定语从句的引导词有关系代词who， whom，which，that， as；关系副词when， where，why；关系形容词whose。关系代词who，whom，whose， which和as能引导非限制性定语从句，而that不能；非限制性定语从句中即使缺宾语，引导词也不能省略；关系副词when，where能引导非限制性定语从句，而why不能。
1．定语从句中缺主语，修饰人时用who 或that，修饰物时用which 或that引导。
如：Is this the factory which 或that makes TV sets？
2．从句中缺宾语，修饰人时用 who 或whom 或that或省略引导词；修饰物时用which 或that或省略引导词。
如：Gone are the days which 或that we spent together in the village．
3．从句中缺时间状语，用when或介词＋which引导。
如：The day finally came when 或on which I was given a job．
4．从句中缺地点状语，用where或介词＋which引导。如：
Please put the letter on the desk where 或on which he can easily find it．
5．从句中缺原因状语或先行词是 reason时，引导词用why 或for which 或 that。
如：This is the reason why 或for which 或 that he didn't come to the meeting．
6．从句中缺定语，人和物都用 whose引导。
如：A child whose parents are dead is called an orphan．
7．当先行词是way时，其定语从句的引导词用in which 或that。
如：The way in which 或that he looks at problems is wrong．
