At a glance
- The vowel before 르 decides 라 or 러.
- Only 아/어 endings trigger the change.
- One lesson explains the rule with audio and a quiz.
The next section states the rule once, in one paragraph, so the word lists can build on it.
What Is 르 Irregular?
The 르 irregular (르 불규칙) is a conjugation class in which a stem ending in 르 changes when an ending begins with 아 or 어. A stem (어간) is the verb without its final 다, and an ending (어미) is what you add to it. For 모르다 the stem is 모르. With 아요 it becomes 몰라요, not 모르아요.
Three things happen in one step. The vowel ㅡ of 르 drops (ㅡ 탈락). The remaining ㄹ moves back to close the previous syllable, so 모 becomes 몰. A second ㄹ is added at the start of the ending, so 아요 becomes 라요. This second ㄹ is called ㄹ 첨가 (ㄹ insertion), and it is the signature of the class.
A regular verb keeps its stem whole: 먹다 gives 먹어요. A different class, the ㅡ-drop verbs, drops the ㅡ without the second ㄹ: 쓰다 gives 써요. The 르 irregular combines both ideas. The 르 irregular lesson breaks the steps down further, and the sibling class is on the ㅡ irregular hub. The next section lists the words.
The 르-Irregular Word List
This site's verb dictionary list has 14 common 르 irregular words: 7 verbs and 7 adjectives, counting the two-word adjective 예의 바르다 (polite), which conjugates like 바르다. The ending that follows the doubled ㄹ depends on the vowel in the syllable before 르. If that vowel is ㅏ or ㅗ, the ending is 라 (아 with ㄹ). For every other vowel, it is 러 (어 with ㄹ). The tables group the words by this choice.
Words That Take 라 (after ㅏ or ㅗ)
| Word | Meaning | Polite present | Polite past | Dictionary page |
|---|---|---|---|---|
| 모르다 | to not know | 몰라요 | 몰랐어요 | moreuda conjugation |
| 다르다 | to be different | 달라요 | 달랐어요 | dareuda conjugation |
| 빠르다 | to be fast | 빨라요 | 빨랐어요 | ppareuda conjugation |
| 고르다 | to choose | 골라요 | 골랐어요 | goreuda conjugation |
| 자르다 | to cut | 잘라요 | 잘랐어요 | jareuda conjugation |
| 마르다 | to dry; to be thin | 말라요 | 말랐어요 | mareuda conjugation |
| 오르다 | to climb; to rise | 올라요 | 올랐어요 | oreuda conjugation |
| 목마르다 | to be thirsty | 목말라요 | 목말랐어요 | mongmareuda conjugation |
| 예의 바르다 | to be polite | 예의 발라요 | 예의 발랐어요 | yeui bareuda conjugation |
Words That Take 러 (after any other vowel)
| Word | Meaning | Polite present | Polite past | Dictionary page |
|---|---|---|---|---|
| 부르다 | to call; to sing | 불러요 | 불렀어요 | bureuda conjugation |
| 누르다 | to press | 눌러요 | 눌렀어요 | nureuda conjugation |
| 이르다 | to be early | 일러요 | 일렀어요 | ireuda conjugation |
| 게으르다 | to be lazy | 게을러요 | 게을렀어요 | geeureuda conjugation |
| 배부르다 | to be full (of food) | 배불러요 | 배불렀어요 | baebureuda conjugation |
Notice that the vowel to check is the one in the syllable just before 르, so 목마르다 follows 마 and gives 라, while 게으르다 follows 으 and gives 러. Every form in the tables was cross-checked with the site's conjugation engine. The next section covers the verbs that look like these and are not.
Which 르 Words Are Not 르 Irregular?
Three common verbs end in 르 and do not double the ㄹ. 따르다 ("to follow"), 치르다 ("to pay; to hold [an exam]") and 들르다 ("to stop by") belong to the ㅡ-drop class. The ㅡ drops, and the ㄹ stays single. A fourth word, 이르다 in the sense "to reach", is a different irregular class.
| Word | Meaning | Polite present | Why it is different |
|---|---|---|---|
| 따르다 | to follow | 따라요 | ㅡ drops; no doubled ㄹ (not 딸라요) |
| 치르다 | to pay; to hold (an exam) | 치러요 | ㅡ drops; no doubled ㄹ (not 칠러요) |
| 들르다 | to stop by | 들러요 | ㅡ drops, so 들르 + 어요 = 들러요; no doubled ㄹ |
| 이르다 | to reach; to arrive at | 이르러요 | 러 irregular: 러 is added after the stem |
The 이르다 pair deserves care. 이르다 as "to be early" is a 르 irregular (일러요), and 이르다 as "to reach" is a 러 irregular (이르러요). They are separate dictionary entries with separate pages: early and reach. The rare 러 class is explained in 러 and 우 irregulars. The next section shows which endings trigger the change.
