Learn the rule (or how to avoid the issue).
Noun Clauses with “Whoever” and “Whomever”
But you’d be wrong—“whoever” was the right choice when we were thinking about the clause “whoever did this” by itself, and it’s still the right choice now. But what about that “to,” in “I want to speak to whoever did this”? The answer is that the object of “to” is not “whoever.” It’s the entire clause “whoever did this.” Remember, this is a noun clause; they call it that because the whole thing acts like a noun, and in this case, the whole thing is the object of “to.”
Let’s try another example, with the noun clause “whomever I hire.” Suppose it’s part of the sentence “Whomever I hire will start immediately.” What is the subject of “will start immediately”? It’s easy to trick yourself again, and turn that “whomever” into a “whoever” because it looks like the subject of the sentence. But again, we made the right choice when we looked at “whomever I hire” in isolation, and it’s still the right choice. The subject of “will start immediately” is the entire noun clause “whomever I hire.”
To choose between “whoever” and “whomever,” look only at the noun clause in which it appears, and disregard the rest of the sentence around it.
Is “Whom” Becoming Extinct?
I’m sorry to say that learning this rule is unlikely to save you from “whom”-related grammar anxiety, for two reasons. First, the reason there is so much confusion about “whom” that I have now spent three episodes discussing it is that it’s a dying word. It appears so rarely that casual speakers don’t have enough data to figure out how to use it just through context. If they haven’t learned about it specifically in a grammar book, they’ll make their best guess about how to use “whom,” and often that best guess is that you use “whom” when you want to sound especially formal, regardless of whether it’s a subject or an object.
If “whom” survives at all, this sentiment could well become the accepted standard, like it or not. Worse, if that’s the rule your audience is going by, they might regard you as stuffy and high-falutin’, when all you’re trying to do is use standard grammar. It’s completely unfair!
Second, even those who have learned about “whom” have often learned only enough to cause confusion in the more difficult sentences. Even if you’re among “whom”-supporters, at least some of them will be firmly convinced that “Whom do you think will come to the party?” is standard grammar. At least some of them will be convinced that “I want to speak to whomever did this” is correct, and want to change your “whoever” to a “whomever.” Although the rules I’ve given are considered standard now, the misconceptions could well become standard in the future. In the minds of some grammarians today, they already are (1).