A large family of Korean endings has two spellings, written -아/어: the polite present -아/어요, the past marker -았/었-, the connective -아/어서, the obligation form -아/어야, the plain command -아/어라, and the resultant -아/어 있다. Every one of them forces the same decision — 아 or 어? This page is the reference sheet that settles it once, mechanically, for all of them. Bookmark the table; the rule underneath it never changes.
The rule in one line
Find the last vowel of the stem:
- If it is ㅏ or ㅗ (the two "bright" vowels, 양성모음) → the ending takes 아.
- For anything else — ㅓ, ㅜ, ㅡ, ㅣ, ㅐ, ㅔ, ㅟ, ㅢ … → the ending takes 어.
- The single exception is the stem 하, which takes an archaic -여 and contracts to 해.
The reframing an English speaker needs: only two vowels trigger 아. Memorize that tiny set — ㅏ and ㅗ — and let everything else default to 어. Do not try to feel out each verb one at a time; you are matching a sound, not interpreting a meaning.
The selection table
| Stem's last vowel | Selected ending | Example (dictionary) | 해요체 form |
|---|---|---|---|
| ㅏ | 아 | 살다 (live) | 살아요 (sarayo) |
| ㅗ | 아 | 좋다 (be good) | 좋아요 (joayo) |
| ㅓ | 어 | 먹다 (eat) | 먹어요 (meogeoyo) |
| ㅜ | 어 | 배우다 (learn) | 배워요 (baewoyo) |
| ㅣ | 어 | 마시다 (drink) | 마셔요 (masyeoyo) |
| ㅐ | 어 | 보내다 (send) | 보내요 (bonaeyo) |
| ㅔ | 어 | 세다 (be strong) | 세요 (seyo) |
| ㅡ | (drops — see note) | 쓰다 (write) | 써요 (sseoyo) |
| 하 | 여 → 해 | 공부하다 (study) | 공부해요 (gongbuhaeyo) |
Two rows need a word of warning. The ㅜ, ㅣ, ㅐ, ㅔ rows also contract once the vowel is chosen (배우 + 어 → 배워, 마시 + 어 → 마셔) — that fusion is a second step, handled on the contraction table. The ㅡ row is special: a bare ㅡ has no harmony value of its own, so it drops before -아/어 and the syllable before it decides the vowel. That is the ㅡ-drop pattern, a separate page — here just note that you never keep the ㅡ (×쓰어요 → 써요).
One choice, every ending
The value of nailing this down is that the identical choice drives every -아/어 ending. Decide once that 살- is bright and 먹- is dark, and you are done for all of them:
| Ending | Bright stem 살- (live) | Dark stem 먹- (eat) |
|---|---|---|
| Present -아/어요 | 살아요 | 먹어요 |
| Past -았/었- | 살았어요 | 먹었어요 |
| "and so" -아/어서 | 살아서 | 먹어서 |
| "must" -아/어야 | 살아야 | 먹어야 |
| Resultant -아/어 있다 | (살아 있다) | — |
| Plain command -아/어라 | 살아라 | 먹어라 |
You never re-decide per ending. This is why the harmony choice is worth memorizing before anything else in the verb system.
Bright stems (ㅏ, ㅗ) take 아
와, 오늘 날씨 진짜 좋아요.
wa, oneul nalssi jinjja joayo
Wow, the weather's really nice today. (좋-: last vowel ㅗ → 아)
저는 부산에서 살아요.
jeoneun Busaneseo sarayo
I live in Busan. (살-: last vowel ㅏ → 아)
택배가 드디어 왔어요.
taekbaega deudieo wasseoyo
The package finally came. (오-: ㅗ → 아, then 오 + 았 → 왔)
Everything else takes 어
저는 보통 아침을 안 먹어요.
jeoneun botong achimeul an meogeoyo
I usually don't eat breakfast. (먹-: ㅓ → 어)
요즘 유튜브로 수영을 배워요.
yojeum yutyubeuro suyeong-eul baewoyo
These days I'm learning to swim on YouTube. (배우-: ㅜ → 어 → 배워)
저는 커피를 하루에 세 잔 마셔요.
jeoneun keopireul harue se jan masyeoyo
I drink three cups of coffee a day. (마시-: ㅣ → 어 → 마셔)
집에 도착하면 문자 보내요.
jibe dochakamyeon munja bonaeyo
Text me when you get home. (보내-: ㅐ → 어, collapses to 보내)
The exception: 하 → 해
There is exactly one systematic exception, and it happens to be the most productive stem in the language. 하 refuses -아/어 and instead takes the archaic allomorph -여, which contracts to 해. Because every 하다 verb — 공부하다, 사랑하다, 운동하다, and thousands more — inherits this, you learn 해 once and it covers the whole class.
