第三讲 复合句
作为必考项，复合句属应知应会内容。每年高考单选题中涉及复合句的题，少则2道、多则3道。复合句的种类很多，出现频度最高的是定语从句，其次为状语从句和名词性从句。
一. 名词性从句：
1．名词性从句主要分为四大类：主语从句、宾语从句、表语从句和同位语从句。是由if, whether, that 和各种疑问词充当连接词所引导的从句，其功同名词一样。
2．名词性从句的语序：名词性从句在句中要用陈述句语序。
如：He asked me what was the matter with me.
We’ve heard the news that we’ll move into the new house.
Whatever you say will interest us all.
(一)主语从句
1．定义：主语从句是在复合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。用作主语的从句叫做主语从句。
2．构成：关联词+简单句
3．引导主语从句的关联词有三类：
1) 从属连词that：由that引导的从句,通常用形式主语来代替。
That he has disappeared worries his parents.
It worries his parents that he has disappeared.
It is not likely that he can win the lottery.
It is a big surprise that he is still alive.
2) 从属连词whether。如：
Whether he’ll come here isn’t clear. 他是否会来这里还不清楚。
Whether or not she will go to Japan is up to her.
Whether he will take part in the play is not clear.
3) 连接代词who, whom, whose, what, which, whoever, whatever, whichever
由what等代词引导的从句,表示”所的(东西)”，实际上等于一个现行词加上一个定语从句，也可以由-ever等代词引导。
What she did is not yet known. 她干了什么尚不清楚。
What they are talking about is nothing valuable.
What I really want is to have a good rest.
Whatever she did is wrong.
Whoever passes the exam can get 50 yuan.
Whoever used to have another name raise your hand.
Whoever comes is welcome. 不论谁来都欢迎。
连接副词 where, when, how, why, 如：
When she will be back is still a question.
Where they had put the files troubled the spy.
How this happened is not clear to anyone. 这事怎样发生的，谁也不清楚。
Wherever you are is my home ---- my only home.
你所在的任何地方就是我的家----我唯一的家。
4．主语从句常出现在下面的三种结构中。
1)主语从句＋谓语
That she will come to our party is certain.
2)It +be+名词(形容词、过去分词)＋that从句
(1) It is ＋名词＋从句
It is a fact that 事实是
It is an honor that? 非常荣幸
It is common knowledge that ? ...是常识
(2) it is ＋形容词＋从句
It is natural that 很自然
It is strange that? 奇怪的是
在这种结构中，that引导的从句后置。而使用it作形式主语，它也可以与前面讲到的结构换用。用于该结构的形容词很多，常见的有： obvious, clear, likely, true, certain...
该结构中，由于使用了某些形容词、名词词组、过去分词，后面引导的主语从句要使用虚拟语气。关于这一点请参见《虚拟语气》一章。
(3) it ＋过去分词＋从句
It is reported that 据报道
It has been proved that 已证实
例句：
It is common knowledge that the whale is not a fish.
It is quite clear that the elephant is like a huge fan.
It is said that our school will be rebuilt.
3)It +seem(happen等不及物动词)＋that从句
It seems that 似乎
It happened that 碰巧
It seems that Mary is not coming at all.
用于该结构的不及物动词有：seem, happen, appear, matter...
该结果有的可以用不定式结构转换。如上面句子可转换为：
Mary doesn't seem to be coming at all.
5. 主语从句不可位于句首的五种情况
1) if 引导的主语从句不可居于复合句句首。
2) It is said , (reported) 结构中的主语从句不可提前。
例如：
It is said that President Jingo will visit our school next week. (right)
That President Jiang will visit our school next week is said. (wrong)
3) It happens? It occurs?结构中的主语从句不可提前。
例如：
It occurred to him that he failed in the examination. (right)
That he failed in the examination occurred to him. (wrong)
4) It doesn’t matter how/whether 结构中的主语从句不可提前。
例如：
It doesn’t matter whether he is wrong or not. (right)
Whether he is wrong or not doesn’t matter. (wrong)
5) 含主语从句的复合句是疑问句时，主语从句不可提前。
例如：
Is it likely that it will rain in the evening? (right)
Is that will rain in the evening likely? (wrong)
6. What 与that 在引导主语从句时的区别
What 引导主语从句时在句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如：
What you said yesterday is right.
That she is still alive is a consolation.
(二)宾语从句
宾语从句就是在复合句中作宾语的名词性从句，通常放在主句谓语动词(及物动词)或介词之后。
1. 作动词的宾语
1) 由that引导的宾语从句(that 通常可以省略)
例如：I heard that be joined the army.
2) 由what, whether (if) 引导的宾语从句
例如：She did not know what had happened.
I wonder whether you can change this note for me.
3) 动词＋间接宾语＋宾语从句。
例如：She told me that she would accept my invitation.
2. 作介词的宾语
例如：Our success depends upon how well we can cooperate with one another.
3. 作形容词的宾语
例如：I am afraid (that) I’ve made a mistake.
That 引导的从句常跟在下列形容词后作宾语：
anxious, aware, certain, confident, convinced, determined, glad, proud, surprised, worried, sorry, thankful, ashamed, disappointed, annoyed, pleased, hurt, satisfied, content 等。
4. It 可以作为形式宾语
It 不仅可以作为形式主语，还可以作为形式宾语而真正的宾语that 从句则放在句尾，特别是在带复合宾语的句子中。
例如：We heard it that she would get married next month..
5. 连接代词
1) 由连接代词或副词引起的从句.
Please show me how to make him happy.
I don’t know who did all the cleaning.
Have you decided whom you will take to Australia?
She still wondered when she would leave school.
I am wondering whether/if the dress is too short.
He advised me which books I should read.
还可以做介词的宾语.
The singer still worries about where to live.
The price depends on how many you will buy.
2) 由关系代词型what等代词引起的从句.
I will tell you what I know.
We’ll give whatever help you need.
I plan to read whichever book you recommend.
His father was not satisfied with what he had.
She walked up to where I stood.
3) 由that引起的从句,在believe, think, suppose后常不加that.
在think, believe, suppose, expect等动词引起的宾语从句中,有时谓语尽管是否定意思,也只将前面的词否定。
I don’t think you can beat me.
He doesn’t expect we need worry.
有时在宾语和谓语之间可以插入一个间接宾语或状语。
She reminded me that I had a meeting to attend.
