Who, whom and that

People often ask about the difference between who and whom, but I wonder if whom is dying out of the language. If you wish to use whom correctly, here are the rules.

Who and whom are pronouns we use to refer to people.

who

Use who when the person you mentioned previously in the sentence is the subject.

The man who won the prize didn’t come. (man = subject)

You can use either who or which to refer to collectives, such as group, team.

It was the group who/which decided.

whom

Use whom to refer to the person previously mentioned in a sentence when they are the object, not the subject.

The man whom I invited couldn’t come. (The man = object, I = subject)

Whom is a relative pronoun when it refers to a noun preceding it. If you use whom in a question, it becomes an interrogative pronoun.

Whom does he most admire? (Whom is still the object. He is the subject.)

I think this usage may be declining. I think it is okay to say:

Who does he admire most?