In nearly twenty-eight years at The Baltimore Sun, as copy editor, copy desk chief, assistant managing editor for the copy desk, and now the grandly titled Night Content Production Manager, I have been the newsroom go-to person for questions of grammar and usage. And the most frequent question brought to me is "Should this be who or whom?"
As I have remarked before, it is significant about the course of the language that educated native speakers should be at so much trouble on this point, so liable to get the grammar wrong.
Robert Lane Greene, writing as Johnson at The Economist, addresses the whom question, going over some familiar ground about shifting usage: Though whom is clearly on decline, it remains essential for people writing formal English prose to master the who/whom distinction.
He is at some trouble to point out that mastering whom is more complicated than just saying who=subject, whom=object. You have to worry out the syntax when the pronoun is part of a relative clause.
One of his examples, Isaac Newton, whom some contend was autistic, is wrong. Recasting the relative clause shows this: some contend [that] who/he was autistic. If the pronoun is the subject of a clause, it must be who.
But Isaac Newton, whom some considered autistic is correct: some considered whom/him autistic.
Summing up: "What Johnson likes about this case is that it really requires an understanding of some syntax: what a relative clause is (eg, 'whom some consider autistic'), the cases and their roles (I, he and who versus me, him and whom), and verbs that take a direct object (consider) versus those that take a clause (contend). To understand this requires going past superficial rules to understanding the plumbing."
But it doesn't just stop at the grammar. It never stops at the grammar.
In speech, who appears to have pretty much supplanted whom, just as lie/laid/laid appears largely to have done away with lie/lay/lain. And caviling about the way people talk in casual speech is idle.
And because whom largely survives in formal English, using it in any other context, either speech or writing, can appear pompous and pretentious. That taint of formality was apparent more than eighty years ago when James Thurber wrote in "Ladies' and Gentlemen's Guide to English Usage" (his pastiche of Fowler): "The number of people who use 'whom' and 'who' wrongly is appalling. The problem is a difficult one and it is complicated by the importance of tone, or taste. Take the common expression, 'Whom are you, anyways?' That is, of course, strictly speaking, correct—and yet how formal, how stilted! The usage to be preferred in ordinary speech and writing is 'Who are you, anyways?' 'Whom' should be used in the nominative case only when a note of dignity or austerity is desired."
For copy editors, those of us expected to leap registers at a single bound, there is no substitute for mastering the plumbing. We have to gauge the appropriate register in the texts we edit; and when that register is formal, we have to tease out the syntax.
Or, when I'm at the desk, you could just ask me.