一、主语从句（subject clause）
在主句中用作主语的主谓结构称之为主语从句。
例句：
That he will come to the discussion is certain.
他来参加讨论是确定的。
That the moon moves round the earth is well known to all of us.
月球绕地球转动，这是我们大家都熟知的。
When the meeting is to be held
has not yet been decide.
会议什么时候召开还没有决定。
主语从句放在句首，句子常常显得比较笨重，因此通常可以把it放在句首，作形式主语，而将主语从句放在后面。例如上面的句子可以分别改写为：
It is certain that he will come to
the discussion.
It is well known to all of us that
the moon moves round the earth.
二、宾语从句（object clause）
在主句中作谓语动词、介词及非谓语动词的宾语的主谓结构称之为宾语从句。
在引导宾语从句时，从属连词that在口语中和非正式文本中常省略。
1. 动词后的宾语从句
We know that a parrot can’t really
speak.
我们知道鹦鹉不会真的说话。
He wants to tell us what he thinks.
他想告诉我们他所想的事情。
Knowing that it was going to rain,
they decided to work inside the house.
知道要下雨了，于是他们决定在室内工作。(现在分词knowing的宾语从句)
I want to know whether/if you still
work in the factory.
我想知道你是否还在工厂工作。（不定式to know的宾语从句）
The club will give whoever wins a
prize.
获胜者俱乐部将颁奖。
Up to now we can’t say whether his
theory can stand the test.
到目前为止我们还不能说他的理论是否经得住考验。
2. 形容词的宾语从句
有些形容词可以用that引导宾语从句，表示说话人对某一事物的态度并带有感情色彩。常见的这类形容词有：
afraid,amazed,astonished,aware,certain,confident,delighted,glad, grateful,happy, proud,sad,sorry,sure,surprised等。
I am glad that you have come.
你来了，我真高兴。
I am afraid that you are wrong on
this point.
恐怕你在这点上是错误的。
He is quite confident that he will
pass the examination.
他很有信心通过这个考试。
三、表语从句（predicative clause）
在主句中担当表语的主谓结构称之为表语从句。
One idea is that fish is the best
brain food.
有一种看法认为鱼是最好的补脑食品。
The problem is where we can
hold our meeting.
问题是我们可以在哪儿举行会议。
My question is how information
is stored in the long-term memory.
我的问题是信息是怎样储存在长期记忆中的。
That is what he really wants.
那就是他真想要的东西。
It seems that everything goes
smoothly.
似乎一切都进行得很顺利。
四、同位语从句
同位语从句用于对前面出现的名词作进一步说明，一般用连词that引导，由于先行名词的意义不同，也可用whether,who,when,where,what,why,how等引导。
常见的先行名词有：
fact,idea,belief,news,hope,conclusion,evidence,suggestion,order,problem,report,decision.
有时由于谓语较短，将同位语从句位于谓语之后。
如：
I had no idea how many books I
could borrow at a time.
The news came that their team
had won the championship.
名词性从句的用法及定义
1．that 引导主语从句时，that 没有意义，但不能省略。
It worried her a bit that her hair was turning gray.
她的头发正在变白，这使她很不安。
that引导主语从句，it作形式主语，that不能省略。
That she is a rich woman is known
to us all.
众所周知，她是个富有的女人。
这是that 引导主语从句，that 不能省略。这句话可以改为用it 作形式主语的句型。
2．从句作主语时，多数情况下由 it 作形式主语，而把主语从句放在后面，尤其是谓语部分（包括宾语）较短的情况下。
例：
①It wasn’t very clear what she
meant.
不清楚她是什么意思。
②It is important that he should
come on time.
他按时来是很重要的。
③It is true that that man on the left is a well-known writer here.
左边那个人是本地的一位著名作家，这是真的。
这里，第一个that 引导主语从句，是单纯的连词，无词义，不作句子成分。第二个that 是指示代词，作句子成分，是man 的定语。
3．whether 既可以引导主语从句也可以引导宾语从句，但if不能引导主语从句。whether 后面可以加or not, 而if 不能与or not 连用。作介词宾语时不用if.
如：
①Whether I knew John doesn’t
matter.
= It doesn’t matter whether I knew
John.
