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18. 定语从句
定语从句（Attributive Clauses）在句中做定语，修饰一个名词或代词，被修饰的名词,词组或代词即先行词。定语从句通常出现在先行词之后，由关系词（关系代词或关系副词）引出。
关系代词有：who, whom, whose, that, which等。
关系副词有：when, where, why等。
18.1 关系代词引导的定语从句
关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。
1）who, whom, that
这些词代替的先行词是人的名词或代词，在从句中所起作用如下：
Is he the man who/that wants to see you?
他就是你想见的人吗？（who/that在从句中作主语）
He is the man whom/ that I saw yesterday.
他就是我昨天见的那个人。（whom/that在从句中作宾语）
2) Whose 用来指人或物，(只用作定语, 若指物，它还可以同of which互换）, 例如：
They rushed over to help the man whose car had broken down. 那人车坏了，大家都跑过去帮忙。
Please pass me the book whose (of which) cover is green. 请递给我那本绿皮的书。
3）which, that
它们所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等，例如：
A prosperity which / that had never been seen before appears in the countryside. 农村出现了前所未有的繁荣。（which / that在句中作宾语）
The package (which / that) you are carrying is about to come unwrapped. 你拿的包快散了。(which / that在句中作宾语）
18.2 关系副词引导的定语从句
关系副词可代替的先行词是时间、地点或理由的名词，在从句中作状语。
1）when, where, why
关系副词when, where, why的含义相当于"介词+ which"结构，因此常常和"介词+ which"结构交替使用，例如：
There are occasions when (on which) one must yield. 任何人都有不得不屈服的时候。
Beijing is the place where (in which) I was born. 北京是我的出生地。
Is this the reason why (for which) he refused our offer? 这就是他拒绝我们帮助他的理由吗？
2）that代替关系副词
that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和"介词+ which"引导的定语从句，在口语中that常被省略，例如：
His father died the year (that / when / in which) he was born. 他父亲在他出生那年逝世了。
He is unlikely to find the place (that / where / in which) he lived forty years ago. 他不大可能找到他四十年前居住过的地方。
18.3 判断关系代词与关系副词
方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
This is the mountain village where I stayed last year.
I'll never forget the days when I worked together with you.
判断改错（注：先显示题，再显示答案，横线；用不同的颜色表示出。）
（错） This is the mountain village where I visited last year.
（错） I will never forget the days when I spent in the countryside.
（对） This is the mountain village (which) I visited last year.
（对） I'll never forget the days (which) I spent in the countryside.
习惯上总把表地点或时间的名词与关系副词 where, when联系在一起。此两题错在关系词的误用上。
方法二： 准确判断先行词在定语从句中的成分(主、谓、宾、定、状)，也能正确选择出关系代词/关系副词。
例1. Is this museum ___ you visited a few days age?
A. where B. that C. on which D. the one
例2. Is this the museum ____ the exhibition was held.
A. where B. that C. on which D. the one
答案：例1 D，例2 A
例1变为肯定句： This museum is ___ you visited a few days ago.
例2变为肯定句： This is the museum ___ the exhibition was held.
在句1中，所缺部分为宾语，而where, that, on which都不能起到宾语的作用，只有the one既做了主句的表语，又可做从句的宾语，可以省略关系代词，所以应选D。
而句2中, 主、谓、宾俱全，从句部分为句子的状语表地点，既可用副词where，又因 in the museum词组，可用介词in + which 引导地点状语。而此题中，介词on 用的不对，所以选A。
关系词的选择依据在从句中所做的成分，先行词在从句中做主、定、宾语时，选择关系代词 (who, whom, that, which,
whose)； 先行词在从句中做状语时，应选择关系副词 ( where 地点状语，when 时间状语，why 原因状语) 。
18.4 限制性和非限制性定语从句
1) 定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，例如：
This is the house which we bought last month. 这是我们上个月买的那幢房子。（限制性）
The house, which we bought last month, is very nice.这幢房子很漂亮，是我们上个月买的。（非限制性）
2) 当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的，例如：
Charles Smith, who was my former teacher, retired last year. 查理·史密斯去年退休了，他曾经是我的老师。
My house, which I bought last year, has got a lovely garden. 我去年买的的那幢房子带着个漂亮的花园。
This novel, which I have read three times, is very touching. 这本小说很动人，我已经读了三遍。
3) 非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数，例如：
He seems not to have grasped what I meant, which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。
Liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。
说明：关系代词that和关系副词why不能引导非限制性定语从句。
18.5 介词+关系词
1）介词后面的关系词不能省略。
2）that前不能有介词。
3） 某些在从句中充当时间，地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换。
This is the house in which I lived two years ago.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?
