Ⅰ. 定義
定語從句，起形容詞的作用，在句中常用來修飾名詞或代詞。被修飾的詞稱為先行詞,引導定語從句的詞稱為關系詞, 關系詞的作用一是放在先行詞與定語從句中間起引導作用;二是在意義上代替先行詞,并在從句中充當一個成分。其中關系代詞：who, whom, whose, which, that, as;關系副詞：when, where, why。
eg. She is the girl who sings best of all.
The pen which my uncle gave me is missing.
He lives in a house whose windows face south.
The factory where my father works is in the east of the city.
Perhaps the day will come when people will be able to breathe clean air in cities.
Ⅱ. 關系代詞
1. 先行詞是人，作主語，關系代詞用who, that
eg. He is a man( ) never leaves today’s work till tomorrow.
The boy ( ) is standing there is my cousin.
2. 先行詞是人，作賓語，關系代詞用 whom, who, that,
eg. Here is the man ( ) you’ve been expecting to meet.
The man ( ) you met yesterday is Mr. Smith.
3. 先行詞是物，作主語，關系代詞用which, that
eg . The train ( ) has just left is for Guangzhou.
Children like to read books ( ) have wonderful pictures.
4. 先行詞是物，作賓語，關系代詞用which, that,或省略
eg. The book ( ) you borrowed yesterday is really interesting.
The pen ( ) my uncle gave me is missing.
5. 先行詞是人、物，作定語，關系代詞用whose
eg. He is the professor ( ) name was Jackson.
China, ( ) population is the largest in the world, is developing very fast.
Ⅲ. 關系副詞
1. 先行詞是表示時間的名詞，在定從中作時間狀語，關系代詞用when
eg. I can’t remember the date ( ) he went abroad.
I’ll never forget the day ( ) I joined the army.
2. 先行詞是表示地點的名詞，在定從中作地點狀語，關系代詞用where; 其中注意表示抽象概念的地點名詞，如，situation、stage、degree、point等表示方面或程度時，也需用where
eg. This is the village ( ) Uncle Wang once lived.
They have reached the point ( ) they have to separate with each other.
He’s got himself into a dangerous situation ( ) he is likely to lose control over the plane.
3. 先行詞是reason，在定從中作原因狀語，關系代詞用why
eg. I don’t know the reason ( ) he was late.
None of us know the reason ( ) Tom was absent from the meeting.
4.引導定語從句的關系副詞也可以用“適當介詞 + which”來代替。
eg. October 1, 1949 was the day when ( = ) the People’s Republic of China was founded.
This is the factory where(= ) we worked a year ago.
I don’t believe the reason why (= ) he was late for school.
Ⅳ. 關系代詞that & which的區別:
⒈ 只用that的情況
① 先行詞為all, everything, anything, nothing, little, much等不定代詞時。
eg. There is nothing ( ) can Pvent him from doing it.
② 先行詞被any, only, few, no, very, little 等修飾時。
eg. This is the very book ( ) I’m looking for.
③ 先行詞被形容詞最高級或序數詞修飾時。
eg. The first place ( ) they visited in Guilin was Elephant Trunk Hill.
This is the best film ( ) I have ever seen.
④ 先行詞既有人又有物時。
eg. He talked about things and persons ( ) they remembered in the school.
⑤ 先行詞被the only, the very修飾時。
eg. Mr. Smith is the only foreigner ( ) he knows.
⑥ 句中已有who或which,為了避免重復時。
eg. Who is the man ( ) is standing beside Tom?
⒉ 不能用 that的情況：
① 引導非限制性定語從句;
eg. He had failed in the maths exam , ( ) made his father very angry.
② 介詞 + 關系代詞。
eg. This is the room in( ) my father lived last year.
Ⅴ. as引導定語從句時的用法(as 相當于that & which)
① as引導限制性定語從句通常用于the same … as, such … as結構中。
eg. This is the same book ( ) I lent you.
Such machines ( ) are used in our workshop are made in China.
② as引導非限制性定語從句既可放在主句之前，也可放在主句之后，位置靈活，用來修飾整個句子。通常用下列句型：as is known to all, as is said, as is reported, as is announced, as we all know, as I expect 等。
eg. ( ) I expected, he got the first place again in this mid-term examination.
Taiwan, ( ) we all know, belongs to China.
Ⅵ. 限制性定語從句和非限制性定語從句的主要區別:
限制性定語從句: 一般緊跟在先行詞后面,不用逗號把從句與先行詞分隔開來。使先行詞的意思十分明確,成為特定的人或物,是句子中不可缺少的成分,少了它句子就會失去意義不能成立,或意思不清楚,不能說明問題。通常譯為定語。
非限制性定語從句: 通常由逗號與句子其他成分隔開。只是對先行詞作進一步的說明,沒有它句子仍能成立,意思仍很清楚。通常譯為并列的句子。
eg. I was the only person in our office ( ) was invited.(去掉定語從句，意思就不完整)
Tom’s father, ( ) is over sixty, still works hard day and night.(整個句子可分成兩句來翻譯)
Ⅶ. 分隔定語從句
即先行詞與關系代詞、副詞之間被介詞短語，同位語，謂語等分隔開來。
此種定語從句，在選擇關系詞時，要注意找準先行詞。
eg. There is an exPssion in his eyes ( )I can’t understand.
I was the only person in my office ( ) was invited to the important ball.
I suggest you choose someone I think ( ) is very kind and friendly.
