The ㅅ irregular (ㅅ 불규칙, 시옷 불규칙) is the quietest of the irregular classes and, for that reason, the one learners most often mispronounce. Its rule is almost too simple: before a vowel- or 으-initial ending, the stem's final ㅅ just drops, leaving the stem vowel exposed. 짓다 ("build / make") + 어요 → 지어요. No mutation, no insertion — the ㅅ is simply gone. The catch is what happens next: the two vowels left touching each other do not merge, and resisting that merge is the whole skill.
The rule
Stem-final ㅅ disappears before an ending beginning with a vowel (아/어) or with 으. Before a consonant-initial ending, the ㅅ stays.
| Ending type | Example | 짓다 becomes | ㅅ dropped? |
|---|---|---|---|
| Vowel-initial (아/어) | -어요, -었어요 | 지어요, 지었어요 | yes |
| 으-initial | -(으)면, -(으)세요 | 지으면, 지으세요 | yes |
| Consonant-initial | -고, -지, -습니다 | 짓고, 짓지, 짓습니다 | no |
아기 이름을 뭐라고 지었어요?
agi ireumeul mworago jieosseoyo?
What did you name the baby?
저 아파트는 작년에 새로 지었어요.
jeo apateuneun jangnyeone saero jieosseoyo
That apartment was newly built last year.
집을 지으면 마당도 만들 거예요.
jibeul jieumyeon madangdo mandeul geoyeyo
When I build a house, I'll make a yard too.
The reframe: a hiatus you must keep as two syllables
Here is the feature that makes ㅅ unique among the irregulars. When the ㅅ drops, you are left with two vowels sitting next to each other with nothing between them — 지 + 어 → 지어, 나 + 아 → 나아. Korean would normally love to smash such a sequence into a single glided syllable (the way 가지다 → 가져요). The ㅅ irregular refuses to. 지어요 is pronounced 지-어-요, three full syllables — never the contracted ×져요.
Why? Because there was a consonant there. The dropped ㅅ leaves behind a syllable boundary — a silent seam — that blocks the two vowels from fusing. Compare:
- 가지다 (a plain vowel stem) + 어요 → the ㅣ and 어 glide together → 가져요 (two syllables, 가-져)
- 짓다 (ㅅ dropped) + 어요 → the seam blocks the glide → 지어요 (three syllables, 지-어-요)
Vowel harmony still selects the ending
As with every 아/어 class, the choice of 아 vs 어 depends on the stem vowel, applied after the ㅅ drops:
- 짓다 (vowel ㅣ) → 지 + 어요 → 지어요
- 낫다 (vowel ㅏ, bright) → 나 + 아요 → 나아요
감기가 아직 안 나았어요.
gamgiga ajik an naasseoyo
My cold still hasn't gotten better.
이 약을 먹으면 금방 나아요.
i yageul meogeumyeon geumbang naayo
If you take this medicine, you'll get better quickly.
낫다 doubles as the comparative "be better," and it conjugates the same way:
이게 저것보다 훨씬 나아요.
ige jeogeotboda hwolssin naayo
This one is far better than that one.
The core members
The ㅅ irregulars are a short, closed set. Learn these five and you have them all:
| Dictionary form | Meaning | 해요 form | Syllables |
|---|---|---|---|
| 짓다 | build / compose / cook (rice) / name | 지어요 | 지-어-요 |
| 낫다 | heal / be better | 나아요 | 나-아-요 |
| 붓다 | pour / (of a body part) swell | 부어요 | 부-어-요 |
| 잇다 | connect / join | 이어요 | 이-어-요 |
| 젓다 | stir / row | 저어요 | 저-어-요 |
컵에 뜨거운 물을 부어 주세요.
keobe tteugeoun mureul bueo juseyo
Please pour hot water into the cup.
어제 많이 울어서 눈이 퉁퉁 부었어요.
eoje mani ureoseo nuni tungtung bueosseoyo
I cried a lot yesterday, so my eyes are all puffy.
이 다리가 두 섬을 이어요.
i dariga du seomeul ieoyo
This bridge connects the two islands.
설탕을 넣고 천천히 저어요.
seoltang-eul neoko cheoncheonhi jeoeoyo
Add the sugar and stir slowly.
으-endings: 지으면, 나으면
The 으-type endings behave the same as vowel endings: the ㅅ drops, and the 으 attaches to the bare stem vowel.
