—in English! In English! I’m sure this is nowhere near the top of the list of mistakes humans make. This might not even be second on the English grammar list, but I think it comes right after the one where someone, trying deliberately to be high-class, says “between him and I.”
This error is using “whom” when “who” is actually correct (or in this case, “whomever” and “whoever.”). First, the rule: when you have a subordinate clause, work from the inside out. Here’s an example of the mistake, from Edge of Adventure. Look at the first panel in the bottom row. Can you tell why he should have said “whoever”?
Yes, “to” is a preposition, and the clause that comes after it is its object. But that clause has its own subject and verb! And since we work from the inside out, being the subject of that clause takes precedence over the whole clause being an object, so it’s “whoever did this.” If you really want a “whom” in that sentence you could say something like “…to whomever I find on the trail.” Now “I” is the subject, and “whomever” is the direct object of “I find.” Make sense?
So sometimes you have permission to use “who.” Be careful.