They explained to us that they didn’t mean to make us angry.
有时在这种带有复合宾语的句子中, that引起的从句常常移到后面, 前面用一个it作为形式宾语。
I thought it very impossible that she would come.
They took it for granted that the singer was coming.
6. 容易出错的内容
1) 与主句的时态呼应
(1)当主句的谓语动词是现在或将来时态时，宾语从句的谓语动词可以和主句的谓语动词时态不一致，就是说可根据实际需要用不同的时态。如：
I hear he'll be back in a week.
I hear Mr. Evans lives in Boston.
I hear she has gone to Shanghai.
I hear he came back yesterday.
(2)当主句中的谓语动词是一般过去时，宾语从句的谓语动词要用和过去相关的时态，可以是一般过去时、过去进行时、过去将来时和过去完成时等。如:
She said she hoped to be back soon.
She said they were having a meeting.
She said she would visit her uncle next Saturday.
She said she had seen the film the day before.
(3)在“Could you tell us请告诉我们厖好吗?”这种表示请求的疑问句中，用could比用can 较为委婉客气一些，但could不表示过去时，所以宾语从句中的谓语动词时态可根据实际需要用不同的时态。如：
Could you tell us if(whether)Kate's father works in that hospital?
Could you tell us if(whether)Alice worked out the problem herself?
(4) 如果宾语从句所叙述的是客观真理、自然现象、名言警句或谚语等，不管主句是什么时态，从句都用原时态。如：
Our geography teacher told us that the earth goes around the sun.
When I was young, my father often told me that knowledge is power (力量).
The teacher told us the sun is much bigger than the earth.
2) 从句部分的语序
宾语从句的语序和一般陈述句相同，即主谓次序不颠倒。因此，由连接代词(who、whose、what和which等)、连接副词(where、when、why和how)或连词if(或whether)引导的疑问句，改成宾语从句时，语序需要改变。如：
Do you know where Mary lives?
Nobody knows what they fought about.
He asked whose dictionary this was.
He asked me if(whether)I could help him.
但是，当连接代词在宾语从句中作主语时，从句的语序与以疑问代词作主语的特殊疑问句的语序相同。
如：He asked which picture was John's.
3) 否定转移
若主句谓语动词为Think, consider, suppose, believe, expect, fancy, guess, imagine等，其后的宾语从句若含有否定意义，一般要把否定词转移到主句谓语上，从句谓语用肯定式。例如：
I don’t think this dress fits you well.(我认为这件衣服不适合你穿。)
We believe that he can finish it in time.
We don't believe that he can finish it in time.
请注意：当主句中的谓语动词为hope时，则不用否定转移。只说：
I hope he won't be ill.(我希望他不要生病。)
4) 带宾语从句的复合句改成简单句
宾语从句在复合句中作主句的宾语，它的位置与陈述句基本结构中的宾语相同，所以，在实际运用中，可以用不定式、名词或复合宾语等代替宾语从句，构成简单句。如：
① He hopes he will be able to see her again.
He hopes to see her again.
② I don't know when we'll start.
I don't know when to start.
③ The man didn't understand what he said.
The man didn't catch his words.
④ I heard she was singing in the next room.
I heard him singing in the next room.
⑤ I found it was interesting to skate on real ice.
I found it interesting to skate on real ice.
5) 宾语从句前通常需要有引导词
①如果宾语从句是由陈述句转变而来的，其引导词用that，常可以省略。如：
I hope (that) I can study English better.
②如果宾语从句是由一般疑问句转变而来的，其引导词使用if / whether, 意为"是否"。
Mr Chen asked , "Are you all here?"→Mr Chen asked if / whether we were all here.
③如果宾语从句是由特殊疑问句转变而来的，其引导词使用连接代词what / which /who / whose 或 连接副词when / where / why / how 等。这些连接词都要充当从句中的一个成分，故不能省略。如：
Tom asked me, "When did you begin to study English?"
→Tom asked me when I began to study English.
(三)表语从句
1．定义：用作表语的从句叫做表语从句。
2．构成：
表语从句在复合句中作表语的名词性从句，放在系动词之后。
一般结构是“主语＋连系动词＋表语从句”。
可以接表语从句的连系动词有be, look, remain, seem等。
另外，常用的还有the reason is that?和It is because 等结构。
3．引导表语从句的关联词的种类：
1) that引导的表语从句
基本结构：主语 + 系动词 + that从句
例句：The fact is that we have lost the game. 事实是我们已经输了这场比赛。
But the fact remains that we are behind the other classes.
The reason he is late for school is that he missed the early bus.
The trouble is that I have lost his address. 麻烦是我把他的地址丢了。
2) 从属连词whether, as, as if。如：
He looked just as he had looked ten years before. 他看起来还与十年前一样。
The question is whether they will be able to help us. 问题是他们是否能帮我们。
The question is whether we can make good preparation in such a short time.
从属连词because引导的表语从句
It is because I have ever heard of the story. 那是因为我曾经听说过这个故事。
注：从属连词if一般不用来引导表语从句，但as if却可引导表语从句，如：
All this was over twenty years ago, but it’s as if it was only yesterday.这都是20多年前的事了，但宛如昨天一样。
能跟表语从句的谓语动词一般为系动词be, seem, look等。如：
It looked as if it was going to rain. 看起来天要下雨了。
3) 连接代词who, whom, whose, what, which, whoever, whatever, whichever；
连接副词 where, when, how, why；如：
The problem is who we can get to replace her. 问题是我们能找到谁去替换她呢。
The question is how he did it. 问题是他是如何做此事的。
That was what she did this morning on reaching the attic. 那就是她今晨上了阁楼干的。
That is why I tell you the news. 那就是我为什么告诉你这个消息的原因。
This is why we can’t get the support of the people.
