為什麼in which等於where或when？-介系詞加which的用法

which, where, when, why的用法

首先，我們先介紹一個重要的觀念：介系詞加上名詞或代名詞等於形容詞或副詞。而我們知道，which 是關係代名詞 – 具有連接詞功能的代名詞（想要進一步了解關係代名詞的用法，可以閱讀who, whom, whose的用法分別與that, which, who, whom的用法差異），而where, when 跟why是關係副詞（也就是具有連接詞功能的副詞）。由此可得，介系詞加which可以等於where, when跟why。

利用疑問句了解where, when, why

現在，先來複習一下6Ｗ疑問句。where問動作發生的地點，也就是地方副詞; when問動作發生的時間，也就是時間副詞; 而why問動作的原因。要記得，英文句子結構裡，疑問句的主詞跟動詞要倒裝。

1. He lives in New York.
   Where does John live?
   （where出現，句子的地方副詞就不見）
2. He visited Japan in 2018.
   When did he visit Japan? 
   （when出現，句子的時間副詞就不見）
3. He stayed up late for the test.
   Why did he stay up late?
   （why出現，句子的原因副詞就不見）

where, when跟why當關係副詞

了解where, when跟why代替句子的哪個部分後，我們用他們來造形容詞子句。要注意形容詞子句不是疑問句，主詞動詞不要倒裝。

1. He went to  Hong Kong.  He stayed in Hong Kong for a month.
   ＝He went to Hong Kong, where he stayed for a month.
   （在第二個句子中，in Hong Kong是地方副詞，用where代替，將where移到第二個句子的句首，並且將第二句放到第一句的Hong Kong後面）
2. She died on July 15th.  On the day, all her family except her were out on holiday. 
   =She died on July 15th, when all her family except her were out on holiday.
   （在第二個句子中，on the day是時間副詞，用when代替，因為the day = July 15th，所以將第二個句子放到July 15th後面）
3. That was the reason.  She did not come to your party for the reason.
   =That was the reason why she did not come to your party.
   （在第二個句子中，for the reason是原因副詞，用why代替，將why移到第二個句子的前面）

複習了以上這些基礎概念後，我們來將which跟where、which跟when、還有which跟why在形容詞子句裡的用法，一一對照說明清楚。

which, in which, where

which是關係代名詞，取代句子中的名詞或代名詞，而變成形容詞子句。

1. She put the basket on the table.  Her cat lay in the basket.  
   =She put the basket which her cat lay in on the table.
   (which 代替名詞the basket，in可以留在後面）
   =She put the basket in which her cat lay on the table.
   (in 也可以移到前面）

where則是關係副詞，取代句子中的地方副詞，讓句子變成形容詞子句。

1. She put the basket on the table.  Her cat lay in the basket.  
   =She put the basket where her cat lay on the table.
   (in the basket是地方副詞，用where代替）

一般來說，只有顯而易見的情況，使用where，（例如in the place, on the chair等），不然，還是用介系詞加上which來表達會比較清楚一點。下面列舉一些不同的介系詞加上which的例子。

1. She stood under the tree.  They had buried their treasure near the tree.
   =She stood under the tree near which they had buried their treasure.
   (不用where，因為讀者無法由where這個字，清楚知道位置。）
2. In the room, there was a window.  They put a table at the window.
   ＝In the room, there was a window at which they put a table.
   ＝In the room, there was a window where they put a table.
   (由前後文可以知道桌子跟窗戶的位置關係，所以可以使用where）
3. They swam in the river.  They put up their tent by the river,
   =They swam in the river by which they put up their tent.
   （不用where，因為無法清楚表達帳篷跟河的位置關係。）
4. Her cat lay under the chair.  She sat on the chair.
   =Her cat lay under the chair on which she sat.
   =Her cat lay under the chair where she sat.
   (可用where，因為大部分的情況是坐在椅子上.)

which, in which, when

應用同樣的概念，when取代句子中的時間副詞，而which一樣取代句子中的名詞。

1. She was born in 1945.  World War II came to an end in 1945.
   =She was born in 1945, in which World War II came to an end.
   =She was born in 1945, when World War II ended.
2. I like spring.  In spring flowers and trees come to life.
   =I like spring, in which flowers and trees come to life.
   =I like spring when flowers and trees come to life.
3. I will always remember the day.  On the day I lost my daughter.
   =I will always remember the day on which I lost my daughter.
   =I will always remember the day when I lost my daughter.
4. I did not know the time.  The earthquake hit at the time.
   =I did not know the time at which the earthquake hit.
   =I did not know the time when the earthquake hit.

which, for which, why

why取代句子中的原因，使用which的話就只有用for which

1.  That was the reason.  She worked so hard for the reason.
   =That was the reason for which she worked so hard.
   =That was the reason why she worked so hard.

接下來，要請讀者自己多造幾個句子，以便讓自己更熟練這個文法重點了。此外，如果你有其他文法上的疑惑，可以到我們『英文文法』專頁，看看有沒有文章探討相關文法問題。