but作为转折连词和介词的用法，很常见，很简单，前期文章多有论述，今天专门讲解这个词作为关系代词引导定语从句的用法。引导定语从句的有who, whose, why, that, which, where 等关系代词和关系副词，但是but 也可以作为关系代词引导定语从句，今后应该是一个热门考点：
1. but 作为关系代词引导定语从句时，一般用于否定句中，相当于 who…not或that…not及which…not。主句一般时否定句，而but引导的出本身带有否定意味，这样就是双重否定来加强肯定语气。but在从句中可以作主语、宾语。也就是说不必再加上其他词作主语或宾语了,即there is（are） no + 名词 + who(whom, which, that)…not
= there is（are） no + 名词 + but……
例：There is no one who is not interested in it.
=There is no one but is interested in it
There is nothing that he can not do.
=There is nothing but he can do.
There is no book which he doesn't like to read.
= There is no book but he likes to read..
There is no man but wants to spend Spring Festival with family.
=There is no man who does not want to spend Spring Festival with family. 大家注意原句中用的是wants.
There are few people but make mistakes.
=There are few people who do not make mistakes.
There are very few grammar rules but have exception.
= There are very few grammar rules which don’t have exception.
There is not a man but tears in his eyes.
= There is not a man who does not tear in his eyes.
2. but 引导定语从句时，常可以用省略的形式。
No one but is interested in it
Nothing but he can do.
No book but he likes to read..
No man but wants to spend Spring Festival with family.
Few people but make mistakes.
Very few grammar rules but have exception.
Not a man but tears in his eyes.
There are very few but who admire his talents.