(四)同位语从句
1．定义：同位语从句就是在复合句中作名词的同位语的名词性从句。
2．用法：同位语从句的先行词多为advice、demand、doubt、fact、hope、idea、information、message、news、order、problem、promise、question、request 、reply、report、remark、suggestion、thought 、truth、wish、word等，关联词多用从属连词that。如：
They were all very much worried over the fact that you were sick.对你生病这件事，他们都很焦虑。
Where did you get the idea that I could not come?你在哪儿听说我不能来？
Early in the day came the news that Germany had declared war on Russia.德国已对俄国宣战的消息一大早就传来了。
注：同位语从句偶尔由从属连词whether引导。如：
I have no idea whether he’ll come or not. 我不知道他是否来。
连接代词who, which, what和连接副词where, when, why, how亦可引导同位语从句。
The question who should do the work requires consideration.谁该干这项工作，这个问题需要考虑。
We haven’t yet settled the question where we are going to spend our summer vacation.到哪儿去度暑假，这个问题我们还没有决定。
It is a question how he did it.那是一个他如何做了此事的问题。
3．同位语从句的功能
同位语从句对于名词进一步解释，说明名词的具体内容，一般由that引导，例如：
The king’s decision that the prisoner would be set free surprised all the people.
The order that all the soldiers should stay still is given by the general.
4．同位语在句子中的位置
同位语从句有时可以不紧跟在它所说明的名词后面，而是被别的词隔开。例如：
He got the news from Mary that the sports meeting was put off.
5．同位语从句与定语从句的区别
1) 定语从句中的that既代替先行词，同时以在从句中作某个成分(主语或宾语)，而同位语从句中的that是连词，只起连接主句与从句的作用，不充当句中任何成分。
2) 定语从句是形容词性的，其功能是修饰先行词，对先行词加以限定，描述定的性质或特征；同位语从句是名词性的，其功能是对名词进行补充说明。例如：
The news that he told me is that Tom would go abroad next year.(他告诉我的消息是汤姆明年将出国。)
(第一个that引导的从句是定语从句，that在从句中作宾语)
The news that Tom would go abroad is told by him.(汤姆将出国的消息是他讲的。)
(同位语从句，that在句中不作任何成分)
(五)名词性从句中连接词的运用
名词性从句中的连接词有连词that / whether / as if，连接代词what / who/ which / whose / whatever / whoever / whomever / whichever，连接副词where / when / why / how / wherever / whenever。
1. that的用法。
(1)主语从句、表语从句、同位语从句中用that但不能省略。如：
That they are good at English is known to us all.
The problem is that we don’t have enough money.
She expressed the hope that they would come to China one day.
(2)宾语从句中的连接词that有时可省有时又不可省，在以下几种情况中that不能省略：
(A)当that从句和主句谓语动词之间有插入词语或者从句主语之间有插入语时，that不可省略；
(B)当that 从句与另一名词性从句并列作宾语时，that不能省；
(C)当that作介词宾语时，that不可省掉。如：
He judged that,because he was a child, he did not understand wine.
Everyone knew what happened and that she was worried.
The reason lies in that she works harder than the others do.
2. if, whether 的用法
(1) 间接引语位于句首时或者是间接引语提前时用whether不用if。如：
Thank you, but whether I’ll be free I’m not sure at the moment.
(2) whether可引导一个让步状语从句表示“不管”、“无论”，而if不能。如：
Whether he comes or not, we will begin our party on time.
3. 疑问词 + ever和no matter + 疑问词的区别。
(1)疑问词 + ever可引导名词性从句，在主从句中要充当一定的部分。如：
Whoever breaks the rule must be punished.
You can choose whatever you like in the shop.
(2)疑问词 + ever还可引导让步状语从句。如：
Whoever breaks the rule, he must be punished,
Whatever you do, you must do it well.
(3)no matter + 疑问词只能引导让步状语从句。如：
No matter what you do, you must do it well.
No matter who breaks the rule, he must be punished.
4. when和where引导的同位语从句与定语从句的区别。
when 和where前面的名词若是表示时间、地点的名词，则when和where引导的是定语从句，否则则为同位语从句。如：
They put forward the question where they could get the money.
This is the place where the accident happened.
(六)名词性从句中主句和从句的一致
主语从句作主语相当于单数第三人称作主语，谓语动词用单数，如果由and 连接两个或两个以上的主语从句作主语时，谓语动词用复数；由两个或多个连接词引导一个主语从句，谓语动词用单数。如：
When the meeting will begin has not been decided yet.
When they will start and where they go have not been decided yet.
When and where the meeting will begin has not been decided.
二、定语从句
(一)定语从句及相关术语
1. 定语从句：修饰一个名词或代词的从句称为定语从句，一般紧跟在它所修饰的先行词后面。
2. 关系词：引导定语从句的关联词成为关系词。
关系词有关系代词和关系副词。
关系代词有that, which, who, whom, whose, as等。
关系副词有where, when, why等。
关系词常有3个作用：引导定语从句；代替先行词；在定语从句中担当一个成分。
(二)关系代词引导的定语从句
1. who指人，在从句中做主语
The boys who are playing football are from Class One.
Yesterday I helped an old man who lost his way.
2. whom指人，在定语从句中充当宾语，常可省略。
Mr. Liu is the person (whom) you talked about on the bus.
Mr. Ling is just the boy whom I want to see.
注意：关系代词whom在口语和非正式语体中常用who代替，可省略。
The man who/whom you met just now is my friend.
3. which指物，在定语从句中做主语或者宾语，做宾语时可省略。
Football is a game which is liked by most boys.
This is the pen (which) he bought yesterday.
4. that指人时，相当于who或者whom；指物时，相当于which。在定语从句中做主语或者宾语，做宾语时可省略。
The number of the people that/who come to visit the city each year rises one million.
Where is the man that/whom I saw this morning?
5. whose通常指人，也可指物，在定语从句中做定语
He has a friend whose father is a doctor.
whose指物时，常用以下结构来代替
The classroom whose door is broken will soon be repaired.
The classroom the door of which is broken will soon be repaired.
Do you like the book whose cover is yellow?
Do you like the book the color of which is yellow?
(三)介词+关系代词引导的定语从句
关系代词在定语从句中做介词宾语时，从句常由介词+关系代词引导
The school (that/which) he once studied in is very famous.
The school in which he once studied is very famous.
Tomorrow I will bring here a magazine (that/which) you asked for.
Tomorrow I will bring here a magazine for which you asked.
We’ll go to hear the famous singer (whom/that/who) we have often talked about.
We’ll go to hear the famous singer about whom we have often talked.
