Relative Clause 關係從句

Relative pronoun 關係代名詞: that, which, whichever, who, whoever, whom, whomever, whose, of which

你可以視之為引導詞，將一句完整句子*附上主要句子上。由 relative pronoun 作主詞的句子是用以形容在前面的名詞 (non-defining) 或界定/確認主句裡所提及的物/事 (defining)。
注意：為了清楚無誤，必須將附句直接放到要形容或要界定的名詞後。
*要有動詞；動詞與 relative pronoun 協調。

non-defining (不介定): The door, which was bright red, was very conspicuous.
defining (介定): The woman who is standing near the window is a doctor.

有什么分別？看不見嗎？就是那孖逗號了。

Who 與主格代名詞一組 I, he, she, it, they, we, you
Whom 是受格代名詞那組 me, him, her, it, them, us, you

e.g. The boy whom we visited is her nephew.
--> The boy is her nephew.
--> We visited the boy (him).
响 第二句入面 the boy 是受詞，用代名詞時要用受格 him/whom。因為第一句是主句，第二句才是附上的；所以要將附句放到要界定的名詞後便變成 The boy whom we visited is her nephew. 即使 The boy (主句中) 是主詞。