DIFFERENCES BETWEEN THE USE OF 'WHO' AND 'WHOM'

I know a lot of our students in our Skype English classes perhaps wrongly get taught this in school in Spain and elsewhere but I'm not sure if it should be focused on due to the fact that 'whom' has become somewhat redundant in the English language. Very rarely do you hear it. Anyway, Azucena in Switzerland asked me about this the other day during our class so here is the explanation:
'Whom' is an object pronoun. It should be used to refer to the object of a sentence. While 'who' is a subject pronoun which refers to the subject. If you're stuck, you can try this rule: if the pronoun can be replaced by he or she, then use who. If the pronoun can be replaced by him or her, then use whom.

he/she = who
him/her = whom
Examples:
Who/Whom wrote the letter?
He/she wrote the letter. Therefore, 'who' is correct.
Who/Whom should I vote for?
Should I vote for him/her? Therefore, 'whom' is correct.
As indicated in the beginning, the reality is that ‘whom’ is nowadays not used very much. We tend to use ‘who’ for everything now. Have a great day!
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