LEARN KOREAN (한국어) [GRAMMAR] #1

WHAT (뭐/무엇/무슨)

Now that you've learned all the easy ways to ask questions, let's work on the hard ways. Figuring out how to ask "what" in Korean is probably the hardest thing you will come across (grammatically) for a while. Essentially, there are three ways to say "what:"

뭐 – which is a pronoun
무엇 – which is a pronoun
무슨 – which is a word that can be placed before nouns to describe them

Let me explain how each one is used.

뭐 and 무엇
These two essentially have the same meaning and function. Let me introduce 뭐 first.

뭐 can be used similar to 언제, 어디 and 누구. That is, to represent an unknown thing in a sentence. For example:

밥을 먹었어 - I ate rice
뭐 먹었어요? - What did you eat?

계란을 샀어요 - I bought eggs
뭐 샀어요? - What did you buy?

Like 누구, "뭐" and "what" act as a pronouns in their respective sentences. More examples:

파일을 첨부했어요 - I attached the file
뭐 첨부했어요? - What did you attach?

치마를 입었어요 - I put on a skirt
뭐 입었어요? - What did you put on/wear?

Particles are not usually attached to 뭐 when asking a question like this. For example, these would be unnatural:

뭐를 먹었어요?
뭐를 첨부했어요?
뭐를 입었어요?

One of the times it is possible to attach a particle to 뭐 is when asking somebody what they are referring to in a previous sentence where a noun was omitted. For example, if you look at this dialogue:

Person 1: 저는 많이 먹었어요 - I ate a lot
Person 2: 뭐를? - what? (you ate a lot of what?)

Here, the first person didn't specifically indicate what he/she ate. The second person is asking for clarification of what was eaten, and can use "뭐를." Here, "뭐" essentially acts as the noun that was omitted in the previous sentence.

무엇 is very similar to 뭐. However, it is more common to attach ~을 to 무엇 than with 뭐. For example:

무엇을 먹었어? - What did you eat?
무엇을 입었어요? - What did you put on/wear?
무엇을 샀어요? - What did you buy?

When used before 이다 to ask what something "is," it is more common to use 뭐 than to use 무엇. For example:

이것이 뭐야? - What is this?
이름이 뭐예요? - What is your name?
점심이 뭐야? - What is (for) lunch?

Instead of:
이것이 무엇이야?
이름이 무엇이야?
점심이 무엇이야?

무슨
무슨 also translates to "what" but it is instead placed before nouns to describe them.

For example:

그 영화를 보고 싶어요? - Do you want to see that movie?
무서운 영화를 보고 싶어요? - Do you want to see a scary movie?
무슨 영화를 보고 싶어요? - What movie do you want to see?

The dictionary form of 무슨 is 무슨. Although it looks like an adjective with ~ㄴ/은 attached to it, the word itself is 무슨, and thus, is not actually an adjective. However, it looks and feels like an adjective because of how it is used in sentences.

무슨 is used when the speaker doesn't know what an object is, and is asking about what it may be. The most common situations you will see 무슨 used are the following:

그것이 무슨 냄새야? - What is that smell?
무슨 생각(을) 해? - What are you thinking?
그것이 무슨 소리야? - What is that sound?
무슨 말이야? - What do you mean?
(The last two examples are often used to ask "what do you mean" or "I can't understand what you are trying to say")

One way I like to think of 무슨 and how it can be distinguished from 어떤 and 어느, is that 무슨 is used when the speaker is asking a question and has no idea what the answer will be. The answer could be almost an unlimited choice of options. For example, if I ask:

무슨 냄새야? - What is that smell?

I might use that if I just walk into a room and smell something for the first time. Because of this, I would not know the source of the smell and would have no idea what the answer to my question might be. The answer could be anywhere from "my fart" to "the toaster."

Likewise, if I ask:

무슨 생각(을) 해? - What are you thinking?

I might be looking at somebody and seeing them staring into space. In this case, I would not be able to even guess what that person is thinking, so I have no idea what the answer to my question might be. The answer could be anywhere from "my future" to "eating pizza."