The ㅡ-Drop (으 탈락) Table | Korean Grammar

Stems whose final vowel is ㅡ — 크다, 쓰다, 바쁘다, 예쁘다, 아프다, 모으다 — behave in one clean, predictable way when they meet an 아/어 ending: the ㅡ drops entirely, and the choice of 아 vs 어 then falls to the vowel in the syllable before it. This is often listed among the "irregulars," but it is 100% regular — every plain ㅡ-final stem does it, with no exceptions. This page is the lookup table, plus the one boundary you must respect: 르-stems are a genuinely different beast.

The rule

A bare ㅡ has no harmony value of its own — it is neither bright nor dark. So when an 아/어 ending arrives, the ㅡ simply deletes, and harmony is decided by the vowel one syllable back:

If that preceding vowel is ㅏ or ㅗ → 아 (바빠, 아파, 모아).
If it is anything else, or there is no preceding syllable at all → 어 (예뻐, 기뻐, 커, 써).

The reframing English speakers need: do not look for harmony on the ㅡ itself — it vanishes. Read one syllable back. That is why it is 바빠 (preceding ㅏ) but 예뻐 (preceding ㅕ), and why a one-syllable stem like 크- with nothing behind it defaults to 커.

The ㅡ-drop table

Dictionary	Stem	Vowel that governs harmony	아/어 → result	해요체 (reading)
크다 (be big)	크-	none → default 어	ㅋ + 어 → 커	커요 (keoyo)
쓰다 (write/use)	쓰-	none → default 어	ㅆ + 어 → 써	써요 (sseoyo)
바쁘다 (be busy)	바쁘-	ㅏ (bright) → 아	바ㅃ + 아 → 바빠	바빠요 (bappayo)
아프다 (hurt)	아프-	ㅏ (bright) → 아	아ㅍ + 아 → 아파	아파요 (apayo)
모으다 (gather)	모으-	ㅗ (bright) → 아	모 + 아 → 모아	모아요 (moayo)
예쁘다 (be pretty)	예쁘-	ㅕ (not bright) → 어	예ㅃ + 어 → 예뻐	예뻐요 (yeppeoyo)
기쁘다 (be glad)	기쁘-	ㅣ (not bright) → 어	기ㅃ + 어 → 기뻐	기뻐요 (gippeoyo)
슬프다 (be sad)	슬프-	ㅡ (not bright) → 어	슬ㅍ + 어 → 슬퍼	슬퍼요 (seulpeoyo)

Notice the mechanics: the ㅡ is deleted, the leftover consonant (ㅃ, ㅍ, ㅋ, ㅆ) re-attaches as the onset of the new syllable, and the 아/어 the previous vowel selected fills it in. 바쁘 → drop ㅡ → 바ㅃ → the ㅏ in 바 is bright → 아 → 바빠. This applies through the whole conjugation: past 바빴어요, connective 바빠서, and so on.

Bright preceding vowel → 아

요즘 일이 너무 많아서 정말 바빠요.

yojeum iri neomu manaseo jeongmal bappayo

I'm swamped with work these days, so I'm really busy. (바쁘-: preceding ㅏ → 아 → 바빠)

아침부터 머리가 좀 아파요.

achimbuteo meoriga jom apayo

I've had a bit of a headache since this morning. (아프-: preceding ㅏ → 아 → 아파)

아이들이 낙엽을 한곳에 모아요.

aideuri nagyeobeul hangose moayo

The kids are gathering the fallen leaves in one spot. (모으-: preceding ㅗ → 아 → 모아)

Non-bright or no preceding vowel → 어

이 옷 진짜 예뻐요. 어디서 샀어요?

i ot jinjja yeppeoyo. eodiseo sasseoyo?

This outfit is really pretty. Where did you buy it? (예쁘-: preceding ㅕ → 어 → 예뻐)

합격 소식 들으니까 정말 기뻐요.

hapgyeok sosik deureunikka jeongmal gippeoyo

I'm so glad to hear you passed. (기쁘-: preceding ㅣ → 어 → 기뻐)

글씨 좀 더 크게 써요.

geulssi jom deo keuge sseoyo

Write the letters a bit bigger. (쓰-: no preceding vowel → 어 → 써)

키가 언제 이렇게 컸어요?

kiga eonje ireoke keosseoyo?

