定語從句）在句中做定語，修飾一個名詞或代詞，被修飾的名詞，片語或代詞即先行詞。那麼，定語從句包括哪些？
一、 限定性定語從句
1. that即可代表事物也可代表人，which代表事物；它們在從句中作主語或賓語，that在從句中作賓語時常可省略關係詞，which在從句中作賓語則不能省略。而且，如果which在從句中作“不及物動詞＋介詞”的介詞的賓語，注意介詞不要丟掉，而且介詞總是放在關係代詞which的前邊，但有的則放在它原來的位置
2. which作賓語時，根據先行詞與定語從句之間的語義關係，先行詞與which之間的介詞不能丟
3. 代表物時多用which，但在帶有下列詞的句子中用that而不用which，這些詞包括all, anything, much等，這時的that常被省略
4. who和whom引導的從句用來修飾人，分別作從句中的主語和賓語，whom作賓語時，要注意它可以作動詞的賓語也可以作介詞的賓語
5. where是關係副詞，用來表示地點的定語從句
6. when引導定語從句表示時間
［注］值得一提的是，表示時間“time"一詞的定語從句只用when引導，有時不用任何關係代詞，當然也不用that引導
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 besiness trip, he brings a lot of living necessities, such as towers, soap, toothbrush etc.
7. whose是關係代詞，修飾名詞作定語，相當於所修飾成分的前置所有格
8. 當從句的邏輯主語是some, any, no, somebody, anybody, nobody, something, anything, everything或nothing時，常用there is來引導
二、非限定性定語從句：
非限定性定語從句的'作用是對所修飾的成分作進一步說明，通常和主句間用逗號隔開，將從句拿掉後其他部分仍可成立
1. which引導的非限定性定語從句來說明前面整個句子的情況或主句的某一部分
2. 在引導限定性定語從句時，that有時相當於in which, at which, for which或at which
Attitudes towards daydreaming are changing in much the same way that(in which) attitudes towards night dreaming have changed. 人們對白日做夢的態度正在改變，這與人們對夜間做夢的看法的變化有非常相似之處。
I like the music for the very reason that(for which) he dislike it. 我出於某種原因喜歡這種音樂，而他恰恰與我相反。
We arrived the day that(on which) they left. 剛好我們到的那天他們走了。
3. 有時as也可用作關係代詞
4. 在非限定性定語從句中，不能用that，而用who, whom代表人，用which代表事物.
一.定語從句及相關術語
1.定語從句：修飾一個名詞或代詞的從句稱為定語從句，一般緊跟在它所修飾的先行詞後面。
2.關係詞：引導定語從句的關聯詞成為關係詞
關係詞有關係代詞和關係副詞。關係代詞有that, which, who, whom, whose, as等；關係副詞有where, when, why等。
關係詞常有3個作用：1，引導定語從句。2，代替先行詞。3，在定語從句中擔當一個成分。
二.關係代詞引導的定語從句
指人，在從句中做主語
(1) The boys who are playing football are from Class One.
(2) Yesterday I helped an old man who lost his way.
2. whom指人，在定語從句中充當賓語，常可省略。
(1) Mr. Liu is the person (whom) you talked about on the bus.
(2) Mr. Ling is just the boy whom I want to see.
注意：關係代詞whom在口語和非正式語體中常用who代替，可省略。
(3) The man who/whom you met just now is my friend.
3. which指物，在定語從句中做主語或者賓語，做賓語時可省略
(1) Football is a game which is liked by most boys.
(2) This is the pen (which) he bought yesterday.
4. that指人時，相當於who或者whom；指物時，相當於which。在賓語從句中做主語或者賓語，做賓語時可省略。
(5) The number of the people that/who come to visit the city each year rises one million.
(6) Where is the man that/whom I saw this morning?
5. whose通常指人，也可指物，在定語從句中做定語
(1) He has a friend whose father is a doctor.
(2) I once lived in a house whose roof has fallen in.
whose指物時，常用以下結構來代替
(3) The classroom whose door is broken will soon be repaired.
(4) The classroom the door of which is broken will soon be repaired.
(5) Do you like the book whose cover is yellow?
(6) Do you like the book the color of which is yellow?
三.介詞+關係代詞引導的定語從句
關係代詞在定語從句中做介詞賓語時，從句常由介詞+關係代詞引導
(1) The school (that/which) he once studied in is very famous.
(2) The school in which he once studied is very famous.
(3) Tomorrow I will bring here a magazine (that/which) you asked for.
(4) Tomorrow I will bring here a magazine for which you asked.
(5) We’ll go to hear the famous singer (whom/that/who) we have often talked about.
(6) We’ll go to hear the famous singer about whom we have often talked.
注意：1. 含有介詞的動詞短語一般不拆開使用，如：look for, look after, take care of等(1) This is the watch which/that I am looking for. (T)
(2) This is the watch for which I am looking. (F)
2. 若介詞放在關係代詞前，關係代詞指人時用whom，不可用who或者that；指物時用which，不能用that；關係代詞是所有格時用whose
(1) The man with whom you talked is my friend. (T)
(2) The man who/that you talked with is my friend. (F)
(3) The plane in which we flew to Canada is very comfortable. (T)
(4) The plane in that we flew in to Canada is very comfortable.(F)
