누구 omission of the subject marker

Question

"누구예요?"

In the following question/use of 누구, I was wondering several things:

1. Why do we not use the subject marking particle 가 next to 누구? My understanding is that 누구 is not considered a subject in this instance, but if 누구 is not the subject then what is the subject of "누구예요?"

2. In this example "누가 제인이에요?", the subject marking particle is used, so I'm curious why it is not used in "누구예요?".

As ever, thank you!

Answer 1

누구예요 can't have subject marker (-가) because -가 is not compatible with -예요. Consider the basic form:

X는/X가 Y예요. = X is Y.

E.g.,

[이 책]은 [제 거]예요. / [이 책]이 [제 거]예요.

Here, X is the subject. In English, Y is called "predicative complement (PC)" (보어) - not sure if it's also how Y is called in official Korean grammar, but you can see that it's clearly not the subject. As a result, you cannot attach -(이/가) and -예요 to the same word, because the word cannot be subject and PC at the same time.

In the question "누구예요?", subject is omitted and inferred by context - most likely something like "그 사람" (that person). So the question is basically,

A: (그 사람은) X다. -> (change X to 누구) -> (그 사람은) 누구예요?

Of course you can do it the other way:

B: X가 그 사람이다. -> (change X to 누구) -> 누가 그 사람이예요?

In English, they can be both translated as "Who is that person?" or something similar, but A is asking you to describe the person ("Who is he?" "Oh he's my brother."), while B is asking you to identify who is the particular person ("We found the CCTV footage of him." "Who is that person?" "The second one at the top.")

Answer 2

This answer may not be 100% airtight, but I think it will help. Consider that 누구가/누가 will be used when the person (누구) is volitionally doing something, or is being differentiated/located.

In "누구예요?" the verb is 이다, basically meaning "to be" or "is." There's no action taken by that person in order to "be," and that person is not being differentiated from anyone else here (you're already referring to a particular person, if not explicitly then by context; there are no doubts about to which person you are referring, only doubts about some information about them).

너 누구야? -- Who are you?

저 사람 누구예요? -- Who is that person over there?

누가 마틴이에요? -- Who (meaning, which person) is Martin?

누가 책을 샀어? -- Who bought the book?

누가 훔쳤어. -- Somebody stole it.

누가 그 사람이에요? -- Who (meaning, which person) is that person (that you just told me a story about, or some such context)?

So again, in the first two examples, the person I'm asking about is clear. And there's no volitional action taking place.

In the next four examples, there is either a volitional action taken by someone, or I'm trying to differentiate/locate a particular person.

Answer 3

1.

Why do we not use the subject marking particle 가 next to 누구?

• This is because 누구 is not a subject in this case.

My understanding is that 누구 is not considered a subject in this instance,

• Yes, your understanding is correct.

but if 누구 is not the subject then what is the subject of "누구예요?"

• The subject is unspecified in this sentence thus it depends on the context.
• Suppose I was walking down the road with one dude and he says hi to a lady I haven't met before. Then I can ask him "누구에요?" - "Who is she?". The subject is implicit but is clear from the context.

2.

In this example "누가 제인이에요?", the subject marking particle is used, so I'm curious why it is not used in "누구예요?".

• The sentence "누구에요?" is deliberately skipping the subject.
• If you want to specify the subject explicitly in the sentence you can go by:
  • "누가 누구에요?" - "누구가 누구에요?" - "Who is who?"
  • "그 여자는 누구에요?" - "Who is the lady?"
  • "당신은 누구에요?" - "Who are you?"
  • "내가 누구에요?" - "Who am I?"