Endings That Trigger the Change
Only endings that start with 아 or 어 trigger the 르 irregular. Endings that start with 으 or a consonant leave the stem whole. The shortest proof is 모르다: 몰라요 ("I don't know") has the change, while 모르면 ("if [I] don't know"), 모릅니다 ("[I] don't know", formal) and 모르는 ("not knowing") do not.
| Ending | 모르다 | 부르다 | Changes? |
|---|---|---|---|
| -아요/-어요 polite present | 몰라요 | 불러요 | yes |
| -았어요/-었어요 polite past | 몰랐어요 | 불렀어요 | yes |
| -아서/-어서 "because" | 몰라서 | 불러서 | yes |
| -(으)면 "if" | 모르면 | 부르면 | no |
| -ㅂ니다/-습니다 formal | 모릅니다 | 부릅니다 | no |
| -는 present modifier | 모르는 | 부르는 | no |
| -(으)ㄹ 거예요 future | 모를 거예요 | 부를 거예요 | no |
This explains why a learner can know 몰라요 and still be surprised by 모릅니다. The class is a rule about where the ending begins, not about the verb alone. The next section turns the page into a plan.
Learn the 르 Irregular: Where Should You Start?
Start with 모르다 and 다르다, because the verb 모르다 and the adjective 다르다 are both A1 words on this site. Then add 빠르다, 고르다 and 부르다. The 르 irregular is a mid-sized class on this site's 474-word verb list: 14 entries, one more than the ㅡ class and behind 36 for ㅂ irregular and 26 for ㄹ-stem words. This count describes the site's word list, not word frequency in speech.
| If you want to... | Read | What you get |
|---|---|---|
| learn the rule step by step | Korean 르 Irregular Explained | rule, 라/러 choice, exceptions, audio and quiz |
| see how the ㅡ-drop class differs | ㅡ irregular | verbs such as 쓰다 → 써요 and 크다 → 커요 |
| meet the rare 러 and 우 classes | 러 and 우 irregulars | 이르다 (reach) and 푸르다 |
| compare all seven classes | Korean irregular verbs | the class grid and the recognition lesson |
Korean 르 Irregular Explained
The lesson walks through 모르다 → 몰라요 in small steps and gives a test for 라 versus 러. You finish able to conjugate the 14 words above in the polite present and past and to reject 따르다, 치르다 and 들르다.
What this page does not cover. It lists the class but does not conjugate every word in every speech level. The lesson and the dictionary pages do that. About this page. Last updated 2026-10-09. The Korean text and spoken forms on this page were machine-generated and reviewed and signed off by Min-ji Park on 15 October 2026. Forms were cross-checked with the site's rule-based conjugation engine. Romanization follows the Revised Romanization of Korean and is shown only as a learning aid.
Frequently Asked Questions
What is 르 irregular? The 르 irregular is a conjugation class in which a stem ending in 르 loses its ㅡ and gains an extra ㄹ before an ending that starts with 아 or 어. The result is 모르다 → 몰라요 and 부르다 → 불러요. Endings that do not start with 아 or 어, such as -면 and -ㅂ니다, leave the stem whole.
Why is 모르다 몰라요? The stem 모르 meets the ending 아요. The vowel ㅡ of 르 drops, the remaining ㄹ moves back to close the syllable 몰, and a second ㄹ starts the ending, giving 몰 + 라요. The ㅗ of 모 is a bright vowel, so the ending is 라, not 러. The past is 몰랐어요.
Is 따르다 a 르 irregular? No. 따르다 ("to follow") belongs to the ㅡ-drop class: the ㅡ drops but the ㄹ is not doubled, so the polite present is 따라요, not 딸라요. The same holds for 치르다 (치러요) and 들르다 (들러요). The doubled ㄹ is the signature of the 르 irregular.
How do I choose 라 or 러? Look at the vowel in the syllable before 르. If it is ㅏ or ㅗ, the ending is 라: 다르다 → 달라요, 모르다 → 몰라요. For any other vowel, the ending is 러: 부르다 → 불러요, 누르다 → 눌러요, 이르다 → 일러요. This is ordinary vowel harmony, the same rule that picks 아요 or 어요.