Do you remember the day when you joined our club?
18.6 as, which 非限定性定语从句
由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。
As we know, smoking is harmful to one's health.
The sun heats the earth, which is very important to us.
典型例题
1）Alice received an invitation from her boss, ___came as a surprise.
A. it B. that C. which D. he
答案C. 此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。
2）The weather turned out to be very good, ___ was more than we could expect.
A. what B. which C. that D. it
答案B。which可代替句子，用于非限定性定语从句，而what不可。That 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。
3）It rained hard yesterday, ____ prevented me from going to the park..
A. that B. which C. as D. it
答案B.
as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：
(1） as 引导的定语从句可置于句首，而which不可。
(2） as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which.。
在本题中，prevent由于是行为动词，所以正确选项应为B。
As 的用法
例1. the same… as；such…as 中的as 是一种固定结构, 和……一样……。
I have got into the same trouble as he (has).
例2. as可引导非限制性从句，常带有'正如'。
As we know, smoking is harmful to one's health.
As is know, smoking is harmful to one's health.
As是关系代词。例1中的as作know的宾语；例2中，它充当从句的主语，谓语动词know要用被动式。
18.7 先行词和关系词二合一
1)Whoever spits in public will be punished here.
(Whoever 可以用 anyone who 代替)
2)The parents will use what they have to send their son to technical school.
(what 可以用all that代替)
18.8 what/whatever;that/what; who/whoever
1）what = the thing which；whatever = anything
What you want has been sent here.
Whatever you want makes no difference to me.
2) who= the person that whoever= anyone who
（错）Who breaks the law will be punished.
（错）Whoever robbed the bank is not clear.
（对）Whoever breaks the law will be punished.
（对）Who robbed the bank is not clear.
3) that 和 what
当that引导定语从句时 ，通常用作关系代词，而引导名词性从句时，是个不充当任何成分的连接词。宾语从句和表语从句中的that常可省略。What只能引导名词性从 句， 用作连接代词，作从句的具体成分，且不能省略。
I think (that) you will like the stamps.
What we need is more practice.
18.9 关系代词that 的用法
1）不用that的情况
a) 在引导非限定性定语从句时。
(错) The tree, that is four hundred years old, is very famous here.
b) 介词后不能用。
We depend on the land from which we get our food.
We depend on the land that/which we get our food from.
2) 只能用that作为定语从句的关系代词的情况
a) 在there be 句型中，只用that，不用which。
b) 在不定代词，如：anything, nothing, the one, all, much, few, any, little等作先行词时，只用that，不用which。
c) 先行词有the only, the very修饰时，只用that。
d) 先行词为序数词、数词、形容词最高级时，只用that。.
e) 先行词既有人，又有物时。
举例：
All that is needed is a supply of oil.
所需的只是供油问题。
Finally, the thief handed everything that he had stolen to the police.
那贼最终把偷的全部东西交给了警察。
19. 状语从句
19.1 地点状语从句
地点状语从句通常由where, wherever 引导。
Where I live there are plenty of trees.
我住的地方树很多。
Wherever I am I will be thinking of you.
不管我在哪里我都会想到你。
19.2 方式状语从句
方式状语从句通常由as, (just) as…so…, as if, as though引导。
1） as, (just) as…so…引导的方式状语从句通常位于主句后，但在(just) as…so…结构中位于句首，这时as从句带有比喻的含义，意思是"正如…"，"就像"，多用于正式文体，例如：
Always do to the others as you would be done by.
