“Who” and “whom”’ cause all sorts of problems for writers. No one seems to know when to use which one, and whether to even bother with “whom” at all. More on that in a minute.
“Who” is a subject pronoun. It is the subject of a verb, even if that verb is in a dependent clause.
“Whom” is an object pronoun. It is the object of a verb or a preposition.
Substitute “he” or “him” to determine whether to use “who” or “whom.” If “he” makes sense, use “who.” If “him” makes sense, you can use “whom” (both have an M).
– The employee, who/whom the boss promoted after only six months, ended up doing well in her new post. (The boss promoted HE? No, the boss promoted HIM = whom)
– The employee, who/whom everyone said was incompetent, got promoted after only six months.
(Everyone said HIM was incompetent? No, everyone said HE was incompetent = who). This one is wrong a lot — editors change a lot of overcorrected “whoms.”
Usage of “who” and “whom” is in transition, and “whom” is dropping out of English.
If you’re considering pounding the table about that, realize that English used to have case (different forms for subjects and objects) for all nouns, and now it doesn’t. English also used to have subject and object forms for second-person pronouns (it’s all “you” now, in singular and plural, which explains the development of “y’all,” “youse,” “you guys” and so on, but that’s another story) but has dropped that as well. It’s only natural for languages to change, and the English language is a remarkably resilient piece of work — it has changed in all sorts of ways over the centuries, and it has come through just fine. One more change isn’t going to send it tumbling off a cliff to wrack and ruin.
So, back to “whom”: It’s being replaced by “who” everywhere except directly following a preposition.
An interrogative (question) sentence like “Who did you see with my brother?” would have had “whom” in times past, but gets “who” almost exclusively now, unless you’re speaking with an incurable fusspot. Likewise, a declarative sentence like “I saw the neighbor who you’re always talking about” would also have had “whom,” but most people will say “who” these days (or leave it out entirely), because the object is not directly after the preposition.
Garner’s has the above usage at Stage 4 (“Ubiquitous but …,” which is the last stop before “Fully accepted”). Many other usage guides (“Woe is I” and “The Elephants of Style,” to name two) recognize the change and advise using “whom” only in the most formal contexts. Even Theodore Bernstein, not known for playing fast and loose with the rules, noted that “The waves of changes are washing against the pronouns who and whom. As to who, the day is surely coming when it will completely displace whom standing at the head of a sentence or clause …” This was in his 1971 book “Miss Thistlebottom’s Hobgoblins.” He went on to say that “the revolution has not yet arrived. It is brewing, though, and it has been for a long time.”
By now, in 2012, it looks like the revolution’s here. Give it a few years of disarray, as most revolutions require, then let it settle down, and wait for “whom” to get the mark of “archaic” in the dictionaries.
*Edited to correct title of “Miss Thistlebottom’s Hobgoblins.”