Irregular ㅅ Verbs

This rule only happens under specific conditions. You need a verb stem ending in ㅅ. You also need a suffix starting with a vowel. Examples of suffixes include -아요/어요 or -아서/어서. When these two meet, the ㅅ gets scared and leaves. However, it leaves a space behind. The vowels do not merge into one. This is very important. For example, 낫다 becomes 나아요, not 나요. It is like the ㅅ was never there. But it still keeps the vowels apart like a tiny ghost.

1. 1Find the verb stem by removing 다.
2. 2Check if the stem ends with ㅅ.
3. 3Look at the grammar ending you want to add.
4. 4If the ending starts with a vowel, drop the ㅅ.
5. 5If the ending starts with a consonant, keep the ㅅ.
6. 6Conjugate using the original stem's vowel.
7. 7Do not merge the remaining vowels together.

You use this for a specific list of verbs.

• Use 낫다 (to recover) when you feel better after a cold.
• Use 짓다 (to build) when you talk about making a house.
• Use 붓다 (to pour) when you are making coffee or tea.
• Use 젓다 (to stir) when you mix sugar into your drink.
• Use 잇다 (to connect) when you link two ideas or things.
• Use 긋다 (to draw a line) when you are studying with a highlighter.

Real-world scenarios make this easier. Imagine you are at a cafe. You need to stir your latte. You would say 커피를 저어요. Or imagine you were sick yesterday. Today you feel great. You tell your friend, 이제 다 나았어요! It sounds much better than saying the ㅅ out loud. Native speakers do this without thinking. You will too with a bit of practice.

Not every verb ending in ㅅ is irregular. Some verbs are very stubborn. They keep their ㅅ no matter what. These are regular ㅅ verbs.

• 웃다 (to laugh) stays as 웃어요.
• 씻다 (to wash) stays as 씻어요.
• 벗다 (to take off clothes) stays as 벗어요.
• 빗다 (to comb hair) stays as 빗어요.
• 솟다 (to soar) stays as 솟아요.
• 뺏다 (to snatch) stays as 뺏어요.

Yes, even native speakers mess this up sometimes. It is a common trap. Think of these regular verbs as the "Strong ㅅ" group. They love their ㅅ and will not let it go. You just have to memorize this small list. Most daily physical actions like washing or laughing are regular.

The biggest mistake is merging vowels. Many people try to say 나요 instead of 나아요. Remember the ghost ㅅ! It keeps that extra 아 or 어 in place. Another mistake is dropping the ㅅ before consonants. If you add -고 or -지, the ㅅ stays. So it is 낫고, not 나고. Only vowels cause the disappearing act. Also, do not forget which verbs are regular. Saying 우어요 instead of 웃어요 will sound very strange. It sounds like you are saying "to pour" instead of "to laugh." That could lead to a funny misunderstanding at a party!

Compare this to ㄷ irregulars like 듣다 (to listen). In those, the ㄷ changes to ㄹ. In our ㅅ rule, the letter just disappears entirely. It does not change into something else. Also, compare it to regular verbs like 먹다. Regular verbs never change their stem. The ㅅ irregular is unique because it leaves a "gap" between vowels. Most other irregulars merge vowels when a letter drops. For example, 쓰다 becomes 써요. But 짓다 stays as 지어요. It is a very polite irregular rule. It leaves the vowels exactly where they were.