你希望人家怎样待你，你就要怎样待人。
As water is to fish, so air is to man.
我们离不开空气，犹如鱼儿离不开水。
Just as we sweep our rooms, so we should sweep backward ideas from our minds.
正如打扫房屋一样，我们也要扫除我们头脑中落后的东西。
2） as if, as though
两者的意义和用法相同，引出的状语从句谓语多用虚拟语气，表示与事实相反，有时也用陈述语气，表示所说情况是事实或实现的可能性较大。汉译常作"仿佛……似的"，"好像……似的"，例如：
They completely ignore these facts as if (as though) they never existed.
他们完全忽略了这些事实，就仿佛它不存在似的。（与事实相反，谓语用虚拟语气。）
He looks as if (as though) he had been hit by lighting.
他那样子就像被雷击了似的。（与事实相反，谓语用虚拟语气。）
It looks as if the weather may pick up very soon.
看来天气很快就会好起来。（实现的可能性较大，谓语用陈述语气。）
说明：as if / as though也可以引导一个分词短语、不定式短语或无动词短语，例如：
He stared at me as if seeing me for first time.
他目不转睛地看着我，就像第一次看见我似的。
He cleared his throat as if to say something.
他清了清嗓子，像要说什么似的。
The waves dashed on the rocks as if in anger.
波涛冲击着岩石，好像很愤怒。
19.3 原因状语从句
比较：because, since, as和for
1） because语势最强，用来说明人所不知的原因，回答why提出的问题。当原因是显而易见的或已为人们所知，就用as或 since。
I didn't go, because I was afraid.
Since /As the weather is so bad, we have to delay our journey.
2） 由because引导的从句如果放在句末，且前面有逗 号，则可以用for来代替。但如果不是说明直接原因，而是多种情况加以推断，就只能用for。
He is absent today, because / for he is ill.
He must be ill, for he is absent today.
19.4 目的状语从句
表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case等词引导，例如：
You must speak louder so that /in order that you can be heard by all.
He wrote the name down for fear that(lest) he should forget it.
Better take more clothes in case the weather is cold.
19.5 结果状语从句
结果状语从句常由so… that 或 such…that引导，掌握这两个句型，首先要了解so 和 such与其后的词的搭配规律。
比较：so和 such
其规律由so与such的不同词性决定。such 是形容词，修饰名词或名词词组，so 是副词，只能修饰形容词或副词。 so 还可与表示数量的形容词many, few, much, little连用，形成固定搭配。
so foolish such a fool
so nice a flower such a nice flower
so many / few flowers such nice flowers
so much / little money. such rapid progress
so many people such a lot of people
（ so many 已成固定搭配，a lot of 虽相当于 many，但 a lot of 为名词性的，只能用such搭配。）
so…that与such…that之间的转换既为 so与such之间的转换。
The boy is so young that he can't go to school.
He is such a young boy that he can't go to school
19.6 条件状语从句
连接词主要有 if, unless, as/so long as, on condition that 等。.
if 引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚拟语气中阐述。
unless = if not.
Let's go out for a walk unless you are too tired.
If you are not too tied, let's go out for a walk.
典型例题
You will be late ___ you leave immediately.
A. unless B. until C. if D. or
答案A。 句意：除非你立即走，否则你就回迟到的。可转化为 If you dong leave immediately, you will
be late. B、D句意不对，or表转折，句子如为 You leave immediately or you will be late.
19.7 让步状语从句
though, although
注意： 当有though, although时，后面的从句不能有but，但是 though 和yet可连用
Although it's raining, they are still working in the field.
虽然在下雨，但他们仍在地里干活。
He is very old, but he still works very hard.
虽然他很老，但仍然努力地工作。
Though the sore be healed, yet a scar may remain.
伤口虽愈合，但伤疤留下了。 （谚语）
典型例题
1） ___she is young, she knows quite a lot.
A. When B. However C. Although D. Unless
答案：C。意为虽然她很年轻，却知道许多。
2) as, though 引导的倒装句
as / though引导的让步从句必须表语或状语提前（形容词、副词、分词、实义动词提前）。
Child as /though he was, he knew what was the right thing to do.
