as作为代词的用法

as之前若有名词，则as = as + the + 前面的名词 + 关系代词（who, whom, which）,因此可以将as 可视为关系代词，并在所引导的从句中作主语，宾语和be动词之后的表语。但只用于下列短语中：

注意：

① such + n. 之后不可用like（像）加以修饰。

Such a man like him is bad. (错)

Such a man as him is bad.（对）

② as 可替代主句。单独使用as时，as也可以作关系代词，等于which，用来代替整个主句。

He is nice, which is known to us

= he is nice , as is known to us(他人很好，我们都知道)

③ as引导的从句可置于主句的前后，而which引导的从句只能置于主句之后。

例. He is nice, as we all know= as we all know, he is nice

④只能与单数可数名词使用的结构。