Words Where ㅅ Disappears

Some verbs and adjectives ending in the consonant ㅅ are irregular.

When these words meet an ending that starts with a vowel, the ㅅ disappears.

The change depends on the first letter of the ending you attach.

Before a Vowel (ㅅ Drops)

If you add endings like -아요/어요 or -(으)면 , the ㅅ disappears.

짓다 + 어요 = 지어요

Before a Consonant (ㅅ Stays)

If you add endings like -고 or -지만 , the ㅅ stays in place.

짓다 + 고 = 짓고

Here are three highly frequent words that follow this rule:

Dictionary Form · + 고 · + 아요/어요 · + (으)면

짓다 (to build/make) · 짓고 · 지어요 · 지으면

낫다 (to recover/be better) · 낫고 · 나아요 · 나으면

붓다 (to pour/swell) · 붓고 · 부어요 · 부으면

Here is a very common beginner mistake to avoid.

Even when the ㅅ disappears, the word still remembers that it originally had a bottom consonant. You must attach the endings meant for consonants.

낫다 + (으)면

Use -으면 because 낫다 originally has a consonant.

낫다 + 으면 = 나으면 (Correct)

낫다 + 면 = 나면 (Incorrect)

낫다 + 아요/어요

Use -아요 and keep the sounds separate. Do not combine them.

낫다 + 아요 = 나아요 (Correct)

낫다 + 아요 = 나요 (Incorrect)

Not every word ending in ㅅ is irregular! Many common words keep their ㅅ no matter what ending you attach.

Dictionary Form · + 아요/어요 · + (으)면