引自 Oxford Dictionary 的解釋，請參閱
A continuing debate in English usage is the question of when to use who and
when to use whom. According to formal grammar, who forms the subjective case
and so should be used in subject position in a sentence, as in who decided
this? The form whom, on the other hand, forms the objective case and so
should be used in object position in a sentence, as in whom do you think we
should support?; to whom do you wish to speak? Although there are some
speakers who still use who and whom according to the rules of formal grammar
as stated here, there are many more who rarely use whom at all; its use has
retreated steadily and is now largely restricted to formal contexts. The
normal practice in modern English is to use who instead of whom (and, where
applicable, to put the preposition at the end of the sentence): who do you
wish to speak to?; who do you think we should support? Such uses are today
broadly accepted in standard English.
※ 引述《tirole (Jean)》之銘言：
: He will call "his children" after work ?
: 改成Wh問句
: 正確答案是 Who will he call after work?
: 我的答案是Whom will he call after work ?
: 問對象應該是受詞 用whom才對吧？
: 還是在電話上是通用呢？ 謝謝