定语从句 ，修饰一个名词或代词，或整个句子，被修饰的名词词组或代词即先行词。定语从句通常出现在先行词之后，由关系词引出。
关系词1.连接 2. 替代 3.作成分
关系代词有作主。宾。表。定：who, whom , that, whose等。
关系副词有：when, where, why（修饰the reason）等。
18.1 关系代词引导的定语从句
关系代词在句中充当主语、宾语、定语等成分。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 代替人作主语。宾 The man will succeed. He has a positive attitude.
2--whom代替人在定语从句中作宾语，介词后只能用whom
This is the person. I talked to the person just now.
3.which指代物,在定语从句中既可作主语也可作宾语
Thinking is the key. The key opens the doors of the world.
4 whose 用来指人或物，作定语,They rushed over to help the man whose car had broken down.
5., that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. 断，找，放
18.2 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）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。
18.3 判断关系代词与关系副词
方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
（对） This is the mountain village （which） I visited last year.
（对） I\'ll never forget the days （which） I spent in the countryside.
方法二： 准确判断先行词在定语从句中的成分（主、谓、宾、定、状），也能正确选择出关系代词/关系副词。
that ---- which
只能用that 做关系代词的情况
1.当先行词是不定代词时,如:All ,few, little, much, every, something, anything, everything, none, any等 There is little that we can do in such a short time.
2.当先行词被不定代词，或the only, the very, the same, the last等修饰时
This is the very dictionary that I want to buy.
3.当人和物合做先行词时they want all the things and people that are there.
4.当先行词被序数词或形容词最高级修饰时,或本身就是
This is the first place that we visit in London
5.在疑问词who、which、what开头的句子中，避免重复
Who is the man that is standing there?
6.主句是there be 结构，修饰主语的定语从句用that，而不用which.
只用which不用that
1. 在介词后，只用which this is the pen with which I wrote a letter.
2.先行词为that， those时，用which， 而不用that.例如：What’s that which is under the desk？
注意：（1）当定语从句中含有介词，介词放在句末时，who， that， which可省略，但介词在关系代词前时，只能用“介词+which/whom”结构。例如：This is the house in which we lived last year.这是我们去年居住的房子。
Please tell me from whom you borrowed the English novel.请告诉我你从谁那借的这本英文小说。
（2）含有介词的固定动词词组中，介词不可前置，只能放在原来的位置上。例如：
This is the person whom you are looking for. 这就是你要找的那个人。
(3) one of + 复数名词+定语从句与the only one of +复数名词+定语从句
He is one of the students who have been to Beijing.
8.关系代词的省略
⑴ 关系代词在定语从句中作宾语
Here is the book (which) the teacher mentioned yesterday.
第二篇：初三定语从句总结
定语从句
在复合句(包括主句和从句)中, . 定语从句必须放在被修饰的词之后.被定语从句修饰的名词或代词叫做先行词. 如:
·The man who lives next to us sells vegetables.住在我们隔壁的那个人是卖蔬菜的. ·You must do everything that I do.你必须做我所做的一切.
其中man 和everything 均为先行词,分别受到其后的定语从句who lives next to us 和that I do 的修饰.
初中阶段要掌握的是由that, which, who, whom 等关系代词引导的定语从句.关系代词可在从句中作主语,宾语或表语.通常which指事物,who指人(作宾语时用whom), that 既可指人也可指物. 但在使用时有所区别.
(一) 下列情况,.
1. 先行词是等不定代词或由不定代词时. 如:
·All that is worth doing should be done well.一切值得做的事都应该做好.
2. 时. 如:
·There is little money that I can spend on books. 我几乎无钱买书.
·The only thing that she could do was to go to the police for help. 她唯一能做的事就是去求助于警察.
3. . 如:
·We will never forget the first lesson (that) our chemistry teacher gave us. 化学老师上的第一课我们永远难忘.
4. . 如:
·What is the smallest thing that can be seen under a microscope? 显微镜下能看见最小的东西是做什么?
5. . 如:
·The visitor spoke highly of the children and the performances (that) they saw at the Children’s Palace. 来宾们高度评价他们在少年宫见到的孩子们及其表演.
6. 当主句为who 或which开头的特殊疑问句时, 为避免重复, that. 如:
·Which of us that knows any English doesn’t know the meaning of UFO? 我们懂英语的人中谁不知道UFO的意思?
7. 当关系代词在定语从句用. 如:
·Tom is not the boy (that) he used to be. 汤姆已不是过去的那个男孩了.
8. . 如:
·There is something that I must deal with right now. 我有事必须马上处理.
9. 等时, 用that, 如:
·The real problem with pollution is people- the way(that) people think about their environment. 污染的实质问题是人-人们在考虑其自身环境时就是这样想的.
(二) 下列情况, .
1. . 如:
·Let’s discuss the question, which we are interested in. 咱们讨论下这个问题, 这个问题我们大家都很感兴趣.
2. . 如:
·His house, for which he paid 10,000 Yuan ten years ago, is now worth.30,000 Yuan.他的房子现
在值三万元, 十年前他是花一万元买的.
(三) 下列情况, 定语从句须用who(whom)引导.
1. 当先行词. 如:
·Any who breaks the law will be punished. 任何人犯了法都会受到惩罚.
2. 先行词为. 如:
·Those who hadn’t bought the ticket for the train crowded in the waiting hall. 那些未买着票的人拥挤在候车室里.
3. , 但如直接
位于介词后作宾语时, 只能用whom. 如:
·The guest (who/ whom) I ‘ll first introduce to you is a little girl. 我首先要介绍给你们的客人是一位小姑娘.
·I met a few friends of mine, among whom one was my old classmate.
我遇见了几位朋友, 其中一位是我的老同学.