定語從句由關係詞（關係代詞、關係副詞）引導，關係代詞、關係副詞位於定語從句句首。
定語從句的特殊用法
定語從句由關係代詞who、whom、whose、which、what、as和關係副詞where、when、why等引導，但須記住：
不能引導定語從句.
2.關係詞的分析須考慮它在定語從句中的`成分。
一.指人的關係代詞有who、whose、whom、that.試分析：
Theoldmanwho/whom/thatwevisitedyesterdayisafamousartist.
MissWangistakingcareofthechildwhoseparentshavegonetoBeijing.
Themanwithwhommyfathershookhandsjustnowisourheadmaster.（=Themanwho/whomthatmyfathershookhandswithjustnowisourheadmaster.）注：
A．指人時有時只用who不宜用that。
1．先行詞爲one、ones或anyone
（1）ThecomradeIwanttolearnfromistheonewhostudieshardandworkshard.
（2）Anyonewhobreaksthelawshouldbepunished.
2．先行詞爲these時
ThesewhoaregoingtoBeijingarethebeststudentsofourschool.
3．在therebe開頭的句子中
Thereisastudentwhowantstoseeyou.
4．一個句子中帶有兩個定語從句，其中一個定語從句的關係代詞是that，另一個宜用who，以免重複。
Thestudentthatwonthefirstprizeisthemonitorwhoworkshards.
5．在非限制性定語從句中
A。Imetafriendofmineinthestreet,whohadjustcomefromJapan.
B．主句以who開頭的句子中,只用that,不用who。
二．指物的關係代詞有which、whose(=ofwhich)、that.試分析：
ethebookswhich/thatwerewrittenbyLuXun.
esks(which/that)wemadelastyearwereverygood.
isthehouseinwhichwelivedlastyear.(=Thisisthehousewhich/thatwelivedinlastyear.)
eintheroomwhosewindowsfacesouth.(=Iliveintheroom,thewindowsofwhichfacesouth.)
注：
A.介詞如果位於作爲其賓語的關係代詞之前時，只能用whom、which不能用who或that.
(1)irlaboutwhomtheyweretalkingisourmonitor.
(2)ookinwhichtherearemanyinterestingthingswaswrittenbyLiMing.
B.部分短語動詞中的介詞不可與動詞拆開，在定語從句中其介詞不可前置，只能放在其動詞之後。
Isthisthebookwhichsheislookingfor?
Theoldmanwho/whomtheyarewaitingforisProfessorLi.
Thechildwho/whomsheislookingafterisWangPing’sson.
C．指物時，下列情況下只能用that，不宜用which。
（1）先行詞爲不定代詞，如All、much、anything、everything、nothing、something、none、theone等。
Wearewillingtodoanythingthatisgoodtothepeople.
Ihavetoldthemall(that)Iknow.
Allthatcanbedonehasbeendone.
（2）先行詞是序數詞或被序數詞、修飾時。
ThefirstbookthatIreadlastnightwasanEnglishnovel.
（3）先行詞是形容詞最高級或被最高級修飾時。
ThisisoneofthemostinterestingfilmsthatIhaveeverseen.
Thisisthebestthatcanbedonenow.
（4）如果有兩個或兩個以上分別表示人和物的先行詞時(先行詞既有人又有物)，定語從句的關係代詞用which和who都不合適，只能用that。
Weknownothingaboutthedoctorsandthehospitalsthatyouaretalkingabout.
Therearesheepandmenthatcanbeseenonthehill.
（5）如果先行詞被theonly、thevery、thelast、thesame、any、few、little、no、all、oneof、just修飾時。
Thisistheonlybookthatcanbelenttoyou.
（6）當主句是以which開頭的特殊問句時，關係代詞只用that。
Whichisthedictionarythatheusedyesterday?
D．只物時，下列情況下只能用which，不宜用that。
（1）關係代詞放在介詞之後
Thisisthefactoryinwhichweonceworked.
（2）非限制性定語從句中
Thisisthebook,whichiswrittenbyLuXun.
（3）that，Those作主語時
ThosewhichareonthedeskareEnglishbooks.
E．先行詞前有such、thesame、as時,關係代詞用as，不用that,但thesame…as…表示同樣的,thesame…that…表示同一的
Heknowsasmanypeopleasarepresentatthemeeting.
Suchpeopleasyourefertoarerarenowadays.
三．比較When/which、where/which、why.
whichIstillneverforget.
ThisisthedaywhenIjoinedtheparty.
whichhespentreadingthebooks.
whereIfoundthebook.
whichmakesmachines.
Thisistheplacewhichweoncevisited.
whichIwillneverforget.
whichIamlookingfor.
