I'm never sure which one to use when messaging friends or writing work emails. Like, is it 'who did you talk to' or 'whom did you talk to'? I know there's a rule but I can't remember it and honestly nobody seems to care anymore.
Just use 'who' in casual contexts and stop worrying about it. Seriously, most people won't notice, and those who do care are increasingly seen as pedantic. The rule itself is simple though: 'who' is for the subject of a sentence (the person doing something), and 'whom' is for the object (the person something is being done to). So "who did you talk to" technically breaks the rule - it should be "whom did you talk to" because the person is receiving the action of talking. But in real life, especially in texts and emails to friends, literally nobody will call you out for using 'who'.
Even in work emails, the register matters less than you'd think. If you're texting a coworker "who should I contact about this?" or "who did you see at the conference?" you're fine. The only place where 'whom' still shows up regularly is formal writing - like application letters or official correspondence - and even then it's becoming rarer. If you genuinely want to be safe and sound natural in casual writing, stick with 'who' across the board. The language is shifting that way anyway.
I've found that in work emails I'll sometimes catch myself about to write "whom" and then delete it because it sounds stiff, but in a quick text to a mate I never think twice - it's always "who" and nobody's ever pulled me up on it. The honest answer is that "who" is the subject form (who did it?) and "whom" is the object form (I talked to whom?), but in casual writing, almost everyone defaults to "who" and it lands fine, while "whom" now reads as either try-hard or genuinely old-school depending on context.
The practical rule: use 'who' as your default everywhere unless you're genuinely certain the word is the object of a verb or preposition (in which case it's 'whom'). Most people won't clock it either way in casual writing, and forcing 'whom' often reads more awkward than getting it technically wrong. If you find yourself hesitating mid-message, that's your cue to just go with 'who' and move on - it's become the natural choice in informal contexts and nobody's going to mark you down for it.
In casual writing, you're basically safe sticking with 'who' across the board - most readers won't even register it as wrong. The rule itself is straightforward (who = subject, whom = object), but it's become so optional in everyday speech that enforcing it in texts or informal emails can actually make you sound a bit stiff. If you're writing something more formal, you might want to think it through, but honestly, the days of this distinction mattering to anyone except the occasional grammar stickler are long past.
Here's the thing - the rule everyone's describing is technically correct, but it's actually breaking down in real speech, so those earlier answers are playing it safe by defaulting to "who" everywhere. The honest take is that "whom" has been dying for decades, and in 2026 it's genuinely rare to hear it in casual contexts, even from educated speakers. If you want to nail it, yes, "who" = subject and "whom" = object (so "whom did you talk to" is technically right), but the rule is so counterintuitive that most people get it wrong instinctively - and native speakers increasingly just say "who" anyway. For work emails, I'd say use "who" unless you're certain the formal tone demands otherwise; nobody's going to think you're sloppy, and forcing "whom" can actually make you sound like you're trying too hard.
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