一. 定语从句的基本定义放在名词或代词后面，由关系代词或关系副词引导的修饰该名词或代词的从句叫定语从句。
被修饰的词叫先行词。
The boy who is reading is Tom.Hospital is a place where a doctor works.二. 关系词的分类1、关系代词关系代词在定语从句中作主语、宾语、表语和定语，常用的关系代词有：that, which, who, whom, whose 2. 关系副词关系副词在定语从句中作状语，常用的关系副词有：when, where, why三. 关系代词的基本用法和注意点①who指人,在定语从句中作主语或宾语。
作宾语时，可省略。
The man (who) I talked with is our teacher.A person who steals things is called a thief.②whom指人,在定语从句中作宾语，可省略。
The man (whom) I nodded to is Mr. Li.③which 指物，在定语从句中作主语或宾语。
作宾语时，可省略。
These are the trees which were planted last year.This recorder （which）he is using is made in Japan.④that 指人或物，在定语从句中作主语或宾语。
作宾语时，可省略。
A plane is a machine that can fly.He is the man (that) I told you about.⑤whose指人或物, 在定语从句中作定语。
不可省略。
This is the little girl whose parents were killed in the great earthquake.We live in a house whose windows face south..2、关系代词的用法注意点(1) that和which都可以指物，但以下5种情况只能用that 不能用which。
①当先行词中有人又有物时。
如：Do you know the things and persons that they are talking about?②当先行词为不定代词all, one, few, little, no, some, any, everything, nothing, nobody, none等时。
如：This is all that I want from the school.③当先行词被only, just, very, right, last等修饰时。
如：This is the very book that I am looking for these days.④当先行词被最高级修饰时。
如：The TV tower is the highest building that has been built in this city.⑤当先行词被序数词修饰时。
如：The first lesson that I learned will never be forgotten.(2) that和who都可以指人，但下面两种情况，多用who。
①先行词为all, anyone, one, ones等时。
如：All who heard the news were excited.②先行词为those, he和people时。
如：Those who want to go please sign your names here.He who does not reach the Great Wall is not a true man.(3) whose引导的定语从句注意点①whose引导定语从句，其后应紧跟名词，构成名词短语。
②whose与它所修饰的名词一起可以作介词的宾语。
如：The boss in whose department he worked had heard the news.他工作所在部门的老板已经听说了这个消息。
③whose引导的定语从句，其先行词既可以指人也可以指物。
④whose的先行词指物时，可用of which代替，但语序不同，即whose+名词= the+名词+of which，或= of which + the + 名词。
如：The novel whose title (= the title of which或of which the title) is Red and Black is very interesting.⑤whose的先行词指人时，可用of whom代替，但语序不同，即whose+名词= the+名词+of whom，或= of whom + the + 名词。
如：The boy whose mother (= the mother of whom或of whom the mother) is a doctor is my friend.(4) 关系代词在从句中作主语时，从句的谓语动词的人称和数必须与先行词保持一致。
如：Those who are against the plan put up your hands.Tom is one of the students who were praised by the teacher yesterday.Tom is the only one of the students who was praised by the teacher yesterday.巩固练习：1. 用定语从句合并句子(1) The scientist is very famous in the world.We met her yesterday.The scientist who we met yesterday is very famous in the world.whomthatØ(2) The dress is new. She is wearing it.The dress which she is wearing is new.thatØ巩固练习：2. 用适当的关系词填空1.The girl __________is standing next to our teacher is her daughter.2. The girl _________________our teacher is talking with is a famous singer.3. The girl________ mother is a teacher can speak English very well.4. I can’t find the bo ok ____________is borrowed from the library.5. I can’t find the book ________________you lent to me.四. 介词+which/ whom引导的定语从句1. 介词的选用原则：（1）根据定语从句谓语动词的习惯搭配来决定。
This is the book on which I spent 8 dollars.This is the book for which I paid 8 dollars.(2) 根据先行词的习惯搭配来决定。
I remember the day on which I joined the Party.I remember the days during which I lived there.2. 当介词放在关系代词前面时，关系代词只能用whom(指人)或which(指物)，且关系代词不能省略。
The man with whom you talked just now is my neighbor.I can’t find the pen with which I was writing .3. 当介词位于定语从句末尾时，可用which/that(指物), who/whom/that(指人)作从句中介词的宾语.而且作介词宾语的关系代词可以省略。
Dad is a person__(whom/who/that_ I can easily talk to.Is this the play _(which/that) you were talking about just now?4. 在一些固定搭配的动词短语中，由于动词和介词不可分割，因此不能把介词置于关系代词之前。
如：This is the watch (that/ which) I am looking for.The babies (who/ whom/ that) the nurse is looking after are very healthy.5. 先行词是the way，意为“方式，方法”时，引导定语从句的关系词用that/ in which或省略。
I didn't like the way _______________ she talked to me.The way _________________he teaches English is interesting.1. when用关系副词when时，先行词指时间，when在定语从句中作时间状语，when可换成“介词+关系代词”。
如：I still remember the day when (= on which) I first came to Nanjing.My father was born in the year when (= in which) World War Ⅱbroke out.2. where用关系副词where时，先行词指地点，where在定语从句中作地点状语，where可换成“介词+关系代词”。
如：This is the farm where (= on which) we worked when we were young.The school where (= in which) his mother teaches is in the west of the city.3. why用关系副词why时，先行词指原因，why在定语从句中作原因状语，why可换成“介词+关系代词”。
如：There are several reasons why (= for which) the boys should be punished.Tom couldn’t give the teacher the reason why (= for which) he was late for school.4. 关系副词的用法注意点(1)当先行词为time，表示“次数”时，应用关系词that 或省略。