who 和whom有什麼分別?

問問題的時侯可以用who 同whom 發問, 但有些分別

用who 問問題的時侯 verb to be (is, am are) 後面通常都係refer to subject 主語:
Who is he? "He" is Tom
Who is the person sitting next to you. "The person".... is John"

用whom 問問題的時侯 verb to be (is, am are) 後面通常都係refer to OBJECT 賓語:
Whom are you talking to? I am talking to "Jane"
Whom do I love? I love "Mary"

係關係子句 (relative clause) 來看,
we use WHO as the SUBJECT of the clause
例如 Mary is the woman who wears blue clothes (The woman wears blue clothes) 所以who 用係描述subject 上面 而
we use WHOM as the OBJECT of the clause
例如 The police whom I am talking to wears green uniform. (I am talking to the police) 所以whom 用係抽述object