定语从句就是修饰名词或者代词的从句，相当于形容词修饰名词的功能，通常放在被修饰的名词后面。被修饰的名词或者代词因其位置在定语从句前面，叫作先行词。首先在概念上，需要明白定语从句的以下五个特点：
1. 定语从句为一个从句，从句里有谓语动词，相当于形容词的作用；
2. 定语从句前面一定有所修饰的名词或者代词，即先行词；
3. 定语从句和先行词之间要用连接词连接；
4. 连接词在定语从句中如果充当成分（主语或者宾语），被称作关系代词；连接词在定语从句中如果不充当成分，被称作关系副词；
5. 定语从句的结构为：先行词+关系词（分为关系代词和关系副词）+从句。
1 定语从句中的关系代词
定语从句的关系代词（Relative Pronoun）有that, which, who, whom, whose。关系代词在定语从句中充当成分，用来指代先行词是人或者物的名词或代词。
① 先行词是人，关系代词在定语从句中充当主语时，用who / that连接。
例 The man who / that talks to my mother is Mr. Li. 和我妈妈说话的那个人是李先生。（指人，作主语）
Do you know the girl who / that is standing in the corner of the room? 你认识那个站在角落里的女孩吗？（指人，作主语）
② 先行词是人，关系代词在定语从句中充当宾语时，用whom / that连接，可以省略。
例 This is the student（that / whom）I taught two years ago. 这个就是我两年前教过的学生。（指人，作宾语）
The young man（whom / that）I met yesterday could speak Japanese. 我昨天见的那个年轻人会说日语。（指人，作宾语）
③ 先行词是物，关系代词在定语从句中充当主语或宾语，用关系代词which / that。如果关系代词作宾语时，可以省略。
例 The building which / that stands at the foot of the hill is a hospital. 坐落在山脚下的那栋建筑是一所医院。（指物，作主语）
This is the place（which / that）we would like to visit. 这就是我们想要参观的地方。（指物，作宾语）
④ 先行词是人或物，关系代词在定语从句充当定语，用关系代词whose，相当于先行词的所有格。若先行词指代人，关系代词whose可以替换为of whom；若先行词指代物，关系代词whose可以替换为of which。
例 You are the only one whose（of whom）words they would like to listen to. 只有你的话他们愿意听。（指人，作定语）
This is the building whose windows were all painted blue. 这就是窗户全漆成蓝色的那幢大楼。（指物，作定语）
⑤ 定语从句中关系代词只能用that，不用which的情况：
a. 当先行词是all, everything, nothing, something, anything, little, none, few等不定代词时。
例 All that we need is your encouragement. 我们所需要的就是你的鼓励。
There is nothing that I couldn’t do. 没有我做不了的事情。
b. 当先行词既有人又有物时。
例 He spoke of the things and persons that he had seen abroad. 他说起在国外见到的人和事。
The passengers and parcels that filled the car were mixed. 车里的旅客和行李都混在一起了。
c. 先行词被形容词的最高级或序数词修饰时。
例 This is one of the best films that I have ever seen. 这是我看过的最棒的电影之一。
I will never forget the first English lesson that I learnt at college. 我永远不会忘记在大学里上的第一节英语课。
d. 先行词被the very, the only, the last, just, all, any, every, no等修饰时。
例 This is the only problem that confronts us now. 这是目前摆在我们面前的唯一问题。
This is the very book that I am looking for. 这正是我想要找的那本书。
e. 关系代词在从句中作表语时。
例 He is no longer the man that he was fifteen years ago. 他不再是15年前的那个人了。（作hewas的表语）
The town is not the tourist attraction that it once was. 这座小城不再是从前的旅游胜地了。（作itoncewas的表语）
f. 在疑问词who，which，what等开头的句子中时。
例 Which one is the point that you just mentioned? 你刚才提到的是哪一点？
Who is the lady that is waiting for you? 在等你的那位女士是谁？
g. 主语是there be句型。
例 There is a man that lives in that village. 有一个住在村子里的人。
There are three rooms in the hotel that are available. 酒店里还有三间空房。
⑥ 定语从句中关系代词只能用which，不用that的情况：
a. which前可接介词，that则不能。
例 This was the reason for which that I came to see you. 这就是我来见你的原因。
The math teacher today introduced a new concept of which I have never heard. 数学老师今天介绍了一个我从未听说过的概念。
b. 当先行词本身为that时。
例 What’s that which he asked for? 他要的是什么？
He has found that which he had lost yesterday. 他找到了昨天丢的东西。
2 定语从句中的关系副词
定语从句中的关系副词（Relative Adverb）有when, where, why。关系副词不影响定语从句的完整性，不作定语从句的主语或宾语成分，只起状语作用，表示时间、地点或原因等。关系副词的意思相当于“介词+which结构”。