= Though he was a small child, he knew what was the right thing to do.
注意： a. 句首名词不能带任何冠词。
b. 句首是实义动词，其他助动词放在主语后。如果实义动词有宾语和状语，随实义动词一起放在主语之前。
Try hard as he will, he never seems able to do the work satisfactorily.
= Though he tries hard, he never seems…
虽然他尽了努力，但他的工作总做的不尽人意。
3) ever if, even though. 即使
We'll make a trip even though the weather is bad.
4) whether…or- 不管……都
Whether you believe it or not, it is true.
5) "no matter +疑问词" 或"疑问词+后缀ever"
No matter what happened, he would not mind.
Whatever happened, he would not mind.
替换：no matter what = whatever
no matter who = whoever
no matter when = whenever
no matter where = wherever
no matter which = whichever
no matter how = however
注意：no matter 不能引导主语从句和宾语从句。
（错）No matter what you say is of no use now.
（对）Whatever you say is of no use now.
你现在说什么也没用了。(Whatever you say是主语从句)
（错）Prisoners have to eat no matter what they're given,
（对）Prisoners have to eat whatever they're given. 囚犯们只能给什么吃什么。
19.8 比较while, when, as
1）as, when 引导短暂性动作的动词。
Just as / Just when / When I stopped my car, a man came up to me.
2）当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。
When you have finished your work, you may have a rest.
3）从句表示"随时间推移"连词能用as，不用when 或while。
As the day went on, the weather got worse.
日子一天天过去，天气越变越坏。
19.9 比较until和till
此两个连词意义相同。肯定形式表示的意思是"做某事直至某时"，动词必须是延续性的。否定形式表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可 以。 正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。
肯定句：
I slept until midnight. 我一直睡到半夜时醒了。
Wait till I call you. 等着我叫你。
（在肯定句中可用before代替 Let's get in the wheat before the sun sets.）
否定句：
She didn't arrive until 6 o'clock.
她直到6点才到。
Don't get off the bus until it has stopped.
公共汽车停稳后再下车。
I didn't manage to do it until you had explained how. 直到你教我后，我才会做。
1)Until可用于句首，而till通常不用于句首。
Until you told me, I had heard nothing of what happened.
直到你告诉我以前，出了什么事我一点也不知道。
2)Until when 疑问句中，until要放在句首。
---Until when are you staying? 你呆到什么时候？
--- Until next Monday. 呆到下周一。
注意：否定句可用另外两种句式表示。
(1）Not until …在句首，主句用倒装。
Not until the early years of the 19th century did man know what heat is.
直到19 世纪初，人类才知道热能是什么。
Not until I began to work did I realize how much time I had wasted.
直到我开始工作，我才认识到了我已蹉跎了几多岁月。
(2) It is not until… that…
19.10 表示"一…就…"的结构
hardly/scarcely…when/before, no sooner…than 和as soon as都可以表示"一…就…"的意思，例：
I had hardly / scarcely got home when it began to rain.
I had no sooner got home than it began to rain.
As soon as I got home, it began to rain.
注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构：
Hardly / Scarcely had I got home when it began to rain.
No sooner had I got home than it began to rain.
20. 连词
连词是一种虚词，
它不能独立担任句子成分而只起连接词与词，短语与短语以及句与句的作用。连词主要可分为两类：并列连词和从属连词。并列连词用来连接平行的词、词组和分
句。如：and, but, or, nor, so, therefore, yet, however, for, hence, as well
as, both…and, not only…but also, either…or, neither…nor, (and)then等等。
20.1 并列连词与并列结构
并列连词引导两个并列的句子。
1) and 与or
判断改错：
(错) They sat down and talk about something.
(错) They started to dance and sang.
(错) I saw two men sitting behind and whisper there.
(对) They sat down and talked about something.
(对) They started to dance and sing.
(对)I saw two men sitting behind and whispering there.
