一、定义：

在复合句中，修饰某一名词或代词的从句叫做定语从句。定语从句所修饰的词叫做先行词。定语从句放在先行词的后面。引导定语从句的词叫做关系代词（that, which, who, whom, whose）或关系副词(when, where)，关系代词和关系副词放在先行词与定语从句之间，起联系的作用，同时又作定语从句的一个成分。

二、关系代词在定语从句中的用法：

1．that指人或物，在定语从句中可作主语或宾语。

①This is the pen that you are looking for. 这是你要找的那支钢笔。(宾语)

②The girl that has long hair is my sister.留着长发的那个女孩是我妹妹。（主语）

2．which指物，在定语从句中可作主语或宾语。

①The bike which is made in Tianjin sells well.天津产的自行车销售很好。（主语）

②The fish which we bought were not fresh.我们买的鱼不新鲜。(宾语)

3．who, whom指人，在定语从句中可作主语或宾语。

①The boy who broke the window is called Tom.打碎窗户的男孩叫Tom. （主语）

②The person to whom he is talking is my father.

正在和他谈话的那个人是我父亲。(宾语)

4．whose指人或物，在定语从句中作定语。

①The girl whose bag is new is called Ann.新书包的那个女孩叫Ann。(指人)

②He lives in a house whose widows open to the south.

他住在窗户朝南的那所房子。(指物)

三、只用which不用that的情况：

1．在介词后只用which，不能用that。

This is the bank in which the robbery happened.这是那所发生抢劫案的银行。

2．先行词本身是that时，只能用which，不能用that。

The clock is that which tells the time.钟表是用来报时的。

四、只用that不用which的情况：

1．先行词被形容词最高级修饰时只能用that。

This is the most beautiful mountain that I have seen. 这是我所见过的最美丽的山。

2．先行词被序数词修饰时只能用that。

The first English novel that I read was Thirty-nine Steps.

我读的第一本英文小说是《39级台阶》。

3. 先行词前有all, any, no, little, much, many, the only, the very, the last等修饰词时只能用that。

①Here are all the books that I have.　这就是我所有的书。

②This is the only book that I like.这是我唯一喜欢的一本书。

4．先行词是everything, something, anything, all, none, much, little, many, few等不定代词时，只能用that。

Finally, the thief handed in everything that he had stolen.最后小偷交出了他所偷的东西。

5．先行词同时含有“人”和“物”的名词时，只能用that。

I can remember the people and some pictures that I saw in the room.

我能记得我在房间里看到的人和一些图画。

6．先行词是the one时，只能用that。

This is the one that you want.　这就是你想要的。

7．在以who引导的疑问句后，为了避免重复，只能用that。

Who is the girl that is standing there? 站在那边的那个女孩是谁？

五、在介词后只能用whom，不能用who。

The girl to whom I talked just now is from America.

我刚刚与之谈话的那个女孩是来自美国的。

六、定语从句中主谓一致的问题：

当关系代词在定语从句中作主语时，定语从句中的谓语动词要与先行词的人称和数保持一致(我们要知道，关系代词所代指的就是先行词，这里有一个等量关系)。

①Tom is one of the boys who are from the USA. Tom是众多来自美国的男孩中的一个。

②Tom is the only boy that is from the USA. Tom是惟一从美国来的男孩。

七、定语从句中的介词与副词的问题：

当关系代词在定语从句中作宾语时，如果定语从句中的谓语动词是不及物动词时，要加介词或副词。(定语从句中的不及物动词加介词或副词构成固定的及物动词短语后，不能把介词或副词提前到关系代词前。)

①He is the old man who/whom we looked after last year.他是我们去年照顾的那个老人。

②That is the book which I am looking for.那就是我要找的书。

八、关系副词when与where的使用：

1．when指时间：

I will never forget the time when we worked on the farm.

我将永远不会忘记我们在农场劳动的那段时光。

2．where指地点(where=in等介词＋which)：

This is the house where(=in which) he lived last year.这是他去年住的房子。

九、定语从句与作定语的①动词不定式、②介词短语、③现在分词短语、④过去分词短语的转换：

①She has much work that she must do.=She has much work to do.她有许多要做的工作。

②The man in the car is Mr. Green.=The man who is in the car is Mr. Green.

  在车上的人是格林先生。

③The girl watering flowers there is my sister.=The girl who is watering flowers there is my sister.在浇花的女孩是我妹妹。

④The boy saved in the river has come back to life.= The boy who was saved in the river has come back to life.从河里救起的男孩苏醒过来了。