限制性和非限制性定语从句

例如：

1）This is the house which we bought last month.（限制性）

The house,which we bought last month,is very nice.（非限制性）

2)当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的，例如：

Charles Smith,who was my former teacher,retired last year.

My house,which I bought last year,has got a lovely garden.

This novel,which I have read three times,is very touching.

3)非限制性定语从句还能将整个主句作为先行词,对其进行修饰,这时从句谓语动词要用第三人称单数，例如：

He seems not to have grasped what I meant,which greatly upsets me.

Liquid water changes to vapor,which is called evaporation.

说明：关系代词that和关系副词why不能引导非限制性定语从句。