Korean's irregular verbs are famous for one trap in particular: two verbs can end in the same final consonant and yet conjugate completely differently. 덥다 ("hot") becomes 더워요, but 입다 ("wear") becomes 입어요 — same ㅂ, opposite outcomes. Because of this, learners make mistakes in both directions. They under-apply the irregular rule, regularizing a true irregular (×덥어요), and they over-apply it, irregularizing an innocent regular verb (×이워요). This page shows both failure modes side by side, so you learn to treat irregularity as a property of the specific verb, not of its final consonant.
The one fact that fixes everything: irregularity is lexical
Here is the mental model to install. The final consonant ㅂ, ㄷ, or 르 does not tell you whether a verb is irregular. Two verbs can share a final consonant and belong to different classes. Whether a stem is irregular is a fact stored per verb — you learn it with the word, the way you learn its meaning.
That is genuinely harder than what English trains you for, and it's worth being honest about: there is no reliable shape-based shortcut. You cannot look at 덥다 and 입다 and predict from spelling which one warps. You memorize that 덥다 is ㅂ-irregular and 입다 is regular, the same way an English learner simply memorizes that "sing" → "sang" but "bring" → "brought" (not ×"brang").
Under-application: regularizing a true irregular
This is the beginner error: you know the -아/어요 rule and apply it mechanically, ignoring that the stem transforms. The result sounds instantly foreign.
ㅂ-irregular — the ㅂ turns into 우/오 before a vowel ending. 덥다 → 더워요, not ×덥어요:
오늘 밖에 너무 더워요.
oneul bakke neomu deowoyo
It's so hot outside today.
겨울 바다는 정말 추워요.
gyeoul badaneun jeongmal chuwoyo
The winter sea is really cold.
ㄷ-irregular — the ㄷ becomes ㄹ before a vowel. 듣다 → 들어요, not ×듣어요:
저는 이 노래 자주 들어요.
jeoneun i norae jaju deureoyo
I listen to this song often.
르-irregular — the ㅡ drops and an extra ㄹ appears. 모르다 → 몰라요, not ×모르아요:
길을 몰라서 한참 헤맸어요.
gireul mollaseo hancham hemaesseoyo
I didn't know the way, so I wandered around for a while.
발음이 너무 빨라서 못 알아들었어요.
bareumi neomu ppallaseo mot aradeureosseoyo
The pronunciation was so fast I couldn't catch it.
Over-application: irregularizing a look-alike regular
Once learners know about ㅂ- and ㄷ-irregulars, they overshoot: they see any final ㅂ or ㄷ and reach for the irregular transformation. But many of the most common verbs with these consonants are perfectly regular — the ending just attaches with plain liaison.
Regular ㅂ — 입다 ("wear") keeps its ㅂ: 입어요, not ×이워요:
이 셔츠 어제도 입었어요.
i syeocheu eojedo ibeosseoyo
I wore this shirt yesterday too.
Regular ㄷ — 믿다 ("believe") keeps its ㄷ: 믿어요, not ×미더요:
저는 그 사람 말을 믿어요.
jeoneun geu saram mareul mideoyo
I believe what that person says.
Regular (ㅂ) — 좁다 ("narrow") is regular: 좁아요, not ×조와요:
이 방은 좀 좁아요.
i bang-eun jom jobayo
This room is a bit narrow/cramped.
Notice that these regulars just liaise — the final consonant slides onto the vowel of the ending (입 + 어요 → 이버요, 믿 + 어요 → 미더요 in sound), with no stem change at all. That is exactly the behavior a learner "forgets" when they over-apply the irregular pattern.
The pairs you must memorize
The safest way to internalize this is by contrastive pairs — an irregular next to its regular look-alike. These are the high-frequency ones worth drilling:
| Final | Irregular (stem changes) | Regular (just liaises) |
|---|---|---|
| ㅂ | 덥다 → 더워요, 춥다 → 추워요, 돕다 → 도와요 | 입다 → 입어요, 좁다 → 좁아요, 잡다 → 잡아요 |
| ㄷ | 듣다 → 들어요, 걷다 → 걸어요, 묻다(ask) → 물어요 | 믿다 → 믿어요, 받다 → 받아요, 닫다 → 닫아요 |
| 르 | 모르다 → 몰라요, 빠르다 → 빨라요, 부르다 → 불러요 | (르-stems are almost all irregular; the rare exceptions like 따르다 → 따라요 simply drop ㅡ) |
Two details worth flagging honestly:
- 돕다 and 곱다 are ㅂ-irregular but take 오 (→ 도와요, 고와요), not 우, unlike 덥다/춥다 (→ 더워요/추워요). They are the only two that do this. Just memorize the pair.
