一、知识梳理/提炼
1. can和could的用法
表示能力或客观可能性，还可以表示请求和允许。如： Can you finish this work tonight? Man cannot live without air.
— Can I go now? — Yes, you can.
注意：①could也可表示请求，语气委婉，主要用于疑问句，不可用于肯定句，答语应用can（即could不能用于现在时态的简略答语中）。如： Could I come to see you tomorrow?
Yes, you can. （否定答语可用No, I'm afraid not.） ②can表示能力时，还可用be able to代替。如： I'll not be able to come this afternoon. 2. may和might的用法 1)表示许可。
表示请求、允许时，might比may的语气更委婉一些，否定回答时要用mustn't表示“不可以”、“禁止”、“阻止”之意。如： You may drive the car.
— Might I use your pen? — No, you can’t/ mustn't. Yes, you can/may. 用May I ... 征询对方许可在文体上比较正式，在口气上比较客气。在日常口语中，用Can I ... 征询对方意见在现代口语中更为常见。 2) 用于祈使句中表示祝愿。如： 祝你成功！ May you succeed!
3)表示推测、可能（疑问句不能用于此意）。 他现在可能很忙。 He may be very busy now. 3. must和have to的用法 1) 表示必须、必要。如： You must come in time.
回答must引出的问句时，如果是否定的回答，不能用mustn't，而要用needn't或don't have to。 — Must we hand in our exercise books today?
— Yes, you must. No, you don’t have to/needn’t. 2) “must be + 表语”的结构表示对现在的推测，它的否定或疑问式用can代替must。 这肯定是你的笔吧。 This must be your pen. 3) have to的含义与must相似，两者往往可以互换使用，但have to有各种形式，随have的变化而定。must与have to有下列几点不同：
① must表示的是说话人的主观看法，而have to则往往强调客观需要。如： The play is not interesting. I really must go now. 我现在必须得走了 我在你这么大的时候必须得工作。 I had to work when I was your age. ② must一般只表现在，have to则有更多的时态形式。 ③ 二者的否定意义不大相同。如：
You mustn't go. 你不准去。 You don't have to go. 你不必去。
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4. need的用法
1) need表示“需要”或“必须 You needn’t come so early.
— Need I finish the work today?
— Yes, you must/have to/should/ought to. 2) need 也可以做实义动词，表示“需要”，人做主语时，为sb. need to do, 物做主语时为 sth. need doing 或 sth. need to be done.如：
The garden needs watering/to be watered. I don't think you need to worry about this. 5. dare的用法
1）dare作情态动词时，主要用于疑问句、否定句和条件从句中，一般不用在肯定句中。如： How dare you say I'm unfair. He daren't speak English before such a crowd, dare he? 2）dare 可以做实义动词，敢;胆敢[+to-v]，如： He did not dare to leave his car there. 6. shall和should的用法
1） 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。如： Shall we begin our lesson?
When shall he be able to leave the hospital?
2）shall用于第二、第三人称，表示说话人给对方命令、警告、允诺或威胁。如： You shall fail if you don't work harder. （警告）
He shall have the book when I finish reading. （允诺） He shall be punished. （威胁） should的含义较多，用法较活，现介绍三种其特殊用法。请看下面的句子： ① I should think it would be better to try it again. 我倒是认为最好再试一试。 ② You are mistaken, I should say. 依我看，你是搞错了。 ③ I should advise you not to do that. 我倒是劝你别这样做。
④ This is something I should have liked to ask you. 这是我本来想问你的。
从以上例句可以看出：情态动词should用于第一人称时可以表示说话人的一种谦逊、客气、委婉的语气。
should还可以用在if引导的条件从句，表示一件事听起来可能性很小，但也不是完全没有可能。相当于“万一”的意思。从句谓语should do，主句谓语却不一定用虚拟语气。如： ⑤ 你万一见到她，请让她给我打个电话。Ask her to ring me up if you should see her.
⑥如果你万一改变主意，请让我们知道。 If you should change your mind, please let us know. ⑦ Should I (If I should) be free tomorrow I will come.
此外，Why(or How) + should结构表示说话人对某事不能理解，感到意外、惊异等意思。意为“竟会”。如：
⑧你今天为何竟会来得这么晚？Why should you be so late today? ⑨ — where is Betty living?
—我怎么知道？ How should I know? ⑩我真不知道你凭什么认为这件事是我干的。I don't know why you should think that I did it. 7. will和would的用法
1）表示请求、建议等，would比will委婉客气。如： Would you pass me the book?
2）表示意志、愿望和决心。如： I will never do that again.
They asked if we would do that again. 3）表料想或猜想。如：
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It would be about ten when he left home. What would she be doing there?
I thought he would have told you all about it. 8. ought to的用法
1）ought to表示应该。如：
You ought to take care of him. He ought to be home by now. 9. used to，had better，would rather的用法 1）used to do过去常常做某事（现在已不做）
当他小的时候他常常5点钟就起床。He used to get up at 5 am when he was young. Be used to do 被用来做某事 be used to doing 习惯于做某事 2）had better do意为“最好做某事”，后接不带to的不定式。如： — We had better go now.
— Yes, we had (we'd better / we had better).
