but 既是介词，也是连接词和副词，

而且（这一点很多人不知道）在一些情况下也是名词。

下面提供这四个词性的例句：

（连词）

I got up early today, but I was still late for school.

（介词）

I trusted no one but him.

（副词）

He is but a shadow of his former self.

（名词）

Just do what I say. No ifs, whens or buts!