Korean ㅅ Irregular Explained: Why 낫다 Becomes 나아요

What you'll learn

• Say what the ㅅ irregular is and recognise the verbs in its closed list.
• Form the polite present, past and future of 낫다 and 짓다 without adding a stray ㅅ.
• Tell 낫다 from its sound-alike 낮다, and 붓다 from 붙다.
• Spot regular ㅅ verbs such as 웃다, 씻다 and 벗다.

Prerequisites: you know a verb is a stem plus an ending, as in How Korean verbs work, and you have met the idea of irregular classes in how to recognize irregular verbs. Time: about 30 minutes.

Key facts

• Before a vowel, a final ㅅ drops: 낫 + 아요 = 나아요.
• Before a consonant, the ㅅ stays: 낫고, 짓습니다.
• Core verbs: 낫다, 짓다, 붓다, 잇다.
• Regular look-alikes: 웃다, 씻다, 벗다.
• 낫다 (recover) is irregular; 낮다 (low) is regular.

The first section defines the term, so that the rest of the page can use it without repeating the definition.

What Is the Korean ㅅ Irregular?

The Korean ㅅ irregular (ㅅ 불규칙) is a conjugation pattern in which the stem-final ㅅ is deleted before an ending that begins with a vowel. A conjugation is the set of forms a verb takes when you add endings. Most Korean verbs add endings without changing their stem. A few classes of verbs change, and these are called irregular (불규칙).

Here are the terms you will see in dictionaries and grammar books.

The rule has two parts, and each part has an example. First, the ㅅ drops before a vowel: 낫 + 아요 gives 나아요. Second, the ㅅ stays before a consonant: 낫 + 고 gives 낫고. The class is documented in the Standard Korean Language Dictionary (표준국어대사전) and in the NIKL Hangul Orthography (한글 맞춤법), whose Article 18 covers stems that change when an ending is added.

Compare a regular verb. 웃다 ("to laugh") keeps its ㅅ everywhere: 웃어요, 웃고. That contrast is the whole difficulty of this class, because the written form of the dictionary entry (낫다 and 웃다) gives no hint of which pattern follows. The next section shows the rule in action.

The Rule: ㅅ Drops before Vowels

The ㅅ drops whenever the ending starts with a vowel, and that includes the linking vowel 으 in endings such as -(으)면. The ending is then attached to the bare stem. Here is the worked example for 낫다, step by step.

1. Remove 다. 낫다 becomes the stem 낫.
2. Look at the first sound of the ending. For 아요 it is the vowel ㅏ. For 고 it is the consonant ㄱ.
3. If it is a vowel, delete the ㅅ. 낫 loses ㅅ and becomes 나.
4. Choose 아 or 어 by vowel harmony. Vowel harmony is the rule that picks 아 after the vowels ㅏ and ㅗ and 어 after other vowels. The vowel of 낫 is ㅏ, so the ending is 아요.
5. Join them. 나 + 아요 gives 나아요. The two vowels stay as two separate syllables.

You will know it worked when the polite present has no ㅅ and has two vowels in a row. If the answer is 낫아요, the ㅅ was not deleted.

The table below runs the same rule across the endings learners need first. Vowel-start endings are on the left side, consonant-start endings on the right.

All forms in this table were cross-checked with the site's conjugation engine. The sound change in the brackets is the ordinary batchim rule: a final ㅅ sounds like [ㄷ] when nothing vowel-like follows it, and a [ㄷ] before ㄱ, ㅅ or ㅈ makes that next consonant tense. The page on Korean final sounds explains why.

Notice that the choice between "stay" and "drop" depends only on the first sound of the ending. That is why 으 matters: -(으)면 looks like it begins with a consonant, but its 으 is a vowel, and it triggers the drop. The next section lists every verb that follows the rule.

The ㅅ-Irregular Verb List

The ㅅ irregular is a closed list, which means no new verbs join it. Six verbs are usually given, and four of them have pages in this site's verb dictionary. Here they are, with the forms you need first.

The site's verb dictionary has a full page for the four most useful verbs. Each page lists every form with audio: 낫다, 짓다, 붓다 and 잇다. This site rates 낫다, 짓다 and 붓다 as level B1 and 잇다 as B2. 긋다 and 젓다 have no separate dictionary pages.

Here are the verbs in sentences, so that you hear the drop in context.

Notice that 짓다 and 붓다 each carry two senses, and both senses follow the same rule. 짓다 appears in set phrases that learners meet early: 밥을 짓다 ("to cook rice"), 농사를 짓다 ("to farm") and 웃음을 짓다 ("to give a smile"). 붓다 also appears in cooking, as in 밥에 물을 붓다 ("pour water onto rice"), which is why the Korean cooking verbs page lists it. The next section answers the question that the past forms raise.

What Is the past Tense of 낫다?

The polite past of 낫다 is 나았어요. It is built from the stem 낫, the past marker 았, and the polite ending 어요: 낫 + 았 + 어요, with the ㅅ dropped before 았. The past marker also starts with a vowel, so the same drop applies.

