ㅂ, ㄷ, ㅅ, 르 and ㅎ: irregular verbs

The change only happens before a vowel. That means 아요 and 어요, the past built on them, and the 을 of the future. Before a consonant, as in 듣습니다 and 춥습니다, the stem stays as it is.

Each section below has a builder with regular look-alikes mixed in. It goes from the stem to the 해요 form, which is the one to learn.

Before a vowel, ㅂ turns into 우, and that 우 merges with the ending: 춥 + 어요 becomes 추우 + 어요, then 추워요. In the future, that 우 counts as a vowel, so it takes plain ㄹ: 추울 거예요.

This is the biggest group, and it's mostly adjectives, including a lot of words for feelings and textures. It's also open: every adjective ending in 롭다, 스럽다 or 답다 follows it, so nobody can give you a final count.

Two verbs take 오 instead and end in 와: 돕다, to help, becomes 도와요, and 곱다, to be lovely, becomes 고와요. Their future still has 우: 도울 거예요.

Before a vowel, ㄷ becomes ㄹ: 듣 + 어요 gives 들어요, and the future is 들을 거예요. Before a consonant the ㄷ comes back, so you still write 듣습니다.

The group is small and closed, so learn it as a list: 듣다, 걷다 (to walk), 묻다 (to ask), 깨닫다 and 싣다. Most verbs ending in ㄷ are regular, including very common ones like 받다 and 닫다, and that's why the irregular few are easy to get wrong.

Before a vowel, ㅅ drops. The odd part is that nothing merges across the gap it leaves: 낫 + 아요 gives 나아요, never 나요. The future keeps its 으 for the same reason, 나을 거예요.

This group is small too: 낫다, 짓다, 붓다, 긋다, 잇다 and 젓다. Plenty of other verbs ending in ㅅ are regular. 웃다 and 씻다, two of the first verbs you'll learn, both keep their ㅅ.

Before 아요 or 어요, 르 becomes ㄹ라 or ㄹ러. The syllable in front picks up a ㄹ, and the ending starts with another: 모르 + 아요 gives 몰라요, and 부르 + 어요 gives 불러요.

The vowel comes from the syllable before 르. 모 has ㅗ, so it takes 라. 부 has ㅜ, so it takes 러.

The future is untouched, because 르 already ends in a vowel: 모를 거예요. Nearly every verb ending in 르 follows this pattern, so here guessing irregular is almost always right.

These are adjectives. Before a vowel they drop ㅎ and the vowel changes to ㅐ: 그렇 + 어요 gives 그래요, and 빨갛 + 아요 gives 빨개요. A ㅑ becomes ㅒ instead, so 하얗다 gives 하얘요.

Before 으, the ㅎ and the 으 both disappear. That's where 그럴 거예요 comes from, and 빨간, the form that goes before a noun in lesson 10.

The group is small: 이렇다, 그렇다, 저렇다, 어떻다, the colour adjectives and a few shape words like 동그랗다. Action verbs ending in ㅎ are regular, and so is 좋다. Lesson 18 covers the first four.

푸다, to scoop, is the only 우 irregular. Where 주다 contracts to 줘요, 푸다 drops its ㅜ and gives 퍼요, never 풔요.

The 러 group keeps its 르 and turns the ending into 러. 푸르다, to be blue or green as of the sky or trees, becomes 푸르러요, and 이르다 in the sense of "to reach" becomes 이르러요.

Its twin 이르다, meaning "to be early" or "to tell on someone", is an ordinary 르 irregular and becomes 일러요. None of these will come up for a while, so don't lose sleep over them.

These change too, but every verb of their shape changes the same way, so they're easier to treat as part of the regular system. Korean grammar counts ㄹ and ㅡ stems as regular for that reason.

하다 is formally irregular, because it takes 여 rather than 아 or 어. That gives 하여, which shortens to 해. It's the pattern you'll use most, and it never varies: 공부하다 becomes 공부해요.

ㄹ stems drop their ㄹ before ㄴ, ㅂ and ㅅ, so 살다 gives 삽니다, and later 사세요 and 사는. Many textbooks teach them with the irregulars anyway, since the change surprises people.

ㅡ stems drop ㅡ before 아 or 어: 쓰다 becomes 써요, and 바쁘다 becomes 바빠요. As with 르, the vowel before it picks the ending, so 바 gives 바빠요 and 예 gives 예뻐요.

Spelling narrows it down, but it can't settle the question. Several common verbs are two different words with the same dictionary form, one regular and one not.

For everything else, these rules of thumb get you most of the way.

Try it. Each sentence below has one conjugated verb.

When you're not sure, look the verb up on the verb pages. Every verb in the course has a full conjugation table there, built on the same rules as this lesson, and the conjugator says so when a verb could go either way.