4、先行词：被定语从句修饰的名词、代词称为先行词。
关系代词引导的定语从句举例
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：
(1) 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）
(2) 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）
(1) 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。
(2) 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：
(1) 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）
(2) 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）
限定性定语从句
一、关系代词（在句中作主语、宾语或定语）
1. that既可代表事物也可代表人，which代表事物；它们在从句中作主语或宾语，that在从句中作宾语时常可省略关系词，which在从句中作宾语也可以省略。[eg：this is the book （which）you want。]
2而且，如果which在从句中作“不及物动词＋介词”的介词的宾语，注意介词不要丢掉，而且介词总是放在关系代词which的前边，但有的则放在它原来的位置
3. 代表物时多用which，但在带有下列词的句子中用that而不用which，这些词包括当先行词是anything, everything, nothing , none等不定代词时，或者是由every, any, all, some, no, little, few, much等修饰时等，这时的that常被省略 还有先行词前有序数词或形容词最高级修饰时,或先行词就是序数词或最高级时.以及先行词中既有人又有物时.还有句中前面有which时,都只能用that
4. who和whom引导的从句用来修饰人，分别作从句中的主语和宾语，whom作宾语时，要注意它可以作动词的宾语也可以作介词的宾语
5. whose是关系代词，修饰名词作定语，相当于所修饰成分的前置所有格.它引导的从句可以修饰人和物, 当它引导的从句修饰物体时, 可以与 of which 调换,表达的意思一样。
二、关系副词（在句中作状语）
关系副词=介词+关系代词
why=for which
where=in/ at/ on/ ... which (介词同先行词搭配)
when=during/ on/ in/ ... which (介词同先行词搭配)
1. where是关系副词，用来表示地点的定语从句。
2. when引导定语从句表示时间〔注〕值得一提的是，表示时间“time"一词的定语从句只用when引导，有时不用任何关系代词，当然也不用that引导。
By the time you arrived in London, we had stayed there for two weeks.
I still remember the first time I met her.
Each time he goes to business trip, he brings a lot of living necessities, such as towels, soap, toothbrush etc。
3. 当从句的逻辑主语是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing时，常用there is来引导
There is somebody here who wants to speak to you. 这里有人要和你说话。
关系代词引导的定语从句
1.who指人在从句中做主语
(1) The boys who are playing football are from Class One. 在踢足球的男孩们是一班的.
(2) Yesterday I helped an old man who lost his way. 昨天，我帮助了一个迷路的老人.
2. whom指人，在定语从句中充当宾语，常省略。（注：who和whom已无太大区别，基本可以通用。唯一区别是who可以做主语而whom不可以。）
(1) Mr. Liu is the person (whom) you talked with on the bus. 刘先生就是在公交车上和你聊天的那个人.
(2) Mr. Ling is just the boy whom I want to see. 凌先生恰巧就是我想见的那个男孩.
(3) The man who/whom you met just now is my friend. 你刚刚见到的那个人就是我的朋友.
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。
如果在从句中做宾语,就用whom或who.比如: He is the man whom/who I talk to. 他就是那个和我聊天的男人.
如果是在从句中作主语就只能用who.比如: He is the man who has an English book. 他就是那个有英语书的男人.
3. whose通常指人，也可指物，在定语从句中做定语。
(1) He has a friend whose father is a doctor.
(2) I once lived in a house whose roof has fallen in.whose指物时，常用以下结构来代替
(3) The classroom whose door is broken will soon be repaired.
(4) The classroom the door of which is broken will soon be repaired.
(5) Do you like the book whose color is yellow?
(6) Do you like the book the color of which is yellow?
4.which指物，在定语从句中做主语或者宾语，做宾语时可省略。
(1) Football is a game which is liked by most boys. 足球是大多数男孩都喜欢的游戏.
(2) This is the pen (which) he bought yesterday. 这是他昨天刚买的钢笔.
5. 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。
(5) The number of the people that/who come to visit the city each year rises one million.
(6) Where is the man that/whom I saw this morning?
关系副词引导的定语从句
1. when指时间，在定语从句中做时间状语
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.
2. where指地点，在定语从句中做地点状语
(1) Shanghai is the city where I was born.
(2) 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
(1) Please tell me the reason why you missed the plane.
(2) 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
(1) The reason why/ for which he refused the invitation is not clear,
(2) From the year when/in which he was going to school he began to know what he wanted when he grew up.
PS：that也不是万能的……
关系代词that 的用法
(1)不用that的情况
(a) 在引导非限定性定语从句时。
(错)The tree, that is four hundred years old, Is very famous here.
(b) 介词后不能用。
We depend on the land from which we get our food.
We depend on the land that/which we get our food from.
(2) 只能用that作为定语从句的关系代词的情况
(a) 在there be 句型中，只用that，不用which。
(b) 在不定代词，如：anything, nothing, the one, all, much, few, any, little等作先行词时，只用that，不用which。
(c) 先行词有the only, the very,the same,the last,just修饰时，只用that。
(d) 先行词为序数词、数词、形容词最高级时，只用that,不能用which。.
(e) 先行词既有人，又有物时。
(f) 先行词指物，在主句中作表语时．
(g) 为了避免重复．
(h)先行词是the way或the reason时，that可作关系副词，也可省略
(i) 主句的主语是疑问词who /which时
举例：
Is this the book that you borrowed in the library?
这是你在图书馆借的那本书吗？
Who that break the window should be punished．
谁打碎了窗户都要受到惩罚．
All that is needed is a supply of oil.
所需的只是供油问题。
Finally, the thief handed everything that he had stolen to the police.
那贼最终把偷的全部东西交给了警察。
[编辑本段]难点分析
（一）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，each等修饰时
(1) Have you taken down everything (that) Mr. Li has said?
(2) There seems to be nothing (that) seems impossible for him in the world.
(3) All that can be done has been done.
(4) There is little (that) I can do for you.
注意1：部分时候that可以省略，如部分例句将that用括号括住。
注意2：当先行词指人时，偶尔也可以用who
(4) 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，the same,the last 修饰时
(1) This is the very good dictionary that I want to buy,
(2) 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
(3) 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
(1) Who is the man that is standing there?
(2) 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?
7.当关系代词在定语从句中做表语
The village is no longer the one that it used to be 10 years ago.
8.当在there be句型中，通常情况下用that，不用which
详见度娘百科
参考资料：度娘百科