解析：
第一句： and 连接两个并列的谓语，所以 talk 应改为 talked。
第二句：and 连接两个并列的动词不定式，第二个不定式往往省略to，因此sang 应改为 sing。
第三句：and 连接感观动词saw 后面的用作的宾补的两个并列分词结构，因此whisper应改为whispering。
注意：and 还可以和祈使句或名词词组连用表示条件。（or也有此用法）
Make up your mind, and you'll get the chance.
= If you make up your mind, you'll get the chance.
One more effort, and you'll succeed.
= If you make one more effort, you'll succeed.
2) both …and 两者都
She plays (both) the piano and the guitar.
3) not only…but (also), as well as不但…而且）
She plays not only the piano, but (also) the guitar.
注意： not only… but also 关联两个分句时，一个分句因有否定词not 而必须倒装。
Not only does he like reading stories, but also he can even write some.
4) neithe…nor 意思为"既不……也不……"谓语动词采用就近原则，与nor后的词保持一致。
Neither you nor he is to blame.
20.2 比较and和or
1) 并列结构中，or通常用于否定句，and用于肯定句。
2) 但有时and 也可用于否定句。请注意其不同特点：
There is no air or water in the moon.
There is no air and no water on the moon.
在否定中并列结构用or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用and。
典型例题
---I don't like chicken ___ fish.
---I don't like chicken, ___ I like fish very much.
A. and； and B. and； but C. or； but D. or；and
答案C。否定句中表并列用or, but 表转折。
判断改错：
(错) We will die without air and water.
(错) We can't live without air or water.
(对) We will die without air or water.
(对) We can't live without air and water.
20.3 表示选择的并列结构
1) or 意思为"否则"。
I must work hard, or I'll fail in the exam.
2) either…or 意思为"或者……或者……"。注意谓语动词采用就近原则。
Either you or I am right.
20.4 表示转折或对比
1) but表示转折，while表示对比。
Some people love cats, while others hate them.
典型例题
--- Would you like to come to dinner tonight?
--- I'd like to, ___ I'm too busy.
A. and B. so C. as D. but
答案D。but与前面形成转折，符合语意。而表并列的and， 结果的so，原因的as都不符合句意。
2) not…but… 意思为"不是……而是……"
not 和but 后面的用词要遵循一致原则。
They were not the bones of an animal, but (the bones) of a human being.
20.5 表原因关系
1) for
判断改错：
(错) For he is ill, he is absent today.
(对) He is absent today, for he is ill.
for是并列连词，不能置于含两个并列分句的句子的句首，只能将其放在两个分句中间。
2) so, therefore
He hurt his leg, so he couldn't play in the game.
注意：
a. 两个并列连词不能连用，但therefore, then, yet.可以和并列连词连用。
You can watch TV, and or you can go to bed.
He hurt his leg, and so / and therefore he couldn't play in the game.
b. although… yet…，但although不与 but连用。
(错) Although he was weak, but he tried his best to do the work..
(对) Although he was weak, yet he tried his best to do the work.
20.6 比较so和 such
其规律由so与such的不同词性决定。such 是形容词，修饰名词或名词词组，so是副词，只能修饰形容词或副
词。so 还可与表示数量的形容词many，few，much， little连用，形成固定搭配。
so + adj. such + a(n) + n.
so + adj. + a(n) + n. such + n. (pl.)
so + adj. + n. (pl.) such +n. (pl.)
so + adj. + n. [不可数] such +n. [不可数]
so foolish such a fool
so nice a flower such a nice flower
so many/ few flowers such nice flowers
so much/little money. such rapid progress
so many people such a lot of people
so many 已成固定搭配，a lot of 虽相当于 many，但 a lot of 为名词性的，只能用such搭配。
so…that与such…that之间的转换既为 so与such之间的转换。
21. 情态动词
21.1 情态动词的语法特征
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。
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。
21.2 比较can 和be able to
1）can could 表示能力；可能 (过去时用could),
只用于现在式和过去式(could)。be able to可以用于各种时态。
They will be able to tell you the news soon. 他很快就能告诉你消息了。
2）只用be able to
a. 位于助动词后。
b. 情态动词后。
c. 表示过去某时刻动作时。
d. 用于句首表示条件。
e. 表示成功地做了某事时，只能用was/were able to， 不能用could。
He was able to flee Europe before the war broke out.
