뭐 / 무슨 / 어느 / 어떤 in Questions

English gets away with just two words here — "what" and "which" — and stretches them over every situation. Korean splits the same territory across four words, and the first thing you must decide is not which meaning but what shape: do you need a word that stands alone in a noun slot, or a word that leans on a following noun? 뭐 stands alone; 무슨, 어느, and 어떤 must be glued to a noun. Getting that structural split right is more than half the battle; the meaning differences are the finer tuning on top.

The core meanings of these words are introduced under 어느 · 어떤 · 무슨; this page is about deploying them in real questions.

The one structural rule

뭐 (and its fuller written form 무엇) is a pronoun. It fills a noun slot by itself, the way "what" does in "What do you eat?"

무슨, 어느, 어떤 are determiners (관형사). They cannot stand alone — each one must be followed by a noun, exactly the way you cannot end an English sentence on "which":

무슨 vs 어느 vs 어떤: the finer tuning

All three determiners precede a noun, but they probe different things. Here is the split that trips people up:

무슨 throws the net wide. It asks "what sort of _?" with no menu in front of you — the answer could be anything.

어느 assumes a closed, known set and asks you to pick one member of it — which is why it pairs so naturally with 것 ("which one") and with choices laid out in front of you.

어떤 probes quality or description — what something is like. Asked about a person, 어떤 사람이에요? means "what's he like / what kind of person is he?", not "which person."

The 무슨 / 어느 contrast is the sharpest one for English speakers, because English "which" quietly covers both. If the options are a known, countable set — two roads, three shirts on the rack, the countries of the world as a fixed list — Korean wants 어느:

뭐 or 무엇? Spoken versus written

The pronoun has two shapes, and choosing between them is purely a matter of register, not meaning. 뭐 is the everyday, spoken, contracted form — what you say in conversation, texting, and casual writing. 무엇 is the full, formal form, at home in writing, careful speech, exam questions, and service language. They are the same word; 뭐 is simply 무엇 worn down by daily use, much as English "what're" reduces "what are."

Notice that the polite everyday middle ground uses 뭐 too: 이거 뭐예요? ("What's this?") is the ordinary 해요체 version, sitting between casual 뭐야 and formal 무엇입니까. Object-marked, 뭐 becomes 뭐를 or, contracted, 뭘 — 뭘 좋아해요? ("What do you like?"). The particle is freely droppable, as everywhere in casual Korean.

어떤 also means "a certain" in statements

Outside of questions, 어떤 does double duty as "a certain / some": 어떤 사람이 왔어요 is not a question at all but a statement, "a certain person came." Context and intonation tell the two apart — the same overlap between question word and vague reference that runs through all of Korean, treated in full on question word or 'something'?.

무슨 in fixed expressions

Two of the most frequent questions in daily Korean are built on 무슨, and they are worth learning as whole units because English does not translate them literally. 무슨 일이에요? — literally "what matter is it?" — is the all-purpose "What's going on? / What's the matter? / What happened?" And 무슨 소리예요? — literally "what sound is it?" — means "What are you talking about? / What do you mean?", often with a note of surprise or disbelief.

These lean on 무슨 precisely because it asks an open "what kind of" — the speaker has no menu of options, just an open-ended "what is this?" Swapping in 어느 or 어떤 here would sound wrong, which is a good check on your feel for the three determiners: only 무슨 fits the sense "what sort of thing is happening, out of anything it could be?"

Common Mistakes

1. Using the pronoun 뭐 where a determiner is required. If a noun follows, you cannot use 뭐 — you need 무슨/어느/어떤.

2. Using the determiner 무슨 with no following noun. The mirror error: a determiner left dangling with nothing to modify needs to become the pronoun 뭐.

3. Using 무슨 to choose from a closed set. When the options are specific and known, Korean wants 어느, not 무슨.

4. Using 무슨 to ask what someone is like. "What's he like?" is a question about quality — that is 어떤, not 무슨. 무슨 사람 asks what category of person, which is not what you mean.

Key Takeaways

• Shape first: 뭐/무엇 is a pronoun (stands alone); 무슨/어느/어떤 are determiners (must precede a noun).
• 무슨 = open "what kind of"; 어느 = pick one from a closed set; 어떤 = "what's it like / what quality."
• English "which" collapses 무슨 and 어느 — use 어느 when you could point at the options.
• 어떤 doubles as "a certain / some" in statements — intonation and context disambiguate.