注意：
1. 含有介词的动词短语一般不拆开使用，如：look for, look after, take care of 等。
This is the watch which/that I am looking for. (T)
This is the watch for which I am looking. (F)
2. 若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，不能用that；关系代词是所有格时用whose 。
The man with whom you talked is my friend. (T)
The man with who/that you talked is my friend. (F)
The plane in which we flew to Canada is very comfortable. (T)
The plane in that we flew in to Canada is very comfortable. (F)
3. “介词+关系代词”前可有some, any, none, both, all, neither, most, each, few等代词或者数词。
He loved his parents deeply, both of whom are very kind to him.
In the basket there are quite many apples, some of which have gone bad.
There are forty students in our class in all, most of whom are from big cities.
(四)关系副词引导的定语从句
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？
1. when指时间，在定语从句中做时间状语
I still remember the day when I first came to the school.
The time when we got together finally came.
2. where指地点，在定语从句中做地点状语
Shanghai is the city where I was born.
The house where I lived ten years ago has been pulled down.
3. why指原因，在定语从句中做原因状语
Please tell me the reason why you missed the plane.
I don’t know the reason why he looks unhappy today.
注意：关系副词引导的从句可以由“介词+关系代词”引导的从句替换。
The reason why/ for which he refused the invitation is not clear.
From the year when/in which he was going to school he began to know what he wanted when he grew up.
Great changes have taken place in the city in which./where I was born.
4. 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.
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) 。
(五)限制性定语从句和非限制性定语从句
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：
限制性定语从句举例：
The teacher told me that Tom was the only person that I could depend on.
China is a country which has a long history.
This is the house which we bought last month.这是我们上个月买的那幢房子。
非限制性定语从句举例：
His mother, who loves him very much, is strict with him.
China, which was founded in 1949, is becoming more and more powerful.
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。
要注意区分以下几个句子的不同：
His brother who is now a doctor always encourages him to go to college.
他那当医生的哥哥常鼓励他要考上大学。(他还有其他的哥哥)
His brother, who is now a doctor, always encourages him to go to college.
他的哥哥是当医生的，常鼓励他要考上大学。(他只有一个哥哥)
难点分析
1. 限制性定语从句只能用that的几种情况
(1) 当先行词是anything, everything, nothing (something 除外), few, all, none, little, some等代词时，或者是由every, any, all, some, no, little, few, much等修饰时
Have you taken down everything that Mr. Li has said?
There seems to be nothing that seems impossible for him in the world.
All that can be done has been done.
There is little that I can do for you.
注意：当先行词指人时，偶尔也可以用who
Any man that/.who has a sense of duty won’t do such a thing.
(2) 当先行词被序数词修饰
The first place that they visited in London was the Big Ben.
(3) 当先行词被形容词最高级修饰时
This is the best film that I have seen.
(4) 当形容词被the very, the only 修饰时
This is the very dictionary that I want to buy.
After the fire in his house, the old car is the only thing that he owned.
当先行词指人时，偶尔也可以用who
Wang Hua is the only person in our school who will attend the meeting.
(5) 当先行词前面有who, which等疑问代词时
Who is the man that is standing there?
Which is the T-shirt that fits me most?
(6) 当先行词既有人，也有动物或者物体时
Can you remember the scientist and his theory that we have learned?
2. 不用that的情况
(1)在引导非限定性定语从句时
例句：He can speak English fluently, which impressed me most. 他的英语讲得很流利，给我留下了深刻印象。
(2)介词后不能用
例句：This is the house in which I have lived for 2 years. 这就是我居住了两年的房子。
3. 关系代词as和which引导的定语从句
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.
(1) As和which都可以在定语从句中做主语或者宾语，代表前面整个句子。
He married her, as/which was natural.
He was honest, as/which we can see.
(2) as 引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which引导的非限制性定语从句只能放在主句之后。另外，as有“正如，正像”的意思。
As is known to all, China is a developing country.
He is from the south, as we can see from his accent.
John, as you know, is a famous writer.
He has been to Paris more than several times, which I don’t believe.
注意：当主句和从句存在逻辑上的因果关系时，常用which
Tom was always late for school, which made his teacher angry.
(3) 当先行次受such, the same修饰时，常用as 。
I have never heard such a story as he tells.
He is not such a fool as he looks.
This is the same book as I lost last week.
注意：当先行词由the same修饰时，偶尔也用that引导定语从句，但是和由as所引导的定语从句意思不同
She wore the same dress that she wore at Mary’s wedding.
她穿着她在Mary婚礼上穿过的一条裙子。
She wore the same dress as her young sister wore.
她穿着和她妹妹所穿的一样的裙子。
4. 以the way为先行词的定语从句通常由in which, that引导，而且通常可以省略。
The way in which/ that he answered the question was surprising.
5. 定语从句中关系代词与先行词的一致性
定语从句中关系代词一般应与它所指代的先行词的单复数保持主谓一致。例如：
The students who were here just now are from No,2 Senior Middle School.
但注意下列一组句子：
He is the only one of the students who was here just now.
He is one of the students who were here just now.
如果"one of +复数名词"后跟有定语从句，一般情况下"one of"后的复数名词为先行词，但当one前有the only,the very,just the修饰时，先行词则为one。
6. 区分定语从句和同位语从句
(1) 定语从句修饰先行词，它和先行词是修饰关系；同位语从句说明先行词的具体内容，是补充说明的关系。
The plane that has just taken off is for London. 定语从句
The fact that he has been dead is clear. 同位语从句
(2) 定语从句由关系代词或者关系副词引导，关系词在句中充当成分，有时可以省略；同位语从句主要由that引导，在句中一般不做成分；句子也可以由when, where, how, why, whether, what等词引导，充当成分。
The news he told me is true.
The news that he has just died is true.
The problem that we are facing now is how we can collect so much money. 定语
The problem how we can collect so much money is difficult to solve.
(3) 同位语从句和先行词一般可以用be动词发展成一个完整的句子，而定语从句不可以。
The idea that we could ask the teacher for advice is wonderful. 同位语
The idea was that we could ask the teacher for advice.
The fact that the earth moves around the earth is known to all.
The fact is that the earth moves around the earth.
7. 定语从句与强调结构
It is the place where they lived before.
It is in the place that they lived before.
第一个句子为定语从句，where指代the place,在定语从句中作状语，第二个句子为强调结构，强调in the place, that没有意义，把in the place 放回后面7句子，句子意思完整。
Where is it that he found the lost watch?(强调句型，强调疑问副词where)。
Where is the watch that he found yesterday.(定语从句，that指代the watch)
8. 定语从句与并列结构
He has two sons, neither of whom looks like him.