저는 매일 한국어를 공부해요.
jeoneun maeil hangugeoreul gongbuhaeyo
I study Korean every day. (공부하- → 공부해)
주말에 보통 뭐 해요?
jumare botong mwo haeyo?
What do you usually do on weekends? (하- → 해)
Reframing for English speakers
English vowel changes (sing/sang, foot/feet) carry meaning — tense, number. Korean 아/어 harmony carries none: it is the same ending either way, selected by sound alone. So the instinct to "understand why" a verb takes 아 will only slow you down. There is nothing to understand; there is only the last vowel to read. Within a few weeks the choice becomes invisible, exactly because it is mechanical.
Common Mistakes
1. Defaulting a bright stem to -어요. A ㅏ/ㅗ stem must take 아.
❌ 날씨가 좋어요.
Wrong — 좋- has ㅗ (bright), so it takes 아 → 좋아요.
✅ 날씨가 좋아요.
nalssiga joayo
The weather is nice.
2. Using 아 after a ㅜ stem. ㅜ is not bright — it takes 어 (then contracts).
❌ 요즘 기타를 배우아요.
Wrong — 배우- ends in ㅜ (dark) → 어 → 배워요, never ×배우아요.
✅ 요즘 기타를 배워요.
yojeum gitareul baewoyo
I'm learning guitar these days.
3. Using 아 after a ㅓ stem. The most basic dark vowel still gets 어.
❌ 저는 아침을 안 먹아요.
Wrong — 먹- has ㅓ → 어 → 먹어요, not ×먹아요.
✅ 저는 아침을 안 먹어요.
jeoneun achimeul an meogeoyo
I don't eat breakfast.
4. Applying plain harmony to 하다. 하 takes 여 → 해, never 아/어.
❌ 지금 공부하아요.
Wrong — 하다 is the exception: 하 + 여 → 해 → 공부해요.
✅ 지금 공부해요.
jigeum gongbuhaeyo
I'm studying right now.
Key Takeaways
- Last vowel ㅏ or ㅗ → 아; everything else → 어. Only two vowels trigger 아 — memorize that set and default the rest.
- It is the last vowel of the stem that counts (기다리- → 기다려요, keyed off ㅣ).
- The choice is phonological colour-matching, not meaning — no English semantic analog.
- The one exception is 하 → 해 (하 + 여), inherited by every 하다 verb.
- The same choice fires on every -아/어 ending — decide once per stem (살아요 / 살았어요 / 살아서).
- ㅜ/ㅣ/ㅐ/ㅔ stems then contract (see the contraction table); ㅡ stems drop the ㅡ (see the ㅡ-drop table).
Now practice Korean
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Start learning Korean→Related Topics
- The Vowel-Contraction TableTOPIK 1 — The obligatory stem-vowel + 아/어 fusions that produce every 해요체 and past form — 가+아→가, 오+아→와, 주+어→줘, 마시+어→마셔 — plus the 되/돼 spelling test. The uncontracted forms are simply wrong.
- The ㅡ-Drop (으 탈락) TableTOPIK 2 — A fully regular alternation: a stem whose final vowel is ㅡ drops it before any 아/어 ending, and the syllable before the dropped ㅡ then decides harmony — 바쁘다→바빠, 예쁘다→예뻐, 크다→커. The 르-stems are a separate irregular.
- Past Tense -았/었/였: Formation TableTOPIK 1 — The complete formation table for the past-tense infix -았/었/였-, which slots in before the ending and is chosen by the same ㅏ/ㅗ harmony as the present. One infix, four speech levels, no irregular 'went' to memorize — plus the vowel-boundary contractions (갔어요, 왔어요, 마셨어요, 됐어요).
- Vowel Harmony: Choosing -아 vs -어TOPIK 1 — One rule fixes the shape of every -아/어 ending: if the stem's LAST vowel is ㅏ or ㅗ (bright), use 아; for anything else, use 어. The single memorized exception is 하다 → 해.