定语从句（attributive clauses）在句中做定语，修饰一个名词或代词，被修饰的名词,词组或代词即先行词。定语从句通常出现在先行词之后，由关系词（关系代词或关系副词）引出。关系代词有：who,whom,whose,that,which等。关系副词有：when,where,why等。关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。1）who,whom,that
这些词代替的先行词是人的名词或代词，在从句中所起作用如下：
** he the man who/that wants to see you?他就是你想见的人吗？（who/that在从句中作主语）
he ** the man whom/that i saw yesterday.
他就是我昨天见的那个人。（whom/that在从句中作宾语）
2)whose 用来指人或物，(只用作定语,若指物，它还可以同of which互换）,例如：
they rushed over to help the man whose car had broken down.那人车坏了，大家都跑过去帮忙。please pass me the book whose(of which)cover ** green.请递给我那本绿皮的书。3）which,that
它们所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等，例如：
a prosperity which/that had never been seen before appears in the countryside.农村出现了前所未有的繁荣。（which/that在句中作主语）
the package(which/that)you are carrying ** about to come unwrapped.你拿的包快散了。(which/that在句中作宾语）
关系副词可代替的先行词是时间、地点或理由的名词，在从句中作状语。1）when,where,why
关系副词when,where,why的含义相当于"介词+which"结构，因此常常和"介词+which"结构交替使用，例如：
there are occasions when(on which)one must yield.任何人都有不得不屈服的时候。beijing ** the place where(in which)i was born.北京是我的出生地。** th** the reason why(for which)he refused our offer?这就是他拒绝我们帮助他的理由吗？2）that代替关系副词
that可以用于表示时间、地点、方式、理由的名词后取代when,where,why和"介词+which"引导的定语从句，在口语中that常被省略，例如：
h** father died the year(that/when/in which)he was born.他父亲在他出生那年逝世了。he ** unlikely to find the place(that/where/in which)he lived forty years ago.他不大可能找到他四十年前居住过的地方。判断关系代词与关系副词
方法一：用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
th** ** the mountain village where i stayed last year.
i'll never forget the days when i worked together with you.
判断改错（注：先显示题，再显示答案，横线；用不同的颜色表示出。（错）th** ** the mountain village where i v**ited last year.
（错）i will never forget the days when i spent in the countryside.
（对）th** ** the mountain village(which)i v**ited last year.
（对）i'll never forget the days(which)i spent in the countryside.
习惯上总把表地点或时间的名词与关系副词 where,when联系在一起。此两题错在关系词的误用上。方法二：准确判断先行词在定语从句中的成分(主、谓、宾、定、状)，也能正确选择出关系代词/关系副词。例1.** th** museum_you v**ited a few days age?a.where b.that c.on which d.the one
例2.** th** the museum_the exhibition was held.
a.where b.that c.on which d.the one
答案：例1 d，例2 a
例1变为肯定句：th** museum **_you v**ited a few days ago.
例2变为肯定句：th** ** the museum_the exhibition was held.
在句1中，所缺部分为宾语，而where,that,on which都不能起到宾语的作用，只有the one既做了主句的表语，又可做从句的宾语，可以省略关系代词，所以应选d。而句2中,主、谓、宾俱全，从句部分为句子的状语表地点，既可用副词where，又因 in the museum词组，可用介词in+which 引导地点状语。而此题中，介词on 用的不对，所以选a。关系词的选择依据在从句中所做的成分，先行词在从句中做主、定、宾语时，选择关系代词(who,whom,that,which,whose)；先行词在从句中做状语时，应选择关系副词(where 地点状语，when 时间状语，why 原因状语)。1)定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，例如：
th** ** the house which we bought last month.这是我们上个月买的那幢房子。（限制性）
the house,which we bought last month,** very nice.这幢房子很漂亮，是我们上个月买的。（非限制性）
2)当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的，例如：
charles smith,who was my former teacher,retired last year.查理·史密斯去年退休了，他曾经是我的老师。my house,which i bought last year,has got a lovely garden.我去年买的的那幢房子带着个漂亮的花园。th** novel,which i h**e read three times,** very touching.这本小说很动人，我已经读了三遍。3)非限制性定语从句还能将整个主句作为先行词,对其进行修饰,这时从句谓语动词要用第三人称单数，例如：
he seems not to h**e grasped what i meant,which greatly upsets me.他似乎没抓住我的意思，这使我心烦。liquid water changes to vapor,which ** called evaporation.液态水变为蒸汽，这就叫做蒸发。说明：关系代词that和关系副词why不能引导非限制性定语从句。1）介词后面的关系词不能省略。2）that前不能有介词。3）某些在从句中充当时间，地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换。th** ** the house in which i lived two years ago.
th** ** the house where i lived two years ago.
do you remember the day on which you joined our club?do you remember the day when you joined our club?由as,which 引导的非限定性定语从句，as和which可代整个主句，相当于and th**或and that。as一般放在句首，which在句中。as we know,smoking ** harmful to one's health.
the sun heats the earth,which ** very important to us.
典型例题
1）alice received an invitation from her boss,_came as a surpr**e.
a.it b.that c.which d.he
答案c.此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。2）the weather turned out to be very good,_was than we could expect.
a.what b.which c.that d.it
答案b。which可代替句子，用于非限定性定语从句，而what不可。that 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。3）it rained hard yesterday,_prevented me from going to the park.
a.that b.which c.as d.it
答案b.
as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：
(1）as 引导的定语从句可置于句首，而which不可。(2）as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which.在本题中，prevent由于是行为动词，所以正确选项应为b。as 的用法
例1.the same…as；such…as 中的as 是一种固定结构,和…一样…。i h**e got into the same trouble as he(has).
例2.as可引导非限制性从句，常带有'正如'。as we know,smoking ** harmful to one's health.
as ** know,smoking ** harmful to one's health.
as是关系代词。例1中的as作know的宾语；例2中，它充当从句的主语，谓语动词know要用被动式。1)whoever spits in public will be pun**hed here.
(whoever 可以用 anyone who 代替)
2)the parents will use what they h**e to send their son to technical school.
(what 可以用all that代替)
1）what=the thing which；whatever=anything
what you want has been sent here.
whatever you want makes no difference to me.
2)who=the person that whoever=anyone who
（错）who breaks the law will be pun**hed.
（错）whoever robbed the bank ** not clear.
（对）whoever breaks the law will be pun**hed.
（对）who robbed the bank ** not clear.
3)that 和 what
当that引导定语从句时，通常用作关系代词，而引导名词性从句时，是个不充当任何成分的连接词。宾语从句和表语从句中的that常可省略。what只能引导名词性从 句，用作连接代词，作从句的具体成分，且不能省略。i think(that)you will like the stamps.
what we need ** practice.
1）不用that的情况
a)在引导非限定性定语从句时。(错)the tree,that ** four hundred years old,** very famous here.
b)介词后不能用。we depend on the land from which we get our food.
we depend on the land that/which we get our food from.
2)只能用that作为定语从句的关系代词的情况
a)在there be 句型中，只用that，不用which。b)在不定代词，如：anything,nothing,the one,all,much,few,any,little等作先行词时，只用that，不用which。c)先行词有the only,the very修饰时，只用that。d)先行词为序数词、数词、形容词**时，只用that。e)先行词既有人，又有物时。举例：
all that ** needed ** a supply of oil.
所需的只是供油问题。finally,the thief handed everything that he had stolen to the police.
那贼最终把偷的全部东西交给了**。