He has two sons, and neither of them looks like him.
I've got two sisters. Both of them are in Shanghai.
第一个句子为定语从句，关系代词whom指代two sons,在定语从名中介词of的宾语。第二个句子为并列结构，由并列连词and连接，人称代词them指代two sons。第三个为两个独立的句子，两个句子中间用句号，两句开头的处一个字母都大写。
9. 定语从句与状语从句
He found the books where he had put.
He found the books in the place where he had put.
第一个句子为状语从句，where he had put 作主句He found the books 的地点状语。第二个句子为定语从句，where引导从句修饰the place。
This is such an interesting book that I'd like to read it.
This is such an interesting book as I'd like to read.
第一个句子为结果状语从句，在结果状语从句中，it指代book,作read的宾语。第二个句子为定语从句，关系代词as指代先行词book的定语从句中read的宾语。
10. 定语从句中的先行词
Is this book the one that you bought yesterday?
Is this the book that you bought yesterday?
第一个句子中，this book是主句的主语，the one 是先行词。在第二个句子中this是主句的主语，the book是先行词。一定要避免出现：Is this book that you bought yesterday?
三、状语从句
1. 定义：在句中作状语的从句是状语从句，修饰主句中的动词、形容词或副词等。状语从句由从属连词引导，从属连词在句中不充当句子成分，只起连接作用，状语从句放在句首时，要用逗号，放在句尾时不用。
2. 分类：根据意义上的不同，状语从句可分为：
时间状语从句、地点状语从句、原因状语从句、目的状语从句、条件状语从句、结果状语从句、让步状语从句、方式状语从句、比较状语从句
(一)时间状语从句
1. 引导时间状语从句的连词有：as, when(whenever), before, after, as soon as, until(till), since, every time, once.
(1) 表示同时性，即主从句的谓语动作同时发生或几乎同时发生。
其连词有：when (当厖的时候), while(当厖的时候), as(当厖的时候), as soon as(一厖就厖), once(一旦厖)等。如：
Strike while the iron is hot.趁热打铁。
While I am washing the floor, you can be cleaning the windows.
我洗地板的时候，你可以擦窗户。(while含有对比的意思)
As / When I came home, I met an old schoolmate of mine.
我回家的时候遇到了我的一位老同学。
I’ll ring you up as soon as I get an answer from him.
我一有他的答复就给你打电话。
Once you see him, you will never forget him.
你一旦见过他，就不会忘了他的。
(2) 表示先时或后时，即主句的谓语动作发生在从句之前或之后，主要连词有：after(在厖之后), before(在厖之前), when(=after)等。如：
After / When the children had gone to bed, she began to prepare her lessons.
(从句的动作发生在主句的动作之前，所以从句用了过去完成时) 孩子睡觉了以后她开始备课。
He had learned English for three years before he went to London.
(主句的动作发生在从句的动作之前，所以主句用了过去完成时)他去伦敦之前已学了三年英语。
It was not long before I forgot it all.(It is / was / will be 卋efore是常用句型)
He ran off before I could stop him.(主句和从句的动作几乎同时发生，时态一致)
我还没来得及阻止他他就跑掉了。(注意before在汉语中的译义)
(3) 表示习惯性、经常性，即从句描述的不是一次性动作，而是经常发生的习惯性动作。主要连词有every time(每次), each time(每次), whenever(每当)等。例如：
Whenever we met with difficulties, they came to help us.
每当我们遇上困难的时候，他们就来帮我们。
Each time he came to town he would visit our school.
他每次进城，总要来看看我们的学校。
Every time I went to his house, he was out.
我每次去他家，他都出去了。
(4) 表示持续性或瞬间性，主要连词有：since(自从), ever since(自从), until(直到厖才/为止), till(直到厖才/为止)等。如：
It is just a week since we arrived here.(It is /was?since是常用句型)
我们到这儿刚刚一星期。(主句的动作或状态持续时间较短，不能用ever since)
You have been reading to me ever since James went out.
(ever 放在since之前是用来表示说话者强调主句动作或状态持续时间长)
自从James走后你一直在给我朗读。
The big clock which used to strike the hours day and night was damaged during the war and has been silent ever since.
( ever since可以放在句末， since则不能)
这只一向日夜不停打点报时的大钟在战争中损坏了，从此就一直不响了。
My uncle went to Tibet in 1951. He has been living there ever since.
我叔叔于1951年去了西藏，从那以后他一直生活在那里。
Things went well until / till one night an accident happened.
事情一切正常，直到有一天晚上发生了意外。
I knew nothing about it until / till he told me.
(但Until he told me, I knew nothing about it. “till”不位于句首。)
他告诉我了我才知道。
2. 主句是一般将来时，时间状语从句用一般现在时表将来，主句是过去将来时，从句用一般过去时表示过去将来时，主句是一般过去时，从句用一般过去时。
I’ll call you when I get there.
They said they would leave when they got the new.
They left as soon as they got the new.
例如：
(1) Whenever 无论什么时候，随时
Whenever someone throws in some rubbish, the truck produces a piece of music.
每当有人扔进一些垃圾时，它(汽车)就放一段音乐。
Whenever we’re in trouble, they will help us.
I go to the theatre, whenever I am free.
Come and see me whenever you want to.你随时来看我。
(2) till和until(表示“直到厖”)句首多用until
在肯定句中表示“直到厖为止”，主句谓语动词要用延续性动词。
I was waiting until/till he arrived.
在否定句中表示“直到厖才”主句谓语动词常用终止性动词，这时until和till常被before替换。
I didn’t leave till/until she came back.
before
(3) since: 主句用完成时，从句用一般过去时，since引导的从句间或可用现在完成时。
It is two years since I have studied English.
We have known each other since we were children.
We have been friends (ever since) since we met at school.
It is 厖 (一段时间)+since+一般过去时态句子。
It is two years since my sister married.
厖(一段时间) have/has passed since +一般过去时态句子
Two sisters have/has passed since my sister married.
Since+时间点
I have been at home since three o’clock this afternoon.
Maria has been in China since two years ago.
(4) every time, each time, next time
Every time you get back at night, you drop your boots on the floor.
Every time I catch cold, I have pain in my back.
