When to use who or whom Who: should be used to refer to the subject of a sentence. Whom should be used to refer to the object of a verb or preposition. The subject in a sentence refers to the person or thing carrying out an action. In this example the aunt is the subject since she was the one who spoke to them. The object in a sentence refers to the person or thing that receives the action of the verb. In this example the people the aunt spoke to is the object Note: "which" is not used for people