一、定语从句
在复合句中， 修饰名词或代词的从句叫定语从句，被修饰的名词或代词叫先行词，引导定语从句的有关系代词 who, whom, whose, which, that等和关系副词where, when, why等，关系代词和关系副词在定语从句中担任句子成份。
1.由who引导的定语从句中，who用作主语， 如：This is the boy who often helps me.
2.由whom引导的定语从句中，whom用作宾语，如：The man whom you are waiting for has gone home.
3.由whose引导的定语从句中，whose用作定语 ，如 ：Do you know the girl whose skirt is white?
4.由which引导的定语从句中，which用作主语或谓语动词的宾语或介词的宾语，如：
5.由that引导的定语从句中，that可以指人或物，在从句中作主语或谓语动词的宾语，但不能放在介词后面作介词宾语，如：
The book that I bought yesterday was written by Lu Xun.
6.由when, where, why引导的定语从句，如:
I don't know the reason why he was late.
This is the place where we have lived for 5 years.
I'll never forget the day when I met Mr Li for the first time.
注意：先行词是表示地点时，如果从句的谓语动词是及物的，就用 that(which)，如果从句的谓语动词是不及物的，就用where引导。This is the house Which /that he has lived in for 15 years.(Where he has lived for 15 year.)
7. 限制性定语从句和非限制性定语从句
(1)限制性定语从句是句中不可缺少的组成部分，主句和从句之间不用逗号分开。引导非限制性定语从句的关系代词有who, whom, whose, which, of which等，这些关系代词都不能省略。
(2)非限制性定语从句是对主句先行词的补充说明，没有这种从句，不影响主句意思的完整，一般用逗号把主句和从句分开， 关系代词用 which,不用that;指人时可用who,如 ：I have two brothers, who are both students.
二、状语从句
由从句担任的状语，在句子中可修饰谓语（或其它动词）、形容词、副词或是整个句子，它可以用来表示时间、地点、原因、目的、结果、条件、方式、比较、让步等。状语从句是一较大的语法项目，也是近几年高考题中常见的一个重要试点。高考中已考查了时间、让步、地点、条件、目的等状语从句，这些从句仍是今后高考热点，应作充分准备。同时对方式状语从句也应引起重视。
1、时间状语从句
表示时间的状语从句可由when, as, while, whenever, after, before, till (until), since, once, as soon as (或the moment ), by the time, no sooner than, hardly (scarcely) when, every time等引导。
When I came into the office, the teachers were having a meeting.
He started as soon as he received the news.
Once you see him, you will never forget him.
No sooner had I gone to bed than I went to sleep.
2、原因状语从句
原因状语从句是表示原因或理由的，引导这类从句的最常用的连词是because, since, as , now that（既然）等，for 表示因果关系时（它引导的不是从句）为并列连词，语气不如because强。
He is disappointed because he didn't get the position.
As it is raining, I will not go out.
Now that you mention it, I do remember.
3、地点状语从句
引导地点状语从句的连词是where 和wherever等。
Sit wherever you like.
Make a mark where you have a question.
4、目的状语从句
引导目的状语从句最常用的词（组）是so, so that（从句谓语常有情态动词）, in order that, in case（以防，以免）等。
Speak clearly, so that they may understand you.
She has bought the book in order that she could follow the TV lessons.
He left early in case he should miss the train.
5、结果状语从句
结果状语从句是表示事态结果的从句，通常主句是原因，从句是结果。由so that （从句谓语一般没有情态动词）, so that, such that等引导。
She was ill, so that she didnt attend the meeting.
He was so excited that he could not say a word.
She is such a good teacher that everyone admires her.
6、条件状语从句
条件状语从句分真实性（有可能实现的事情）与非真实性（条件与事实相反或者在说话者看来不大可能实现的事情）条件句。引导条件状语从句的词（组）主要有if, unless, so (as) long as, on condition that, so (as) far as, if only ( = if )。注意：条件从句中的if 不能用whether替换。
If he is not in the office, he must be out for lunch.
You may borrow the book so long as you keep it clean.
So far as I know（据我所知）, he will be away for three months.
You can go swimming on condition that ( = if ) you dont go too far away from the river bank.
If he had come a few minutes earlier, he could have seen her.
7、让步状语从句
让步状语从句可由although, though, as, even if (though), however, whatever, whether or, no matter who (when, what, ) 等引导。注意：as引导的让步状语从句一般是倒装的。
Though he is a child, he knows a lot.
Child as he is, he knows a lot.
Whatever ( = No matter what ) you say, Ill never change my mind.
8、方式状语从句
方式状语从句常由as, as if (though), the way, rather than等引导。
You must do the exercise as I show you.
He acted as if nothing had happened.
9、比较状语从句
比较状语从句常用than, so (as) as, the more the more等引导。
I have made a lot more mistakes than you have.
He smokes cigarettes as expensive as he can afford.
The busier he is, the happier he feels.
三、名词性从句
在句子中起名词作用的句子叫名词从句 (Noun Clauses）。 名词从句的功能相当于名词词组, 它在复合句中能担任主语、宾语、表语、同位语、介词宾语等，因此根据它在句中不同的语法功能，名词从句又可分别称为主语从句、宾语从句、表语从句和同位语从句。
引导名词性从句的连接词可分为三类：连词：that（无任何词意）；whether, if（均表示“是否”表明从句内容的不确定性）；as if ,as though（均表示“好像”，“似乎”）。
以上在从句中均不充当任何成分
连接代词：what, whatever, who, whoever, whom, whose, which. Whichever, whomever
连接副词：when, where, how, why
具体分类
1．主语从句
作句子主语的从句叫主语从句。主语从句通常由从属连词that，whether，if和连接代词what，who，which，whatever，whoever以及连接副词how，when，where，why等词引导。that在句中无词义，只起连接作用；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，在从句中充当从句的成分。例如：
What he wants to tell us is not clear. 他要跟我们说什么，还不清楚。
Who will win the match is still unknown. 谁能赢得这场比赛还不得而知。
2．宾语从句
名词句用作宾语的从句叫宾语从句。引导宾语从句的关联词与引导主语从句表语从句的关联词大致一样，在句中可以作谓语动词或介词及非谓语动词的宾语。
（1） 由连接词that引导的宾语从句
由连接词that引导宾语从句时，that在句中不担任任何成分，在口语或非正式的文体中常被省去，但如从句是并列句时,第二个分句前的that不可省。例如：
He has told me that he will go to Shanghai tomorrow. 他已经告诉我他明天要去上海。
（2）用who，whom, which, whose, what, when, where, why, how, whoever, whatever, whichever等关联词引导的宾语从句相当于特殊疑问句，应注意句子语序要用陈述语序。例如：
I want to know what he has told you. 我想知道他告诉了你什么。
3．表语从句
在句中作表语的从句叫表语从句。引导表语从句的关联词与引导主语从句的关联词大致一样，表语从句位于连系动词后，有时用as if引导。其基本结构为：主语 系动词 that从句。例如：
The fact is that we have lost the game. 事实是我们已经输了这场比赛。
That's just what I want. 这正是我想要的。
4． 同位语从句
同位语从句说明其前面的名词的具体内容。同位语从句通常由that引导，可用于同位语从句的名词有advice，demand，doubt，fact，hope，idea，information，message，news，order，problem，promise，question，request，suggestion，truth，wish，word等。例如：
The news that we won the game is exciting. 我们赢得这场比赛的消息令人激动。
I have no idea when he will come back home. 我不知道他什么时候回来。