(every time 分写不可以合写) 比较everyday (adj) 日常的，普通的
every day 是名词短语，每天，天天
Next time I go there, I will visit them.
(5) once 一旦就
Once you begin, you must go on. 你一开了头，就应该继续下去。
(二)地点状语从句
地点状语从句用where, wherever引导
We should go where the people need us.
我们应该去人民需要我们的地方。
Where there is a will, there is a way.有志者，事竟成。
Wherever they went, they received a worm welcome.
无论他们走到哪儿都受到热烈欢迎。
Wuhan lies where the Yangtze and the Han River meet.
武汉位于长江和汉水汇合处。
You’d better make a mark where you have any questions.
(这里where引导的从句不是定语从句) 哪儿有问题，你最好在哪儿做个记号。
He would keep in touch with us wherever he was .
他无论在什么地方，总是与我们保持联系。
(三)原因状语从句
表示原因的状语从句可以由as(由于), because(因为), since(既然), now (that) (既然), considering that(顾及到), seeing that(由于)等连词引导：
I do it because I like it.因为我喜欢我才干。(because不能与 so连用)
He couldn’t have seen me, because I was not there.
他不可能见过我，因为当时我不在那儿。
Seeing (that) quite a few people were absent, we decided to put the meeting off.
由于好些人都没到会，我们决定延期开会。
Now that/Since you are all here, let’s try and reach a decision.
既然大家都来了，咱们就设法做出一个决定吧。
As she was ill, she didn’t come to the party.
由于病了，她没来参加晚会。
Considering that they are just beginners, they are doing quite a good job.
考虑到他们才刚刚学做，他们干得算很不错的了。
注意：
原因状语从句用because(因为)，since(既然), as(由于)引导
1、字母由多到少，语气由强到弱。
2、由why提问必须用because回答。
Since, as不回答why的提问，而且从句一般放在句首，because一般放在主句之后。
3、because of +名词
Because of the rain, we didn’t go to the park.
4、because 和so不可连用，只能选其一。(另有although, but)
Why didn’t he come to school? Because he was ill.
5、for并列连词，不能放在句首，主要放在两个并列句之间。For所提供的理由为一个补充说明，而且前面常有逗号隔开。
The days we short, for it is December now.
(四)目的状语从句
引导目的状语从句的主要连词有:that, so that(以便), in order that(为了), for fear that(以便), in case(万一)等，从句中常常使用一些情态动词，如：can, could, may, might, should等。
Let’s take the front seats (so) that we may see more clearly.
我们坐前排吧，这样我们看得更清楚些。
School was closed early in order that the children might go home ahead of the storm.
早点儿放学是为了让孩子们在暴风雨到来之前回家。
He took the name down for fear that he should forget it.
他把名字写下省得忘了。(该从句中一般用情态动词should+动词原形，或省略should)
Better take more clothes in case the weather is cold.
最好多带些衣服以防天气会冷。
He studied hard so that he might succeed.他努力学习，以便成功。
I’ll speak slowly so that you can take notes.我慢慢讲，以便你们能做笔记。
They hurried to the station in order that they could catch the train.
他们急忙赶往火车站，以便能赶上火车。
I took a taxi so that I could get there earlier.
I’m going to the lecture early so that I may get a good seat.
(五)条件状语从句
表示条件的状语从句可以由if(如果), unless(除非), in case(万一), so /as long as(只要), as/ so far as(就厖而言), on condition that(条件是厖), suppose(假设), supposing(假设)(仅用在问句中)等词或词组引导。一般情况下当主句是将来时的时候，从句要用一般现在时。
As/So long as we don’t lose heart, we’ll find a way to overcome the difficulty.
只要我们不灰心，我们就能找到克服困难的方法。
Send us a message in case you have any difficulty.
万一你有什么困难，请给我们一个信儿。
If you leave at 6 o’clock tomorrow morning, you’d better get to bed now.
如果你明早6点钟走，你最好现在就上床。
We’ll let you use the room on condition that you keep it clean and tidy.
只要你能保持整洁，我们可以让你使用这个房间。
As/So far as I know, he is an expert on DNA.
据我所知，他是一个DNA专家。
He’ll accept the job unless the salary is too low/ if the salary is not too low.
他会接受这项工作的，除非薪水太少/如果薪水不太少的话。
Suppose/Supposing we can’t get enough food, what shall we do?
假设我们弄不到足够的食物，那我们怎么办？
As long as you are not afraid of difficulties, you are sure to succeed.
只要你不怕困难，你肯定能成功。
(六)结果状语从句
引导结果状语从句的连词有：that, so that(从句中不带情态动词), so卼hat(如此厖以致厖), such卼hat(如此厖以致厖)等。
What has happened that you all look so excited?
发生了什么事，使你们都显得如此兴奋？
He didn’t plan his time well, so that/so he didn’t finish the work in time.
他没把时间计划好，结果没按时完成这项工作。
We left in such a hurry that we forgot to lock the door.
我们走得匆忙，把门都忘了锁了。(such是形容词，后接名词)
The village is so small that it cannot be shown in the map.
这村子太小，所以这地图上没有。(so是副词，后接形容词或副词)
Jenny is such a clever girl that all the teachers like her very much = Jenny is so clever a girl that?
Jenny是如此聪明的女孩，以至老师们都非常喜欢她。
但是，当名词前有many, much, few, little(少)修饰时，要用so,不能用such。例如：
I have had so many falls that I am black and blue all over.
我摔了许多跤，以至于浑身青一块，紫一块。
He has so few friends that he often feels lonely.
他朋友很少，所以经常感到孤独。
I had so little money then that I couldn’t afford a little present.
我当时囊肿羞涩，连一份小小礼物都买不起。
结果状语从句由such卼hat, so?that, so that, that 引导
1. such?that 的常用句型
such +a/an +形容词+可数名词单数+that
such +形容词+可数名词单数+that
Such+形容词+可数名词复数(不可数名词)+that
注意so many (much, few, little) +名词，such a lot of (或lots of)+名词是惯用法，不可乱用。
She is such a beautiful girl that we all like her.
They were such beautiful flower that we bought home.
It was such delicious food that they ate it up.
2. so+形容词或副词+that
so+形容词+a/an+可数名词单数+that
He is so rich that he can buy lot of things for himself.
He works so hard that he did everything well.
It was so hot a day that we all went swimming.
It was such a good day that we all went swimming.