① 先行词为“时间的名词”用when：time（day, night, morning, week, month, year）＋when ...。
例 I don’t remember the day when / on which he left. 我不记得他离开的那天。
This is was the time when /at which she left for Nanjing. 这就是她动身去南京的时间。
② 先行词为“表示地点的名词”用where：place (room, house, hotel, museum, school, street, stage, country等)＋where ...。
例 That is the house where / in which he has lived for two years. 那就是他住了两年的房子。
The library where / in which my father works is the largest one in Zhengzhou. 我父亲工作的图书馆是郑州最大的图书馆。
③ 先行词为“表示原因的名词”why：reason＋why ...（表示原因的名词只有一个）。
例 That is the reason why / for which I didn’t tell you in the first place. 这就是我一开始没有告诉你的原因。
Do you know the reason why / for which he didn’t go to school yesterday? 你不知道他昨天没去学校的原因吗？
④ 除了具体的地点名词后面可以跟关系副词where，其他如job, case, point, conditions, situation等表示“情况，方面”等抽象名词后面也可以跟关系副词where引导的定语从句，同样可以和“介词+which结构”互换。
例 This is a job where / from which you can learn something. 这是一份你可以从中学到东西的工作。
There are many cases where / in which this method cannot be used. 在某些情况下，这个方法不适用。
They are in an unpleasant situation where / in which all efforts seem useless. 他们的处境不容乐观，似乎所有的努力都付诸东流了。
I will show you the point where / in which you are wrong. 我将指出你错误的地方。
⑤ 先行词是the way, 在从句中作状语，一般情况下用that或者in which引导定语从句，that可以省略。
例 He told me the way (that) / in which I solve the problem. 他告诉了我解决这个问题的方法。
I don’t like the way (that) / in which he speaks to me. 我不喜欢他跟我说话的方式。(www.xing528.com)
3 非限制性定语从句
非限制性定语从句是定语从句的一种，它在句中是独立的成分，不受主句的限制。将非限制性定语从句去掉，主句也完整。从形式上看，非限制性定语从句经常用逗号和主句分开，从功能上，非限制性定语从句只对先行词起补充说明的作用。
① 非限制性定语从句和限制性定语从句的主要区别：
a. 非限制性定语从句和先行词及主句的关系没有限制性定语从句紧密，在形式上，非限制性定语从句和主句一般用逗号隔开，而限制性定语从句紧跟在先行词后面。试比较下面两个句子：
例 That friend whom I introduced to you yesterday is going to retire next month.我昨天给你介绍的那位朋友下个月就要退休了。（限制性定语从句，和先行词关系紧密，若去掉，不知道所指的是哪位朋友）
My friend, who has served on the International Olympic Committee all his life, is going to retire next month. 我有位朋友，他一辈子服务于国际奥林匹克委员会，下个月就要退休了。（非限制性定语从句，和先行词关系不紧密，用逗号和主句分开，目的不在于对哪位朋友做出限定，而是对朋友的信息做补充说明）
b. 非限制性定语从句中的关系词不可以省略。
例 This young man had a new girl friend, whom he wanted to impress. 这个年轻小伙新交了一个女朋友，他想给她留下好印象。（whom在非限制定语从句中虽然充当宾语，但是不能省略）
Jim was seriously ill, which she did not know. 吉姆病得很重，她并不知道。（which在非限制性定语从句中充当宾语，但不能省略）
c. 非限制性定语从句的先行词可以为整个主句，此时关系词经常由which引导。限制性定语从句的先行词通常是名词或代词，没有整个主句的情况。
例 He left the office early today, which was a little strange. 他今天很早就离开办公室了，这有点奇怪。（which在这里指代他今天很早离开办公室这件事，代替前面整个主句部分）
This girl married as soon as she graduated from college, which I can’t believe. 这个女孩一毕业就结婚了，这让我很难相信。（which在这里指代女孩一毕业就结婚这件事，代替前面整个主句部分）
② 非限制性定语从句不可用that引导，在非限制性定语从句中用who（作主语）， whom（作宾语）指人，用which（作主语/宾语）指物，用whose作定语（指人/物）。
例 The famous basketball star, who tried to come back, attracted a lot of attention. 这位试图回归的著名篮球明星吸引了众人的关注。
The film, whose director is a young woman, is very instructive. 这部电影很有教育意义，导演是位年轻女性。
③ 非限制性定语从句不用why引导， 需用for which替代why。
例 None of us accepted the reason he explained, for which he was absent. 我们没有一个人接受他所解释的缺席的理由。
4 “介词+关系代词”结构问题
①“介词+关系代词”结构可以引导限制性定语从句，也可以引导非限制性定语从句。
