（一）定义及相关术语
1.定语从句：修饰某一名词或代词的从句叫定语从句。定语从句一般紧跟在它所修饰的先行词之后。
2.先行词：被定语从句修饰的词叫先行词。
3.关系词：引导定语从句的词叫关系词。关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等；关系副词有when, where, why等。
关系词通常有三个作用：
A、引导定语从句；B、代替先行词；C、在定语从句中担当一个成分。
The man who is shaking hands with my father is a policeman.
该句中，who is shaking hands with my father是定语从句，修饰先行词the man，"who"是引导定语从句的关系词，代替先行词the man，在定语从句中作主语。
（二）关系代词引导的定语从句
1.who 指人，在定语从句中作主语。
The boys who are playing football are from Class One.
正在踢足球的男孩是一班的。
Those who want to go to the museum must be at the school gate at 7 tomorrow morning.
想去博物馆的人必须在明晨7点到大门口集合。
Yesterday I helped an old man who had lost his way.
昨天我帮助了一位迷路的老人。
That is the teacher who teaches us physics.
那就是教我们物理的老师。
2.whom 指人，在定语从句中做宾语，常可省略。
Mr Liu is the person ( whom ) you talked about on the bus.
刘先生就是你们在公共汽车上谈论的那个人。
Li Ming is just the boy ( whom ) I want to see.
李明正是我想要见的男孩。
The professor ( whom ) you are waiting for has come.
你正在等的教授已经来了。
The girl ( whom ) the teacher often praises is our monitor.
老师经常表扬的那个女孩是我们的班长。
注意：关系代词whom 在口语或非正式文体中常可用who 来代替，也可省略。
The man ( whom / who )you met just now is my old friend.
3.Which 指物，在定语从句中做主语或宾语，做宾语时常可省略。
Football is a game which is liked by most boys.
足球是大多数男孩所喜欢的运动。
The factory which makes computers is far away from here.
制造计算机的那家公司离这很远。
He likes to read books which are written by foreign writers.
他喜欢外国作家写的书。
The house which is by the lake looks nice.
湖边的那幢房子看上去很漂亮。
This is the pen ( which ) he bought yesterday.
这是他昨天买的钢笔。
The film ( which ) they went to see last night was not interesting at all.
他们昨晚看的电影一点意思也没有。
4.That 指人时，相当于who 或whom；指物时，相当于which。在定语从句中作主语或宾语，作宾语时常可省略。
The number of people that / who come to visit this city each year reaches one million.
每年来参观这座城市的人数达一百万。
Where is the man that / whom I saw this morning?
我今天早上看到的那个人在哪儿？
The person that /whom you introduced to me is very kind.
你介绍给我的那个人很友好。
The season that / which comes after spring is summer.
春天以后的季节是夏季。
Yesterday I received a letter that / which came from Australia.
昨天我收到了一封来自澳大利亚的信。
5.Whose 通常指人，也可指物，在定语从句中做定语。
I visited a scientist whose name is known all over the country.
我拜访了一个全国知名科学家。
He has a friend whose father is a doctor.
他有一个爸爸当医生的朋友。
I once lived in the house whose roof has fallen in.
我曾经住在那幢屋顶已经倒塌了的房子里。
注意：指物时，常用下列结构来代替：
The classroom whose door is broken will soon be repaired.
The classroom the door of which is broken will soon be repaired.
Do you like the book whose cover is yellow? Do you like the book the cover of which is yellow?
（三）“介词+关系代词”引导的定语从句
关系代词在定语从句中作介词宾语时，从句常常由“介词+关系代词”引出。
The school (which / that) he once studied in is very famous.
The school in which he once studied is very famous.
他曾经就读过的学校很出名。
Tomorrow I'll bring here the magazine (which / that) you asked for.
Tomorrow I'll bring here the magazine for which you asked.
明天我将把你要的杂志带来。
This is the boy (whom / who / that) I played tennis with yesterday.
This is the boy with whom I played tennis yesterday.
这是我昨天跟他打台球的男孩。
We'll go to hear the famous singer (whom / who / that) we have often talked about.
We'll go to hear the famous singer about whom we have often talked.
我们将去听那位我们经常谈论的著名歌唱家演唱。
注意：
1.含有介词的短语动词一般不拆开，介词仍放在短语动词的后面。如：look for, look after, take care of等。
This is the watch (which / that) I am looking for.（正）这是我正在找的手表。
This is the watch for which I am looking.（误）
The babies (whom / who / that) the nurse is looking after are very healthy.（正）
那个保姆照看的小宝宝们都很健康。
The babies after whom the nurse is looking are very healthy.（误）
2.若介词放在关系代词前，关系代词指人时只可用whom，不可用who, that；关系代词指物时只可用which，不可用that。关系代词是所有格时用whose。
The man with whom you talked just now is my neighbour.（正）你刚才跟他谈话的那个人是我的邻居。
The man with that / who you talked just now is my neighbour.（误）
The plane in which we flew to Canada was really comfortable.（正）我们去加拿大所乘坐的飞机实在很舒服。
The plane in that we flew to Canada was really comfortable.（误）
3．“介词+关系代词”前还可有some, any, none, all, both, neither, many, most, each, few 等代词或者数词。如：
He loves his parents deeply, both of whom are very kind to him.
