unit8 情态动词和助动词
一、考点聚焦
1、 情态动词的基本用法
(1)can、be able to 和could
①can和be able to都表示能力，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 相当于managed to，表示经过一番努力，终于能够完成某事。如：
can you use chopsticks?
the wounded man still was able to get to the village and was saved in the
end.
②can和could
can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。如：
could you help me carry the bag?
can i help you?
(2)may/might
①may/might表示可能，但may比might可能性大。如：-why isn’t he in class?
he may be sick.(生病的可能性较大)
—
he might be sick.(生病的可能性较小)
②may/might表示“允许”，may用于现在时或将来时，might常用在间接引语中表过去时，但might也可用于现在时间，表示比较委婉的语气，回答用may。如：

he says we may leave.
he said we might leave.
③may / might 表示建议或请求，但might比may 更客气，意思更肯定而无过去时态的含义。
yes, you can / may.
—may / might i use your bike? —
no, you mustn’t
（3）must
①must表示必须，应该，没有时态变化。如：
you must do everything as i do.
②must表示肯定的推测。如：
the light is still on, so he must be at home.
③mustn’t 表示禁止做某事。如：
you mustn’t smoke in the office.
（4）have to
have to 表示“必须、不得不”，是由于某种外界（客观）原因而“必须”，“不得不”做某事，也可表示经常的或习惯性的事“必须”做。have to的否定形式表示不必。have to可用于多种时态中。如：
you will have to clean your own boots when you join the army.
i have to be at my office every evening.
（5）should / ought to
①should和ought to表示应当、应该，前者比后者语气轻。如：
you should / ought to work hard.
②should / ought to work hard.
since she is not here, whe should / ought to be in the classroom.
③should / ought to的否定形式表示禁止之意。如：
children shouldn’t smoke.
④should可表示陈述意见，推出建议或请求；而ought to可以表示劝告之意。如：
you ought to respect your parents.
he suggested that they should leave at once.
（6）will / would
①will 用于各种人称表示“意志”、“意愿”或“决心”等，否定式won’t + 动词。如：
i will tell you all about it.
tom won’t do such a thing.
②will用于疑问句中，常用在第二称时表示说话人向对方提出“请求”或“询问”如：
will you please tell her the news when you see her?
③will 表示习惯性的动作，有“总是”、“惯于”的含义。如：
fish will die out of water.
④would 表示客气的请求、建议或意愿。如：
would you please be quiet?
would you like coffee?
⑤would 表示过去反复发生的动作。如：
when i passed my school i would see my teachers who taught me 5 years ago.
（7）need
need 作“必要”讲，既可作情态动词，也可作实义动词。作实义动词时后面的动词不定式要带to，其变化与一般动词相同。如：
i need to think it over.
—need you go now? —yes, i must./no, i needn’t
（8）dare
dare表示“敢”的意思。作为情态动词时，主要用在疑问句和否定句中。dare若作实义动词，后面可带to的不定式，此时to也可以省略。dare与need的用法相似。如：
how dare you say that?
she doesn’t date(to)ask her father.
（9）used to
used to表示过去常常发生的动作或存在的习惯，但现在已不复存在了。如：
he used to smoke.
（10）shall
①shall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 teacher says.
you shall have the book as soon as i finish it.
②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?
2、情态动词表示推测或判断的用法
下表即是表示推测的情态动词使用的场合：

情态动词 对现在和未来的推测 对过去的推测 使 用 场 合
must must + 动词原形 must have done 肯定句
may / might may / might + 动词原形 may / might have done 肯定句、否定句
can /could can / could do can / could have done 否定句、疑问名（could可用于肯定句）
should 用来表示一种估计的情况“按理会/估计会”should do/be should have done 肯定句、否定句、疑问句
例如：
it must have rained last night.
she may not be at home. = it is possible that she is not at home.
she can’t be at home. = it is impossible that she is at home.
they should be there right now.
3、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”，而shouldn’t 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 shouldn’t 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）needn’t have done表示“本无必要做某事而实际上做了”。如：
you needn’t 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.
二、精典名题导解
选择填空
1. i was really anxious about you. you________home without a word.(nmet 2001)
a.mustn’t have b.shouldn’t have left
c.couldn’t have left d.needn’t have
解析：答案为b。本题考查的是情态动词在虚拟语气中的用法。题目给出的条件是“我确实非常担心你”，因此后面可知应是责备you不应该没说一句话就离开了。
2.—are you coming to jeff’s party?
—i’m not sure. i__________ go to the concert instead.(nmet 2000)
a.must b.would c.should d.might
解析：答案为d。本题考查情态动词的基本用法。由题目中“i’m not sure”,表明我可能去jeff’s party，也可能去音乐会，故用might。
3. —will you stay for lunch?
—sorry, ____________. my brother is coming to see me.(nmet 99)
a.i mustn’t b.i can’t c.i needn’t d.i won’t
解析：答案为b。本题考查表示请求的英语口语，用will来向第二人称提问的疑问结构，是表示一种请求和意愿，是用疑问的形式来表达较为婉转的祈使语气，意思是“请你……，好吗”，对于这种问句的肯定回答是：suree! gertainly! yes, of course. i’d be glad to 等；否定回答通常是：i’m sorry, i can’t. no, i’m afraid i can’t. i’m sorry, but … i’d like to, but …等。注意情态动词表客气的用法及其在一般疑问句中的问与答。

