【摘  要】定语从句是高中英语的语法重点，它是用一个句子对另一个句子成份的修饰与限定，但在运用过程中会出现较多的失误，原因为学生在学习过程中对一些细节及本质理解掌握不够好，现对这些地方加以说明与阐述。
【关键词】限定；成份；用法
        定语从句是用一个句子对另一个句子的一个成份或部分进行修饰与限定，被修饰的词叫先行词，由名词或代词充当。引导定语从句的关系词有that. which. who. whose. whete. when. why.定语从句从类型上分为限定型定语从句与非限定性定语从句。连接词是连接从句与修饰词的桥梁，它在句中起连接作用并充当从句中的某个成份，如：主语、宾语、状语等。
        1．限定性定语从句：
        1）由that引导的定语从句，that在从句中指人或物，在从句中作主语或宾语，但不能放在介词后作介词宾语。
        eg.  i know the girl that attended the party.     （作主语）
        that’s the job that i’m huntirg for.      （作宾语）
        2）由which引导定语从句，which在从句中指人、指物，在从句中作主语或宾语，也可作介词的宾语。WWw.11665.COM
        eg.  he came from a farmily which was very poor.  （作主语）
        this is the pen which you want.              （作宾语）
        this is the room in which i want to cive.       （作介词的定语）
        3）由who. whom.  whose引导定语从句
        who作主语.whom作宾语.whose作定语.
        eg.  i met someone who said he knew you.       （作主语）
        is that the man whom you referred to?       （作宾语）
        confucius is the philosopher whose influerce has been the greatest.（作定语）
        4）when. where. why由引导定语从句。
        先行词表时间，在从句中充当状语用when引导.
        先行词表地点，在从句中充当状语用where引导，充当宾语由that或which引导。
        先行词表原因，在从句中充当状语用why引导.
        eg.  it is also a time when there were many great philosophers.
        c. f  1) this is the room where he cived last year.      （作状语）
        2) this is the school which he visited last year.      （作宾语）
        the reason why people are unhappy is that they do not have erough love.（作状语）
        同时在限定性定语从句中that. which的用法还有另外一些限制与要求。

        a．只能用that，不能用which连接的定语从句。
        1．先行词部分有不定代词，few. all. little. much. something. nothing. everthirg时.
        eg.  all that we have to do is to practise every day.
        2．先行词部分有序数词或形容词最高级修饰时。
        eg.  the last lesson that i learned will be forgotten.
        3．先行词被all. any. every. few. little. no. some修饰时。
        eg.  i have read all the books that you gave me.
        4．先行词被the only. the very. the same. the last修饰时。
        eg.  he is the only person that i want to talk to.
        5．先行词部分既有人、又有物时。
        eg.  they talked of thirgs and persons that they remembered in the factory.
        b．只能用which不能用that.
        1．如句中有两个定语从句，其中一个用that则另一个用which。
        eg.  let me show you the novel that i borrowed from the library which was nearly open to us.
        2．前面紧接介词
        eg.  this is the story about which he is talking now.
        3.that不能用在非限定性定语从句中。
        2．非限定性定语从句。
        1）限定性定句从句表明修饰语与中心词之间的关系密切,如去掉从句，则意义不完整。
        2）非限定性定语从句表明先行词与修饰语的关系不十分密切，去掉从句、主句子意思仍完整，形式上用逗号把主，从句隔开。
        eg.  tom’s father, who is over severty, still works hard day and night.
        总之定语从句在使用过程中有时也相当于分词短语，是掌握分词短语作后置定语的前提与基础，充分理解定语从句的作用，对于更好掌握修饰修语具有重大作用。

参考文献：
[1]　章振邦主编《简明英语语法》。
[2]　高中英语教学参考《人民教育出版社》。