Aspect at a Glance: -고 있다, -아/어 있다, -는 중이다 (Formation Map)

Korean has three constructions that all land near the English idea of "be …-ing," and beginners often treat them as interchangeable. They are not. This page is a formation map: it lays out how each one is built and — more importantly — which verbs each can even attach to. That input restriction is what decides which construction is grammatical in a given sentence, before meaning ever enters the picture. The full "what each one means" comparison is deliberately owned by the Tense, Aspect & Mood group; here we build the forms and learn their limits.

The three forms side by side

Three things to read off this chart. First, in -고 있다 and -아/어 있다 it is 있다 that inflects for tense and register; in -는 중이다 it is the copula 이다. Second, only -아/어 있다 uses vowel harmony (앉아, 열려), because only it uses the bare -아/어 connective — the other two use fixed shapes (-고, -는). Third, the "Attaches to" column is the one that actually decides grammaticality, so the rest of the page drills into it.

Same verb, three constructions, three meanings

The clearest way to feel the difference is to run one verb through all three. Take 앉다 "sit." Every construction is buildable, and each says something genuinely different:

Where the forms break: buildability contrasts

Now the restrictions that make some of these ungrammatical, not just different in nuance.

A transitive activity has no resultant state. 읽다 "read" produces no lingering "read state," so -아/어 있다 simply cannot attach. The progressive is fine; the resultant is a non-form.

For that same verb, ×읽어 있다 is impossible — there is no state of "being read" that a person holds. If you catch yourself building -아/어 있다 on a verb that takes a direct object, stop: you almost certainly want -고 있다 instead. (The one workaround is to switch to an intransitive partner and drop the object: 문을 열다 → 문이 열려 있다 "the door is open.")

Adjectives take none of the three. Descriptive verbs (형용사) like 좋다, 예쁘다, 바쁘다 describe states, not actions, so there is no ×좋고 있다, no ×좋아 있다, and no ×좋은 중이다. To say something is good/pretty/busy right now, you use the plain present of the adjective — full stop.

A quick decision path

When you want to express something ongoing, ask three questions in order:

1. Is the verb an adjective (descriptive)? If yes, use none of these — just the plain present (바빠요, 좋아요).
2. Am I describing a settled state after a change (seated, open, on, hung), and is the verb intransitive? Use -아/어 있다 (앉아 있다, 열려 있다).
3. Otherwise — an action unfolding. Use -고 있다 for the general progressive (먹고 있다), or -는 중이다 when you want to stress right in the middle of it (먹는 중이에요), or a noun + 중 for a fixed activity (회의 중).

For the deeper meaning contrasts — the semantics of progressive vs. resultant, and edge cases like 죽고 있다 "is dying" vs. 죽어 있다 "is dead" — head to the go-itda vs. a-eo-itda page and the choosing guide.

Common Mistakes

1. Assuming the three are freely interchangeable. For "is already seated," only -아/어 있다 works; -고 있다 means the motion of sitting down.

2. Building -아/어 있다 on a transitive verb. 쓰다 "write" takes an object and has no resultant state; use the progressive.

3. Putting an aspect form on an adjective. Descriptive verbs use the plain present, never -고 있다 / -는 중이다.

4. Choosing -는 중이다 for a durable state. 중이다 is for an action mid-process; a lasting stance takes -아/어 있다.

Key Takeaways

• -고 있다 (any action verb, progressive), -아/어 있다 (intransitive change-of-state only, resultant, uses harmony), -는 중이다 (action verbs, mid-process; also noun + 중) — three builds, not free variants.
• The "attaches to" restriction decides grammaticality: ×읽어 있다 (transitive has no resultant state), ×좋고 있다 (adjectives take none).
• One verb proves the system: 앉고 있다 (sitting down) ≠ 앉아 있다 (seated) ≠ 앉는 중이다 (mid-sit).
• This page maps the forms; for what each one means, go to the Tense, Aspect & Mood group.