몰라요, Not 모라요: The Two Irregular Verbs Behind Korea's Most Common Words (르 and ㄷ)

You’ve met one irregular verb already: 맵다 (spicy) doesn’t become 맵어요, it becomes 매워요 — the ㅂ melts into 워. But Korean has more than one of these, and two of them hide inside words you’ll say every day.

Try to say “I don’t know” — that’s 모르다 — and a Korean says 몰라요, not 모라요. Try “I’m listening” — 듣다 — and it comes out 들어요, not 듣어요. Two more patterns, two more surprises. Here’s the good news: both of them come down to one thing — a ㄹ shows up where you didn’t expect it.

The two rules, up front

Both of these break the plain -아요/-어요 rule you learned, and both do it by bringing in a ㄹ. Learn them as a pair.

르 verbs: drop the ㅡ, and double the ㄹ. ㄷ verbs: the bottom ㄷ turns into ㄹ.

• 모르다 (not know) → 몰 + 라요 → 몰라요🔊 (I don’t know)
• 듣다 (listen) → 들 + 어요 → 들어요🔊 (I’m listening)

That’s the whole idea. In both, a ㄹ appears. The rest of this post is just when and how. ==Both irregulars work by bringing a ㄹ into the verb.==

The 르 verbs: double the ㄹ

When a verb’s dictionary form ends in 르, you don’t just add -아요/-어요. Instead: drop the ㅡ from 르, and the ㄹ doubles — one ㄹ drops down to close the syllable before it, and the other starts the ending.

💡 Words · 모르다 → (not) know · 빠르다 → (be) fast · 부르다 → to call, to sing · 다르다 → (be) different

Look at 모르다 → 몰라요. The 르 lost its ㅡ, and a ㄹ landed on the bottom of 모, making 몰. Then 라요 follows. 모라요 is the trap — that’s what you get if you only drop the ㅡ and forget to double the ㄹ.

Which ending, 라 or 러? Look at the vowel one syllable before 르. If it’s ㅏ or ㅗ, use 라; otherwise use 러 — the same bright/dark feel as the regular -아요/-어요 split:

• 모르다 → 모 has ㅗ → 몰라요🔊
• 빠르다 → 빠 has ㅏ → 빨라요🔊
• 부르다 → 부 has ㅜ → 불러요🔊

The ㄷ verbs: ㄷ becomes ㄹ

The other pattern is simpler to say: when a verb’s stem ends in ㄷ, that ㄷ changes into ㄹ before the -아요/-어요 ending.

💡 Words · 듣다 → to listen, to hear · 걷다 → to walk

듣다 → drop 다 → 듣 → the bottom ㄷ turns into ㄹ → 들 → add 어요 → 들어요. The ㄷ didn’t stay; it became ㄹ. 듣어요 is the trap — that keeps the ㄷ, which the irregular never does.

💡 Notice the ㄹ again — just like the 르 verbs. That’s why we learn them together: both irregulars end up with a ㄹ where the plain rule wouldn’t put one.

In the past: the ㄹ stays

You already know the past tense — drop 요, put a ㅆ on the bottom, add 어요. It works here too. You just start from the irregular form (the one with the ㄹ already in it):

몰라요 → drop 요 → 몰라 → ㅆ on the bottom → 몰랐 → add 어요 → 몰랐어요. The irregular ㄹ is already there; the past tense just stacks on top, exactly like every other verb.

Where they show up

These aren’t rare textbook words — they’re in ordinary conversation. Watch:

💡 Words · 이 — this · 노래 — song · 알아요? — do you know? · 아니요 — no · 잘 — well / really · 같이 — together · 좋아요 — good, I like it

The honest catch: not every ㄷ verb is irregular

Here’s the part worth hearing straight — the same trap you met with the ㅂ verbs. Not every verb ending in ㄷ changes. Some keep the ㄷ and conjugate normally:

• 받다 (receive) → 받아요🔊 — regular, not 발아요
• 닫다 (close) → 닫아요🔊 — regular, not 달아요

Look at 듣다 (listen) and 닫다 (close): they end the same way, look almost identical — yet 듣다 is irregular (들어요) and 닫다 is regular (닫아요). There’s no clue in the spelling. Whether a ㄷ verb is irregular is a fact you learn with the word, not a rule you can predict — just like 춥다 (irregular) and 좁다 (regular) from last time.

The good news: the two irregular ㄷ verbs you’ll actually reach for are 듣다 (listen) and 걷다 (walk). Learn those two, and you’ve got the ones that come up. The regular ones (받다, 닫다, 믿다) just follow the plain rule.

💡 르 verbs don’t have this problem — almost all 르 verbs are irregular, so you can treat “ends in 르 → double the ㄹ” as your default and be right nearly every time.

Now say your own

Turn each dictionary form into its polite -요 form. Say it out loud before opening the answer.

1. 빠르다 (be fast) — a 르 verb.

answer

빨라요🔊 — drop the ㅡ, double the ㄹ → 빨라요. (it’s fast) 빠 has ㅏ, so it’s 라, not 러.

2. 걷다 (walk) — a ㄷ verb.

answer

걸어요🔊 — the bottom ㄷ turns into ㄹ → 걸 → add 어요 → 걸어요. (I walk) Not 걷어요 — the ㄷ never stays.

3. 모르다 (not know) — now put it in the past: “I didn’t know.”

answer

몰랐어요🔊 — first the irregular form (몰라요), then the past: drop 요, ㅆ on the bottom, add 어요 → 몰랐어요. (I didn’t know)

Quick check

Q1 — make the 르 form. 모르다 (not know) becomes:

why

The ㅡ drops and the ㄹ doubles → 몰라요. 모라요 is the trap: it drops the ㅡ but forgets to double the ㄹ.

Q2 — regular or irregular? You want to say “I receive” from 받다. Which is right?

why

받다 is regular → 받아요 (the ㄷ stays). It looks just like 듣다, but it doesn’t change — that’s the honest catch. You learn it word by word.

Q3 — from last time. Back with the ㅂ irregular, 맵다 (spicy) becomes:

why

The ㅂ melts into 워 → 매워요. 맵어요 is the trap — it keeps the ㅂ, which the ㅂ irregular never does. Three irregulars now, and each one swaps in a new sound: ㅂ→워, 르→ㄹㄹ, ㄷ→ㄹ.

Before you go

• 르 verbs: drop the ㅡ and double the ㄹ — 모르다 → 몰라요, 빠르다 → 빨라요 (라/러 follows the vowel before 르)
• ㄷ verbs: the bottom ㄷ turns into ㄹ — 듣다 → 들어요, 걷다 → 걸어요
• Past tense stacks right on top: 몰라요 → 몰랐어요, 들어요 → 들었어요
• The honest catch: some ㄷ verbs are regular (받다 → 받아요, 닫다 → 닫아요) — you learn which is which with the word. (르 verbs are almost all irregular — safe to assume.)

📌 Pocket cheat sheet: 르 → drop ㅡ, double the ㄹ (몰라요). ㄷ → ㄷ becomes ㄹ (들어요). Both bring in a ㄹ.

That’s three irregular patterns down — ㅂ, 르, and ㄷ. You can now handle the irregular verbs hiding in everyday speech. Next up, a word that feels perfectly safe in English but quietly marks you as a foreigner the moment it leaves your mouth: 당신.