限制性定语从句与非限制性定语从句的区别限制性定语从句提供有关主语或宾语的重要信息，起限定作用，与被修饰部分的关系紧密，如果省略该从句会使主句语义表达不完整。
例如：This is the very pers on that is wan ted by the policeHe is the man who /that lives n ext door .It was a meeting whose importanee I did not realize at the time .非限制性定语从句只是用来对被修饰部分作补充性的说明，与先行词关系比较松散，先行词与从句间可以用逗号隔开，从句可略去：He will not be able to spe nd the holiday with his family, which is a big annoyance to him.The minister , who is to visit our university , is said to be a Qin ghua Uni versity graduate.The book, which your sister bought you in Xinhua Bookstore , is very useful in impro ving your spoke n En glish.The bus in essma n, whose suitcase has bee n found by a stra nger , has left for Beiji ng.如果定语从句的先行词是专有名词或是带有形容词性物主代词(my, his, etc)或形容词性指示代词(this, that, etc) 作限定词的名词词组，其后的定语从句通常为非限制性的。
例如：The Thames which is now clea n eno ugh to swim in , was polluted for overa hun dred years.My mother, who has been on a visit to Australia , will fly back tomorrow.All of these books, which have been donated by visiting professors , are tobe used by the children in Hope School.限制性定语从句的先行词只能是名词，代词或名词性词组，而非限制性定语从句的先行词除了是名词及名词性词组外，还可能是句子的一部分或是整个句子。
例如：They say he plays truant, which he doesn 't. [which 指代plays trua nt]The meeti ng was put off till n ext mon th, as we hoped. [as 扌旨前面的句子]下面的表格归纳了前面已提到的两者不同之处：表一：限制性定语从句与非限制性定语从句的区别3.2定语从句中的关系代词321关系代词that, which, who 在定语从句中做主语在限制性定语从句中，who或that用于指人，that或which用于指物，它们在定语从句中代替名词性主语或代词性主语，不能省略。
例如：He is the manwho/that lives here .[不能说：x He is the man who he lives here.]The bag which /that has been put there for a long time belongs to Wang Hong.3.2.2 who(m), which, that 在定语从句中作宾语表示人的时候用who(m)或that,它们在从句中代替名词性宾语或宾格代词，作定语从句宾语的whom/that通常可以省略，在口语中常用who代替whom例如：He' s the man whom that I met .There are some people here who I want you to meet.表示动物和东西的时候应用which/that:The pieces of music (that ) he has composedare sung by manypop sin gers.Taxes consist of money ( that ) people pay to support their gover nment.They' re the postcards which I sent from America .3.2.3 who(m), which 或that作介词的宾语，关系代词可省略。
定语从句的介词的位置非常重要，我们可以说：He is the person to whom I wrote .［非常正式用法］(但不可以说：x to who).或：He is the person who (n) I wrote to . /He is the person (whorj)I wrote to .This is the pan in which I boiled the milk .［非常正式用法］或：This is the pan which I boiled the milk in . / This is the pan (that/which ) I boiled the milk in3.2.4 whose + 名词关系代词whose是既可用于限制性定语从句，也可用于非限制性定语从句，在从句中作定语，一般用来指人，代替所有格形容词( my, his, your, her, its 等)，在从句中当定语，没有阴性、阳性或单数、复数的变化；有时也可指物，指物时可以用of which 代替。
例如：The professor whose daughter teaches you English is Dr. Williams.The bicycle whose brake was damagedhas now been repaired. =The bicycle, the brake of which was damaged has now been repaired.Edis on is a great inven tor whose fame is world-wide .3.2.5 that 的用法1、that只用于限制性定语从句，既可指人，又可指物，在句中用做主语或宾语。
(见 3.2.1、3.2.2 )2、当先行词是all ，much little, the one, anything, something, nothing,everything, none 等不定代词时，关系代词只用that。
例如：that can be done about it .There is littleThat's all that I knew about itIs there anything that I can do for you ?Have you done everything that is assigned to you ?3、先行词被形容词最高级以及first, last, any, only, few, much, no, some, very等词修饰时，关系代词只用that。
例如：It is the most interesting film that I ' ve ever read .The best thing that he could do at prese nt is to leave.This is the first time that he has bee n there .She is the only one that has fini shed her task on time .At the very beg inning, we have just too muchwork that n eeds to be done.4、在there be 句型中，只用that, 不用which。
例如：There are some people that I ' d like to introduce to you .There is a very interesting story that every child would like to liste n to .5、先行词既有人，又有物时，用that o例如：A victim is a person, animal or thing that suffers pain, death, harm, etc .The man and his dog that were n app ing outside the room were photographed by the journ alist.6、在“ It is + 名词+定语从句1 +定语从句2”的强调结构中，从句2要用that o例如：It is always the mouth which talks too muchthat in curs troubles .（言多必失。
）It is only a man who is quite experieneed that can fulfill this task .3.2.6 which 的用法1、which 一般只用于指物（a），有时也用来指性别不明的婴儿（b）。
例如：a: The tiles which fell off the roof caused serious damage. b: The babywhich the nurse has just brought in is John' s child.2、如果指物的关系代词紧跟在介词后面，只能用which，不能用that。
例如：This is the house in which she spent her childhood.The agency from which we bought our tickets is bankrupt.3、引导非限制性定语从句时，用来指物替代名词词组。
例如：This book, which has only been reviewed , was published a year ago.4、替代整个句子或句子的一部分：The meeting has been put off till next Friday, which is good news to them .（指代整个主句）She said that her son would becomea scientist , which we thought possible.（指代that 分句）She is very attentive in class , which he rarely is.（指代整个短语）3.2.7 as 的用法1、as引导限制性定语从句时，常与such或the same连用，构成thesame…as; such…as结构，as用于代替指人或物的先行词。