Vowel-Stem Contractions: 가 + 아 → 가, 오 + 아 → 와, 보 + 아 → 봐 | Korean Grammar

Once you learn that the 해요체 present adds -아/어요 to a stem, you hit an immediate problem: what happens when the stem already ends in a vowel? You cannot simply glue -아요 onto 가- and say ×가아요 — nobody does. Two vowels colliding across the stem–ending seam fuse, and the fusion is obligatory. This page teaches the four fusion patterns, and the single reframing that makes them easy: these are not irregular verbs.

The reframing: these are sound-fusions, not irregularities

English speakers meet these forms and file them under "exceptions to memorize," which makes Korean feel far more chaotic than it is. Drop that framing. 가다 is a perfectly regular verb. The rule "add -아/어" applies to it exactly as written — 가 + 아 — but Korean phonology does not permit two identical vowels to sit in adjacent syllables here, so they collapse into one. The "long" form 가아요 is not a rarer or more formal variant; it is simply impossible to say, the way English doesn't is not a fancy version of does not but the only form anyone actually speaks in conversation.

So think of the contracted form as the only real form. There is no hidden longhand underneath 가요 waiting to be uncontracted. This matters because the same -아/어 slot feeds the past tense and dozens of connectives, so every contraction you learn here pays off many times over (가요 → 갔어요, 봐요 → 봤어요).

Pattern 1 — Identical vowels merge into one

When the stem's final vowel is the same as the vowel that harmony wants to add, the two simply become one. Nothing is left to write.

A ㅏ-stem takes -아 by harmony, and ㅏ + 아 → ㅏ:

저 이제 집에 가요.

jeo ije jibe gayo

I'm heading home now. (가다: 가 + 아 → 가)

주말에 보통 장을 봐요… 아, 오늘은 그냥 자요.

jumare botong jang-eul bwayo… a, oneureun geunyang jayo

I usually do the grocery shopping on weekends… ah, today I'll just sleep. (자다: 자 + 아 → 자)

A ㅓ-stem takes -어, and ㅓ + 어 → ㅓ; likewise a ㅕ-stem (켜다, 펴다):

이 버스 시청 앞에 서요?

i beoseu sicheong ape seoyo?

Does this bus stop in front of city hall? (서다: 서 + 어 → 서)

저는 아침에 일어나면 항상 라디오를 켜요.

jeoneun achime ireonamyeon hangsang radioreul kyeoyo

When I get up in the morning I always turn on the radio. (켜다: 켜 + 어 → 켜)

💡

If the stem vowel and the harmony vowel are the same (사다, 자다 with ㅏ; 서다, 건너다 with ㅓ), you write nothing extra — the stem is already the whole present form minus 요. 사다 → 사요, not ×사아요.

Pattern 2 — ㅗ + 아 → ㅘ

A stem ending in ㅗ takes -아 by harmony, and ㅗ glides into the following 아 to make ㅘ. This is the pattern behind two of the most common verbs in the language, 오다 (to come) and 보다 (to see/watch).

친구가 내일 우리 집에 놀러 와요.

chinguga naeil uri jibe nolleo wayo

A friend is coming over to my place tomorrow. (오다: 오 + 아 → 와)

저는 주말마다 넷플릭스로 영화 봐요.

jeoneun jumalmada netpeullikseuro yeonghwa bwayo

I watch a movie on Netflix every weekend. (보다: 보 + 아 → 봐)

Dictionary	Stem	ㅗ + 아	Present	Reading
오다 (come)	오-	오 + 아 → 와	와요	wayo
보다 (see)	보-	보 + 아 → 봐	봐요	bwayo
쏘다 (shoot)	쏘-	쏘 + 아 → 쏴	쏴요	sswayo

The only exception to notice: one-syllable ㅗ-stems can optionally stay uncontracted in careful writing (보아요 exists on the page), but in speech and normal writing the fused 와요/봐요 is overwhelmingly the norm. Multi-syllable ㅗ-stems contract even more rigidly.

Pattern 3 — ㅜ + 어 → ㅝ

A stem ending in ㅜ takes -어 (ㅜ is not ㅏ/ㅗ, so it gets the dark vowel), and ㅜ glides into 어 to make ㅝ. This catches a whole family of everyday verbs: 주다 (give), 배우다 (learn), 추다 (dance), 싸우다 (fight).

