1、定語從句的概念

定語從句是指在復合句中，修飾限定某一名詞或代詞的從句。

例如：You must buy me the house which is near Xiangshan.

上面例句中的the house就是后面定語從句所修飾或限定的詞，叫先行詞，定語從句放在先行詞的后面。

2、關系詞（連接詞）

引導定語從句的關系詞有關系代詞：that, which, who (賓格whom, 所有格whose) 和關系副詞where, when, why。關系詞放在先行詞和定語從句之間，起連接作用，同時還做定語從句的一個成分。

3、that與which的用法區分

1）只能用that，不能用which作為定語從句關系代詞的情況

a）當先行詞由不定代詞anything, nothing, the one, all, much, few, any, little等代替時，關系代詞只能用that而不能用which 。例如：There is nothing that I can do

b）先行詞有the only, the very, the same, the last修飾時。例如：The last place that I visited was the hospital.

c）先行詞為序數詞、數詞、形容詞較高級。例如：This is the first composition that he has written in English.

d）先行詞既有人，又有物時。例如：He talked about the teachers and schools that he had visited.

2）只用which不用that的情況

a）引導非限定性定語從句時例如：The tree, which is four hundred years old, is very famous here.

b）介詞后用which例如：We depend on the land from which we get our food.

4、關系副詞引導的定語從句

關系副詞可代替的先行詞是時間、地點或理由的名詞，在從句中作狀語。

1）先行詞是表示地點名詞時（country, school, room…），而關系詞代替先行詞在定語從句中充當地點狀語，一般用where引導定語從句。也可以用介詞+which的結構。值得留意的是which前的介詞選擇是根據先行詞與介詞的搭配關系而定。

例如：He wants to find the place in which (=where) he lived forty years ago.

2）先行詞是表示時間名詞時，而關系詞代替先行詞在定語從句中充當時間狀語，一般用when引導定語從句。也可以用介詞+which的結構。值得留意的是when前的介詞選擇是根據先行詞與介詞的搭配關系而定。

例如：I cannot forget the first day on which (=when) my family moved into the city.

3）先行詞是the reason，而關系詞代替先行詞在定語從句中充當原因狀語，一般用why引導定語從句。也可以用for + which的結構。

例如：Is this the reason for which (why) he refused our offer?

但是這里要指出的是，假如介詞和Which搭配在一起并不表示以上三種意思，則我們只能留存介詞+Which的形式。如 I know English in which I wrote the love letter.

5、判定關系代詞與關系副詞

方法一：用關系代詞還是關系副詞完全取決于從句中的謂語動詞。及物動詞后面無賓語，就必需要求用關系代詞；而不及物動詞則要求用關系副詞。

方法二：正確判定先行詞在定語從句中的成分（主、謂、賓、定、狀），也能準確選擇出關系代詞/ 關系副詞。

系詞的選擇依據在從句中所做的成分，先行詞在從句中做主、定、賓語時，選擇關系代詞（who, whom,that, which, whose）；先行詞在從句中做狀語時，應選擇關系副詞 （where 地點狀語，when 時間狀語，why 原因狀語）。

6、限定性從句和非限定性從句

1）定語從句有限制性和非限制性兩種。限制性定語從句是先行詞不可缺少的部門，去掉它主句意思往往不明確；非限制性定語從句是先行詞的附加說明，去掉了也不會影響主句的意思，它與主句之間通常用逗號分開。例如：

All the Greeks who are philosophers are very clever. （限制性）

All the Greeks, who are philosophers, are very clever. (非限制性)

2）非限制性定語從句還能將整個主句作為先行詞, 對其進行潤飾, 這時從句謂語動詞要用第三人稱單數。例如：The traffic of Beijing is quite bad, which is known to everyone.

7、定語從句的省略

1) 關系代詞充當從句賓語

前面說到連接詞在定語從句中充當一個成分，有可能是主語、有可能是賓語，相信大家肯定還記得，這里要告訴大家，當這些連接詞充當的是賓語時，可以省略。例如：

The book (that/which) we bought last year is now very popular.

We can see the boys (who/whom/that) the teacher is talking with are quite happy.

2) 關系代詞充當從句主語

當關系代詞充當從句主語時，也可以省略，但是省略后的從句要發生形式的變化，原從句若為主動語態，后面的動詞結構要變成分詞ing形式，原從句若為被動語態，后面的動詞結構直接為過去動詞結構。這種結構在英語語法中稱為分詞作定語。例如：

The novel which was given by the professor mainly discusses the development of Chinese economy.

The novel given by the professor mainly discusses the development of Chinese economy.

The novel which mainly discusses the development of Chinese economy was given by the professor.

The novel mainly discussing the development of Chinese economy was given by the professor.

3) why的先行詞reason或可用that 指代的名詞也是定語從句的原因狀語時，關系代詞或關系副詞可以省略。例如：

That is the reason (for which/why) you dislike it.

I wonder the reason (why/for which) he changed his mind.

4) 表示方式的先行詞way，其后的關系代詞可用that也可省略，例如：

Everyone does not like the way (that) he talks.

Do you know the way (that) the teacher treated his students.