I am wondering why the infinitive verb 모르다 (do not know) is conjugated as 몰라요 in informal style and standard politeness?

모르다 is an irregular verb because the base form 모르 ends with ㅡ so the vowel ㅡ is dropped when followed by vowels (examples: -아/어/여) and after dropping ㅡ, one of -아/어/여 has to be chosen according to the vowel in the previous syllable.

So if we follow the grammatical rule it should be 모르다 -> 모라요.

How come we add an extra 리을 (ㄹ) to get 몰라요 when we conjugate 모르다 in informal style, standard politeness?

Is it another exception because it's easier for the pronunciation because 몰라요 is pronounced "Mol-la-yo"?


  • This is because of rules that have to do with ㄹ specifically and not the ending ㅡ. Something like 모으다 would not turn into 몽아요.
    – user17915
    Mar 30, 2022 at 0:14
  • The regular conjugation “모르어요” (“모르다”+“-어”+“요”) is incorrect. “모르다” is not conjugated the regular way. It’s sometimes used that way (incorrectly), though. And it sounds a bit literary. Jun 13, 2022 at 17:54

1 Answer 1


Yes this is an exception

The irregularity isn't in the verb 몰라요 but it's root 모르다. Verb stems that end in 르 follow this irregular pattern. Here are some more examples of similar verbs:


The link also lists an exception:

Verbs and adjectives with the last syllable 르 have a special form when conjugated with all A/V + 아 / 어 / 여 patterns.

The choice of 아/어 follows the syllable before the final 르. The ㄹ is doubled and the ㅡ is dropped. E.g. 부르다 becomes 불러, and 다르다 becomes 달라.

All verbs/adjectives ending in 르 follow this rule except one (따르다).

If you would like to read up on details, some history on the cause of this irregularity (along with other similar irregular verbs) is given here: https://namu.wiki/w/%ED%95%9C%EA%B5%AD%EC%96%B4/%EB%B6%88%EA%B7%9C%EC%B9%99%20%ED%99%9C%EC%9A%A9

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