1.that既可代表事物也可代表人,which代表事物；它们在从句中作主语或宾语,that在从句中作宾语时常可省略关系词,which在从句中作宾语则不能省略.而且,如果which在从句中作“不及物动词＋介词”的介词的宾语,注意介词不要丢掉,而且介词总是放在关系代词which的前边,但有的则放在它原来的位置
2.which作宾语时,根据先行词与定语从句之间的语义关系,先行词与which之间的介词不能丢
3.代表物时多用which,但在带有下列词的句子中用that而不用which,这些词包括当先行词是anything,everything,nothing ,few,all,none,little,some等代词时,或者是由every,any,all,some,no,little,few,much等修饰时等,这时的that常被省略
4.who和whom引导的从句用来修饰人,分别作从句中的主语和宾语,whom作宾语时,要注意它可以作动词的宾语也可以作介词的宾语
5.where是关系副词,用来表示地点的定语从句
6.when引导定语从句表示时间〔注〕值得一提的是,表示时间“time"一词的定语从句只用when引导,有时不用任何关系代词,当然也不用that引导
By the time you arrive in London,we will have stayed there for two weeks.I still remember the first time I met her.Each time he goes to business trip,he brings a lot of living necessities,such as towers,soap,toothbrush etc.
7.whose是关系代词,修饰名词作定语,相当于所修饰成分的前置所有格.它引导的从句可以修饰人和物,当它引导的从句修饰物体时,可以与 of which 调换,表达的意思一样.
8.当从句的逻辑主语是some,any,no,somebody,anybody,nobody,something,anything,everything或nothing时,常用there is来引导
There is somebody here who wants to speak to you.这里有人要和你说话.
编辑本段（二）非限定性定语从句
非限定性定语从句的作用是对所修饰的成分作进一步说明,通常是引导词和先行词之间用逗号隔开,将从句拿掉后其他部分仍可成立
1.which引导的非限定性定语从句来说明前面整个句子的情况或主句的某一部分
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.
This novel,which I have read three times,is 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 have 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 is called evaporation.液态水变为蒸汽,这就叫做蒸发.
4.有时as也可用作关系代词
5.在非限定性定语从句中,不能用关系副词why和关系代词that,而用who,whom代表人,用which代表事物.；
（十）关系代词that 的用法
(1)不用that的情况
(a) 在引导非限定性定语从句时.
(错)The tree,that is four hundred years old,Is 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,the same,the last,just修饰时,只用that.
(d) 先行词为序数词、数词、形容词最高级时,只用that..
(e) 先行词既有人,又有物时.
(f) 先行词指物,在主句中作表语时．
(g) 为了避免重复．
(h)先行词是the way时
举例：
Is this the book that you borrowed in the library?
这是你在图书馆借的那本书吗?
Who that break the window should be punished．
谁打碎了窗户都要受到惩罚．
All that is needed is 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警察.
