定語從句which與where
which引導定語從句的時候,在從句中作主語,賓語或是表語，分享了定語從句which與where用法。
一、關係副詞與“介詞+which”互換的情形
當“介詞+ which”在定語從句中作時間、地點和原因狀語時，可以用相應的關係副詞when, where和why來替換。
1. when根據情況可以等於in which, at which, on which等。如：
The day when (=on which) she arrived was Thursday. 她到的那天是星期四。
July and August are the months when (=in which) the weather is hot. 七八月是天氣很熱的月份。——摘自《英語常用詞多用途詞典》（金盾出版社）
這種替換有時出現在非限制性定語從句中。如：
We’ll put off the picnic until next week, when (=by then) the weather may be better. 我們將把野餐推遲到下星期，那時天氣可能會好一點。——摘自《張道真英語語法》（商務印書館）
2. where根據情況可以等於in which, at which, on which等。如：
This is the hotel where ( =in which / at which) they were staying. 這就是他們當時住的旅店。——摘自《英語常用詞多用途詞典》（金盾出版社）
Do you remember the place where (=at which) we had lunch? 你記得我們吃午飯的地方嗎? ——摘自《英語用法指南》（外研社）
這種替換有時出現在非限制性定語從句中。如：
The Tower of London, where (=in which so many people lost their lives, is now a tourist attraction. 在倫敦塔中曾有許多人喪命，它現在是旅遊勝地。——摘自《朗文英語語法》（外研社）
3. 關係副詞若要換成“介詞+which”只能是for which。如：
The reason why (=for which) I came here was to be with my family. 我到這裏來的原因是要跟我的家裏人在一起。——摘自《英語用法指南》（外研社）
My success in business, the reason why (=for which) he dislikes me, has been due to hard work. 他為我在事業上的成功而不喜歡我，我的成功歸功於我努力工作。——摘自《朗文英語語法》（外研社）
但是，反過來，for which並不一定能換成why。如：
The documents for which they were searching have been recovered. 他們找尋的文件已經找到了。（此句中的for which也不能換成why，理由同上句）——摘自《高中英語語法詳解》（湖南大學出版社）
二、關係副詞與“介詞+which”不能互換的情形
1. 有些語境需要用特定的介詞來明確其關係，此時若換成關係副詞，則會導致意思不明確或句意不能通順。如：
The ladder on which I was standing began to slip. 我腳下的梯子開始向下滑動。（句中的on which不能換成where，否則意思不明確）
This I did at nine o’clock, after which I sat reading the paper. 九點鐘時我做這事，之後我坐着看報。（句中的after which不能換成when，否則意思不明確）
2. 當“介詞+which”後面接有被which修飾的名詞時，通常不能用關係副詞代替。如：
The programme will continue until 1994 by which time $3million will have been spent.
這個項目將持續到1994年。到那時開支將達到300萬美元。（句中的by which time不能換成when或where，因為which後跟有它所修飾的'名詞time）——摘自《限定詞與數量詞》（外文出版社）
We arrived at noon, by which time the demonstration was over. 我們是中午到的，這時遊業已結束。（句中的by which time不能換成when或where，因為which後跟有它所修飾的名詞time）——摘自《英語常用詞多用途詞典》（金盾出版社）
3. 當“介詞+which”並不表示時間、地點或原因時，自然不能換成關係副詞。
There are three principal routes by which one can drive to North Wales. 開車到北威爾士，有3條主要路線可走。（句中的by which不能換成when或where，因為這裏的by which並不表示時間或地點，介詞by在此表示“通過”）——摘自《英語常用詞多用途詞典》（金盾出版社）
This is a subject about which we might argue for a long while. 這是一個我們可能長時間爭論的問題。（句中的about which不能換成when或where，因為這裏的about which並不表示時間或地點，介詞about在此表示“關於”，所涉及的搭配是argue about）——摘自《張道真英語語法
4、在表語從句和狀語從句中不能互換
1.在表語從句中
Is this hotel ______ you said we were to stay in your letter？.
A. that B. where C. the one D. in which
此題可改為：This hotel is where you said we were to stay in your letter．實際上是由where引導的表語從句，答案為B項。
2.在狀語從句中
We had better put the bottle of dleeping pills__kids can not find it in case they mistake the pills for candies.此句中“where”並非引導定語從句，而是引導地點狀語從句，故不能用"in which".
若用"in which",那句子就變成了定語從句，
in which kids can not find...
= in the sleeping pill kids can not find...
句子就無法理解通了。
3.當定語從句帶有不定式時，只能用prep.+which
如，I want a pen with which to write.
I live in a house in which to spend my rest life.
不能用 I live in a house where to spend my rest life.