상처가 다 나으면 다시 운동하세요.
sangcheoga da na-eumyeon dasi undonghaseyo
Once the wound has fully healed, start exercising again.
라면에 물을 부으니까 넘쳤어요.
ramyeone mureul bueunikka neomcheosseoyo
As I poured water into the ramyeon, it overflowed.
Before consonant endings: ㅅ stays
In front of a consonant-initial ending, the ㅅ is retained — 짓고, 짓지, 짓습니다. (It is pronounced as a [t] batchim there, per the seven-sound rule, but it is written and it stays.)
요즘 새 아파트를 많이 짓습니다.
yojeum sae apateureul mani jitseumnida
A lot of new apartments are being built these days.
약을 먹어도 병이 잘 낫지 않아요.
yageul meogeodo byeong-i jal natji anayo
Even taking medicine, the illness doesn't heal well.
A meaning trap to flag
낫다 "recover / be better" is irregular (나아요), but there are common verbs ending in ㅅ that look identical yet stay regular — 웃다 ("laugh") is 웃어요, not ×우어요. And 낫다 has a near-twin, 낳다 ("give birth"), that ends in ㅎ, not ㅅ, and belongs to yet another class — even though both surface as naayo. Those boundaries are drawn on the ㅅ irregular vs regular ㅅ verbs page.
Common Mistakes
1. Contracting the hiatus. The number-one ㅅ error — collapsing 지어요 to ×져요, 저어요 to ×저요, 나아요 to ×나요.
❌ 커피를 잘 저요.
Incorrect — the hiatus must stay: 저어요 (저-어-요), not 저요.
✅ 커피를 잘 저어요.
keopireul jal jeoeoyo
I stir the coffee well.
2. A different flavor of the same error — 지어요 → ×져요.
❌ 시를 한 편 져요.
Incorrect — 짓다 does not glide; it stays 지어요 (지-어-요).
✅ 시를 한 편 지어요.
sireul han pyeon jieoyo
I compose a poem.
3. Keeping the ㅅ before a vowel. The ㅅ must drop, not liaise.
❌ 상처가 빨리 낫아요.
Incorrect — the ㅅ drops before a vowel: 나아요.
✅ 상처가 빨리 나아요.
sangcheoga ppalli naayo
The wound heals quickly.
4. Wrong vowel harmony. 낫다 is bright (ㅏ), so it takes 아: 나아요, not ×나어요.
❌ 감기가 다 나어요.
Incorrect — bright stem ㅏ takes 아: 나아요.
✅ 감기가 다 나아요.
gamgiga da naayo
My cold is all better.
Key Takeaways
- Stem-final ㅅ drops before a vowel-initial or 으-initial ending; it stays before a consonant ending.
- Uniquely, the dropped ㅅ leaves a two-vowel hiatus that does not contract: 지어요 = 지-어-요, never ×져요.
- Vowel harmony still runs on the bare stem: 짓다 → 지어요, 낫다 → 나아요.
- The core members are 짓다, 낫다, 붓다, 잇다, 젓다 — a short, memorizable list.
- Watch the look-alikes: 웃다 (regular, 웃어요) and 낳다 (ㅎ-class, 낳아요) are handled on the next page.
Now practice Korean
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Start learning Korean→Related Topics
- ㅅ Irregular vs Regular ㅅ Verbs (웃다·씻다)TOPIK 2 — Where the short ㅅ-irregular list ends and the common regular ㅅ verbs (웃다, 씻다, 벗다) begin — plus the 낫다 vs 낳다 trap, two verbs that sound identical but belong to different classes.
- When Irregulars Fire: The Three Ending EnvironmentsTOPIK 1 — Irregular stems only change before certain endings. Sort every ending into three environments — consonant-initial (safe, no change), 으-initial, and 아/어 vowel-initial (the strongest trigger) — and you can predict every irregular form.
- Irregular Predicates at a Glance (Reference Table)TOPIK 2 — One-screen reference for all eight irregular classes — the trigger, the change, a model verb with its 아/어-form and 으-form, and a regular look-alike to guard against over-generalizing each class.
- Regular vs Irregular Predicates: The Big PictureTOPIK 1 — The seven irregular predicate classes are not chaos — each is a small, predictable sound change keyed to the stem's FINAL letter, and adjectives conjugate by the exact same machinery as verbs.