= He managed to flee Europe before the war broke out.
注意：could不表示时态
1）提出委婉的请求，（注意在回答中不可用could）。
--- Could I have the television on?
--- Yes, you can. / No, you can't.
2）在否定，疑问句中表示推测或怀疑。
He couldn't be a bad man.
他不大可能是坏人。
21.3 比较may和might
1） 表示允许或请求；表示没有把握的推测；may 放在句首，表示祝愿。
May God bless you!
He might be at home.
注意： might 表示推测时，不表示时态。只是可能性比may 小。
2） 成语： may/might as well，后面接不带to 的不定式，意为"不妨"。
If that is the case, we may as well try.
典型例题
Peter ___come with us tonight, but he isn't very sure yet.
A. must B. may C. can D. will
答案B. 表可能性只能用may. 此句意可从后半句推出。
21.4 比较have to和must
1) 两词都是'必须'的意思，have to 表示客观的需要， must 表示说话人主观上的看法，既主观上的必要。
My brother was very ill, so I had to call the doctor in the middle of the night. 我弟弟病得很厉害，我只得半夜里把医生请来。(客观上需要做这件事)
He said that they must work hard. 他说他们必须努力工作。（主观上要做这件事）
2) have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务。
He had to look after his sister yesterday.
3） 在否定结构中： don't have to 表示"不必"
mustn't 表示"禁止"，
You don't have to tell him about it. 你不一定要把此事告诉他。
You mustn't tell him about it. 你一定不要把这件事告诉他。
21.5 must表示推测
1) must用在肯定句中表示较有把握的推测，意为"一定"。
2) must表对现在的状态或现在正发生的事情的推测时， must 后面通常接系动词be 的原形或行为动词的进行式。
You have worked hard all day.You must be tired. 你辛苦干一整天，一定累了。（对现在情况的推测判断）
He must be working in his office. 他一定在办公室工作呢。
比较：
He must be staying there.
他现在肯定呆在那里。
He must stay there.
他必须呆在那。
3) must 表示对已发生的事情的推测时，must 要接完成式。
I didn't hear the phone. I must have been asleep. 我刚才没有听到电话，我想必是睡着了。
4) must表示对过去某时正发生的事情的推测，must 后面要接不定式的完成进行式。
---Why didn't you answer my phone call?
---Well, I must have been sleeping, so I didn't hear it.
5) 否定推测用can't。
If Tom didn't leave here until five o'clock, he can't be home yet. 如果汤姆五点才离开这儿，他此时一定还未到家。
21.6 表示推测的用法
can, could, may, might, must 皆可表示推测，其用法如下：
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。
I don't know where she is, she may be in Wuhan.
2）情态动词+动词现在进行时。
表示对现在或将来正在进行的情况进行推测。
At this moment, our teacher must be correcting our exam papers.
这时，我们老师想必在批改试卷。
3）情态动词+动词完成时。
表示对过去情况的推测。
We would have finished this work by the end of next December.
明年十二月底前我们很可能已完成这项工作了。
The road is wet. It must have rained last night.
地是湿的，昨天晚上一定下雨了。
4）情态动词+动词的现在完成进行时。
表示对过去正在发生事情的推测。
Your mother must have been looking for you.
你妈妈一定一直在找你。
5）推测的否定形式，疑问形式用can't, couldn't表示。
Mike can't have found his car, for he came to work by bus this morning.
迈克一定还没有找回他的车，因为早上他是坐公共汽车来上班的。
注意：could, might表示推测时不表示时态，其推测的程度不如can, may。
21.7 情态动词+ have +过去分词
1) may(might) have + done sth, can (could) have + done sth 表示过去，推测过去时间里可能发生的事情。
Philip may (might) have been hurt seriously in the car accident.
Philip can (could) have been hurt seriously in the car accident.
2) must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有"肯定"，"谅必"的意思。
---Linda has gone to work, but her bicycle is still here.
---She must have gone by bus.
3) ought to have done sth, should have done sth
本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。
You ought to (should) have been more careful in this experiment.