3. so that, that都可以引导结果状语从句
He didn’t study hard, (so) that he failed the exam.
4. too卼o, enough卼o 可以引导结果状语从句与so卼hat 替换
so卼hat结构可以用too卼o替换必须具备两个条件，一是主句和结果状语从句的主语必须一致，二是从句中的谓语部分必须含有can(could) not.
She is young that she can’t go to school.
She is too young to go to school.
She isn’t old enough to go to school.
(七)让步状语从句
让步状语从句由although(尽管), though(尽管), however(无论怎样), whatever(无论什么), whoever(无论谁), whomever(无论谁), whichever(无论哪个), whenever(无论何时), wherever(无论哪里), whether(是否), no matter (who, what, where, when, etc) (无论厖), even if(即使), even though(即使)等词引导。如：
We won’t be discouraged even if(=even though) we fail ten times.
我们就是失败十次也不泄气。
It was an exciting game, though / although no goals were scored.
那是一场精彩的球赛，尽管一个球都没进。(though, although不能与 but连用)
Whether you believe it or not, it’s true.
不管你信不信，这是真的。
However (=No matter how) expensive it may be, I’ll take it.
无论它有多贵，我也要买下它。
Don’t let them in, whoever(=no matter who) they are.
不管他们是谁，别让他们进来。
No matter what I say or how I say it, he always thinks I’m wrong.
无论我说什么或怎么说，他总认为是我错。
连词as也可以引导让步状语从句，但从句中要用特殊语序。如：
Young as he is, he knows a lot=Though he is young 或Young though he is, he?
他虽然年轻，但懂得很多。(though 也有这种用法，可以替换as,但although没有这种用法)
though还可以用作副词，放在句末。如：
It was hard work, I enjoyed it, though=It was hard work, but I enjoyed it.那工作很苦，但是我喜欢干。
although, though
even though = even if, whether卭r
however = no matter how
whatever = no matter what
whoever = no matter who
whenever = no matter when
wherever = no matter where
注意：
1) although和though都表示“虽然”只是although 更正式，多用于句首，而though用于句中，二者都可与yet, still连用，但不与but连用。
如：He is unhappy though/although he has a lot of money.
Although/Though it was raining hard, yet they went on playing football.
注：though还可以作副词使用，意为：可是，然而，放在句末。
如：He said he would come, he didn’t, though.他说他会来的，可是他没来。
2) as引导让步状语从句要倒装
as从句一般放在主句之前，要用倒装语序。从句中的表语、状语或动词原形放在句首.若表语是名词，前置时要省略冠词。
如：Child as he is, he knows a lot.尽管他还是个孩子，他却懂得很多。
(八)方式状语从句
方式状语从句常由as(与厖一样), as if(仿佛), as though(仿佛)等词引导：
Do in Rome as the Romans do.入乡随俗。
Leave things as they are.让一切顺其自然。
She stood at the door as if (=as though) she were waiting for someone.
她站在门口，仿佛在等人似的。(由as if或 as though引导的从句中可用虚拟语气)
方式状语从句由as(如同，按照)，as if (though)引导
as和like都有“像”的意思，as是连词，后面连接句子，like是介词后面可加名词、代词或名词性短语。
I did the work as others did. 相当于 I did like others.
You must do as I do.
as if(though)两者意义相同，从句谓语动词常用虚拟语气，但实现可能性较大，则用连接词。
It seems as if/though it’s going to rain.
They are talking as if/though they were old friends.
She treats me as if I were her brother.
例. You must do ______ I told you.
A. after B. before C. where D. as (D)
The students must do ______ the teacher told them.
A. as B. before C. after D. if (A)
(九)比较状语从句
比较状语从句常由比较状语从句由as卆s, not as(so)卆s, than, the+比较级，the+比较级引导等词引导：
It rains more often in Shanghai than in Beijing.上海下的雨比北京的多。
Our country is as big as the whole of Europe.我们的国家同整个欧洲一样大。
The result was not as/so good as I had expected.结果不如我预料的那么好。
The busier he is, the happier he feels.(常见句型)他越忙越开心。
(十)状语从句的省略
1. 时间状语从句中常见的紧缩形式：
Don’t speak until spoken to有人对你说话时你才说。
Once seen, it can never be forgotten.一旦被看见，它便不会被忘记。
While in Beijing, I paid a visit to the Summer Place.在北京时，我参观了颐和园。
Pressure can be reduced when needed.必要时压力非唯心减。
I prefer my milk a little sweet whenever possible.可能的话，我喜欢牛奶甜点。
He was a swimmer when a child.他小时侯就是一名游泳运动员。
She always sings while doing her work.她干活时总唱歌。
2. 条件状语从句中常见的紧缩形式：
Come tomorrow if possible.可能的话就明天来吧。
If so, you must get back and get it.如果这样的话，你必需把它拿来。
I’ll buy a TV set if necessary.如有必要我们就买一台电视机。
He has no money, if any, he will give us.他没有钱，如果有他会给我们的。
If in need, don’t hesitate to ask me for money. 如要钱，不必犹豫，向我要就是了。
The girl never give in unless wrong.这女孩不会屈服的，除非她错了。
Unless repaired, the machine is of no use.这台机器如不修便毫无用处。
3. 方式状语从句中常见的紧缩形式：
Some flowers shut up at night as if (they did this in order) to sleep.
有些花夜间收拢，好象为了睡眠一样。
The woman teacher hurriedly left the classroom as though (she was ) angry.
这位女教师匆匆茫茫离开教室，好象生气了。
Jane seemed as if (she was) good at everything.
琼好象擅长一切。
4. 其它状语从句的紧缩形式：
Though cold, he still wore a shirt.
天气虽然冷，但他还穿一件衬衣。
The man, while (he is ) well over eighty. Can walk faster than I.
这人虽然年过八十，却比我走得快。
Being blind(= As he was blind), he couldn’t see anything.
他瞎了，什么东西也看不见。
辨析：
1.as, when, while的区别
as, when, while都表示主、从句的动作或状态同时发生，但三者意义不尽相同。as和when引导的从句既可表示一点时间，也可表示一段时间，从句中的谓语动词既可以是持续性动词，也可以为短暂性动词，经常可以互换使用；while引导的从句通常表示一段时间，从句中宜用持续性动词作谓语。当从句中的谓语动词为持续性动词时，这三者可以通用(前面例句中已有体现)，再如：
Mother was worried because little Alice was ill, especially as / when / while father was away in France.