我是否认识约翰没有关系。
②Whether or not she’ll come isn’t
clear.
= Whether she’ll come or not isn’t
clear.
= It isn’t clear whether ….
她是否来还不清楚。
It 动词 从句
seem,appear,happen,look,matter,
make,strike,occur
It appeared that he had a happy
childhood.
看来他有一段幸福的童年。
It made us very happy that she was saved.
她能化险为夷令我们大家很高兴。
It is 形容词 从句
true,strange,necessary,important,
certain,wonderful,possible,likely,probable
It is certain that free medical care
will be given to mostpeople in our city.
我们城市的多数人将享受免费医疗，这是一定的。
It is obvious that he has been treated.
很明显他已经被款待了。
It is 名词 从句
fact,surprise,pity,honor,
common knowledge
It is common knowledge that the
moon cannot give out light.
月亮不会发光，这是常识。
It is a surprise that you gave such
an answer to the question.
你对这个问题作了这样的回答，令人吃惊。
It be 分词 从句
said,reported,believed,known,
decided,thought,expected, announced
It is said that Jack has been to
Europe.
据说Jack去过欧洲。
It was reported that a new park will be built.
据报道将要建造一个新的公园。
需要注意的是，作为形式主语的it并无实际意义，只是为了满足语法上的需要，避免句子头重脚轻，它代替的是句子的逻辑主语，而真正主语由从句或不定式充当。形式主语一直都是高频考点，同学们需要多多练习。
从句：定语从句的简化规律
（一）改用“不定式”或“不定式短语”
如果定语从句的时态与主句的时态具有同时性（包括谓语有情态动词）或之后性，则可以用“关系代词或关系副词＋不定式”来简化，或直接用“不定式”来修饰先行词。
We moved to the country so that the children would have a garden in
which they could play in.
我们搬到了乡下，好让孩子们有个花园在里面玩。
改为：
We moved to the country so that the
children would have a garden in which to play.
（二）改用“介词短语”
介词短语替代定语从句有两种方式：
(1)省略“关系副词＋主语＋be动词”，或“关系代词＋be动词”；
(2)根据从句的意思改编。
We have never forgotten the days
(when we were) at college.
我们从来没有忘记在大学对书的日子。
I don’t know the person (who is) in
your office.
在你办公司的那个人我不认识。
He is not a person who likes to
haggle over every ounce.
改为：
He is a person above personal
interests.
他不是一个斤斤计较的人。
（三）改用“现在分词短语”和“过去分词短语”
“现在分词短语”作后置定语
此项要明白三点：
（1）“现在分词短语”与前面的名词一定是主谓关系；
（2）它隐含的时态为与谓语动词同一阶段的时态。例如：谓语是一般现在时或将来时，现在分词所隐含的是现在时、现在正在继续时；如果谓语动词为一般过去时或将来时，现在分词所隐含的时态为过去时、过去正在进行时；
（3）being＋-ed表示“正在进行时的被动语态”。如果信息的中心在什么时候可以用现在分词呢？
当被修饰的名词为“不定代词”、“泛指意义的名词”或“专有名词”，可用现在分句短语作后置定语由于主语是泛指，句子的意思往往表达的是一条“道理”或一件“事实”，所以它们的隐含时为“一般现在时”，此时就可以用分词短语作后置定语。为了看清分词所隐含的时态，配上定语。
为了大家看得明白，配上定语从句，把分词所替代的时间展示出来
Anyone touching that wire will get
an electric stock.
任何人碰到那根电线就会触电。
=Anyone who touches that wire will get an electric stock.
注：虽然被修饰的词是泛指意义的词，但是如果从句里的时态不是同步，则不可以用“现在分词”去作后置定语，只能用“定语从句”。
Do you know anybody who has lost a dog?
你知道有谁丢了一只猫？
定语从句所修饰的先行词可以是名词或代词，也可以是一个句子。定语从句通常位于先行词之后，由关系代词或关系副词引导。
限制性定语从句
限制性定语从句修饰先行词，对先行词起修饰作用，紧接先行词之后，无逗号，若省去，原句意思不完整。
引导定语从句的关系代词有who,whom,whose,which,that等。
who,whom,whose用于指人，whose有时也可指物，相当于of which；which用于指物；that既可指人也可指物，但只用于限制性定语从句中。
如：
The computers and cables which
make up the Internet are owned
by people and organizations.
