought he would have told you all about it.It would be about ten when he left home. Exercises:1.He _ you more help, even though he was very busy.A.might have given

15、 B. might giveC. may have given D. may give A2.A computer _think for itself; it must be told what to do.cant B. couldnt C.may not D. might notA 3.Janny _ have kept her word. I wonder why she changed her mind.must B.shouldC.need D.wouldB4.-Could I borrow your dictionary? -Yes, of course you _. might

16、B. willC. can D. should C 5. -Please dont make a noise. -_ . Ill be as quiet as a mouse. A. Yes, I wont B. No, I wont C. No, I will D. Yes, I will B6. We _ last night, but we went to the concert instead.must have studied B. might studyC. should have studied D. would studyC7.Tom ought not to me your secret, but he meant no harm. A. have told B. tell C. be telling D. having told8. I told Sally how to get here, but perhaps I for her. A. had to write it out B. must have written it out C. should have written it out D.