3）would rather do意为“宁愿做某事”，表选择。如： 我宁愿现在什么也不说。 I'd rather not say anything.
你宁愿在农场工作吗？ Would you rather work on a farm? 10．情态动词的现在完成式的用法
情态动词现在完成式主要有两个功能：表示已经发生的情况和表示虚拟语气。在这两个方面must / mustn’t; can / can’t ; need / needn’t; may / mayn’t; might / mightn’t; should / shouldn’t; ought等情态动词＋完成式表示的意思是有一定区别的
表示已经发生的情况：
1）“must + have + 过去分词”的结构常用在肯定句中，表示过去肯定应经发生过某事。它的否定或疑问式用can代替must。如：他一定是去过上海。 He must have been to Shanghai.
2）may / might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，译为“过去也许发生过某事”。如：他可能已经把真相告诉他妻子了。He might have told his wife the truth. 3）couldn’t have done, 过去不可能做过某事。 He couldn’t have done that. 4）could have done 过去可能做过某事。
表示虚拟语气
1） needn’t have + 过去分词，表示做了不必做的事，译为“本没必要做某事”。如： 你本来不需要等我的。You needn't have waited for me.
2）should have +过去分词，表示应该做某事但实际上未做，译为“本应该做某事”；should not + have过去分词表示本不应该做某事但实际上做了，译为“本不应该某事”。如：
我本来应该提前仔细地计划好一切的。I should have planned everything ahead carefully. 我本来不应该对他态度那么不好的。 I shouldn’t treated him so badly/ rudely.
2） would + have + 过去分词表示过去本来会...(但没发生)，主要用于第二、三人称，表示对已经完成的动作或事态的推测。
如：截止到那时，宾客们本来应该到了。 The guests would have arrived by that time/by then. 4）could have done, 过去本可能做某事但未做。
我本来可以赢这个游戏的，但我后来决定让她赢。I could have won the game but decided to let her win. 5）couldn’t have done, 过去本不可能做成某事。
要是没有你的帮助，我是不可能成功的。 Without your help, I couldn’t have succeeded.
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例题1. As it turned out to be a small house party, we ______so formally. A. needn’t dress up B. did not need have dressed up C. did not need dress up D. needn’t have dressed up
例题2. Mary_____ my letter; otherwise she would have replied before now.
A. couldn’t have received B. ought to have received C. has received D. shouldn’t have received 例题3. ______ you continue your effort and succeed! A. must B. can C. should D. may 例题4. — What does the sign over there read?
—No person________ smoke or carry a lighted cigarette, cigar or pipe in this area. A. will B. may C. shall D. must
例题5. You ______ washed so many clothes, we’ll have a washing machine tomorrow. A. must have B. needn’t
C. needn’t have D. couldn’t have
巩固练习
1 I ____like to make a suggestion.
A) could B) would C) must D) might 2. John's score on the test is the highest in the class; he____ last night. A) should study B) should have studied C) must have studied D) must have to study 3. The room is in a terrible mess; it ____cleaned. (CET-4) A) can't have been B) shouldn't have been C) mustn't have been D) wouldn't have been
4. Nobody knows how people first came to these islands. They ____ from South America on rafts. A) must have sailed B) can sail
C) might have sailed D) should have sailed
5.Mary was not in her bedroom yesterday afternoon. She ____ in her classroom. A) should have been B) must have been C) must be D) should be
6.As he had heart attack, he was told that he ____ continue the work. A) needn't B) may not C) mustn't D) can't 7.You____ to town to see the film yesterday. It will be on TV tonight. A) needn't go B) had better not go C) should not go D) needn't have gone 8.We____ the letter yesterday, but it didn't arrive. A) must receive B) ought to receive
C) must have received D) ought to have received
9. With all the work on hand, he____ to the cinema last night. A) mustn't go B) shouldn't have gone C) could not go D) couldn't have gone 10. Eve was late for class again. She ____earlier. A) should get up B) must get up
C) need to get up D) should have got up 11.I am feeling sick. I____ so much chocolate. A) needn't have eaten B) couldn't have eaten C) mustn't have eaten D) shouldn't have eaten
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12. The road was muddy. It___last night.
A) must rained B) must have rained C) must be rained D) could have rained
13. I know things are hard with you, but you ____try to get over the difficulties. A) can B) may C) must D) ought
14.You should bear in mind that he is not so strong as he____. A) was used to be B) used to be C) was used to D) use to
15. Mary ____my letter, otherwise she would have replied before now. A) should have received B) has received
C) couldn't have received D) ought to have received
16. I ____ you a valuable present for your birthday, but I was short of money. A) would have liked to give B) liked to give C) have liked to give D) would like to give 17.“Where ____ my umbrella?”
“Somebody ____ it away by mistake.”
A) is, must have taken B) is, must take C) have been, must take D) is, takes 18. Tom ____ better than to ask Dick for help.
A) shall know B) shouldn't know C) has known D) should have known 19.You ____ your tooth pulled out before it rot completely. A) had better got B) had to get better C) had better to get D) had better get
20. When we got to the cinema, the film hasn't started yet, so we ____. A) needn't hurry B) didn't need hurry C) needn't to hurry D) needn't have hurried
例一-例五 DADCC
BCACB CDDBD DBCBC AADDD
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