Those who live alone or who are
sick may have trouble in getting
close to other people.
The girl whose parents died in an
accident is living with her
grandmother.
1)当先行词是all,anything,everything,something,nothing等不定代词。
That is all that I've heard from him.
He's the first person that I'm going
to interview this afternoon.
2)关系代词的省略
在从句中作宾语的关系代词常可省略。关系代词紧跟介词，作介词宾语时不可用that，只可用which或whom引导从句，并且不可省略。
如：
This is one of those things with which we have to put up.
This is one of those things (which\that) we have to put up with.
3)引导定语从句的关系副词有when,where,why等。
关系副词在从句中作状语，意义上相当于一个“介词 which”的结构。
如：
No one knows the reason why(=for which) he was so angry that day
* 非限制性定语从句
非限制性定语从句既可修饰先行词，也可修饰整个主句，起补充说明作用，与主句之间有逗号隔开，若省去，原句意思不受影响。不可用that引导非限制性定语从句。关系词不可省略。
如：
Every object has a gravitational pull,which is rather like magnetism.
“介词 which\whom\whose”引导的定语从句
“介词 which\whom\whose”可引导限制性定语从句，也可引导非限制性定语从句，该结构中介词的选择取决于从句谓语动词的固定搭配，或先行词的习惯搭配。
如：
This is the computer on which he spent all his savings.
It is written by a person with whom we are all familiar.
*as引导的定语从句
as引导的定语从句主要用于“such...as”及“the same...as”的结构中，代替先行词是人或物的名词。as引导非限制性定语从句时，代替整个主句，从句可位于主句之前、之后或中间。
如：
These are not such problems as can be easily solved.
(as代替先行词problems)
As is mentioned above,no single company or group can control what happens on the Internet.(as代替主语）
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。
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?
他就是想见你的人吗？（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在句中作主语）
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）
We have never forgotten the days (when we were) at college.
我们从来没有忘记在大学对书的日子。
I don’t know the person (who is) in
your office.
在你办公司的那个人我不认识。
状语从句
✩地点状语从句
引导地点状语从句的连词是where,wherever.
✩原因、结果和目的状语从句
1）引导原因状语从句的从属连词有：because,as,since,now(that),seeing that,considering that,in that等。
2)引导结果状语从句的连词有：
so...that, such...that , so that,that,so等。
Eg.Mickey Mouse is so attractive that the children are reluctant to leave.
3)引导目的状语从句的连词有：
so that,in order that,for fear that,lest等，
从句常使用may,might,can,could,would等情态动词。
Eg. We got up early this morning so that we could catch the first bus to the railway station.
✩条件和让步状语从句
1）引导条件状语从句的连词和词组：
if,unless, as(so) long as,
on condition that,in case,
provided(providing) that, supposing等。
Eg. As long as you have the right equipment,you can use a telephone line to transmit computer data.
2)引导让步状语从句的连词和词组：
though,although,whether,
even though,even if,no matter what
whatever (whenever,wherever,however....) 等。
though,even if等引导状语从句可转换成含有as的部分倒装结构，具有强调意义。
其结构为“形容词（副词、动词、名词） as 主语 谓语”。
Eg. No matter what you may say,I would not change my mind.
✩时间状语从句
引导时间状语从句的从属连词和词组有：
when,whenever,while,as,after,before,since,till,until,once等。
eg. We have learnt quite a lot about it since we came here.