- 묻다 is two different verbs. 묻다 meaning "ask" is ㄷ-irregular (물어요); 묻다 meaning "bury" is regular (묻어요). Same spelling, opposite class — a perfect illustration of why the letter can't decide for you.
저 지금 택시 불러요.
jeo jigeum taeksi bulleoyo
I'm calling a taxi right now.
문 좀 닫아 주세요.
mun jom dada juseyo
Please close the door.
Why English speakers fall into this
English hands you a small, closed list of irregular verbs (go/went, buy/bought), and once you've memorized it, every other verb is safely regular. Nothing in an English verb's spelling signals irregularity — you just know the list. Korean feels different because the irregular behavior is triggered by a visible final consonant, which fools learners into thinking the consonant is the rule. It isn't. ㅂ, ㄷ, and 르 are sites where irregularity can happen, not guarantees that it does. The same ㅂ that warps in 덥다 sits quietly in 입다. Only lexical knowledge — memorizing which verbs are on the list — decides the outcome. Build that list gradually; see the irregular verbs overview and the dedicated pages for the ㅂ-irregular, ㄷ-irregular, and 르-irregular classes.
Common Mistakes
1. Regularizing ㅂ-irregular 덥다. The ㅂ must become 우.
❌ 오늘 너무 덥어요.
oneul neomu deobeoyo
Incorrect — 덥다 is ㅂ-irregular: 더워요.
✅ 오늘 너무 더워요.
oneul neomu deowoyo
It's so hot today.
2. Irregularizing regular 입다. 입다 keeps its ㅂ and just liaises.
❌ 코트를 이워요.
koteureul iwoyo
Incorrect — 입다 is regular: 입어요.
✅ 코트를 입어요.
koteureul ibeoyo
I'm wearing a coat.
3. Regularizing 르-irregular 모르다. ×모르아요 never happens; it's 몰라요.
❌ 저는 답을 모르아요.
jeoneun dabeul moreuayo
Incorrect — 모르다 is 르-irregular: 몰라요.
✅ 저는 답을 몰라요.
jeoneun dabeul mollayo
I don't know the answer.
4. Regularizing ㄷ-irregular 듣다. The ㄷ becomes ㄹ before a vowel.
❌ 음악을 자주 듣어요.
eumageul jaju deudeoyo
Incorrect — 듣다 is ㄷ-irregular: 들어요.
✅ 음악을 자주 들어요.
eumageul jaju deureoyo
I listen to music often.
5. Irregularizing regular 좁다. 좁다 is regular; ×조와요 borrows 덥다's pattern by mistake.
❌ 이 길은 조와요.
i gireun jowayo
Incorrect — 좁다 is regular: 좁아요.
✅ 이 길은 좁아요.
i gireun jobayo
This road is narrow.
Key Takeaways
- The final consonant (ㅂ, ㄷ, 르) marks a site where irregularity is possible — it does not predict whether a given verb is irregular. That is stored per word.
- Under-application regularizes a true irregular: ×덥어요, ×듣어요, ×모르아요. Over-application irregularizes a regular look-alike: ×이워요, ×미더요, ×조와요.
- Memorize by contrastive pairs: 덥다/입다, 듣다/믿다 — irregular next to regular.
- Watch the traps: 돕다/곱다 take 오 (도와요), and 묻다 is irregular ("ask" → 물어요) or regular ("bury" → 묻어요) depending on meaning.
Now practice Korean
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Start learning Korean→Related Topics
- The ㅂ Irregular: 덥다 → 더워요TOPIK 1 — How stem-final ㅂ softens to 우 and fuses with the ending — the class that covers almost every weather and sensation adjective — plus the rule that the ending vowel here is ALWAYS 어 → 워, never 와.
- The ㄷ Irregular: 듣다 → 들어요TOPIK 2 — How stem-final ㄷ mutates to ㄹ before a vowel- or 으-initial ending — 듣다 → 들어요, 들으면, 들으세요 — while staying put before consonant endings (듣고, 듣는).
- The 르 Irregular: 모르다 → 몰라요TOPIK 1 — The high-frequency 르 irregular — before an 아/어 ending the 으 of 르 drops and an extra ㄹ pushes back onto the previous syllable (모르다 → 몰라요, 빠르다 → 빨라요), with 라/러 chosen by vowel harmony.
- 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.
- 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.