情态动词
一、情态动词的基本用法
1.表示必须、一定。
must表示主观上的必须，而have to 表示职责或义务，强调客观。
In crowed places like airport and railway stations, you must take care of your luggage.
There was no bus, so we had to go to school on foot.
2.表示推测或可能性
A.must表示推测仅用在肯定句中，must用于否定句时，表示禁止；can 或
could也可以表示推测, 其中can’t表示“不可能”；对过去的行为动作或状
态的推测用must/may/might/can’t/couldn’t+ have done
She is wearing a long face. She must be angry.
That can’t be my dad, he is now abroad.
B.may 或might 用于肯定句，might可能性较小，否定句可译作“可能不”。
You might just as well tell the manufacturer that the male customers may
not like the design of the furniture.
C.Should/ought to 表示推测时，是指有一定依据的推测、推论或可能性，意
为：可能、应该。
You should /ought to pass her chemistry final.
3.表示请求或许可
A.may 用于疑问句中表示询问许可，May I …答句是Yes, you may.否定句用
No, you mustn’t.还可以用can, could, might等表示许可。
May I use your eraser?
Yes, you may. /No, you mustn’t.
B.can表示许可时基本同may.
You can use my mobile phone on condition that you promise not to lend it
to others.
C.shall 用于第三人称可以表示向第二人称询问是否允许第三人称做某事。
Secretary: Shall he come in?
Manager: Let him in please.
4.表示必要
need 作为情态动词用于疑问句或否定句，Need you…?的肯定句答语是：Yes, I must.否定句的答语是：No, I needn’t/don’t have to.对问句Must…?
表示有必要做某事的肯定答语是：Yes, you must./you have to.否定句的答语是：No, you needn’t/don’t have to/don’t need to.
You needn’t come if you are busy.
You must finish the project by Friday.
5.表示能够
A.表示现在的或一般的能力用can 或be able to, can比be able to 更普遍，
be able to do 表示经过努力所具有的能力，有较多的时态变化。
A left-luggage office is a place where bags can be left for a short time,
especially at a railway station.
Are you able to type?
B.如果表示在过去某一待定的时刻经过努力终于做成了某事，用was/were
able to do sth.相当于managed to do sth或succeed in doing sth, 如果没有做成则可以用couldn’t 或wasn’t/weren’t able to do.
I was able to make her believe me.
6.表示建议或征求意见
A.shall 用于第一、三人称表征求意见或建议。
Shall we meet at the school gate tomorrow morning.
B.will 的疑问句表请求邀请
Will you lend me your eraser?
C.would 表示愿望、意愿、建议或看法。
a.表示强烈的愿望和意愿
“I would do anything for the soldiers.” said the boy.
b.表示请求语气时比will 委婉，并不表示过去意义。wouldn’t 表示请求、
邀请，没有否定的意思。
Wouldn’t you take a seat? 请坐。
c.would表示意愿，用在一些固定短语中，如：would like/would love to
do sth; would rather do sth.
I would like to have gone to the cinema, but I had an unexpected
visitor that evening.
D. had better 表示建议，意为：最好…强调现在或将来。
You’d better come early.
E. Could/might/would表示委婉的请求，肯定答语分别是can/may/will.
Could I sit here?
Of course, you can.
7.表示敢
dare作为情态动词时表示敢，用于疑问句或否定句；作为行为动词时同其他动词一样用于各种句式，跟动词不定式作宾语，在疑问句和否定句中可以省略to, I dare say是一个固定短语，意为“我认为、我相信”。
Tom daren’t go out alone when it is dark. (情态动词)
Tom doesn’t dare (to) go out alone when it is dark. (行为动词)
8.表示应该
should 表示义务、责任、命令、劝告，意为应该，ought to 表示义务、约束力、同should ,但是语气比should强，比must 弱，must意为应当做。
I should pay Tracy a visit, but I’m not sure whether I will have time this
Sunday.
Humans ought to stop polluting nature.
You must take the cost into consideration.
9.表示命令、警告、威胁
A.shall 与第二、三人称连用表示命令、许诺、警告、威胁等，表示说话人强
烈的意志.
You shall get an answer from me by tomorrow.
B.mustn’t是must 的否定形式，表示禁止，是一种命令、威胁或警告。
Tom, you mustn’t leave all your clothes on the floor like this!
10.表示惊讶、难以置信
A.should 用于疑问句中可以表示惊讶、难以置信的事情
Why should he tell a lie?
B.can用于疑问句或否定句可以表示惊讶、不相信等感情色彩。
How can you say that you really understand the whole story if you
have covered only part of the article?
11.表示宁愿
would rather意为宁愿，后跟动词原形，同used to, had better一样也被看
作是情态动词，有时称半情态动词。
She would rather work in the countryside.
