ㅅ-Irregular Verbs (ㅅ 불규칙): Full Table | Korean Grammar

The ㅅ-irregular (ㅅ 불규칙) has the simplest rule of all the classes and the sneakiest consequence. Before a vowel- or 으-initial ending, the stem's final ㅅ simply drops — no mutation, no insertion, it is just gone: 짓다 ("build/compose/cook rice") + 어요 → 지어요. The catch is what the vanished ㅅ leaves behind: two vowels sitting next to each other that must not contract. 지어요 stays three syllables (지-어-요) and never collapses to ×져요. That uncontracted hiatus is the fingerprint of the entire class. This page is the paradigm grid across the closed set, plus a "stays regular" row of look-alikes.

The one-line rule behind the grid

Stem-final ㅅ disappears before an ending beginning with a vowel (아/어) or with 으; before a consonant-initial ending it stays. Harmony (아 vs 어) is then chosen normally by the stem's own vowel, applied to the now-bare stem. The reason the two exposed vowels do not fuse is that a consonant used to be there — the dropped ㅅ leaves a silent seam that blocks the glide. The full "why" is on the ㅅ irregular explained page; this page is the table.

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Picture the vanished ㅅ as an invisible wall: it makes no sound, but it still stands between the two vowels and stops them collapsing into one. That is why 지어요 stays 지-어-요 and never becomes ×져요 — even though a plain vowel stem like 가지다 does glide (가져요). A ㅅ-irregular 해요 form is always one syllable longer than beginners expect.

Full table: the closed set of members

Columns: dictionary form, the everyday polite 해요체 (-아/어요), the causal -(으)니까, the past modifier -(으)ㄴ (the form before a noun), and the past -았/었어요. Every 아/어 and 으 cell shows the ㅅ gone and the hiatus preserved.

Dictionary (meaning)	해요체 -아/어요	Causal -(으)니까	Modifier -(으)ㄴ	Past -았/었어요
짓다 (build/compose/name)	지어요 jieoyo	지으니까 jieunikka	지은 jieun	지었어요 jieosseoyo
붓다 (pour / swell)	부어요 bueoyo	부으니까 bueunikka	부은 bueun	부었어요 bueosseoyo
낫다 (recover / be better)	나아요 naayo	나으니까 na-eunikka	나은 na-eun	나았어요 naasseoyo
젓다 (stir / row)	저어요 jeoeoyo	저으니까 jeo-eunikka	저은 jeo-eun	저었어요 jeoeosseoyo
잇다 (connect / join)	이어요 ieoyo	이으니까 ieunikka	이은 ieun	이었어요 ieosseoyo

The harmony split is visible in the table: 낫다's stem vowel is bright ㅏ, so it takes 아 (나아요), while 짓다, 붓다, 젓다, 잇다 take 어 by their own stem vowels. But the ㅅ drops for all of them, and none of the results contract.

아기 이름을 뭐라고 지었어요?

agi ireumeul mworago jieosseoyo?

What did you name the baby? (짓다 → 지었어요)

컵에 뜨거운 물을 천천히 부어 주세요.

keobe tteugeoun mureul cheoncheonhi bueo juseyo

Please pour hot water into the cup slowly. (붓다 → 부어)

어제 많이 울어서 눈이 퉁퉁 부었어요.

eoje mani ureoseo nuni tungtung bueosseoyo

I cried a lot yesterday, so my eyes are all puffy. (붓다 'swell' → 부었어요)

설탕을 넣고 잘 저으니까 금방 녹았어요.

seoltang-eul neoko jal jeo-eunikka geumbang nogasseoyo

I added sugar and stirred it well, so it dissolved right away. (젓다 → 저으니까)

이 다리가 두 섬을 이어요.

i dariga du seomeul ieoyo

This bridge connects the two islands. (잇다 → 이어요)

낫다 does double duty — and has a dangerous twin

낫다 covers both "recover (from illness)" and the comparative "be better," and both senses run through 나아요:

약을 먹으면 감기가 금방 나아요.

yageul meogeumyeon gamgiga geumbang naayo

If you take medicine, the cold gets better quickly. (낫다 'recover' → 나아요)

이게 저것보다 훨씬 나아요.

ige jeogeotboda hwolssin naayo

This one is far better than that one. (낫다 'be better' → 나아요)

💡

Do not confuse 낫다 with its near-twin 낳다 ("give birth"), which ends in ㅎ, not ㅅ, and belongs to a different class — even though both can surface as naa-. 낫다 → 나아요 (ㅅ drops), but 낳다 → 낳아요 (ㅎ stays in spelling). Same sound, different verb, different table.

