關係代詞在定語從句中作主語時，從句謂語動詞的人稱和數要和先行詞保持一致。下面是本站小編給大家整理的定語從句的概念及用法簡介，希望能幫到大家!
定語從句是由關係代詞和關係副詞引導的從句，其作用是作定語修飾主句的某個成分，定語從句分為限定性和非限定性從句兩種。狀語從句分為時間狀語從句，結果狀語從句，讓步狀語從句，原因狀語從句，條件狀語從句以及行為方式狀語從句。名詞從句包括主語從句，賓語從句，表語從句和同位語從句及there be句型。
定語從句用法在複合句中，修飾名詞或代詞的從句叫定語從句，被修飾的名詞或代詞叫先行詞，引導定語從句的.有關係代詞who,whom,whose,which,that等和關係副詞where,when,why等，關係代詞和關係副詞在定語從句中擔任句子成份。
1.由who引導的定語從句中，who用作主語，如：This is the boy who often helps me.
2.由whom引導的定語從句中，whom用作賓語，如：The man whom you are waiting for has gone home.
3.由whose引導的定語從句中，whose用作定語，如：Do you know the girl whose skirt is white?
4.由which引導的定語從句中，which用作主語或謂語動詞的賓語或介詞的賓語，如：
The room in which there is a machine is a work shop.
The river which is in front of my house is very clean.
This is the pen which you want.
注意：
(1)whom,which用作介詞賓語時，介詞可放在whom、which之前，也可放在從句原來的位置上;但在含有介詞的動詞固定片語中，介詞只能放在原來的位置上。如：He is the very person whom we must take good care of.
(2)引導非限制性定語從句時，必須用關係代詞which，不用that,如：I have lost
my bag,which I like very much.
(3)關係代詞在句中作主語時，從句的謂語動詞的人稱和數必須和先行詞保持一致。
5.由that引導的定語從句中，that可以指人或物，在從句中作主語或謂語動詞的賓語，但不能放在介詞後面作介詞賓語，如：
The book that I bought yesterday was written by Lu Xun.?
注意在下面幾種情況下必須用that引導定語從句。
(1)先行詞是不定代詞all,few,little,much,something,nothing,anything等，如：
All that we have to do is to practise English.
(2)先行詞被序數詞或形容詞最高階所修飾，如
The first letter that I got from him will be kept.
(3)先行詞被all,any,every,each,few,little,no,some等修飾，如
I've eaten up all the food that you gave me.
(4)先行詞被the only,the very,the same,the last修飾時如
He is the only person that I want to talk with.
(5)先行詞既有人又有物時，如:
They talked about persons and things that they met.
(6)當句中已有who時，為避免重複，如：Who is the man that is giving us the
class?
6.由when,where,why引導的定語從句，如:
I don't know the reason why he was late.
This is the place where we have lived for 5 years.
I'll never forget the day when I met Mr Li for the first time.
注意：先行詞是表示地點時，如果從句的謂語動詞是及物的，就用that(which)，如果從句的謂語動詞是不及物的，就用where引導。This is the house Which/that he has lived in for 15 years.(Where he has lived for 15 year.)
7.限制性定語從句和非限制性定語從句
(1)限制性定語從句是句中不可缺少的組成部分，主句和從句之間不用逗號分開。引導非限制性定語從句的關係代詞有who,whom,whose,which,of which等，這些關係代詞都不能省略。
(2)非限制性定語從句是對主句先行詞的補充說明，沒有這種從句，不影響主句意思的完整，一般用逗號把主句和從句分開，關係代詞用which,不用that;指人時可用who,如：I have two brothers,who are both students.
8.如何簡化定語從句
(1).定語從句簡化為形容詞或形容詞短語作後置定語。如:
My grandfather lives in a village that is far away from here.
→My grandfather lives in a village far away from here.我祖父住在離這兒很遠的一個村子。
This is a book that is worth reading.
→This is a book worth reading.這是一本值得看的書。
(2)定語從句簡化為現在分詞或現在分詞短語作前置或後置定語。
The man who is standing under the tree is our English teacher.
→The man standing under the tree is our English teacher.
站在樹下面的那個人是我們的英語老師。
I saw the house that was burning at that time.→I saw the burning house at that time.
當時我看到那房子在燃燒。
(3)定語從句簡化為過去分詞短語作後置定語。
I like to see the films which are directed by Zhang Yimou.→I like to see the films directed by Zhang Yimou.我喜歡看張藝謀導演的電影。
She is the girl who was praised at the school meeting.→She is the girl praised at the school meeting.她就是在校會上受表彰的那個女孩。
(4)定語從句簡化為不定式作後置定語。
He is always the first person that comes to school.→He is always the first person to come to school.他總是第一個到校。
The report which will be given tomorrow is important to us.→The report to be given tomorrow is important to us.明天要作的報告對我們很重要。
(5)定語從句簡化為what從句。
I couldn't remember the words that he said.→I couldn't remember what he said.
我記不得他說的話。
定語從句結構定語從句公式
定語從句=先行詞+關係詞+從句
先行詞
指被定語從句修飾的名詞、代詞或句子。
一般先行詞出現在定語從句的前面。
關係詞
關係詞常有3個作用：
①連線作用，連線主句和定語從句。
②指代先行詞。
③在定語從句中擔當成分。
注：關係代詞有主語、賓語、定語之分。一般who做主語或其賓格形式的whom做賓語(whom作賓語時可省略)，whose作為定語(whose不可省略)。關係代詞在從句中作主語，賓語，定語等，關係副詞在從句中作地點狀語(where)，時間狀語(when)，原因狀語(why)。
定語
定語用來限定、修飾名詞或代詞，是對名詞或代詞起修飾、限定作用的詞、短語(動詞不定式短語、動名詞表示的)漢語中常用“……的”表示。主要由形容詞擔任，此外，名詞、代詞、數詞、分詞、副詞、不定式以及介詞短語也可以來擔任，也可以由一個句子來擔任。單詞作定語時通常放在它所修飾的詞之前，作前置定語。短語、從句作定語時則放在所修飾的詞之後，作後置定語。
被定語從句修飾的名詞、代詞稱為先行詞。如“the girl”，“the book”
如:She is the girl who likes singing. 她就是那個喜歡唱歌的女孩。
