英语中从句总共可以分为三种：
1.名词性从句（用句子代替名词）
2.定语从句（用句子代替形容词）
3.状语从句（用句子代替副词）
名词在句子中可以作为：主语、宾语、表语、同位语
*语序：名词性从句一律用陈述语气
因此名词性从句就又有四种：主语从句、宾语从句、表语从句和同位语从句。
主语从句(subject clause)
一．定义
主语从句（subject clause），顾名思义充当主语的从句一般放在开头 并且位置在谓语动词前面
例如：That he finished writing the composition in such a short time surprised us .
这句话的结构就是最基础的：主＋谓＋宾
主语：That he finished writing the composition in such a short time
谓语：Surprised
宾语：us
二．连接词
引导主语从句的连词主要有：
1、从属连词：that，whether( 连接作用，不充当成分，不能省略，that无意义，whether为"是否")
That he will come is a certain.
Whether it will please them is not easy to say.=It is not easy to see whether it will please them.
注：if有时也可以引导主语从句，只能用在it做形式主语的句型中.If引导的主语从句不能放在句首，通常whether的使用范围更广
It is unclear if he likes the present.
2、连接代词：在句子中充当主语、宾语、表语、定语
who(谁:主、宾、表)，whoever(无论谁:主、宾)，whom(谁:宾语)，whose(谁的:定语)，what(什么:主、宾、表，无范围)，whatever(无论什么:主、宾)，which(哪一个，有范围)whichever(连接作用，充当成分)
What seems easy to some people seems difficult to others .
Which side will win is not clear.
3、连接副词（在句子中充当状语）：when，where，how，why，whenever，wherever，however（连接代词和连接副词在句中既保留自己的疑问含义，又起连接作用，并在句中充当一定的句子成分）
Why he did it remains a mystery.
How he become a great scientist is known to us all.
三．时态
从句时态不受主句时态的影响
Who will be our monitor hasn't been decided yet.
现在还没有决定谁会成为我们的班长。（主句将来时，从句完成式）
四．注意点
①主语从句大多数情况下视为第三人称单数，但也有例外。由what引导的主语从句视情况而定
That price will go up is certain.
价格持续上涨是确定的
Whether we will go for an outing tomorrow remains unknown.
我们明天是否会去郊游仍旧未知。
What caused the accident remains unknown.
事故的起因是未知的
②如果主语从句放在句首表示“是否”的时候，不能用If只能有Whether
If Mary really heard him is really doubtful（false）
值得怀疑的是，是否玛丽真的听了他的话（错误）
whether Mary really heard him is really doubtful（correct）
值得怀疑的是，是否玛丽真的听了他的话（正确）
五．位置
（1）置于句首（通常放在谓语动词之前）
（2）用it作形式主语
为了防止句子头重脚轻，通常把形式主语it放在句首位置，真正主语搁置于句末（It+谓语+宾/表+从句）
（1)It+be+表语(名词，形容词，过去分词)＋主语从句
That he will win the match is certain. → It is certain that he will win the match.
他一定会赢得这场比赛的。
(2)It+不及物动词＋主语从句
It seemed(happened,doesn't matter,has turned out)that...
It doesn't matter whether she will come.
(3)It+及物动词(被动语态)＋主语从句
It has been decided that the exhibition will not open on Sundays.
六．主语从句不可位于句首的五种情况
（1）If引导的主语从句
it is uncertain if he will leave for Beijing tomorrow. （right）
If he will leave for Beijing tomorrow is uncertain（wrong）
他明天是否离开北京是不确定的
（2）It is said , (reported) …结构中的主语从句
It is said that President Jingo will visit our school next week. (right)
That President jin will visit our school next week is said. (wrong)
据说主席金下周会参观我们学校
（3） It happens…, It occurs… 结构中的主语从句
It occurred to him that he failed in the examination. (right)
That he failed in the examination occurred to him. (wrong)
他考试不及格
（3）It doesn’t matter how/whether …结构中的主语从句
It doesn’t matter whether he is wrong or not. (right)
Whether he is wrong or not doesn’t matter. (wrong)
他是否错了已经无关紧要了
七、名词性从句的做题方法
1、首先判断是不是主语从句？（看从句是否在动词前，或者看是不是it做形式主语的主语从句？）
2、其次看从句是否缺成分：如果不缺成分选从属连词；如果缺主干成分，选连接代词；如果缺状语成分，选连接副词。
3、看句子缺什么意思？不缺意思选that；缺什么意思，选什么词？如果缺什么选what缺无论哪一个选whichever等。
宾语从句
一、定义
宾语从句是在复合句中作宾语的名词性从句；通常放在主语谓语动词（及物动词）或介词之后。宾语从句必须是陈述语序;谓语动词、介词、不定式、v-ing形式后面都能跟宾语从句;有些形容词之后，也可以带宾语从句。
宾语从句分为三类:动词的宾语从句、介词的宾语从句、形容词的宾语从句
二、连接词
从属连词：that(口语中可省略)whether，if
连接代词:what,who,which,whatever，whoever等
连接副词：how，when，where，why等
(一)that引导的宾语从句(在非正式场合下可以省略)
可省略that的情况:
1、主语＋及物动词＋that宾语从句
Lucy said (that)he was feeling better.
