1. 有關定語從句的概念
(1)定語從句：就是在復合句里充當定語的從句，它通常緊靠在所修飾的名詞或代詞后面。
(2)先行詞：就是被定語從句修飾的名詞或代詞。
(3)關系詞：引導定語從句的詞叫關系詞。關系詞有關系代詞who, whom, whose, which和that等;關系副詞有when, where, why等。關系詞不僅起連接作用，而且還代表先行詞并在定語從句中擔任某一句子成分，關系代詞作主語、賓語、定語、表語等，關系副詞作狀語。如：
This is the book that my father bought me yesterday. 這就是我父親昨天幫我買的那本書。
說明：句中修飾the book的that my father bought me yesterday就是定語從句;被定語從句所修飾的the book這是先行詞;代表the book的關系代詞that在定語從句中作bought的直接賓語。
The time when he arrives is not known. 他到達的時間還不知道。
說明：句中when he arrives是定語從句，被定語從句修飾的the time是先行詞，關系副詞when作時間狀語。
2. 關系代詞的一般用法
先行詞是人，在從句中作主語用who，作賓語用whom或who，作定語用whose;先行詞是物，在定語從句中作主語或賓語都用which，作定語用of which或whose均可。在限制性定語從句中which, who, whom都可用that代替。關系代詞作賓語時常被省略。
This is the man who helped me yesterday. 這就是昨天幫助我的那個人。(作主語)
The teacher (who/whom/that) you want to see is coming. 你要見的老師來了。(作see的賓語，可以省略)
I met a boy whose father was a astronaut. 我認識一位男孩，他的父親是宇航員。(作定語)
Here is the coat which/that will be made to you. 這是一件做給你的衣服。(作主語)
This is the factory (which/that) we visited last year.這就是我們去年參觀的那家工廠。(作visited的賓語，可以省略)
He has a book whose cover (=the cover of which) is very beautiful. 他有一本封面非常漂亮的書。
3. 關 關系副詞有when, where, why，在定語從句中作狀語，分別表示時間、地點和原因。when的先行詞通常是time, day, season, age, occasion等時間名詞;where的先行詞通常是place, city, town, village, house, case, situation, scenes等地點或情形名詞;why的先行詞只能是reason。關系副詞when和where有時可用“介詞+which”代替，why可用for which代替。如：
There are occasions when (=on which) one must yield. 任何人都有不得不屈服的時候。
Beijing is the place where (=in which) I was born.北京是我的出生地。
Is this the reason why (=for which) he refused our offer?這就是他拒絕我們幫助他的理由嗎?
注意：先行詞雖然是時間或地點，但若在定語從句中作主語或賓語時，要用關系代詞。
(1)The factory where his father worked has closed. 他父親曾工作的那家工廠關閉了。(作狀語)
比較：The factory which/that was built in 1978 has closed. 1978年建的那家工廠關閉了。(作主語)
(2) I’ll never forget the days when we lived together. 我永遠也忘不了我們一起生活的那些日子。(作狀語)
比較：I’ll never forget the days (that) we spent in Australia. 我永遠也忘不了我們在澳大利亞度過的那些日子。(作及物動詞spent的賓語)
(3) The reason (why) she was ill was that she had eaten bad meat. 她生病的原因是她吃了變質的肉。(作狀語，用關系副詞)
比較：The reason (that) he gave for his absence was obviously fabricated.他所說的缺席理由顯然是編造的。(作gave的賓語，用關系代詞)