他深深地爱着他的父母，他们俩待他都很好。.
In the basket there are quite many apples, some of which have gone bad.
篮子里有好些苹果，有些已经坏了。
There are forty students in our class in all, most of whom are from big cities.
我们班总共有40个学生，大多数来自大城市。
Up to now, he has written ten stories, three of which are about country life.
迄今为止，他写了10部小说，其中3部是关于农村生活的。
（四）关系副词引导的定语从句
1.when 指时间，在定语从句中作时间状语。
I still remember the day when I first came to this school.
我仍然记得我第一次来到这所学校的那一天。.
The time when we got together finally arrived.
我们团聚的时刻终于到了。
October 1, 1949 was the day when the People's Republic of China was founded.
1949年10月1日是中华人民共和国成立的日子。
Do you remember the years when he lived in the countryside with his grandparents.
你还记得在农村和你祖父母一起生活的那些年吗？
2.where 指地点，在定语从句中作地点状语。
Shanghai is the city where I was born.
上海是我出生的城市。
The house where I lived ten years ago has been pulled down.
我十年前住的房子已被拆掉了。
I visited the farm where a lot of cows were raised.
我参观了那个饲养了许多奶牛的农场。
Is this the place where they fought the enemy?
这是他们当初打敌人的地方吗？
3.why指原因，在定语从句中作原因状语。
Please tell me the reason why you missed the plane.
请告诉我你误机的原因。
The reason why he was punished is unknown to us.
他受惩罚的原因我们都不知道。
I don't know the reason why he looks unhappy today.
我不知道他今天为何看上去不愉快。
注意：关系副词引导的定语从句经常可以用“介词+关系代词”引导的定语从句来表示。
如：From the years when / in which he was going to primary school in the country he had known what he wanted to be when he grew up.
自从他在农村读小学时，他就已经知道长大后要做什么。
Great changes are taking place in the city where / in which they live.
他们生活的城市正发生巨大的变化。.
The reason why / for which he refused the invitation is quite clear.
他为什么拒绝接受邀请的原因是十分明了的。
（五）限制性定语从句和非限制性定语从句
1、限制性定语从句：
The teacher told me that Tom was the only person that I could depend on.
老师告诉我说汤姆是我唯一的可以依靠的人。.
China is a country which has a long history.
中国是一个历史悠久的国家。
In the street I saw a man who was from Africa.
在街上我看到一个来自非洲的人。
2、非限制性定语从句举例
Last summer I visited the People's Great Hall, in which many important meetings are held every year. 去年夏天，我参观了人民大会堂，在那儿每年都要举行许多重要会议。
注意区分下列几组句子的不同含义：Her brother who is now a soldier always encourages her to go to college. 她那当兵的哥哥总是鼓励她上大学。（意含： 她还有其他哥哥。）
Her brother, who is now a soldier, always encourages her to go to college. 她哥哥是当兵的，他总是鼓励她上大学。（意含： 她只有一个哥哥。）
难点释疑：
（一）限制性定语从句中只能用that 引导定语从句的情况。
1．当先行词是everything, anything, nothing（something 除外）, all, none, few, little, some等代词时，或当先行词受every, any, all, some, no, little, few, much等代词修饰时。如：
Have you taken down everything that Mr. Li said?
李老师讲的你都记下来了吗？
There seems to be nothing that is impossible to him in the world.
对他来说似乎世界上没有什么不可能的事。
All that can be done has been done.
所有能做的都做好了。
There is little that I can do for you.
我不能为你干什么。
He stayed in the library and looked up any information that they needed.
他呆在图书馆查找所需的资料。.
注意：当先行词指人时，偶尔也可用关系代词who，如：
Any man that / who has a sense of duty won't do such a thing.
任何有责任感的人都不会做这样的事。
All the guests that / who were invited to her wedding were important people.
所有应邀来参加她婚礼的客人都是重要人物。
2.当先行词被序数词修饰时。
如：The first place that they visited in London was the Big Ben.
在伦敦他们参观的第一个地方是大本钟。
3.当先行词被形容词最高级修饰时。
如：This is the best film that I have ever seen.
这是我看过的最好的电影。
4.当先行词被the very, the only修饰时。
如：This is the very dictionary that I want to buy.
这正是我要买的词典。
After the fire in his house, the old car is the only thing that he owns.
家里发生了火灾过后，那辆旧车成了他的唯一拥有。.
注意：当先行词指人时，偶尔也可用关系代词who。如：
Wang Hua is the only person in our school who will attend the meeting.
