Who or whom?

Question

One of our readers asked when to use who and when to use whom. Editor Kory Stamper offers some helpful tips below.

Answer

Who is a common pronoun in English, used both in questions ("Who is that?") and to introduce relative clauses ("The man who stole my bike was arrested."). Like many pronouns, who varies in form, between who and whom, depending on its grammatical function. 

The rules

Some teachers and grammarians will tell you that who should be used only in subject position, and whom should be used as the object of a verb or preposition, as in these examples:

Subject position

• Who is the owner of the business? (Who is the subject of is.)
• His boss, who was only 46 years old, died of a heart attack. (Who is the subject of was.)

Object position

• Whom did the candidate choose for his running mate? (Whom is the object of the verb choose).
• Whom were you talking to just now? (Whom is the object of the preposition to.)

What native speakers do

However, native speakers often do not follow these rules.  In spoken English and even in informal written English, most native speakers use who in both subject and object position. Whom is used for objects of verbs and prepositions in formal written English, only, and even then there are situations in which who is more common than whom:

Who is more common than whom when it occurs at the beginning of a clause, as the object of a preposition placed at the end of the clause:
•    The clerk who I was speaking to has left the building. (Who is the object of the preposition to.)

Who is also more common than whom when it begins a question:
•    Who is the taxi driver waiting for?
•    Who did you send the email to?

There is one context in which you should always use whom: after a preposition at the beginning of a sentence or clause, as in these examples:

•    To whom did you send the email? (Not "to who")
•    My geology professor, for whom I am collecting data, is in Iceland for two weeks. (Not "for who")

I hope this helps.