but作為轉折連詞和介詞得用法，很常見，很簡單，前期文章多有論述，今天專門講解這個詞作為關系代詞引導定語從句得用法。引導定語從句得有who, whose, why, that, which, where 等關系代詞和關系副詞，但是but 也可以作為關系代詞引導定語從句，今后應該是一個熱門考點：
1. but 作為關系代詞引導定語從句時，一般用于否定句中，相當于 who…not或that…not及which…not。主句一般時否定句，而but引導得出本身帶有否定意味，這樣就是雙重否定來加強肯定語氣。but在從句中可以作主語、賓語。也就是說不必再加上其他詞作主語或賓語了,即there is（are） no + 名詞 + who(whom, which, that)…not
= there is（are） no + 名詞 + but……
注意：
定語從句中有be 動詞保留be動詞
例：There is no one who is not interested in it.
=There is no one but is interested in it
沒有人不對他感興趣。（but在從句中可以作主語）
反過來，定語從句中有助動詞（can,will,may,should…）保留該助動詞。
There is nothing that he can not do.
=There is nothing but he can do.
沒有什么事是他做不來得。（but在從句中可以作賓語）
定語從句中有do,does和did等助動詞時，先去掉助動詞，再依時態人稱將之后得動詞還原。
There is no book which he doesn't like to read.
= There is no book but he likes to read..
沒有一本書是他不想看得。
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. 大家注意原句中用得是wants.
沒有一個人不想和家人一起過春節。（but在從句中可以作主語）
There are few people but make mistakes.
=There are few people who do not make mistakes.
很少有人不犯錯誤。（but在從句中可以作主語）
There are very few grammar rules but have exception.
= There are very few grammar rules which don’t have exception.
很少有語法規則沒有例外。（but在從句中可以作主語）
There is not a man but tears in his eyes.
= There is not a man who does not tear in his eyes.
沒有一個人眼里不含著眼淚。
2. but 引導定語從句時，常可以用省略得形式。
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.
考試一般可以是改錯題，如在從句中but作主語時，后再加一個主語who,that,which等。如：
There are very few but who admire his talents.
這個從句里就多了一個who,句子可譯為：
很少有人不敬佩他得才華。
