This section discusses the interrogative pronouns who and whom. When these pronouns are used to mean “which or what individual(s),” you must always check to see whether they are acting as the subject or the object of the verb. If the pronoun is acting as a subject, use who. If it is acting as an object, use whom.
You will often see these pronouns in questions and answers. Consider the following sentence:
I don’t know whom Kate married.
In this sentence, the pronoun whom acts as a placeholder for an unknown person – whoever it is whom Kate married. To determine whether this pronoun is acting as the subject or object of the verb, try rearranging the sentence into a question, and then answer it. The form of the answer will tell you which version of the pronoun to use, subjective or objective. Let’s try it:
Question: Who/m did Kate marry?
Answer: Kate married him.
You wouldn’t say “Kate married he.” Since the pronoun used in the answer is the objective “him,” the pronoun in the original sentence should also be in the objective case: whom.
Incorrect: I don’t know who Kate married.
Correct: I don’t know whom Kate married.
Here’s another one to try:
Who took out the trash?
Because the sentence is already a question, all you need to do is answer the question.
Question: Who/m took out the trash?
Answer: He took out the trash.
The person taking out the trash is the subject of the sentence. You wouldn’t say “Him took out the trash,” because “him” is objective. The indefinite pronoun must be in the subjective case: Who.
Incorrect: Whom took out the trash?
Correct: Who took out the trash?