We have but a nanosecond to decide whether to use who or whom in conversation. From “A Grammar Book For You and I – – Oops Me” (a very comprehensive, not too ponderous, guide, incidentally) here is a useful device (the book calls it a “trick”) which will help.
First off, the use of a pronoun to refer to a person should never be which or that; who or whom should always be used. (E.g., “The boy who ran the errand returned promptly.”) This pronoun is available in three cases: subjective (who), objective (whom), and possessive (whose). The use of the possessive whose is most readily apparent, as in “The boy whose watch stopped arrived at the party late” (never to be confused with the contraction who’s [“who is”]; however; that is another column).
Who and whom usually appear in clauses; a clause is an expressed thought which has a subject, a verb, and sometimes an object of the verb. It can be independent (in the previous sentence: “A clause is an expressed thought”) and stand on its own; or it can be a dependent clause (again, previous sentence: “which has a subject. . .”) which modifies an independent clause but does not express a complete thought and cannot stand on its own. To distinguish a clause from a phrase, a phrase is a thought which has neither a subject or a verb (in the preceding sentence “on its own” is a prepositional phrase). Who and whom usually pop up in dependent clauses.
Consider the following sentences (the “who/whom” clauses are all dependent and are italicized) and determine which is correct:
1. The player who/whom practiced most scored the most runs.
2. The player who/whom the coach selected to play had practiced most.
3. The player Posted in Queen’s English / Latin Lovers