定语从句，一个简单句跟在一名词或代词后(先行词)进行修饰限定，所以叫做定语从句。在主句中充当定语成分。那么你知道定语从句的用法吗?下面跟着小编一起来学习一下，希望对大家的学习有所帮助!
一、基本概念：
在复合句中，修饰某一名词或代词的从句叫定语从句。如：
Do you know the man who spoke at the meeting just now?
That is the house where he lived ten years ago.
定语从句所修饰的词叫先行词;定语从句一般用关系代词或关系副词来引导，关系词放在先行词与定语从句之间起连接作用，同时又作从句中的一个成分。
引导定语从句的关系代词有：that, who, whom, whose, which;
关系副词有：when, where, why.
二、关系词的用法：
(一)关系代词的用法：
1. 作主语用who, which和that, 如：
He is the man who/that lives next door.
The train which/that has just left is for Shenzhen.
2. 作宾语用whom, who, which, that, 如：
The man (whom/who/that) we have just seen is a famous writer.
Where is the book (which/that) I bought last week?
注：在非正式文体中，用于指人的关系代词who whom, that 通常可以省略，但在正式文体中通常用whom, 不可省略;用于指物的关系代词which和that 在非正式文体中也通常省略，但在正式文体中一般不省略。
3. 作定语用whose, 如：
(a) He is the man whose car was stolen last week.
(b) It was a meeting whose importance I did not realize at that time.
注：“whose +名词中心词”这一结构在定语从句中既能作主语(如上a句)，又能作宾语(如上b句)。whose 的先行词常用来指人，但有时也可以用来指具体事物或抽象概念，这时可以与of which 结构互换，词序是：“名词+of which”，如：
They came to a house whose back wall had broken down.. (= the back wall of which)
He’s written a book the name of which I’ve completely forgotten. (= whose name)
4. 作表语只用that ，它既可以指人，也可以指物，但时常省略。如：
He is no longer the man that he used to be.
This is no longer the dirty place (that) it used to be.
(二)关系副词的用法：
1.when 指时间，在从句中作时间状语，它的先行词通常有：time, day, morning, night, week, year 等。如：
I still remember the time when I first became a college student.
Do you know the date when Lincoln was born?
注：when时常可以省略，特别是在某些句型和某些时间状语中。如：
Each time he came, he did his best to help us.
But help never stopped coming from the day she fell ill.
2.where指地点，在从句中作地点状语。它的先行词通常有：place, spot, street, house, room,
city, town, country等，如：
This is the hotel where they are staying.
I forget the house where the Smiths lived.
注：where有时也可以省略。如：
This is the place (where) we met yesterday.
3. why指原因或理由，它的先行词只有reason。如：
That is the reason why he is leaving so soon.
注：why时常也可以省略。如：
That is the real reason he did it.
(三) 使用关系副词应注意下列几点：
1. 这三个关系副词在意义上都相当于一定的介词+which结构：
when = on (in, at, during…) + which;
where = in (at, on…) + which;
why = for which. 如：
I was in Beijing on the day when (=on which) he arrived.
The office where (=in which) he works is on the third floor.
This is the chief reason why (=for which) we did it.
2. 当先行词是表时间的time, day等和表地点的place, house等时，一定要注意分析从句的结构，如果缺少主语或宾语时，关系词应该用which或that, 缺少时间状语或地点状语时，才能用when或where，试比较：
I’ll never forget the day when my hometown was liberated.
I’ll never forget the days which/that we spent together last summer.
His father works in a factory where radio parts are made.
His father works in a factory which/that makes radio parts.
3. when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.限制性定语从句与非限制性定语从句
1.限制性定语从句说明先行词的`情况，对先行词起限定作用，与先行词关系十分密切，不可用逗号隔开，也不可省略，否则全句意义就不完整。如：
This is the telegram which he refers to.
Is there anything (that) I can do for you?
2.非限制性定语从句只是对先行词作补充说明，没有限定作用，它与先行词的关系比较松散，因而不是关键性的，如果省略，原句的意义仍然完整。这种从句在朗读时要有停顿，在文字中通常用逗号与主句隔开。如：
This note was left by Tom, who was here a moment ago.
As a boy, he was always making things, most of which were electric.
引导非限制性定语从句的关系词有：who, whom, whose, which, when 和 where，不可以用that和why。
另外，非限制性定语从句从意义上讲，相当于一个并列句，在口语中使用并不普遍，在日常生活中，人们通常用并列句或简单句来表达。如：
I told the story to John, who later did it to his brother.
= I told the story to John, and he later told it to his brother.
Yesterday I happened to see John, who was eager to have a talk with you.
= Yesterday I happened to see John and he was eager to have a talk with you.
3.两种定语从句的内涵不同，限制性定语从句具有涉他性，而非限制性定语从句具有 唯一性，这在理解和翻译时应特别注意。试比较：
All the books there, which have beautiful pictures in them, were written by him.
All the books there that have beautiful pictures in them were written by him.
His brother, who is eighteen years old, is a PLA man. (只有一个)
His brother who is a PLA man is eighteen years old. (不止一个)
4.有时，非限制性定语从句所修饰的不是某一个词，而是整个主句或是主句中的一个部分，这时一般采用which或as来引导。如：
He passed the exam, which/as he hoped he would.
注：(1)as引导的从句可以放在主句之前，而which引导的从句只能放在主句之后。
They are hollow, which makes them very light.
As is known to all, Taiwan is a part of China.
(2)从意义上讲，which指前面主句的内容;而as指代的是作为一般人都知道的常
识性的东西，因此常译成“就象… …那样”。
(3)如果定语从句的内容对主句的内容起消极作用，则用which，而不用as，如：
She stole her friend’s money, which was disgraceful.
He tore up my photo, which upset me.
5.在正式文体中，以the way为先行词的限制性定语从句通常以in which或 that 引导，如：
The way in which you answered the questions was admirable.
但在非正式文体中，人们通常省略in which或 that :
The way (in which) he spoke to us was suspicious.
I don’t like the way (that) you laugh at her.
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