定语从句（Attributive clauses）
在句中修饰名词或代词的从句，因其修饰作用相当于形容词，故称形容词性从句，即通常所说的定语从句。被定语从句修饰的词叫先行词。引导定语从句的有：
（1）关系代词： 先行词为人：who, whom, that, whose
先行词为物：which, that, whose
（2）关系副词：when, where, why
注意： 关系词起三个作用：①连接先行词和定语从句②替代先行词③在从句中担任成分 what不能引导定语从句。定语从句一般紧跟在先行词后，但有时也被一个短语隔开。 例如：I was the only person in my office who was invited.
I. 关系代词引导的定语从句
关系代词所代替的先行词是人或物的.名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。 定语从句的构成: 先行词 + 关系词 + 从句
人 物
主格 Who/ that Which/ that
宾格 Whom/ that/ who Which/ that
定语 whose Whose: …of which
（1）who, whom, that
这些词代替的先行词是人的名词或代词，在从句中作主语和宾语。关系代词充当宾语可以省略。例如：
Is he the man who/that wants to see you? 他就是你想见的人吗?(who/that在从句中作主语) He is the man (whom/ that) I saw yesterday. 他就是我昨天见的那个人。（whom/that在从句中作宾语）
（2）whose 用来指人或物，在定语从句中作定语，。 例如：
Please pass me the book whose cover is red.（指物）
The lawyer whose name is Wang Jin lives in Nanjing.（指人）
（3）which, that所代替的先行词是事物的名词或代词，在从句中可做主语、宾语等。例如： Great changes which / that have never been seen before appears in the countryside.
（which / that在句中作主语）
The package (which / that) you are carrying is about to come unwrapped. 你拿的包快散了。（which / that在句中作宾语）
关系副词when, where, why在从句中充当状语，分别可表时间、地点或原因。
I will never forget the day when I first came to Beijing.
This is the house where Lu Xun once lived.
I know the reason why he came late.