一、定语从句的定义
在复合句中，修饰名词或代词的从句叫定语从句， 被修饰的名词或代词叫先行词， 引导定语从句的引导词分为：关系代词 who, whom, whose, which, that等，和关系副词where, when, why等， 关系代词和关系副词在定语从句中担任句子成份，不可省略。
1.由who引导的定语从句中，who用作主语，
如：This is the boy who often helps me.
2.由whom引导的定语从句中，whom用作宾语，
如：The man whom you are waiting for has gone home.
3.由whose引导的定语从句中，whose用作定语，
如：Do you know the girl whose skirt is white?
4.由which引导的定语从句中，which用作主语或谓语动词的宾语或介词的宾语。
如：The room in which there is a machine is a workshop（车间）.
The river which is in front of my house is very clean. This is the pen which you want.
二、有关系代词引导的定语从句
whom, which用作介词宾语时，介词可放在 whom、which之前，也可放在从句原来的位置上；但在含有介词的动词固定词组中，介词只能放在原来的位置上。
如：He is the very person whom we must take good care of.
引导非限制性定语从句时，必须用关系代词which，不用that。
如：I have lost my bag, which I like very much.
(3)关系代词在句中作主语时，从句的谓语动词的人称和数必须和先行词保持一致。
5.由that引导的定语从句中，that可以指人或物，在从句中作主语或谓语动词的宾语，但不能放在介词后面作介词宾语，即介词后只能用which,不能用that.
如：The book that I bought yesterday was written by Lu Xun.
1.关系词指物时，只用that不用which的情况 ★
① 先行词是all, everything, anything, nothing, no one, little, few, much, some . none等不定代词时。
All that can be done has been done. 所有能做的已经做了。
② 先行词被the only, the very ,the just, the right, the last, the same, all, any, some, no, few, little, much等修饰时。
This is the very book that I am looking for. 这正是我要找的那本书。
③ 先行词是序数词、形容词最高级 或 被序数词、形容词最高级所修饰时。
This is the best film that I have seen. 这是我所看过的最好的电影。
④ 为避免重复, 主句是who或者which引导的特殊疑问句时。例如:
Who is the man that is making a speech? 正在演讲的那个人是谁？
⑤ 先行词既有人又有物时。
They talk about persons things that they met .
⑥ 在there be 句型中，只用that，不用which。
There is a stranger that want to see you. There are many books that he had read.
2.只用which而不用that的情况 ★
① 当关系代词前有介词，先行词指物时。例如:
This is the house of which the windows face south. 这就是窗户朝南的那座房子。
② 在非限制性定语从句中，当关系词表示事物时，只能用which。例如:
The plane landed safely, which made us very happy. 飞机安全降落，这使我们很高兴。
三、由关系副词when, where, why引导的定语从句，如： ◎ why=for which
I don't know the reason why he was late. ◎ where=in/ at/ on/ ... which
This is the place where we have lived for 5 years. ◎ when=during/ on/ in/ ... which
I'll never forget the day when I met Mr. Li for the first time.
注意：先行词是表示地点时，如果从句的谓语动词是及物的，就用 that(which)，如果从句的谓语动词是不及物的，就用where引导。This is the house which /that he has lived in for 15 years. (where he has lived for 15 year.)
四、限制性定语从句和非限制性定语从句
1、限制性定语从句是句中不可缺少的组成部分，主句和从句之间不用逗号隔开，引导限制性定语从句的关系代词有：who, whom, whose, which, of which等，这些关系代词都不可省。
2、非限制性定语从句是对主句先行词的补充说明，没有这种从句，不影响主句意思的完整性，一般用逗号将其与主句隔开，关系代词只用which,不用that; 指人时可用who.
Eg: I have two brothers, who both are both students.
五、如何简化定于从句 ＊＊＊
定语从句简化为形容词或形容词短语作后置定语。
Eg: My grandfather lives in a village which is far away from here.
→ My grandfather lives in a village far away from here.
定语从句简化为现在分词或现在分词短语作前置或后置定语。
Eg: The man who is standing under the tree is our English teacher.
→ The man standing under the tree is our English teacher.
I saw the house that was burning at that time.
→ I saw the house burning at that time.
定语从句简化为过去分词短语作后置定语。
Eg: I like to eat the cakes which are made by my mother.
→ I like to eat the cakes made by my mother.
定语从句简化为不定式作后置定语。
Eg: She is always the first person that comes to school. （主动）
→ She is always the first person to come to school.
The report which will be given tomorrow is very importance for us. （被动）
→ The report to be given tomorrow is very importance for us.
定语从句简化为what从句。
Eg: I couldn’t remember the words that he said.
I couldn’t remember what he said.
六、关系副词的省略
1、The time, every time, each time, the moment等后的关系副词可省略。例如:
By the time （when）he was fourteen years old, Einstein had learnt advanced math all by himself.
到十四岁时，爱因斯坦已经自学了高等数学。
2、在某些表示地点的名词后，关系副词有时也可省略.如the place等。例如:
This is the place（where）we met years ago. 这就是我们多年前见面的地方。
3、先行词the reason后面的关系副词可省略。例如:
The reason （why）he did that is quite clear. 他那样做的理由是非常清楚的。
七、例题精选，思维引导
1. Everyone has his aim in life. However, you can't get fat on one mouthful. Start with the easiest thing______ you can control
A. who B. that C. which
2. The story book_________ you lent me is very interesting.
A. which B. it C. what
3. Shirley is the girl_______ taught me how to use We-chat(微信).
A. whom B. which C. who
4. —Have you seen the documentary named A Bite of China (舌尖上的中国)?
—Yeah! It's the most funny one__________ I have ever seen.
A. that B. what C. which D. where
5. He is unlikely to find the school________ he taught 50 years ago.
A. where B. when C. how D. why
6. Yesterday Li Ming went to the village_________ his family lived ten years ago。
A. when B. which C. where D. that
翻页查看答案【解析】：
【解析】：
1、选B。先行词thing是物，且由最高级修饰，关系代词用that。
2、选A。先行词为The story book，指物，关系词which在从句中作lent的宾语。
3、选C, the girl作先行词，表示人，关系词在从句中作主语，故关系代词用who。
4、选A。先行词one前有最高级修饰，故关系词用that。
5、选A。句惫为:他不可能找到那所他五十年前任教的学校。先行词表示地点，关系词在从句中作地点状语，故用关系副词where。
6、选C。定语从句的先行词为the village, 关系词在从句中充当的是地点状语，故用关系副词where。
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