状语从句常用引导词
✧时间状语从句
常用引导词：
when、as、while、as soon as、before、after、since、till、until
特殊引导词：
the minute、the moment、the second、every time、immediately、the day、 directly、no sooner…than(一……就……)、hardly…when(刚一……就……)、scarcely…when(几乎没有…的时候)
✧地点状语从句
常用引导词：where
特殊引导词：wherever、anywhere、everywhere
✧原因状语从句
常用引导词：because、since、as、for
特殊引导词：seeing that、now that、in that、considering that、given that
✧结果状语从句
常用引导词：so…that、such…that
特殊引导词：such that、to the degree that、to the extent that、to such a degree that
✧目的状语从句
常用引导词：so that、such that
特殊引导词：to the degree that、to the extent that、to such a degree that、in order that
✧条件状语从句
常用引导词：
if、unless、whether(whether…or not)
特殊引导词：
as/so long as、only if、providing/provide that、supposing that、in case that、on condition that
✧让步状语从句
常用引导词：
though、although、even if、even though
特殊引导词：
as(用在让步状语从句中必须要倒装)、while(一般用在句首)、no matter…、in spite of the fact that、whatever、whoever、wherever、whenever、however、whichever
✧方式状语从句
常用引导词：as、as if、how
特殊引导词：the way
✧比较状语从句
常用引导词：as(同级比较)、than(不同程度的比较)
特殊引导词：
the more…the more…、just as…、so…、A to B is what/as C is to D、no…more than、not so much A as B
区分 that 与 what 引导的从句
一、引导主语从句
that与what都可引导主语从句，that在从句中不作句子成分，但不能省略。what 在从句中可作主语、宾语、表语等，不能省略。
如：
What he said at the meeting was
very important．
他在会上所说的非常重要。（宾语）
What surprised us is that he did it
alone．
使我们吃惊的是他一个人做了那项工作。（主语）
That he did it alone surprised us．
他独自完成了那项工作使我们感到吃惊。（that用来引导主语从句，在句中不作成分）
二、引导宾语从句
that与what都可引导宾语从句，that在从句中不作句子成分，一般情况下可以省略，但当有两个以上的宾语从句时，只能省掉第一个that。what 在从句中可作主语、宾语、表语等，不能省略。
如：
They stopped to see what was happening．
他们停下来看发生了什么事情。（主语）
The teacher got angry because of what the boy had done．
那个男孩子做的事情让老师很生气。（what在宾语从句中作宾语）
We must believe that each one of us is able to do something well and that when we discover what this something is we must work hard at it until we succeed．
我们必须相信，我们每一个人都能把某件事情办好；而且，当我们发现这事情是什么的时候，我们就必须努力干下去，直到成功为止。（第一个that可省略，第二个that不能省略）
三、引导表语从句
that与what都可引导表语从句，that在从句中不作句子成分，且不能省略；what 在从句中可作主语、宾语、表语等，不能省略。
如：
Mary is no longer what she used to be．玛丽不再是从前那样了。（what在表语从句中作表语）
The question is what we should do to prevent him from going．
问题是我们怎样做才能阻止他去。（what在表语从句中作动词do的宾语）
The reason why he didn’t come today is that his mother is ill．
他今天没来的原因是他母亲病了。（that只起连接作用）
四、引导同位语从句
that与what都可引导同位语从句修饰表示抽象概念的名词，对所修饰的名词的具体内容进行详细阐述。这类名词有：
fact, idea, news, hope, belief, promise, thought, suggestion, proposal等。that在从句中不作句子成分，但不能省略。what 在从句中可作主语、宾语、表语等，不能省略。
如：
I have no idea what we should do
next．我不知道我们下一步该做什么。（宾语）
He made a promise that he would study hard．他许诺要努力学习。(that只起连接作用)
The boy expressed his hope that he would be a pilot when he grows up．
那个男孩儿表达了他长大后想当一名飞行员的愿望。（that只起连接作用）
五、引导定语从句
that可引导定语从句且在定语从句中作主语或宾语，that既可指人也可指物。that在从句中作宾语时可省略。
如：
This is one of the buildings that were built last year．
这是去年建的楼房之一。（that在定语从句中作主语，指物，不能省略。）
注意：
what不能引导定语从句。
如不能说：
1.He did all what he could to save the patient．
2．All what he needs is more time．
应将句中的what改为that，或去掉what，还可以将以上两句中的all去掉。
六、引导状语从句
so．．．that, such ..．that, so that结构引导状语从句。what不能引导状语从句，但whatever, no matter what可引导让步状语从句。
如：
Put the little plants in the shade so that the sun won’t burn them.
请把幼苗放在阴凉处以免太阳晒枯它们。
Don’t believe him no matter what he says．
无论他说什么，都不要相信他。