例 The papers for which he was searching are under the desk.他刚才一直搜寻的文件在桌子下面。
She spent six years in college, during which time she studied economics. 她上了六年大学，这期间她学习经济学。
②“介词+关系代词”结构中介词的选用要根据上下文表达的具体意思，根据先行词或者定语从句中某些词组或者短语的搭配进行选择。
例 This is the book on which I spent 100 RMB. 这就是我花费100元人民币买的书。（习惯搭配spentmoneyonsth.）
I can’t remember the age at which I went to college. 我不记得上大学的年龄了。（习惯搭配attheageof）
5 as引导定语从句
(1) as引导限制性定语从句
① as引导限制性定语从句多和such或the same连用，构成the same ... as和such ... as的结构。这时，as代替先行词是物或是人的名词。
例 Such books as were recommended by him were valuable. 他所推荐的书都是很珍贵的。
I want to buy the same eye cream as you bought last week. 我想买你上周买的那款眼霜。
② the same ... as和the same ... that结构上相同，但有时候句意不一样。试比较：
例 This is the same magazine as I read yesterday. 这和我昨天读的那本杂志是一样的。
This is the same magazine that I read yesterday. 这就是我昨天读的那本杂志。
(2) as引导非限制性定语从句
① as作为关系代词引导非限制性定语从句时，as代替整个主句的内容。
例 As is well known, he is a liar. 众所周知，他是一个谎话连篇的人。（as替代主句heisaliar）
As is hoped, he won the big prize. 正如所希望的，他赢得了大奖。（as代替hewonthebigprize）
② as引导非限制性定语从句位置比较灵活，可以位于主句前面、中间或后面，一般用逗号与主句分开。
例 As is reported, the US President is going to visit China. 正如报道所说，美国总统即将访问中国。
Professor Wang, as we know, has written a new book. 据我们所知，王教授写了一本新书。
The numbers is falling in the past three years, as shown in the picture. 正如图片所示，在过去三年数字一直呈下降趋势。
注：有些常见的as引导的结构，一般位于句首，也可位于句中或句末：
as is well known 众所周知
as is often the case 情况常常如此
as often happens 这种情况常常发生
as is hoped 正如所希望的
as has been said before 如前所述
as is reported 正如报道所说
雅思/托福真题解析
1. Beyond the practical need to make order out of chaos, the rise of dictionaries is associated with the rise of the English middle class, who were anxious to define and circumscribe the various worlds to conquer—lexical as well as social and commercial.
分析 本句中，who引导的非限制性定语从句修饰the English middle class。
译文 除了规范英语混乱状态的实际需要外，英语字典的兴盛也与英国中产阶级的兴起有关。这些中产阶级渴望对各种要征服的环境进行定义和约束，包括词汇环境、社会环境和商业环境。
2. They were spurred by the inflation of the 1970’s，which，combined with California’s rapid population growth，pushed housing prices，as well as rents, to record levels.
分析 which在句中引导非限定性定语从句
分句1：They were spurred by the inflation of the 1970’s
分句2：which，combined with California’s rapid population growth
分句3：pushed housing prices，as well as rents, to record levels
分句1是整个长句子的主句；分句2是分句1的定语从句，修饰inflation；
分句3同样是分句1的定语从句，主语仍然是上一句中的which。
译文 它们受到了20世纪70年代通货膨胀的刺激，这次通货膨胀与加利福尼亚州人口的迅速增长结合在一起，将房价与租金推到了创纪录水平。
3. In taking up a new life across the Atlantic，the early European settlers of the United States did not abandon the diversions with which their ancestors had traditionally relieved the tedium of life.
分析 介词提前的定语从句：with which ... ，其中which指前面的diversions。
分句1：In taking up a new life across the Atlantic
分句2：the early European settlers of the United States did not abandon the diversions
分句3：with which their ancestors had traditionally relieved the tedium of life
分句1和分句2嵌套；分句2和分句3嵌套；分句1是分句2的状语，分句3是修饰 diversions的定语从句，relieve with的搭配中介词with提前。
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