"선생님이 앉아 있어요."

Translation: The teacher is sitting.

[Ziel0]

Shouldn't it be 앉고 있어요?

[wintertriangles]

For verbs of this type (the name is blanking atm) where they can't really have an object to act on, you instead use ~어/아 있다. 누워 있어 (lying down), 비어 있어 (empty), 써 있어 (standing), 남아 있어 (is [continuously] left).

[Wes375407]

but then why is sleeping 자고- when it doesn't have an object to act on?

[pluckingstrings]

The term is "intransitive," and I believe sleeping is 자고 because unlike in English, in Korean sleeping is transitive- you 'sleep a sleep,' so to speak.

[GeraldMath4]

Really? Can you tell us what the omitted object is? That is, answer 무엇을자고있읍니까?

[ArvindIyer4]

잠을 자다

[GeraldMath4]

Maybe during the time between standing and ending in a seated posture? To label a still from a video?

[rojo999459]

Thanks for clarifying

[Maypurin]

Since the subject is honorific, can you say 앉아 있으세요?

[Subrisus]

I am not positive (I'm only answering because it has been 3 months since you asked your question), but my understanding is that you would not be able to use 앉아 있으세요 for sitting because 세요 makes it an imperative (it would translate closer to telling someone "be sitting" - or just "sit down".

[Gray_Roze]

세요 can be either imperative or honorific. When you're talking about the teacher, you don't need to add the honorific 세, but if you're talking to him or her, you can.