2、主语＋系动词＋形容词＋that宾语从句
I am afraid (that) I've made a mistake.
不可省略that 的情况:
① that引导的宾语从句和主句之间有插入语时
I think,first of all,thatwe must believe in ourselves.
我认为，尤其重要的是，我们必须对自己有信心。
② 宾语从句为主从复合句且从句位于主句之前时
He said that if he came back early,he could some for the discussion.
他说，如果早回来的话，他会来参加讨论会的。
③that引导的宾语从句做直接宾语时，不可省略
She told me that she would accept my invitation
④并列的that宾语从句,第一个that可省,第二个that不可省略.
I think (that)it will clear up tomorrow and that they will go out for a picnic.
我认为明天会是晴天，他们会出去野餐
⑤当it作形式宾语，后接that引导的宾语从句时
We have made itclear that our destination is to learn knowledge.
我们已经表明，我们的目的是学知识。
⑥主语＋及物动词＋to sb +that从句
He explained to us that he had failed to catch the first bus.
(二)if/whether引导的宾语从句
If/whether引导宾语从句时，在从句中不作任何成分，但有具体的含义“是否”。一般情况下，if/whether引导宾语从句时可以互换，但介词后不能用if引导宾语从句，另外不定式前一般不用if引导
I worry about whetherI hurt her feelings.
我担心是否伤害了她的感情。
(三)连接代词或连接副词引导的宾语从句
S＋VT+连接代词/连接副词+S+V＋其他成分
例句：Miller urges job seekers to open their minds to other possibilities beyond whatthey are currently doing.
米勒敦促求职者开拓思路，去发现他们现在所做工作之外的可能性。
例句：The police asked me howthe accident happened.
警察问我事故是如何发生的。
例句：He didn't tell me whenhe would come back.
他没告诉我他什么时候再回来。
例句：Do you know whohas won the champion in the marathon this year ?
三、宾语从句在句中的位置
(一)动词后
① 大多数动词可以带宾语从句
例句：Like most people,I've long understood thatI will be judged by my occupation,that my profession is a gauge people use to see how smart or talented I am.
像大部分人一样，我早就明白人们会通过我从事的工作来判断我，人们通过从事的工作来判断我有多么聪明，多么智慧。
例句：He told me thathe would go to the college next year.
他告诉我他明年上大学。
② 有些“动词+副词”结构后可跟宾语从句
有些“动词+副词”结构如figure out，work out，find out，point out等后可跟宾语从句。
例句：Scientists point outthat the globe is getting warmer and warmer.
科学家指出地球正在逐渐变暖。
例句：Can you figure outwhat the poet really means in this poem ?
你能理解诗人在这首诗中真实用意吗？
③ 动词短语也可带宾语从句
例句：Make surethat all the lights are off before you go to bed.
睡觉前必须确认所有的等都关了。
例句：We should keep in mindthat success will mainly depend on our own hard work.
我们应该牢记，成功主要依靠我们自己的努力工作。
注意！动词find，feel，think，consider，make，believe，guess，suppose，assume等后有宾语补足语时，则需要用it作形式宾语，而将that宾语从句后置。
例句：I think itnecessary that we take regular exercise every day.
我认为每天坚持有规律的锻炼是有必要的。
例句：I've made ita rule that I keep diaries every day.