When did you grow this tall? (크-: past 크 + 었 → 컸)

💡

Two-step it every time: (1) delete the final ㅡ, (2) read the vowel one syllable back to pick 아 or 어. Single-syllable stems (크-, 쓰-) have nothing to read, so they default to 어 → 커, 써. Never keep the ㅡ (×크어요) and never harvest harmony from the wrong syllable (×바뻐요 — the ㅏ in 바 wins, so it's 바빠요).

Boundary: 르-stems are NOT this pattern

Do not extend the ㅡ-drop to stems ending in 르 (모르다, 다르다, 부르다, 빠르다). Those look similar — they end in a ㅡ syllable — but they take a different, irregular path: the ㅡ drops and an extra ㄹ appears, doubling the ㄹ.

모르다 → 몰라(요), not ×모러요
다르다 → 달라(요), not ×다러요
빠르다 → 빨라(요)
부르다 → 불러(요)

That is the 르-irregular, covered on its own 르-irregular reference page. The plain ㅡ-drop on this page covers every other ㅡ-final stem — anything where the last syllable is 쁘, 프, 쓰, 크, 으, etc., but not 르.

Reframing for English speakers

English has "silent" vowels that surface or vanish (the e in make → making), but they are spelling conventions, not harmony triggers. The Korean ㅡ-drop is a live phonological rule with a twist: the vanishing vowel hands off the harmony decision to its neighbor. So the mental model is not "ㅡ is a dark vowel" — it is "ㅡ is a blank that deletes and passes the choice backward." Once that clicks, 바빠 vs 예뻐 stops looking arbitrary: same rule, different neighbor.

Common Mistakes

1. Keeping the ㅡ. The ㅡ must drop before 아/어.

❌ 저는 요즘 너무 바쁘어요.

Wrong — the ㅡ of 바쁘- drops; the preceding ㅏ is bright → 바빠요.

✅ 저는 요즘 너무 바빠요.

jeoneun yojeum neomu bappayo

I'm so busy these days.

2. Harvesting harmony from the wrong syllable. Read the vowel just before the ㅡ, not the first one.

❌ 이 꽃 진짜 예빠요.

Wrong — 예쁘-'s preceding vowel is ㅕ (not bright) → 어 → 예뻐요.

✅ 이 꽃 진짜 예뻐요.

i kkot jinjja yeppeoyo

This flower is really pretty.

3. Defaulting a single-syllable stem to 아. With nothing behind it, ㅡ defaults to 어.

❌ 글씨를 좀 크게 싸요.

Wrong — 쓰- has no preceding vowel → 어 → 써요.

✅ 글씨를 좀 크게 써요.

geulssireul jom keuge sseoyo

Write the letters a bit bigger.

4. Treating a 르-stem as a plain ㅡ-drop. 르-stems double the ㄹ.

❌ 저는 그 사람 이름을 몰르어요.

Wrong — 모르다 is the 르-irregular: 몰라요, not a plain ㅡ-drop.

✅ 저는 그 사람 이름을 몰라요.

jeoneun geu saram ireumeul mollayo

I don't know that person's name.

Key Takeaways

ㅡ-drop is fully regular: every plain ㅡ-final stem deletes its ㅡ before an 아/어 ending.
Harmony is then set by the vowel one syllable back — bright (ㅏ/ㅗ) → 아 (바빠, 아파, 모아); otherwise, or if none → 어 (예뻐, 기뻐, 커, 써).
The ㅡ carries no harmony value of its own — think of it as a blank that deletes and passes the choice backward.
It runs through the whole conjugation: 바빠요 / 바빴어요 / 바빠서.
르-stems are excluded — they are a separate irregular (모르다 → 몰라요, 다르다 → 달라요).

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