요즘 유튜브 보면서 기타를 배워요.

yojeum yutyubeu bomyeonseo gitareul baewoyo

These days I'm learning guitar from YouTube. (배우다: 우 + 어 → 워)

저는 동생한테 매달 용돈을 조금 줘요.

jeoneun dongsaenghante maedal yongdoneul jogeum jwoyo

I give my little sibling a bit of pocket money every month. (주다: 주 + 어 → 줘)

우리 언니는 춤을 진짜 잘 춰요.

uri eonnineun chumeul jinjja jal chwoyo

My older sister dances really well. (추다: 추 + 어 → 춰)

Pattern 4 — ㅐ / ㅔ + 어 collapse (optionally)

Stems ending in ㅐ or ㅔ take -어 by harmony, but the 어 is redundant after these already-frontal vowels and drops in modern usage. So 보내다 (send) becomes 보내요, not 보내어요:

집에 도착하면 문자 보내요.

jibe dochakamyeon munja bonaeyo

Text me when you get home. (보내다: 보내 + 어 → 보내)

이 계곡은 물살이 생각보다 세요.

i gyegogeun mulsari saenggakboda seyo

The current in this valley is stronger than you'd think. (세다: 세 + 어 → 세)

The uncontracted 보내어요 is not wrong — you will see it in careful or slightly formal writing — but in speech it is 보내요. For ㅔ-stems the collapse is essentially total: 세다 → 세요, never ×세어요 in normal use.

Why this pays off everywhere: the past tense

Here is the leverage. The past tense is built on the exact same -아/어 stem, just with -ㅆ어요 instead of -요. So every contraction you learn transfers directly:

어제 친구가 우리 집에 왔어요.

eoje chinguga uri jibe wasseoyo

A friend came to my place yesterday. (와요 → 왔어요)

그 영화 벌써 봤어요.

geu yeonghwa beolsseo bwasseoyo

I already saw that movie. (봐요 → 봤어요)

작년에 태권도를 배웠어요.

jangnyeone taegwondoreul baewosseoyo

I learned taekwondo last year. (배워요 → 배웠어요)

💡

The fusion you learn here is a one-time investment. It reappears, unchanged, in the past (왔어요), the -아/어서 connective (와서), the -아/어도 concessive (와도), and every other ending built on the -아/어 stem. Nail the present contraction and you have effectively conjugated the whole verb.

Notice you never re-derive anything: once you know 오다 → 와, the past is just 왔-, the connective "and" is 와서, the "if" form is 와도. Master the fusion once at the present, and the whole conjugation of that verb falls into place. This is why these pages sit at the very foundation of the verb system, right beside vowel harmony -아/어 and the past tense.

How this differs from English

English contractions like I'm, don't, won't are optional stylistic reductions — you can always expand them (I am, do not) and sound merely a touch more formal. Korean vowel-stem contractions are the opposite: they are obligatory phonological fusions with no valid expanded form. There is no register in which 가아요 becomes correct; it is not "the formal way to say 가요," it is simply not Korean. Coming from English, the instinct to "write it out in full to be safe" actively produces errors here. The contracted form is not a shortcut — it is the word.

Two neighboring pages handle the remaining vowel-stem cases: ㅣ + 어 → ㅕ and 되다 → 돼 for stems ending in ㅣ or ㅚ, and 하다 → 해 for the huge 하다 class, which uses a different allomorph (여) entirely.

Common Mistakes

1. Writing out the long form on a ㅗ-stem. 오 + 아 fuses to 와; there is no ×오아요.

❌ 친구가 내일 와요… 아니, 오아요?

Wrong — 오 + 아 must fuse to 와요; ×오아요 is impossible.

✅ 친구가 내일 와요.

chinguga naeil wayo

A friend is coming tomorrow.

2. Writing out the long form on a ㅜ-stem. 주 + 어 fuses to 줘.

❌ 이거 저 주어요.

Wrong — 주 + 어 must fuse to 줘요; ×주어요 sounds like reading it off the page.

✅ 이거 저 줘요.

igeo jeo jwoyo

Give me this one, please.

3. Adding an extra vowel on an identical-vowel stem. 가 + 아 leaves nothing to add.

❌ 저 지금 집에 가아요.

Wrong — ㅏ + 아 merge; it is just 가요.

✅ 저 지금 집에 가요.

jeo jigeum jibe gayo

I'm going home now.

4. Failing to carry the contraction into the past. The past uses the same fused stem.

❌ 그 영화 봤어요? 아니요, 보았어요는 아직…

Wrong instinct — the past of 봐요 is 봤어요, built on the fused 봐, not ×보아써요.

✅ 그 영화 봤어요.

geu yeonghwa bwasseoyo

I saw that movie.

Key Takeaways

Vowel-final stems fuse with -아/어; the contracted form is the only real form (가아요, 오아요, 주어요 are never said).
Identical vowels merge: 가 + 아 → 가요, 서 + 어 → 서요, 켜 + 어 → 켜요.
ㅗ + 아 → ㅘ: 오다 → 와요, 보다 → 봐요, 쏘다 → 쏴요.
ㅜ + 어 → ㅝ: 주다 → 줘요, 배우다 → 배워요, 추다 → 춰요.
ㅐ/ㅔ + 어 collapse: 보내다 → 보내요, 세다 → 세요.
These are regular phonology, not irregular verbs — and they transfer intact to the past (왔어요, 봤어요) and every -아/어 connective.

Now practice Korean

Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.

Start learning Korean→