我规定自己每天都要写日记。
动词hate，like，take，owe，have，take for granted等表示“痛恨，喜欢，认为”的词或短语和see to“注意，留意”后有宾语补足语时，需要用it作形式宾语，而将宾语从句后置。
例句：I hate it whenthey talk with their mouth full of food.
我讨厌他们满嘴食物时说话。
例句：Please see to it thatthe door is safely locked before you go.
请在走之前确保门都锁好了。
(二）介词后
介词后一般常用wh-类词引导宾语从句。
例句：She is always thinking of howshe can do more for her children.
她总想着如何才能为孩子做得更多。
例句：We are thinking about whetherwe admit students into our club.
我们正在讨论是否让学生加入我们的俱乐部。
用that引导的从句作介词宾语时，需要用形式宾语it替代，然后将that从句放在最后。
例句：You may depend on it thatwe will overcome the difficulty.
(三）形容词后
常可接宾语从句的形容词有sure，certain，glad，pleased，happy，afraid，surprised，satisfied，sorry等表示“情感”等的形容词。
例句：We are pleased thatwe have won the game once again.
再次赢得了比赛，我们都很高兴。
四、宾语从句的否定转移
主句谓语动词是think，believe，imagine，suppose，consider，expect，fancy，guess等(一些主观性的猜测和认为)，且主句的主语是第一人称和一般现在时时，从句的否定一般要转移到主句上来。其反义疑问句一般与宾语从句一致。
例句：I don't thinkit's right to bad-mouth other people.（常用）
=I think it is not right to bad-mouth other people.（不常用）
我认为说别人坏话是不对的。
例句：I don't supposethat's his fault,is it ?
我认为那不是他的错，是不是？
表语从句
一、含义
表语从句是放在连系动词之后，在复合句中充当表语的句子，用来说明主语是什么或者怎么样。
二、连系动词
①be(is,am,are,was,were)
②感官动词(look,sound,taste,small,feel)
③表示状态(keep,remain)
④表示像的(seem,appear)
三、引导词：
>连接词：that, whether, as if/though(好像), because
>连接代词：who, whom, whose, which, what
>连接副词：when, where, why, how
>e.g.
that引导的表语从句
What I want to say is that I'm sorry.
My idea is that we will go to Shanghai for a visit.
总结1：当陈述句充当表语从句时，用that引导，that在从句中无成分，本身无任何意义，不可省略，只是起连接作用。
whether引导的表语从句
The question is whether it is worth doing.
The question is whether we can win them.
总结2：当一般疑问句充当表语语从句时，用whether引导，whether在句中不充当任何成分，但具有“是否”的意义，表示对陈述的事物不明确或不清楚。
由连接代词或连接副词引导
That is what he is worried about.
The problem is who we can get to replace her.
The question is how he did it.
That is where he was born.
总结3：当特殊疑问句充当表语从句时，还用原来的特殊疑问词引导，这类词引出表语从句时，要在从句中充当句子成分（一般充当主语，宾语，表语，定语或状语），并且有一定意义，不可省略。
三、时态
1、主句用现在时或将来时，从句可用任何时态，根据实际情况而定。
2、如果主句是过去的时态，那么从句时态一定要用想对应的过去的某种时态。
It is where he lives.
It is where he lived 10 years ago.
It looked as if was going to rain.
The question was whether his father would come back the next day.
The reason why he was late was that the train had already left.
四、注意事项
(1)the reason ...is that...(原因是...)
(2)That is because...(后跟原因，那就是因为...)
(3)That is why...(后跟后果，那就是为什么)
(4)It seems/louks as if...(看起来好像...)
>>as if/though引导表语从句时，在句中无成分，有意义，“似乎，好像”
He looks as if he were a rich man.（与事实不符，属于虚拟语气）
他看起来好像是个富翁。
It sounds as if someone is knocking at the door.（与事实相符，非虚拟语气） 听起来好像有人在敲门。
总结4：as if /though 引导表语从句时，要注意语气，与事实相符，要用陈述语气。与事实相反，谓动用一般过去式（be用were）；与过去事实相反用had done.
同位语从句
一、含义
什么是同位语？
一个名词或代词后面有时可以跟一个名词（或起类似作用的其他形式），对前者进行解释或补充说明，进一步说明它指的是谁、是什么等,说白了就是前面名词内容的延展
什么是同位语从句？
同位语部分由一个句子充当，那么这个充当同位语的句子就叫做同位语从句。
- The news that his child was safe eased his mind.
