定语从句（形容词性从句）
在句中修饰名词或代词的从句，因其修饰作用相当于形容词，故称形容词性从句，即通常所说的定语从句。被定语从句修饰的词叫先行词。引导定语从句的有：
1）关系代词： 先行词为人：who, whom, that, whose
先行词为物：which, that, whose
2）关系副词：when, where, why
注意： 关系词起三个作用：①连接先行词和定于从句②替代先行词③在从句中担任成分
what不能引导定语从句。定语从句一般紧跟在先行词后，但有时也被一个短语隔开。
例如：I was the only person in my office who was invited.
1. 关系代词和关系副词的一般用法
1) 关系代词在从句中充当主语、宾语或表语等成分，关系代词充当宾语、表语时可以省略：
Here’s a fellow who just walks into a bank and helps himself to so much money. （作主语）
He is no longer the man (that) he used to be. （作表语）
This is the book（that/which）I referred to in my talk. (作宾语)
whose在定语从句中置于名词之前，充当定语，既可指人，又可指物。
whose +n.= the +n.+ of which/whom。例如：
Please pass me the dictionary whose cover is black. （指物）
=Please pass me the dictionary the cover of which is black.
The doctor, whose name was Johnson, lived in a small town in the north of England. （指人）
=The doctor, the name of whom was Johnson, lived in a small town in the north of England.
2) 关系副词when, where, why在从句中充当状语，分别可表时间、地点或原因。
I will never forget the day when I first came to Beijing.
This is the house where Lu Xun once lived.
I know the reason why he came late.
注：先行词是the way时，其后的定语从句关系词有三种，例如：
I like the way in which / (that)the teacher gives his lessons.
从句缺少的是主语、宾语还是状语是确定用关系代词还是关系副词的关键。也就是说要看先行词在定语从句中担任什么成分
试比较：
I will never forget the day (which/that) I spent in Hongkong.
( spent是及物动词，后缺宾语，因此用关系代词或省略 )
I will never forget the day when/on which Hongkong returned to its motherland.
（ 从句主谓宾结构完整，缺状语，因此用关系副词或介词加关系代词 ）
The reason （that/which）he gave for not coming to school yesterday is unbelievable.
( gave是及物动词，后缺宾语，因此用关系代词或省略 )
The reason why he didn’t come to school yesterday is unbelievable.
（ 从句主谓宾结构完整，缺状语，因此用关系副词或介词加关系代词 ）
2．限制性定语从句与非限制性定语从句
限制性定语从句对先行词起限定作用，去掉后主句意义就变得不明确，它与主句之间没有逗号分隔。例如：
This is a shop that sells personal computers.
The watch that I bought yesterday works well.
非限制性定语从句与主句之间的关系相对松散一些，它对先行词起补充说明作用，去掉后不影响主句意义。因此，一些具有区别意义的专有名词及一些表示“唯一”概念的人或物后面常用此类从句。这类从句与主句之间有逗号隔开。例如：
We are all proud of the Great Wall, which is one of the man-made wonders of the world.
My father, who is a doctor, often encourages me to work hard.
注意：在非限制性定语从句中作宾语的关系代词不能省去。
一种特殊的非限制性定语从句
在非限制性定语从句中，有时根据句子意思，常把some, any, none, all, both, several, many, most, neither, either等词、分数或百分比与of whom或of which连用。
He has five children, two of whom are abroad.
(比较：He has five children, and two of them are abroad.)
We have tested three hundred types of boots, none of which is/are completely waterproof.
(比较：We have tested three hundred types of boots, but none of them is/are completely waterproof.)
3．介词+关系代词的用法
关系代词紧跟在介词后面时，不能用that，也不能省略，常用which或whom。
介词的选用可根据从句中的相关词组确定，该介词通常可以放在关系代词之前，也可放在从句之尾。例如：
The man (who/whom/that) I talked about at the meeting is from Beijing University.
=The man about whom I talked at the meeting is from Beijing University.
The palace (which/that) I often pay a visit to was built in the 17th century.
=The palace to which I often pay a visit was built in the 17th century.
但遇固定词组时，介词一般紧跟词组主体，不作前置。如：
Is this the book (which/that) you are looking for? ( 这里介词for一般不提前，因为look for是固定词组，意为“寻找”，介词for若被提前，单个的look意为“看”，句意不符。)
介词也可结合句意、根据先行词确定，此时介词以前置为佳。
Last night I had a dream in which I became a Nobel Prize winner.
The girl with whom I went to the concert yesterday is my sister.
I need a pen with which I can write a letter.
I need a piece of paper on which I can write a letter.
4．关系代词的一些特定用法：that与which；that与who
1）指物时，关系代词that和which一般情况下可换用，但以下几种情况下一般用that，不用which：
①先行词是all, everything, something, anything, nothing, none, few, little, much等不定代词；或是先行词被all, every, some, any, no, few, little等修饰时：
Is there anything (that) I can do for you in town?
