定语从句基本知识
所谓从句，就是一个主谓结构相当于整个句子(这样的句子叫复合句)的一个成分，因此，从句不能单独使用。在复合句中修饰名词或代词、作定语的句子叫定语从句。定语从句是中国人学英语的难点之一。
其实定语从句很有规律，总结如下:
在关系代词中that既可指人又可指物、既可作主语又可作宾语，因此，除了在非限定性定语从句中，用that一般不会出问题。
关系副词的用法比较单一，它们从句中只起状语的作用，表示时间的就用when，表示地点的就用where，而why只修饰一个词，即reason。
定语从句所修饰的词叫“先行词”，因为它总是处在定语从句的前头，比定语从句先行一步。
引导定语从句的词叫关系词，包括关系代词和关系副词。
关系代词：
who，which，that作从句的主语
whom，which，that作从句的宾语(可省略)
whose从句中作定语
关系副词：
When, where, why 在从句中作状语
一、关系代词引导的定语从句
1. That:代表的先行词为人或物，在从句中做主语，宾语和表语。
He is the man that is good at English.
There are some films that I’d like to see.
He isn’t the boy that he used to be.
注意：that引导定语从句时：
1）作宾语时that可省略。
2）That前不可用介词。
在定语从句中，下列情况的关系词宜用that而不用which
1) 当先行词被all, every, no , some, few , little, much, both等修饰时，例如：
This is all that I want to say at the meeting.
2) 当先行词被the last , the very 和the only修饰时。例如：
This is the very pen that I am looking for.
3) 当先行词有序数词时。例如：
You are the first person that I want to ask for.
4)当先行词为anything、everything、nothing时，例如：
Everything that can be done has been done.
5) 先行词有最高级形容词修饰时，例如：
Edison was one of the greatest inventors that ever lived.
6) 当先行词既指人又指物时。例如：
The professor and his achievement that I heard about are admired by them .
2.which: 代表的先行词为物，在从句中做主语，宾语
The film which I saw last night was wonderful.
Guilin is a city which has a 200-year history.
注意：1）作宾语时，which可以省略。
2）Which 也可以代替前面的一个句子或句中的一部分
定语从句中用用which而不用that的情况
1). 在非限制性定语从句
They have three houses, which are built of stone.
2). 当关系代词前有介词时
This is the factory in which we once worked.
3). 当关系代词后面带有插入语时
Here is the English grammar book which, as I have told you, will help improve your English.
I've bought you some books which I think may interest you.
3.who; :代表的先行词为人，在从句中做主语和宾语。
Where is the man who was here?
He is the man who I talked with just now.
4.whose; 代表的先行词为人或物，在从句中做定语。
I saw the man whose face is red.
This is the window whose glass was broken.
5.whom: 代表的先行词为人，在从句中做宾语.
Where is the man whom I met this morning ?
只用who, whom.而不用that的情况
如果先行词是anyone, anybody, everyone, everybody, someone, somebody, those, ones等时，关系代词应该用who 或whom，例如：
Is there anyone here who will go with you?
6. 在same, so和such之后，定语从句用as引导，例如：
I’ve never heard such stories as he tells. 我从来没听说过他讲的这种故事。
I shall be surprised if he does this in the same way as I do.
注意：
1). 当先行词由the same修饰时，偶尔也用that引导定语从句，但是和由as所引导的定语从句意思不同
①She wore the same dress that she wore at Mary’s wedding.
②She wore the same dress as her young sister wore.
2). So/ such … as 与so/ such … that 的区别
This is so interesting a book that I can't put it down.
This is so interesting a book as I can't put down.
二、关系副词引导的定语从句
关系副词引导定语从句在从句中分别表示时间．地点或原因。关系副词when在从句中充当时间状语，where 充当地点状语，why充当原因状语。
1. when指时间，在定语从句中做时间状语
The time when we got together finally came.
注意：当先行词为by the time ,any time , the way, every time, the first time ,the last time 时，关系词不用when而用that或者省略
This is the last time that I shall give you a lesson.
By the time he was 14 he had learned advanced mathematics
2. where指地点，在定语从句中做地点状语
Shanghai is the city where I was born.
3. why指原因，在定语从句中做原因状语
Please tell me the reason why you missed the plane.