He ought not to have thrown the old clothes away.（事实上已扔了。）
ought to 在语气上比should 要强。
4) needn't have done sth 本没必要做某事
I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
5) would like to have done sth 本打算做某事
I would like to have read the article, but I was very busy then.
21.8 should 和ought to
should 和ought to 都为"应该"的意思，可用于各种人称。
---Ought he to go?
---Yes. I think he ought to.
表示要求，命令时，语气由 should（应该）、had better最好）、must（必须）渐强。
21.9 had better表示"最好"
had better 相当于一个助动词，它只有一种形式，它后面要跟动词原形。
had better do sth
had better not do sth
It is pretty cold. You'd better put on my coat.
She'd better not play with the dog.
had better have done sth表示与事实相反的结果，意为"本来最好"。
You had better have come earlier.
21.10 would rather表示"宁愿"
would rather do
would rather not do
would rather… than… 宁愿……而不愿。
还有would sooner, had rather, had sooner都表示"宁愿"、"宁可"的意思。
If I have a choice, I had sooner not continue my studies at this school.
I would rather stay here than go home. = I would stay here rather than go home.
典型例题
----Shall we go skating or stay at home?
----Which ___ do?
A. do you rather B. would you rather C. will you rather D. should you rather
答案B。本题考查情态动词rather的用法，would rather +do sth 意为"宁愿"，本题为疑问句，would 提前，所以选B。
21.11 will和would
注意：
1）would like； Would like to do = want to 想要，为固定搭配。
Would you like to go with me?
2）Will you…? Would you like…? 表示肯定含义的请求劝说时，疑问句中一般用some, 而不是any。
Would you like some cake?
3）否定结构中用will，一般不用would, won't you是一种委婉语气。
Won't you sit down?
21.12 情态动词的回答方式
问句 肯定回答 否定回答
Need you…? Yes, I must. No,I needn't
Must you…? /don't have to.
典型例题
1）---Could I borrow your dictionary?
---Yes, of course, you____.
A. might B. will C. can D. should
答案C.could表示委婉的语气，并不为时态。答语中of course，表示肯定的语气，允许某人做某事时，用can和
may来表达，不能用could或might。复习： will 与you连用，用来提出要求或下命令。should与you 连用，用来提出劝告。
2）---Shall I tell John about it?
---No, you ___. I've told him already.
A. needn't B. wouldn't C. mustn't D. shouldn't
答案A。needn't 不必，不用。 wouldn't 将不, 不会的。 mustn't 禁止、不能。 shouldn't 不应该。本题为不需要，不必的意思，应用needn't。
3）---Don't forget to come to my birthday party tomorrow.
---______.
A. I don't B. I won't C. I can't D. I haven't
答案B. will既可当作情态动词，表请求、建议、也可作为实义动词表"意愿、意志、决心"，本题表示决心，选B。
21.13 带to 的情态动词
带to 的情态动词有四个：ought to, have to, used to, be to, 如加上have got to ,(=must), be able to，为六个。它们的疑问，否定形式应予以注意：
Do they have to pay their bill before the end of the month?
She didn't use to play tennis before she was fourteen.
You ought not to have told her all about it.
Ought he to see a heart specialist at once.?
ought to 本身作为情态动词使用。其他的词作为实义动词使用，变疑问，否定时，须有do 等助动词协助。
典型例题
Tom ought not to ___ me your secret, but he meant no harm.
A.have told B.tell C.be telling D. having told
答案A。由于后句为过去时，告诉秘密的动作又发生在其前因，此地应用过去完成时，但它在情态动词 ought to 后，所以用have。
21.14 比较need和dare
这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只能用于疑问句，否定句和条件句。 need 作实义动词时后面的不定式必须带to，而dare作实义动词用时, 后面的to 时常可以被省略。
1) 实义动词： need （需要, 要求）
need + n. / to do sth
2) 情态动词： need，只用原形need后加do，否定形式为need not。
Need you go yet?
Yes, I must. / No, I needn't.
3) need 的被动含义：need, want, require, worth（形容词）后面接doing也可以表示被动：
need doing = need to be done
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