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）