三、专项训练
1. -jack certainly has a low opinion of janny.
-it_______than hers of him.
a.can’t be any worse 　　b.can be any worse
c.can be some worse 　　 d.can’t be more worse
2. she_______be at home because she phoned me from her office just now.
a.mustn’t b.needn’t c.can’t d.shouldn’t
3. the big fire last night_______the whole building.but the heavy rain helped.
a.might be burning down 　 b.should have been burned down
c.could have burned down 　d.must have been burned down
4. i want to go to the dentist,but you_______with me.
a.need not to go b.don’t need go c.need not go d.need go not
5. -must we take a bus?
-no,you_______,you can walk from here.
a.must not b.don’t have to c.don’t must d.don’t need
6. you_______return the book now.you can keep it till next week if you like.
a.can’t b.mustn’t c.may not d.needn’t
7. -could i borrow your dictionary?
-yes,of course you_______.
a.might b.will c.can d.should
8. -may i stay here for another day?
-no,you_______.
a.mustn’t b.might not c.needn’t d.won’t
9. -you ought to have helped her yesterday.
-yes,i know i_______.
a.ought to 　　　　　b.ought to have
c.ought have done 　 d.ought to have called
10. -_______he open the door?
-yes,please.
a.shall b.will c.can d.would
11. whatever difficulties we_______with,we’ll go on with the experiment.
a.meet b.met c.shall meet d.may meet
12. in the end they_______save the cat on the roof.
a.could b.were able to c.must d.need
13. mr.tom is in poor health.he_______be ill at any time.
a.may b.should c.can d.will
14. -could i see you on sunday?
-yes,of course you_______.
a.can b.might c.will d.should
15. i thought you_______like something to read,so i have brought you some books.
a.may b.must c.could d.might
16. -do you have to go out?
-sorry,but i really_______.
a.have to b.must c.may d.can
17. “manager,some people want to see you,_______they wait in the hall or outside?”asked the secretary.
a.will b.must c.shall d.may
18. there was plenty of time,she_______.
a.needn’t have hurried 　b.mustn’t have hurried
c.have hurried 　　　　　d.couldn’t have hurried
19. you_______walk for miles and miles among the hills without meeting anyone.
a.must b.need c.should d.may
20. you_______do what you like to the whole afternoon.
a.could b.can c.are able to d.can be able
21. look,what you have done! you_______more careful.
a.may be b.had to c.should be d.would be
22. whoever breaks the law_______.
a.can be punished 　　b.is to punish
c.is to be punished 　d.are punished
23. don’t throw the box away.it_______in the future.
a.shall be needed b.is needed c.might need d.might be needed
24. all that_______must be done.
a.should be done b.is done c.was done d.has been done
25. there_______an english evening next saturday.
a.will have b.is going to be c.is to have d.is going to do
26. the news_______about everywhere now.
a.is talking 　　　 b.has been talked
c.is being talked 　d.is being talking
27. we shall stay in the village for one or two days,and then we_______that mountain.
a.go to climb 　　　b.go on climbing
c.will have climbed d.are going to climb
28. suddenly he thought that a bicycle_______be very useful.
a.would b.will c.is to d.should
29. johnny,you_______play with the knife,you_______hurt yourself.
a.won’t;can’t 　　　b.mustn’t;may
c.shouldn’t;must 　 d.can’t;shouldn’t
30. your phone number again? i_______quite catch it.
a.couldn’t b.don’t c.didn’t d.can’t
31. come early tomorrow,_______?
a.don’t you b.do you c.shall you d.will you
32. let’s go to see our teacher who is in hospital,_______?
a.shall we b.will you c.don’t we d.do you
33. everyone_______do his best to study well in order to sense the people well in future.
a.can b.should c.may d.might
34. -may i stop here?
-no,you_______.
a.might not b.needn’t c.mustn’t d.won’t
35. -dare he go to the cinema in the evening?
-_______.
a.i dare too b.no,i don’t c.yes,i do d.no,i daren’t
36. don’t be worried.the news_______be true.
a.may not b.mustn’t c.needn’t d.shan’t
37. i will return your notes as soon as i_______copying them.
a.will finish b.do finish c.finish d.be finished
38. you_______do it even if you want to.
a.can’t b.have to c.mustn’t d.needn’t
39. when_______possible to get some more information?
a.has it b.had it c.would be it d.would it be
40. he_______the test,but he wasn’t careful enough.
a.could have passed 　　b.was able to pass
c.might be able to pass d.must have passed

参考答案
1-10 acccb dcaba 11-20 dbcad bcadb
21-30 ccdab cdabc 31-40 dabcd acbda