When should “whom” be used?

The appropriate usage of "whom" occurs when it is referencing the object of a verb or a preposition in a sentence. For instance, in the sentence "To whom should I address this letter?", "whom" is the object of the preposition "to." This contrasts with "who," which is used as the subject of a verb. Understanding the distinction between subjects and objects in sentence structure is crucial to correctly employing "whom." The use of "whom" enhances clarity and grammatical precision, particularly in formal contexts.