定语从句由关系词（关系代词、关系副词）引导，关系代词、关系副词位于定语从句句首。
定语从句的特殊用法
定语从句由关系代词who、whom、whose、which、what、as和关系副词where、when、why等引导，但须记住：
不能引导定语从句.
2.关系词的分析须考虑它在定语从句中的`成分。
一.指人的关系代词有who、whose、whom、that.试分析：
Theoldmanwho/whom/thatwevisitedyesterdayisafamousartist.
MissWangistakingcareofthechildwhoseparentshavegonetoBeijing.
Themanwithwhommyfathershookhandsjustnowisourheadmaster.（=Themanwho/whomthatmyfathershookhandswithjustnowisourheadmaster.）注：
A．指人时有时只用who不宜用that。
1．先行词为one、ones或anyone
（1）ThecomradeIwanttolearnfromistheonewhostudieshardandworkshard.
（2）Anyonewhobreaksthelawshouldbepunished.
2．先行词为these时
ThesewhoaregoingtoBeijingarethebeststudentsofourschool.
3．在therebe开头的句子中
Thereisastudentwhowantstoseeyou.
4．一个句子中带有两个定语从句，其中一个定语从句的关系代词是that，另一个宜用who，以免重复。
Thestudentthatwonthefirstprizeisthemonitorwhoworkshards.
5．在非限制性定语从句中
A。Imetafriendofmineinthestreet,whohadjustcomefromJapan.
B．主句以who开头的句子中,只用that,不用who。
二．指物的关系代词有which、whose(=ofwhich)、that.试分析：
ethebookswhich/thatwerewrittenbyLuXun.
esks(which/that)wemadelastyearwereverygood.
isthehouseinwhichwelivedlastyear.(=Thisisthehousewhich/thatwelivedinlastyear.)
eintheroomwhosewindowsfacesouth.(=Iliveintheroom,thewindowsofwhichfacesouth.)
注：
A.介词如果位于作为其宾语的关系代词之前时，只能用whom、which不能用who或that.
(1)irlaboutwhomtheyweretalkingisourmonitor.
(2)ookinwhichtherearemanyinterestingthingswaswrittenbyLiMing.
B.部分短语动词中的介词不可与动词拆开，在定语从句中其介词不可前置，只能放在其动词之后。
Isthisthebookwhichsheislookingfor?
Theoldmanwho/whomtheyarewaitingforisProfessorLi.
Thechildwho/whomsheislookingafterisWangPing’sson.
C．指物时，下列情况下只能用that，不宜用which。
（1）先行词为不定代词，如All、much、anything、everything、nothing、something、none、theone等。
Wearewillingtodoanythingthatisgoodtothepeople.
Ihavetoldthemall(that)Iknow.
Allthatcanbedonehasbeendone.
（2）先行词是序数词或被序数词、修饰时。
ThefirstbookthatIreadlastnightwasanEnglishnovel.
（3）先行词是形容词最高级或被最高级修饰时。
ThisisoneofthemostinterestingfilmsthatIhaveeverseen.
Thisisthebestthatcanbedonenow.
（4）如果有两个或两个以上分别表示人和物的先行词时(先行词既有人又有物)，定语从句的关系代词用which和who都不合适，只能用that。
Weknownothingaboutthedoctorsandthehospitalsthatyouaretalkingabout.
Therearesheepandmenthatcanbeseenonthehill.
（5）如果先行词被theonly、thevery、thelast、thesame、any、few、little、no、all、oneof、just修饰时。
Thisistheonlybookthatcanbelenttoyou.
（6）当主句是以which开头的特殊问句时，关系代词只用that。
Whichisthedictionarythatheusedyesterday?
D．只物时，下列情况下只能用which，不宜用that。
（1）关系代词放在介词之后
Thisisthefactoryinwhichweonceworked.
（2）非限制性定语从句中
Thisisthebook,whichiswrittenbyLuXun.
（3）that，Those作主语时
ThosewhichareonthedeskareEnglishbooks.
E．先行词前有such、thesame、as时,关系代词用as，不用that,但thesame…as…表示同样的,thesame…that…表示同一的
Heknowsasmanypeopleasarepresentatthemeeting.
Suchpeopleasyourefertoarerarenowadays.
三．比较When/which、where/which、why.
whichIstillneverforget.
ThisisthedaywhenIjoinedtheparty.
whichhespentreadingthebooks.
whereIfoundthebook.
whichmakesmachines.
Thisistheplacewhichweoncevisited.
whichIwillneverforget.
whichIamlookingfor.
