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……
注意：
定语从句中有be 动词保留be动词
例：There is no one who is not interested in it.
=There is no one but is interested in it
没有人不对他感兴趣。（but在从句中可以作主语）
反过来，定语从句中有助动词（can,will,may,should…）保留该助动词。
There is nothing that he can not do.
=There is nothing but he can do.
没有什么事是他做不来的。（but在从句中可以作宾语）
定语从句中有do,does和did等助动词时，先去掉助动词，再依时态人称将之后的动词还原。
There is no book which he doesn't like to read.
= There is no book but he likes to read..
没有一本书是他不想看的。
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.
没有一个人不想和家人一起过春节。（but在从句中可以作主语）
There are few people but make mistakes.
=There are few people who do not make mistakes.
很少有人不犯错误。（but在从句中可以作主语）
There are very few grammar rules but have exception.
= There are very few grammar rules which don’t have exception.
很少有语法规则没有例外。（but在从句中可以作主语）
There is not a man but tears in his eyes.
= There is not a man who does not tear in his eyes.
没有一个人眼里不含着眼泪。
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.
考试一般可以是改错题，如在从句中but作主语时，后再加一个主语who,that,which等。如：
There are very few but who admire his talents.
这个从句里就多了一个who,句子可译为：
很少有人不敬佩他的才华。