關系代詞which一般指物，在定語從句中作主語或賓語，既可以引導限制性定語從句，又可引導非限制性定語從句。另外“介詞+which”具有替代作用，十分常見。

1.引導限制性定語從句

（1）A shop should keep a stock of those goods which sell best.

商店應存有最暢銷的貨物。

（2）This is the family which is planning to move to the party.

這是要搬進城里的一家。

2.引導非限制性定語從句

（1）用來指代一個句子

Internet is so interesting,which makes all possible happen.

因特網如此有趣，它可以使任何事都有可能發生。

（2）用來指代句子的一部分

When deep in thought,which he often was,he would forget all around him.

他常常陷入沉思，這時他就會忘掉周圍的一切。

（3）如果要引導兩個非限制性定語從句，第二個which前要加and

He bought a book,which was written by LuXun,and which he decided to give to his friend.

他買了本魯迅寫的書，他決定送給朋友。

3.名詞+of+which（=of which+名詞=whose+名詞）通常放在先行詞的后面。

I’d like a room the window of which looks out over the sea.

I’d like a room of which the window looks out over the sea.

I’d like a room whose window looks out over the sea.

我要一間窗戶面臨大海的房間。

4.介詞+which的替代作用

（1）作時間狀語替代when

There used to be a time at which/during which（=when）the Chinese people struggled for freedom.

中國人曾有一段為自由而斗爭的日子。

（2）作地點狀語替代where

This is the office in which（=where）I used to work.

這是我過去工作過的辦公室。

（3）作原因狀語替代why

I’d like you to explain the reason for which（=why）you were absent.

我想讓你解釋一下缺席的原因。

（4）作方式狀語替代that或省略

There are many ways in which（=that/省略）we can solve the problem.

解決這個問題有很多方法。