Students sometimes get confused between when to use “who” and when to use “whom”.
“Who” is usually used to refer to the subject of the sentence, e.g.
Mr. Tan, who is my neighbour, goes for a run every morning.
“Whom” is usually used to refer to the object of the sentence, e.g.
The police arrested the man whom we saw at the mall yesterday.
When in doubt, just turn the sentence into a question and ask yourself which pronoun, “he” or “him”, you would use.
Who goes for a run every morning? Mr. Tan/he, thus we use "who".
Who was arrested by the police? The man/him, thus we use “whom”.
