一、含义
在复合句中用一个句子做定语修饰前面名词或代词的从句叫定语从句 。
先行词:被定语从句所修饰的词
二、引导词
1.功能:关系词起连接作用，引导定语从句
在定语从句中充当成分——主语，宾语，状语，定语，表语。
2.关于指人还是指物
指人:who,whom，that
指物:which,that
3.分类:
关系代词：who，whom, whose, that ,which, as
①who:指人，在从句中做主语、宾语(可省略)
②whom:指人,在从句中做宾语(可省略)
当先行词指人:whose+n.=the+n.+of whom
③whose:指人或物，在从句中做定语
当先行词指物 :whose+n.=the+n.+of which=of which+the+n.
They came to a house whose back wall had broken down.
当先行词指人时:whose+n.=the+n+of whom=of whom+the+n.
④that:指人或物，在从句中做主语、宾语(可省略)、表语(可省略)
⑤which:指物，在从句中做主语、宾语(可省略)
关系副词：when，where，why
如果先行词是表示时间，表示地点，表示原因的词，那么引导词要用关系副词。
a.三个关系副词在意义上相当于"介词+which"结构
①when=on(at,during...)+which
when指时间，在定语从句中作时间状语，他的先行词为时间名词如time、 day 、date、morning、等。
注：当 occasion表示特定的时刻和场合即抽象意义的时间时，关系副词用when.
I still remember the time when I first become a college student.
②where=in(at,on...)+which
Where指地点，在定语从句中做地点状语，它的先行词通常有places、 sport、 street等。
This is the hotel where they are staying
The office in which he works is on the third floor.
注：当point、 situation、 case、 condition 、stage等表达“情况，境地，场合”等抽象意义的地点时，关系副词用where
③why=for which
the reason why + 从句 = for which
This is the reason why he is leaving so soon .
This is the reason for which he is leaving so soon.
先行词是reason且关系词在从句中作原因状语时，用why/for which引导，其中why只能引导限制性定语从句，for which可引导非限制性定语从句
b.当先行词是表示时间的time,day等和表示地点的place,house等和表示地点的place，house等时，一定要注意分析从句的结构，分析从句缺的是什么成分？
①关系词在句中作主语，宾语时，只能选that/which.关系词在句中作状语用where
This is the factory that/which makes paper
This is the factory(that/which) we visited yesterday.
This is the factory where paper makes.
②尽管先行词是指地点的名词，关系词在句中作主语，宾语，但非限制性定语从句只能用which
This is the school, which he visited.
③ 尽管先行词是指地点或地点的名词，关系词在句中作主语或宾语，但非限制性定语从句只能用which
This is the school, which he visited.
Wednesday is the day, which comes before Thursday.
④when和where既可以引导限制性定语从句，也可以引导非限制性定语从句。而why只能引导限制性定语从句。
三、关系词的特殊用法
只用that的情况:
①当先行词为不定代词词something, anything, nothing, everything，all,little,much时
Is there anything that I can do for you?
②当先行词被all, some, any，much,each,little,few,every,no修饰时
These are all the things that I have done today.
③当先行词被the only, the very,the same,thelast 修饰时
This is the only computer that he often turns to for help.
④当先行词被序数词，形容词最高级修饰时
This is the best room that you can see here.
⑤time 作先行词，前面有序数词或last修饰时
This is the last time that I’ll give you pocket money.
⑥尽管先行词指人，但关系词在句中作表语时。
He is no longer the child that he used to be 20 years ago
⑦以 who和which开头的特殊疑问句，尽管先行词指人，为了避免重复
Who is the person that is sitting on the ground ?
⑧当先行词包括人和物时。
We talked about the person and things that we remembered.
只能用which，who,whom的情况
① 在非限制性定语从句中，只能用which指物，用who/whom指人
This is my favorite pen, which I bought yesterday.
He has a son，who has gone abroad for further study.
② 先行词不是一个词，而是前面整个句子的概念时
The boy is very polite, which makes his parents happy.
在"介词+关系代词"引导的定语从句中只能用which指物，whom指人
This is the pen with which I often write.
③ 先行词本身是that，指物时关系词用which，先行词为those，one，he指人时，多用who.
those who respect others are usually respected by others
as引导的定语从句
1、As引导的限制性定语从句中，名词前有such, so ,as, the same修饰时,关系代词用as不用which。
He is not such a fool as he looks.
2、as引导的非限制性定语从句中as有正如像的含义其可以放在主句前也可以放在主句后，可以指代整个主句。
which无"正如"的意思，引导的从句只能放在主句后.
They won the game, which we hadn't expected.
① as 单独引导定语从句。
As we all know (=As is known to us all), Yao Ming is a famous basketball player.
② the same …as… 与…一样
I have the same idea as you.
③ such/so… as… 和…一样
Don’t read such a book as you can’t understand.
④ as…as… 和…一样
In this library, you can borrow as many books as you can.
介词+which/whom
1. 介词+which/whom
① 介词的选择根据下面四种情况
a. 根据定语从句中的谓语动词的搭配
Who is the person with whom you shook hands just now?
b. 根据定语从句中的形容词的搭配
In learning English, he had two things about which he was not sure.
c. 根据定语从句所修饰的先行
This is the bike by which I go to school.
d. 根据句意。
This is the train on which he works.
e.固定短语中的介词不能提前，类似的固定短语有look for 、look after、 take care of listen to 、look forward to、 pick up 等
This is the important thing which you should pay attention to.
② 如果关系词指人，选whom，如果关系词指物，选which。
2. 不定代词+of+which/whom
常用的不定代词有：both, neither, either(两者之一)，all, none, many, most, some, any
Mr. Li has two sons, both of whom are college students.
There are 10.000 books in this library, most of which are interesting.
3. 数词，分词，百分数+of+which/whom
There are 50 students in our class, two thirds of whom are girls.
4. the+名词+of+which=whose+名词
He has just bought a magazine, the cover of which (=whose cover) is missing.
5. 介词+whose+名词
This is our school teaching building, on whose top there is a red flag.
四、主谓一致
①关系代词在从句中作主语时，从句谓语动词单复数根据先行词而定（those who are...）
②one of + 限定词 + 名词复数 + 定语从句（谓语动词用复数）
e.g.She's one of my best friends that are studying here.
③the only/the very/the right one of + 限定词 + 名词复数 + 定语从句（谓语动词用单数）
e.g.She's the only oneof my best friends
that is studying here.
五、定语从句的分类
限制性定语从句:对先行词起修饰限制作用，如果去掉，主句意思就不完整，从句和主句的关系十分密切 ，关系词前不能用逗号分开
The accident happened at the time when I left.
非限制性定语从句:对先行词做附加的说明，与主句的关系不十分密切，较松散。从句和主句之间用逗号分开，相当于一个插入语，不能用that和why引导,关系词不能省略,引导非限制性的定语从句的关系词有：which，as,who, when, where, whom, whose.
His mother ，whom he loved deeply， died ten years ago .
六、定语从句的做题方法
1、首先判断是否为定语从句的结构（从句跟在名词或代词之后，对对名词/代词起修饰作用）。
2、其次关系代词在从句中充当成分，作主语、宾语、表语、定语和状语。
3、如何选择先行词？（根据先行词指人/物以及关系词在从句中充当的成分）
4、看一看有没有特殊情况？（用that的情况，用which的情况）