12.表示偏偏
must可以表示偏偏，偏要，指不愉快的事。
After I gave her my advice, she must go and do the opposite.
二、情态动词+不定式完成时
1. must have done
表示对过去的事情肯定推测，意为：一定做过某事，只能用于肯定句。
It must have rained last night, for the road is all wet.
2. can’t/couldn’t have done
都可使用在疑问句和否定句中表示推测，可看做must表推测对应的否定形
式，can’t 比couldn’t的语气强，强调从现在角度出发推测过去某事的不可
能性, 但当主句的谓语动词为过去式时，表示假定或推断的从句必须用
couldn’t have done.
We knew he couldn’t have crossed the river, because the bridge was broken and there was no boat.
3. could have done
表示过去有能力或有可能做某事，而因某种原因未做，有惋惜、遗憾、批
评、责备的含义。
He could have passed the exam, but he was too careless.
4. should have done
表示本该做某事，而实际上没做，shouldn’t have done 表示本来不应该做
某事，而实际做了。含有指责对方或自责的意味。
I told your friend how to get to the hotel, but perhaps I should have driven
her there.
5. may/might have done
用于对过去的事情进行推测，表明说话人对过去可能发生的行为或存在的
状态的一种怀疑，might表达的可能性比may要小得多。如果主句的谓语动
词是过去时，从句必须用might have done.表某事本来可能发生，而实际上
未发生也只能用might have done.
You might have read about it in the papers.
6. need have done
表示本来需要做某事而没有做，needn’t have done 则表示本来不需要做某
事而做了。
I needn’t have taken the umbrella, for the weather is fine.
7. daren’t have done
用在否定句中表示过去本来不敢做某事，但是现在敢做了。
I daren’t have done it yesterday, but I think I dare now.
8. was/were would like to have done
表示本来打算做某事但是却干了别的事。
I would like to have gone to the party last night but I had to work extra
hours to finish a report.
9. would have done
虚拟语气，表示对过去事情的假设，意为：本来会做。
I would have told you all about the boy’s story, but you didn’t ask me.
形容词和副词的比较等级
1.同级比较
A.双方比较程度相同的时候，用as+形容词或副词的原级+as 这一结构。
I think physics is as important as maths.
B.双方比较程度不同等时，用 not+as/so +形容词或副词的原级+as这
一结构。
It is not as/so warm today as yesterday.
C.当同级比较的形容词与单数可数名词连用时，应注意不定冠词的位置，
通常为：as+形容词+a/an+单数名词+as 这一结构。
Would you like to join us?
Sorry, I’m not so good a player as any of you.
2.比较级
A．比较双方中一方超过另一方的时候，要用形容词/副词的比较级
+than+比较对象这一结构。
Zhang Hua is taller than Wang Ping.
B. 表示…不如…用less+原级+than 这一结构。
The film is less interesting than that one.
C. 除比较句中与than连用表示比较之外，下面的词语后面必须用to构
成比较，常用的词有inferior, superior, junior, senior, prior.
He is superior to Mr. Wang in English.
D. 表示两个人/物之间比较…的，用the +比较级+n+of+the+名词/代词
这一结构。
She is the taller of the two girls.
E. 表示越来越…用形容词比较级+and+ 形容词的比较级； the+形容词/
副词比较级，the +形容词/副词比较级。
It turned warmer and warmer.
The harder he works, the more progress he has made.
F. 表示几倍于…时，用倍数+as…as或倍数+比较级+than…
Our classroom is three times larger than yours.
G. 形容词比较等级前可以用much, very much, even, still, far等来修饰，
表示比较的程度。
Tom’s handwriting is far better than John’s.
H. 其他含有比较级的短语和句式
more…than…与其说…倒不如…
more or less 几乎、大约
more than 多于
less than 少于
sooner or later 迟早、早晚
what’s more 而且
no sooner than…一…就…
not more than=at most 至多，不超过
no more than=only 仅仅、只不过
no less than =as many as 有…之多
not less than =not fewer than 不少于
3. 最高级
A. 表示三者或三者以上的人或物相比的时候，其中一个人或物在某方面
比其他的都强，这就要用到形容词和副词的最高级，the +形容词或副
词的最高级+其他+of/in/among(比较范围)，意为…中最…。
Zhang Hua is the tallest of the three.
He works the hardest in our class.
B. 最高级也可被序数词及much, by far, nearly, almost, nothing like等
词来修饰。
This hat is nothing like the biggest.
注意：
most 前如果没有the, 就无比较的意思，只是用来加强语气。 She is a most beautiful girl.
C. 用比较级来表示最高级
a. 否定词+比较级
Nothing is more valuable than time is.
b. 比较级+than+any other +单数名词
+all the other +复数名词
+anyone else
+any of the other +复数名词
Bob runs faster than any else in our school.
Robert jumps much higher than any of the others.
Our city is more beautiful than any other city in our country.