妈妈担心，因为小艾丽思病了，特别是当父亲远在法国的时候。
如果从句和主句要表示一个人的两个动作交替进行或同时完成时，则多用as，可译为“一边......，一边......”。例如：
He looked behind from to time as he went.
他一边走，一边不时地往后看。
As time goes on, it’s getting warmer and warmer..
随着时间的推移，天气变得越来越暖了。
I thought of it just as you opened your mouth.
你一张嘴我就知道你要说什么。(若表示两个短促动作几乎同时发生时，用as的场合多于when.)
当主从句之间表示转折或对比关系时，多用while, 不用as或when。如：
She thought I was talking about her daughter, while in fact, I was talking about my daughter.
她以为我在谈论她女儿，而事实上，我在谈论我的女儿。
如果表示从句的动作在主句的动作“之前”或“之后”发生时，多用when(=after), 不用as或 while。此外，when还含有“at that moment”的意思(= and then)，引起的句子不能放在句首，也不能用as, while来替换。例如：
He was about to leave when the telephone rang.
他正要离开，忽然电话铃响了。
We were watching TV when suddenly the lights went out.
我们正在看电视，突然灯灭了。
They had just arrived home when it began to rain.
他们刚到家，天就开始下雨了。
2．until与till及 not卽ntil / till的用法
(1) until和till都可表示“直到...为止”，与持续性动词的肯定式连用。如：
He waited until / till we finished our meal.他一直等到我们吃完饭。
(2) 当until和till表示“直到...才...”时，通常与短暂动词的否定式连用，这时，until和till也可用before代替。如：
I didn’t leave until / till / before she came back.直到她回来，我才离开的。
(3) be动词的肯定式和否定式都可以和until或till连用。
(4) until引导的从句可以放在主句之前或主句之后，但till从句一般不放在句首。如：
Until he told me, I knew nothing about it.他告诉我了我才知道。
当not until位于句首时，主句中的主语、谓语要使用倒装语序：
Not until she came back did I leave.
在强调句型中一般用until，不用till。如：
It was not until she took off her dark glasses that I realized she was a famous film star.
( It is /was ?that是常见的强调句型结构 )直到这位大明星摘下墨镜，我才认出她。
3．有时，the time(当的时刻), the moment(当的时刻), by the time(到时候为止), next time(下次), the first time(第一次的时候), the last time(上次的时候)，immediately(一就), instantly(一就), directly(一就)等词或词组以及hardly /scarcely厀hen(刚就), no sooner卼han(刚就)等关联词也可引导表示时间的状语从句。
Be sure to call on us next time you come to town.下次你进城一定来看我们。
By the time he was fourteen, Einstein had learned advanced mathematics all by himself.
(by意为“到...为止”，引起的从句中为一般过去时，主句中用过去完成时)
爱因斯坦到十四岁时就自学完了高等数学。
She rushed into the room immediately / the moment she heard the noise.
她一听到这声音，就冲进房间。
He left me a good impression the first time I met him.
我第一次见他时，他给我留下了好印象。
He had no sooner arrived there than he fell ill.
他刚到达那里就生起病来。
He had hardly finished when someone rose to refute his points.
他还没全说完，就有人起来反驳他的论点。
She had scarcely fallen asleep when a knock at the door awakened her.
她刚要睡着，忽然敲门的声音把她惊醒。
当hardly, scarcely, no sooner位于引起的句子的开头时，常用倒装语序。上面的例句可以依次改写成：
No sooner had he arrived there than he fell ill.
Hardly had he finished when someone rose to refute his points.
Scarcely had she fallen asleep when a knock at the door awakened her.
值得一提的是，这三组关联词引起的句子中，前面常用过去完成时，后面用一般过去时。
4．if和unless的用法
一般情况下，unless相当于if卬ot，可以互换。如：
I won’t let you in unless you show me your pass = I won’t let you in if you don’t show me your pass.
如果你不出示通行证，我就不让你进来。
但是，在下列情况下，两者是有区别的。
(1) unless引导真实条件句，if卬ot可以引导真实条件句或非真实条件句。
(2) unless从句中有否定词时，不能换成if卬ot结构。
(3) 如果主句描述的是情感或情绪活动方面的内容，if卬ot结构不能换成unless。
如：I’ll be quite glad if she doesn’t come this evening.
(她今晚如果不来我很高兴。)
(4) unless表示唯一条件，不能用and连接重复使用，if卬ot则可以。
5．because, since, as, for的区别
(1) 在这四个连词中，because语气最强，它引导的从句表达的是未知的新信息，也是该主从复合句中的焦点，一般都置于主句之后(也可以放在主句之前，用逗号隔开)。在回答”why”引导的特殊疑问句时，一般只能用because；在强调结构”It is/was 卼hat ”中，也只能用because。此外，在关联词“not 卋ut ”结构中，也用because引导的原因状语从句。例如：
It’s because he helped you that I’m prepared to help him.
正是因为他帮助过你，所以我乐意去帮助他。
--Why didn’t you phone me last night?你昨天夜里为什么没给我打电话？
--Because I didn’t want to disturb you.因为我不想在夜里打扰你。
He decided to give up the chance of going aboard, not because he did not want to but because his wife was ill.
他决定放弃出国的机会，不是因为他不想去，而是因为他妻子病了。
(2) since和as语气不如because强，as的语气最弱。他们引导的从句大多置于句首，有时放在主句之后(as从句在复合句中的位置更为灵活)，表达的往往是已知信息，即所指的原因是人们已知的客观事实，所以，复合句的重心在主句，不在从句。例如：
Since you have no license, you are not allowed to drive.
因为你没有驾驶执照，所以不允许你开车。
As he was not well enough, I had to go without him.
由于他身体欠佳，我只好不带他去了。
(3) for的语气不及because, since, as强，为并列连词，引导的分句常放在主句之后，从句前通常用逗号，表示说话者为所做的推断和预测提供理由，或对前一分句进行补充和解释。如：
It must have rained last night, for the ground is wet.
for分句表示说话者推断“昨晚天下雨”的理由。此时，because不能替代for，因为地湿不是造成下雨的直接原因。
原句可改为：The ground is wet, for / because it rained last night.