In short

Korean marks two different “in the middle of” ideas. -고 있다 = an action is unfolding right now (밥을 먹고 있어요, is eating). -아/어 있다 = a subject stays in the state left behind by a change (문이 열려 있어요, the door is open). The first is the action happening; the second is the state that remains after it finished.

The rule

Step 1 - -고 있다: the action is in progress

Attach -고 있다 to the plain verb stem and conjugate 있다 as usual (있어요). It is invariant - no 아/어 choice, no 으, no 받침 rule. It attaches the same way to a vowel-stem, a 받침-stem, and a ㄹ-stem:

Verb stem + 고 있다 -> 먹고 있어요, 하고 있어요, 살고 있어요

This is the ordinary progressive, English am/is/are -ing: 지금 뭐 하고 있어요? (What are you doing now?). Note the space - 있다 is a separate auxiliary verb, so 먹고 있어요 is never written *먹고있어요.

Step 2 - -고 있다 also does “ongoing life” and “wearing”

The same form stretches two more ways:

• Ongoing / habitual over a stretch of life, not just this second: 한국에서 살고 있어요 (I’m living in Korea), 은행에 다니고 있어요 (I work at a bank).
• Wearing. Verbs of putting on - 입다 (clothes), 쓰다 (glasses, hat), 신다 (shoes), 끼다 (rings, gloves) - use -고 있다 for BOTH the act of putting on AND the resulting worn state. So 안경을 쓰고 있어요 is ambiguous: is putting glasses on OR is wearing glasses - context decides. There is no *안경을 써 있어요.

Step 3 - -아/어 있다: the resulting state stays

Take the 아/어 form of the verb (the same one from lesson 10) and add 있다:

Verb’s 아/어 form + 있다 -> 앉아 있어요, 서 있어요, 열려 있어요

This says the subject went into a state and is still in it. 앉아 있어요 is not “sitting down” - it is already seated and staying seated. Crucially, -아/어 있다 only attaches to intransitive verbs - verbs with no object, especially postures (앉다, 서다, 눕다), change-of-state passives in opposed pairs (열리다/닫히다, 켜지다/꺼지다 from 켜다/끄다) and intransitive verbs of motion or remaining (가다, 오다, 남다). A transitive verb with an object can never take it.

Step 4 - The one test: is it happening, or has it happened and stays?

This is the whole lesson. Same event, two forms:

• 문이 닫히고 있어요 (the door is closing - the motion is happening now) vs 문이 닫혀 있어요 (the door is shut - it closed and stays closed).
• 오고 있어요 (is on the way here) vs 와 있어요 (has arrived and is here).

If a person is doing something, reach for -고 있다. If a subject has ended up somewhere or in some position and remains there, reach for -아/어 있다.

Step 5 - Honorific -고 계시다 / -아/어 계시다, and the past

For an honored subject, 있다 becomes the suppletive 계시다 (계세요): 아버지께서 신문을 보고 계세요 (Father is reading the paper); 할머니께서 앉아 계세요 (Grandmother is seated). Never use 계시다 of yourself. For the past, just move 있다 into the past - 있었어요: 아까 밥을 먹고 있었어요 (I was eating earlier), 문이 열려 있었어요 (the door was open).

Step 6 - Adjectives take neither

Descriptive verbs (lesson 11) are already states, so they reject both auxiliaries: not *예뻐 있어요, not *예쁘고 있어요 - just 예뻐요. And when someone deliberately creates a state and leaves it (opened the window on purpose and left it open), Korean uses -아/어 놓다 / -아/어 두다 on the transitive verb (lesson 53) - keep that apart from the plain observed state 열려 있어요.

Forms & patterns

-고 있다 - invariant (attaches to any stem the same way):

-아/어 있다 - the 아/어 choice (intransitive verbs only):

The contrast - same event, two aspects:

Examples

Common mistakes

• 예쁘고 있어요. (yeppeugo isseoyo.) -> 예뻐요. (yeppeoyo.) - Adjectives are already states, so they take neither -고 있다 nor -아/어 있다. Just conjugate the adjective (예쁘다 -> 예뻐요).
• 밥을 먹어 있어요. (babeul meogeo isseoyo.) -> 밥을 먹고 있어요. (babeul meokgo isseoyo.) - 먹다 is transitive and the action is unfolding, so it takes -고 있다. -아/어 있다 never attaches to a transitive verb with an object.
• 앉고 있어요. (ango isseoyo.) -> 앉아 있어요. (anja isseoyo.) - To say you ARE seated (the state), use -아/어 있다. 앉고 있어요 means “in the middle of the sitting-down motion,” which is rarely what you mean.
• 문이 닫히고 있어요. (muni dachigo isseoyo.) -> 문이 닫혀 있어요. (muni dacheo isseoyo.) - If you mean the door is already shut, that is the resulting state -아/어 있다. -고 있다 says the door is still in the act of closing.
• 어머니께서 요리하고 있어요. (Eomeonikkeseo yorihago isseoyo.) -> 어머니께서 요리하고 계세요. (Eomeonikkeseo yorihago gyeseyo.) - For an honored subject the auxiliary 있다 becomes 계시다 (계세요), giving -고 계시다.

Tips

• One test settles it. Is a person doing something (action unfolding)? -> -고 있다. Has a subject ended up in a position or state and stayed there? -> -아/어 있다. “Happening now” vs “happened and remains.”
• The wearing verbs live on -고 있다. 입다, 쓰다, 신다, 끼다 all use -고 있어요 for both “putting on” and “wearing” - there is no *입어 있다. Only context tells you which reading is meant.
• -아/어 있다 has a short guest list. Postures (앉다, 서다, 눕다), change-of-state passives in opposed pairs (열리다/닫히다, 켜지다/꺼지다) and intransitive verbs of motion or remaining (가다, 오다, 남다) - all with no object. Learn them as a set; transitive verbs and adjectives are never on it.
• Observed vs deliberately left. 문이 열려 있어요 just reports an open door. When someone opened it on purpose and left it that way, that is 문을 열어 놓다 (lesson 53) - same open door, different point of view.