孩子平安的消息使他放心了。(句子"that his child was safe" 是 news 的同位语)
The question whether it is right or wrong depends on the result。
这个是对还是错要看结果。(句子"whether it is right or wrong" 是 question 的同位语)
二、先行词(抽象概念的名词)
1.消息：news,information,message,word
2.可能性：possibility
3.事实：fact,truth
4.问题：problem,question,doubt
5.想法：idea,thought,hope,wish
6.建议：advice,suggestion,proposal，recommendation,idea,motion
7.要求：request,demand,requirement,agreement,
insistence,agreement
8.命令：order,instruction,command
9.结论：conclusion
10.表安排决定:decision,plan,resolution
determation
（6、7、8为虚拟语气）
三、引导词
同位语从句的引导词：
1. 从属连词:that(无意义) whether(是否)
2. 连接代词：who, whom, whose, what
She has no idea what life would be like without her husband.
她不知道没有丈夫的生活会是什么样的。
He didn't answer the question whom he got help from.他没有回答他得到谁的帮助的问题。(whom引导同位语从句，在句中做from的宾语，所以要用宾格whom,不能用who)
I have no idea whose watch it is. 我不知道这是谁的表。（whose引导同位语从句,在从句中修饰watch）
3. 连接副词when, where, how, why
He has no idea when he will be back.他不知道什么时候回来。
They haven’t settled the question where they are going to spend their holiday.他们去哪里度假，这个问题还没有定下来。
I have no plan how I shall get in touch with my tutor.
怎样联系我的导师，我没有计划。
四、同位语从句的位置
1.跟在名词或代词后
2.分离同位语从句
通常来说同位语从句一般都紧接在与其同位的名词之后，但有时，为了保持句式的平衡，将同位语从句与被修饰的名词分离，其间出现其他成分，这种被别的词隔开的情况，就叫分离式同位语从句
例:
正常同位语从句：
- The news that these products will no longer be available in the market must be true.这些产品将不再在市场上销售的消息一定是真的。
分离式同位语从句：
- The news must be true that these products will no longer be available in the market.这些产品将不再在市场上销售的消息一定是真的。
常见的分离式同位语从句主要有以下 4 类，分别是：
1、被插入语拆散的同位语从句
2、被定语拆散的同位语从句
3、被状语拆散的同位语从句
4、被谓语拆散的同位语从句
- Nobody would stand out admitting the fact，for some reason，that they lost the game.由于某种原因，没有人会站出来承认他们输掉了比赛这一事实。
"for some reason" 是插入语，而"that ... game" 则是 fact 的同位语。
- I still remember the story，believe it or not，that we got lost on a rainy night.信不信由你，我仍然记得我们在一个雨夜迷路的故事。
"believe it or not" 是插入语，而 "that ... night" 则是 story 的同位语。
- There is a new problem involved in the popularity of private cars that road conditions need to be improved.
私家车的流行所带来的一个新问题就是路况需要改进。
"involved in the popularity of private cars"是 problem 的定语
- Nobody believed her reason for being absent from the exam that she had to meet his parents at the airport.没有人相信她缺考是因为得去机场接她父母。
介词短语"for being absent from the exam" 作定语修饰 reason
- We’ve just heard a warning on the radio that a strong typhoon was coming toward this area.
我们刚刚从收音机里听到警报，说一个强台风正向这个地区逼近。
"on the radio" 是一个方式状语
- We heard the news last night that schools would reduce the burden on students.
我们昨晚听到这个消息：学校要给学生们减负。
"last night" 是一个时间状语
4、被谓语拆散的同位语从句
- A few years ago the belief became general that orange juice and milk should never be drunk at the same meal.
几年前人们普遍相信橙汁与牛奶绝不能在一起食用。
"became general" 是谓语短句
五 、同位语从句和定语从句的区别
1同位语从句和先行词是同等的关系；而定语从句是修饰先行词。
2 that在同位语从句中无词义，不充当句子成分，只起连接作用；而在定语从句中充当主语宾语等句子成分。
3 whether, how, what可以引导同位语从句，不能引导定语从句.
4 who, whom, which, when,where,why用来引导可以引导同位语从句，保持原来疑问词的含义，而他们引导定语从句时，不具有疑问词的含义。
