一、定语从句基本概念
定语从句通常在英语复合句中充当定语的作用,在简单句中,定语往往用来修饰代词、名词或名词性短语,例:
Tom is a handsome boy. Tom是个英俊的男孩。
There is a good boy. 有个乖男孩。
将以上的两句转换为定语从句则为:
Tom is the boy who is handsome.
There is a boy who is good.
二、定语从句中两大要素
了解了定语的作用之后,现在进入定语从句的正式学习。想要辨别定语从句,必须了解定语从句的两大要素:关系代词(或关系副词)、先行词。
本节重点讲解由关系代词引导的定语从句,下一节将为大家带来关系副词引导的定语从句。
首先为大家简单例举一个定语从句。
He is a good person who would like to help anyone. 他是一个好人,肯帮助任何人。
其中person就是先行词,who则为关系代词
who是用来指代这个先行词person,因此称为关系代词。此外,who只能做“人”关系代词,比如boy、girl、people等。
除了who之外,关系代词还有whom、whose、which、that
其中,值得注意的是,当定语从句修饰一个“人”时,选择关系代词必须了解先行词在从句中的位置才能做出决定,我们可以用拆分复合句的方法来判断。例: 
1.He is a good person who would like to help anyone. 他是一个好人,肯帮助任何人。
拆分后:
He is a good person.
The person would like to help anyone.
拆分后可以发现,先行词在第二句中做主语,因此用who.
2.He is the man whom I met yesterday.
拆分后:
He is the man.
I met the man yesterday.
拆分后可以发现,先行词在第二句中做宾语,因此用whom.
当需要使用修饰“物”的关系代词时,例句是这样的:
1.This is a car which(that) is red.
拆分后:
This is a car.
The car is red
拆分后发现,先行词在第二句中做主语.
2.This is the book which you gave me yesterday.
拆分后:
This is the book.
You gave me the book yesterday
拆分后发现,先行词在第二句中做宾语
3.This is the room in which you were born.
拆分后:
This is the room.
You were born in the room
拆分后发现,先行词在第二句中做宾语。特别注意,当第二句中动词之后跟一个介词,在写定语从句时必须把介词提到关系代词之前。
最后一个,当关系代词要指代“人”或“物”的所有格(属格)时,例句是这样的:
This is the bike whose brake was damaged(the brake of which was damaged) 这辆自行车的刹车坏了。
拆分后:
This is the bike.
The bike‘s brake was damaged.或The brake of the bike was damaged.
先行词The bike在第二句中做定语,什么的刹车坏了?The bike的刹车坏了。修饰这个刹车(the brake)