ㅅ irregular verbs: ㅅ drop pattern

The core of this rule is a simple interaction between a consonant and a vowel. In Korean, many verb stems end in the letter ㅅ. For most of these, when you add a grammar ending that starts with a vowel (like ~아요/어요 or ~으세요), the ㅅ simply vanishes. It is not replaced by anything else; it just leaves a gap. However, there is a very important catch that separates this from other irregulars. Even though the ㅅ is gone, the two vowels do not merge together. In regular Korean grammar, if you have two vowels next to each other, they usually combine (like 가다 + 아 becoming 가). But with ㅅ irregulars, the "ghost" of the ㅅ stays behind to keep the vowels apart. For example, 낫다 (to heal) becomes 나아, not 나. It is like the ㅅ left a reserved seat at the table even though it isn't sitting there anymore. This keeps the pronunciation distinct and helps listeners understand which verb you are using.

1. 1Mastering the formation is a three-step process. If you follow these steps, you will never get lost.
2. 2Identify the stem: Take your dictionary form verb and drop the 다. For 짓다 (to build), your stem is 짓.
3. 3Check the next ending: Look at the grammar point you want to attach. Does it start with a vowel? Common vowel endings include ~아/어/여요, ~었/았어요, ~으세요, and ~은/으니까.
4. 4Apply the drop: If the ending starts with a vowel, delete the ㅅ. If the ending starts with a consonant (like ~고, ~지만, or ~네), keep the ㅅ exactly where it is.
5. 5Let's look at 붓다 (to pour/swell) as an example. If you want to say "I pour," you add ~어요. The ㅅ meets a vowel, so it drops: 부 + 어요 = 부어요. But if you want to say "I pour and...", you add ~고. Since ㄱ is a consonant, the ㅅ stays: 붓 + 고 = 붓고. It is a simple "if-then" logic gate that you will eventually do without even thinking.

You will use this pattern with a specific group of verbs. These aren't obscure words; they are part of daily life! Here are the heavy hitters:

• 낫다: Use this when you are feeling better after being sick. "I hope you get well" uses this rule.
• 짓다: Use this for building houses, making rice, or even making a smile.
• 붓다: Use this when pouring water into a cup or when your face is swollen after a long night of studying (or Netflix).
• 젓다: Use this when you are stirring your morning latte or rowing a boat on the Han River.
• 잇다: Use this when you are connecting dots or linking two ideas together.
• 긋다: Use this when you are drawing a line on a piece of paper.

Imagine you are at a restaurant. You might need to stir (젓다) your soup. As you describe what you are doing to your friend, you'll say 저어요. Or maybe you are at a job interview talking about a project you built (지었어요). These scenarios happen all the time!

Here is the tricky part: not every verb ending in ㅅ is irregular. Some verbs are "loyal" and keep their ㅅ no matter what. You just have to memorize the most common regular ones. Think of these as the rule-followers who refuse to leave the party. The most common regular ㅅ verbs are:

• 웃다 (to laugh/smile): 웃어요 (Correct), 우어요 (Wrong!)
• 씻다 (to wash): 씻어요 (Correct), 씨어요 (Wrong!)
• 벗다 (to take off clothes): 벗어요 (Correct), 버어요 (Wrong!)
• 빗다 (to comb hair): 빗어요 (Correct), 비어요 (Wrong!)

Yes, even native speakers might have a brain fart and mix these up occasionally, but as a learner, focusing on these four will cover 90% of your regular ㅅ needs. If you try to wash your hands and say 손을 씨어요, people might look at you funny—it sounds like you are saying the seeds are growing! Stick to 씻어요.

The absolute #1 mistake is vowel contraction. Because we are so used to merging vowels in Korean, it is tempting to turn 지어 into 져. Resist the urge! The ㅅ irregular rule specifically forbids this. If you say 져요, you are actually using the verb 지다 (to lose), which is a completely different word. Imagine telling your boss "I lost the house" instead of "I built the house." That is a very different conversation!

Another mistake is dropping the ㅅ before a consonant. Remember, the ㅅ only hates vowels. If you are using ~고 or ~습니다, the ㅅ is perfectly happy to stay. 짓고 is correct; 지고 is a different verb entirely. Finally, don't forget the "Regular Four" mentioned above. 웃다, 씻다, 벗다, and 빗다 are your friends—don't kick their ㅅ out!

You might confuse this with the ㄷ irregular or the ㅂ irregular. In the ㄷ irregular (like 듣다 -> 들어요), the consonant changes into a new letter (ㄹ). In the ㅂ irregular (like 춥다 -> 추워요), the consonant turns into a vowel (우). The ㅅ irregular is unique because the letter just vanishes into thin air. It doesn't transform; it just leaves a space.

Also, contrast this with the ㄹ drop rule. The ㄹ drops before ㄴ, ㅂ, and ㅅ. The ㅅ irregular is the opposite—it drops before vowels. It is like they have opposite social anxieties. Understanding these specific triggers (vowels vs. specific consonants) is the key to mastering Korean irregulars.