王华是我校唯一出席会议的人。
5.当先行词前面有who, which等疑问代词时。
如：Who is the man that is standing by the gate?
站在门口的那个人是谁？
Which is the T-shirt that fits me most?
哪件T恤衫最合我的身？
6．当先行词为人与动物或人与物时。
如：They talked about the persons and things that they remembered at school
他们谈论着他们所能记起的在校时的人和事。
Look at the man and his donkey that are walking up the street.
瞧瞧那个沿街走来的人和他的毛驴。
（二）关系代词as和which 引导的定语从句
as 和which 引导非限制性定语从句时， 其用法有相同之处，也有不同之处。
1. as 和which都可以在定语从句中做主语或宾语，代表前面整个句子。如：
He married her, as / which was natural.
他跟她结婚了，这是很自然的事。
He is honest, as / which we can see.
他很诚实， 这一点我们看得出来。
2. as 引导的非限制性定语从句可以放在主句之前、主句之后，甚至还可以分割主句。which引导的非限制性定语从句只可放在主句之后。另外，as 常常有“正如、正像”的含义。如：
As is known to all, China is a developing country.
众所周知，中国是发展中国家。
He is from the south, as we can know from his accent.
他是南方人，这一点我们从他的口音可以知道。
John, as you know, is a famous writer.
正如你所知， 约翰是个著名作家。
Zhang Hua has been to Paris more than ten times, which I don't believe.
张华已去过巴黎十多次了，这一点我不相信。
注意：当主句和从句之间存在着逻辑上的因果关系时，关系词往往只用which。如：
Tom was late for school again and again, which made his teacher very angry.
汤姆老是迟到，这使得老师很恼火。.
These tables are made of metal, which made them very heavy.
这些桌子是金属的，这使得这些桌子很重。
3. 当先行词受such, the same 修饰时，关系词常用as。如：
I've never heard such stories as he tells.
我从未听过象他讲的这样的故事。
He is not such a fool as he looks.
他可不象他看上去的那样傻。
This is the same dictionary as I lost last week.
这部词典跟我上星期丢失的一样。
(三) 以the way为先行词的限制性定语从句通常由in which或that引导，而且通常可以省略。
The way (that / in which ) he answered the questions was surprising.
他回答这些问题的方式令人惊奇。
I don't like the way (that / in which) you laugh at her.
我不喜欢你冲她的样子。
（四）关系代词与关系副词的选择
用关系代词还是关系副词引导定语从句主要看关系词在定语从句中的作用（即所担当的成分）。试比较：
A. I know a place where we can have a picnic.
我知道一个我们可以野炊的地方。
I know a place which / that is famous for its beautiful natural scenery.
我知道一个以自然景色优美而闻名的地方。
B. I will never forget the days when we spent our holidays together.
我永远忘不了我们一起度假的日子。
I will never forget the days that / which we spent together.
我永远忘不了我们一起度过的日子。
C. This is the reason why he was dismissed.
这就是他被解雇的原因。
This is the reason that / which he explained to me for his not attending the meeting.
这就是他向我解释的他没有参加会议的原因。.
（五）定语从句与同位语从句的区别
1.定语从句修饰限定先行词，它与先行词是修饰关系；同位语从句说明先行词的具体内容，
它与先行词是同位关系。
The plane that has just taken off is for Paris.（定语从句）
刚起飞的那架飞机是开往巴黎的。
The fact that he has already died is quite clear.（同位语从句）
他已去世了，这个事实很明了。
2.定语从句由关系代词或关系副词引导，关系词在从句中担当相应句子成分，关系代词在从句中作宾语时经常可省略。同位语从句主要由连词that 引导，在从句中一般不担当成分；有时由where, when, how, who, whether, what等连词引导，这些连词则在从句中担当成分。
The news that he told me is true. （定语从句）他告诉我的消息是真的。
The news that he has just died is true. （同位语从句） 他刚刚去世了，这个消息是真的。
The problem that we are facing now is how we can collect so much money. （定语从句）我们现在面临的问题是如何筹集这么多资金。
The problem how we can collect so much money is difficult to solve. （同位语从句）我们如何筹集这么多资金，这个问题很难解决。
The question that he raised puzzled all of us. （定语从句）他提出的问题让我们很为难。
The question whether he is sure to win the game is hard to answer. （同位语从句）他是否一定会赢得那场比赛，这个问题很难回答。
3.同位语从句与先行词一般可以用动词be发展成一个完整的句子,定语从句则不能。
A. The idea that he we could ask the teacher for advice is wonderful. （同位语从句）我们可以向老师请教，这个主意不错。
The idea was that we could ask the teacher for advice.
B. The fact that the earth moves around the sun is known to all. （同位语从句）地球围绕太阳转，这个事实人人皆知。
The fact is that the earth moves around the sun.
C. Pay attention to the problem how we can protect the wild animals. （同位语从句）请注意如何保护野生动物这个问题。
The problem is how we can protect the wild animals.