What is shorted for 뭔?

Question

I searched 뭔 on this site, but I have no result at all.

뭐=무엇

뭔=무엇은?

Is it right?

Answer 1

무엇은 is a logical guess since 뭐 is short for 무엇, but it is wrong.

The reason 뭔 doesn't mean 무엇은 is likely because 무엇은 is a phrase almost never used in practice. If you are asking something phrasing it like English "what is ...?", you'd say 무엇이 or its short form 뭐가, not 무엇은. This is because 은/는 either states some idea you have or present something in contrast with others, and 무엇 just cannot have either of these senses since it is word for the unknown. 무엇 fits 이/가, which states something that happens to be occurring or needed in reality. That is, you have a need to know "what" rather than presenting something from your knowledge or feelings.

In short, 무엇이 and 뭐가 are very common but 무엇은 is almost never heard, and 뭔 means 무슨 which is a determiner like "what", as in "what problem" (무슨 문제). 뭔 is very informal, though, so it is rarely used in texts.

Answer 2

Despite the apparent etymology, "뭔" doesn't retain its meaning from the contraction. The synonym suggested by Standard Korean Language Dictionary is "무슨" (colloquially).

뭔 「관형사」 ‘무슨’을 구어적으로 이르는 말.

Answer 3

“뭔” means either “무슨” or “무엇은.”

To be precise,

1. the single word “뭔” means “무슨” (I’m not sure about its etymology.),

• “그게 뭔_(무슨) 말이야?” _{“What do you mean?”}
• “뭔_(무슨) 내용인지 하나도 모르겠다.” _{“I can’t understand a single word of it.”}

2. and the construction “뭔,” that is the pronoun “뭐”^{←“무어”/“무엇”} and the subject marker “-ㄴ”^{(←“은”/“는”)}, is short for “무엇은.”

• “일을 시작하기 전에 뭔_(무엇은) 가능하고 뭔_(무엇은) 불가능한지 먼저 생각해 보자.” _{“Let’s just think about what is possible and what is not, before getting to work.”}
• “분명히 다들 똑같이 따라했을 텐데, 뭔_(무엇은) 되고, 뭔_(무엇은) 안 되고…, 참 이상하네.” _{“Everyone should have followed the same instructions. Why do some work and some others don’t? That’s weird.”}