Stays-regular warning row: 웃다, 씻다, 벗다, 빗다

Membership is lexical — plenty of common ㅅ-final stems are perfectly regular, keeping their ㅅ and liaising it forward like any batchim. The four to lock in:

Dictionary (meaning)	해요체 -아/어요	Causal -(으)니까	Modifier -(으)ㄴ	Past -았/었어요
웃다 (laugh/smile)	웃어요 useoyo	웃으니까 useunikka	웃은 useun	웃었어요 useosseoyo
씻다 (wash)	씻어요 ssiseoyo	씻으니까 ssiseunikka	씻은 ssiseun	씻었어요 ssiseosseoyo
벗다 (take off)	벗어요 beoseoyo	벗으니까 beoseunikka	벗은 beoseun	벗었어요 beoseosseoyo
빗다 (comb)	빗어요 biseoyo	빗으니까 biseunikka	빗은 biseun	빗었어요 biseosseoyo

The contrast is audible. Irregular 짓다 → 지어요 has no ㅅ sound at all and a two-syllable gap (지-어). Regular 웃다 → 웃어요 keeps the ㅅ, which just slides onto the next syllable — pronounced [우서요] — a smooth single onset with no hiatus. So the hiatus itself is your diagnostic: if you hear a seam, it dropped; if you hear a clean [s] carrying forward, it stayed.

그 이야기를 듣고 다 같이 크게 웃었어요.

geu iyagireul deutgo da gachi keuge useosseoyo

We all burst out laughing when we heard that story. (웃다 regular → 웃었어요)

집에 오면 손부터 깨끗이 씻어요.

jibe omyeon sonbuteo kkaekkeusi ssiseoyo

When I get home, I wash my hands first thing. (씻다 regular → 씻어요)

Why English speakers get this exactly backwards

English is a contracting language: going to becomes gonna, do not becomes don't, and vowels in hiatus tend to glide together. So when an English speaker sees 지 + 어, every instinct says "smooth it out" — and out comes ×져요. The ㅅ-irregular demands the opposite reflex: resist the merge. The seam left by the dropped consonant is doing grammatical work, keeping the two vowels apart. The mental correction is to treat 지어요 like the deliberately careful English "co-operate" (co-op-erate), where the two vowels stay distinct, rather than the casual glide. If your ㅅ-irregular form ever feels "too short" or "too smooth," you have probably contracted a hiatus you were supposed to keep.

Before consonant endings: the ㅅ stays

Like every irregular, the ㅅ class is dormant before consonant-initial endings — 짓고, 짓지, 짓습니다, 낫지 않아요. The ㅅ is written and kept there (pronounced as a [t] batchim per the seven-sound rule).

요즘 이 동네에 새 아파트를 많이 짓습니다.

yojeum i dongnee sae apateureul mani jitseumnida

A lot of new apartments are being built in this neighborhood these days. (짓다 + -습니다, formal)

Common Mistakes

1. Contracting the hiatus. The number-one ㅅ error — collapsing the two vowels.

❌ 커피를 잘 저요.

Wrong — the hiatus must stay two syllables: 저어요 (저-어-요), not ×저요.

✅ 커피를 잘 저어요.

keopireul jal jeoeoyo

I stir the coffee well.

2. Gliding 지어요 into ×져요.

❌ 할아버지가 시를 한 편 져요.

Wrong — 짓다 does not glide; it stays 지어요 (지-어-요).

✅ 할아버지가 시를 한 편 지어요.

harabeojiga sireul han pyeon jieoyo

My grandfather composes a poem.

3. Keeping the ㅅ before a vowel. The ㅅ must drop, not liaise.

❌ 상처가 빨리 낫아요.

Wrong — the ㅅ drops before a vowel: 나아요.

✅ 상처가 빨리 나아요.

sangcheoga ppalli naayo

The wound heals quickly.

4. Assuming every ㅅ-stem is irregular. 웃다 is regular; the ㅅ stays.

❌ 아기가 나를 보고 우어요.

Wrong — 웃다 is a regular ㅅ verb: 웃어요, not ×우어요.

✅ 아기가 나를 보고 웃어요.

agiga nareul bogo useoyo

The baby looks at me and smiles.

Key Takeaways

Stem-final ㅅ drops before a vowel- or 으-initial ending; it stays before a consonant ending (짓고, 짓습니다).
Uniquely among the irregulars, the dropped ㅅ leaves an uncontracted hiatus: 지어요 = 지-어-요, never ×져요.
Harmony still runs on the bare stem: 짓다 → 지어요, but 낫다 → 나아요.
Core members: 짓다, 붓다, 낫다, 젓다, 잇다 — a short, memorizable list.
Membership is lexical: 웃다, 씻다, 벗다, 빗다 stay regular, and 낳다 (ㅎ-class) only looks like 낫다 — check the master chart.

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