I have read all the books (that) you gave me.
注：当something确指某物或某事时，用that或which都可以，如：
There is something that/which keeps worrying me. “有一件事一直令我不安。”
②先行词被形容词最高级或有序数词the first, the second…, the last修饰时：
This is the best film (that) I have ever seen.
The first place (that) we’ll visit is the Great Wall.
③先行词被the only，the very修饰时：
The only thing that matters is to find our way home.
This is the very book (that) I’ve been looking for.
④先行词既有人又有物时：
They talked about the persons and things (that) they remembered in the school.
⑤当主句是由who或which引导的特殊问句时，为避免重复，定语从句中常用that：
Who is the man that is standing by the door?
Who that has common sense will do such a thing?
Which is the dictionary (that) you bought yesterday?
Which that you bought just now is for me?
⑥两个定语从句，一个用which一个用that
Edison built up a factory which produced things that had never been seen before.
2)用which不用that：
①介词后②非限制性定于从句中③两个定语从句，一个用that一个用which
3)当先行词是anyone, those, he, she等代词表“人”时，一般用who而不用that：
Anyone who wants a ticket please sign your name here.
Those who want to go to the English party must be at the school gate by 7:30 p.m.
He who doesn’t reach the Great Wall is not a true man.
但当关系代词在定语从句中作表语时，通常用that而不用who：
He is no longer the man that he used to be.
5．定语从句中的as及其与which的异同
1）as引导的限制性定语从句：
当先行词有the same, such, as, so修饰时，要用as代替who(m), which, that来引导定语从句：
I’d like to have the same books as are used in your school.
He is not such a person as I expected.
He will marry as pretty a girl as he can find.
注意区别：
It was such a good film that I saw it yesterday.
Don’t talk about such things as you don’t understand.
Here is so big a stone that no one can move it.
Here is so big a stone as no one can move.
His speech was so clear that we could understand well.
He knows as many people as are present.
Yesterday she bought the same book as I have.
He is the same man that gave us a talk last year.
2）as引导的非限制性定语从句与which引导的非限制性定语从句的异同
which和as都可以指代主句中的一部分或整个句子的内容，有时可以互换：
Our team lost the game, as/which was reported in the newspaper.
She was terrified, as/which I could see from her eyes.
区别：①as引导的非限制性定语从句可以放在主句前面、插在主句中间或放在主句末尾；而which引导的非限制性定语从句只能放在主句后面。例如：
As anybody can see, the elephant is like a snake.
=The elephant, as anybody can see, is like a snake.
=The elephant is like a snake, as anybody can see.
Mary was late again, which made the teacher angry.
②as引导的从句有“正如”、“正像”之意，常用句型有：
as we all know, as is known to all, as everybody can see, as is expected等。
例如：As we all know, paper was first made in China.
Which引导的从句是对主句的评论或主句造成的结果。Which= and this
He failed in the experiment, which was unexpected.
He stole the money, which was disgraceful.
6. He is one of the workers who live in the factory.
He is the only one of the workers who has been there.
典型例题分析
1．All ____ is needed is a supply of oil. ( ’89 )
A. the thing B. that C. what D. which
解析：本题考查引导定语从句的关系词，what只能用于名词性从句，因此A/D可以排除，又因先行词为不定代词all，所以答案为B。
2．He paid the boys $10 for washing ten windows, most of ____ hadn’t been cleaned for at least a year. ( ’90 )
A. these B. those C. that D. which
解析：本题考察非限制性定语从句。从句子结构上看，两句之间用的是逗号，无连词连接，故确定为从属句，介词后面的关系代词代物，只能用which，答案为D。
3．In the dark street, there wasn’t a single person ____ she could turn for help. ( ’92 )
A. that B. who C. from whom D. to whom
解析：本题考查定语从句中介词加关系代词的用法。根据句意“向某人求助”是turn to sb. for help，其中介词to可提前，故答案为D。本句也可以如下表达：In the dark street, there wasn’t a single person (who/whom/that) she could turn to for help.)
4．After living in Paris for fifty years, he returned to the small town ____ he grew up as a child.
A. which B. where C. that D. when ( ’96 )
解析：本题考查关系代词和关系副词的用法，从句he grew up as a child不缺主语或宾语，排除关系代词which和that，又因先行词是表地点的，故答案为A。
5．Dorothy was always speaking highly of her role in the play, ____, of course, made the others unhappy. ( 2000 )
A. who B. which C. this D. what
解析：本题考查非限制性定语从句指代整个句子的用法，意为“老是自赞她在剧中表演的角色，这件事当然令他人不快。”指代前面所说的整句话，用which。故答案为B。从句中插入of course增加了考测难度，解题时可先把它忽略。
6．It was about 600 years ago ____ the first clock with a face and an hour hand was made. ( ’97 )
A. that B. until C. before D. when
解析：本题考查强调结构It was … that…，不管被强调的是时间还是地点，that不变，该结构与定语从句非常相似，注意区别。