用来说明主句中某一名词或代词（有时也可说明整个主句或主句中一部分）而起定语作用的句子叫作定语从句。

一．词引导的定语从句

1. 关系代词用来指代先行词是人或物的名词或代词

句子成分   用于限制从句或非限制性从句     只用于限制性从句

           代替人        代替物            代替人或物

主语   Who               which               that

主语   Whom              which               that

宾语   Whose(=of whom)   whose(=of which)

    例１：This is the detective who came from London.

    例２：The book which I am reading is written by Tomas Hardy.

    例３：The desk whose leg is broken is very old.

    例４：This is the room that Shakespeare was born in.

２．关系代词的用法

    (1) 如果先行词是all, much, anything, something, nothing, everything, little, none等不定代词，关系代词一般只用that，不用which。例如：

    All the people that are present burst into tears.

    (2) 如果先等词被形容词最高级以及first, last, any, only, few, mush, no, some, very等词修饰，关系代词常用that,不用which, who，或whom。例如：

    (3) 非限制性定语从句中，不能用关系代词that,作宾语用的关系代词也不能省略。例如：

    There are about seven million people taking part in the election, most of whom、are well educated.joozone.com