比较分句：由从属关联词as/than引导的具有比较意义的分句。（之所以用从属关联词这个术语，是为了避免as/than是从属连词还是代词/副词的争议。）比较分句可以作形容词或副词的补足语、作句子或句子一部分的补充语、作方式状语、或作名词的修饰语等。

主句，as we know. (补充语）

She is beautiful, as is her sister. （补充语）

She is as beartiful as her sister is. (形容词的补足语）

This is the same bag as I lost yesterday. (形容词的补足语）

She runs as fast as I do. (副词的补足语）

Do as I said. (方式状语）

Life as we know it needs water and air to survive. （名词的限制性修饰语）

传统语法对以上as分句有不同的分析。

名词性关系分句：由融合型关系代词/关系副词引导的名词性从句。

This is what I bought yesterday.

Whoever said that was lying.

This is where I was born.