The table gives the past forms of the two main verbs in three speech levels.

Two details cause mistakes. First, the past marker follows vowel harmony: 나았 (ㅏ stem) takes 았, while 지었 (ㅣ stem) takes 었. The vowel ㅣ is neutral and defaults to 어. Second, the spoken form of 나았어요 is [나아써요], four syllables, with the ㅆ sounding tense. Do not shorten it to 났어요, which is the past of a different verb, 나다 ("to come out").

For the future with -(으)ㄹ 거예요, the ㅅ also drops: 나을 거예요 ("I will get better") and 지을 거예요 ("I will build"). The ending -(으)ㄹ looks as if it starts with the consonant ㄹ, so learners sometimes keep the ㅅ and write 낫을 거예요. Remember that the linking vowel 으 comes first (나을 = 나 + 을), and a vowel triggers the drop. The next section tackles the sound-alike that causes most confusion.

What Is the Difference between 낫다 and 낮다?

낫다 ("to recover") and 낮다 ("to be low") sound the same in the dictionary form, [낟따], but only 낫다 is a ㅅ-irregular verb. 낮다 has a final ㅈ, and it is a regular adjective: 낮아요, 낮은. The two words are homophones (동음이의어), which means they share a pronunciation but have different spellings and meanings.

Here is the quick way to avoid the mix-up. In speech, 나아요 and 낮아요 differ: 나아요 has a clear vowel break [나-아-요], while 낮아요 is pronounced [나자요], with the ㅈ moving to the next syllable. Listen for that.

The second sound-alike pair is 붓다 and 붙다. Both are [붇따] in the dictionary form. 붓다 ("to pour; to swell") is ㅅ irregular: 부어요. 붙다 ("to stick") is regular: 붙어요. The first has a ㅅ that drops, and the second has a ㅌ that does not.

A related spelling trap is writing the polite present as *낫아요 or *붓어요. Those forms do not exist. The next section covers the opposite problem, which is dropping a ㅅ that should stay.

Which ㅅ Verbs Are Regular?

Many verbs end in ㅅ and keep it. The rule for telling them apart is simple: form the polite present, and if the ㅅ is still there, the verb is regular. The table lists the regular ㅅ verbs that learners meet most often next to their pronunciations.

The lesson on regular verbs that look irregular compares these verbs with their irregular look-alikes in more detail. Use it when you meet a new verb that ends in ㅅ and you are unsure.

Compare one irregular and one regular verb side by side, because the written dictionary forms look alike and the conjugations differ.

There is no sound clue in the dictionary form. The class is a property of each word, so you learn it with the word. Because the irregular list is closed and short, it is easier to memorise the six irregular verbs than to check each ㅅ verb. The next section shows what the irregular forms sound like.

How the ㅅ Irregular Sounds

The drop leaves two vowels next to each other, and Korean pronounces each vowel as its own syllable. 나아요 is three syllables [나-아-요], and 지어요 is three syllables [지-어-요]. Learners often merge them into one sound, such as [나요] or [저요], and that changes the word.

Two tips help with the hiatus, which is the term for two vowel sounds meeting without a consonant between them.

1. Keep a tiny pause. Say the first syllable, then the second, with no glide: 나 - 아, 지 - 어.
2. Do not insert a consonant. English speakers sometimes add a y or w sound between the vowels. Korean does not.

The clips below play the main irregular forms first and then two consonant forms where the ㅅ stays.

When the ㅅ is kept, the final sound changes in the usual batchim way. 낫고 sounds like [낟꼬] and 짓습니다 sounds like [짇씀니다]. That is regular batchim behaviour, not part of the irregular rule. The next section puts the class in perspective.

How Much Does the ㅅ Irregular Matter?

For a beginner, the ㅅ irregular matters less than the ㅂ, ㄷ and 르 classes, because it covers few words. This site's verb dictionary list contains 474 entries. Of these, 4 are ㅅ irregular (낫다, 짓다, 붓다, 잇다). By comparison, 36 are ㅂ irregular, 14 are 르 irregular and 6 are ㄷ irregular. This count describes the site's word list, not how often the words are used in speech.

In everyday speech and writing, 낫다 and 짓다 are the two to know first. 낫다 turns up in health talk: 감기가 빨리 나으면 좋겠어요 ("I hope my cold gets better soon"). 짓다 turns up in phrases about building, naming and farming. 붓다 and 잇다 come later.

A sensible plan is to learn the rule once, memorise 낫다 and 짓다 with an audio clip each, and then move to bigger classes. The irregular verbs chart shows all seven classes side by side, so you can see where ㅅ fits. The next section lets you test what you have learned.

Practice

Try the eight questions below before you open the answers. Each answer is given in the explanation that follows.

The answers are 나아요, 지어요, 부었어요, 이으면, 웃다, 씻어요, 낫다 and 낮다, and 짓고. The ㅅ verbs follow one test: if a vowel follows and the verb is on the closed list, drop the ㅅ.

Common Mistakes

• Keeping the ㅅ before a vowel. 낫아요 and 짓어요 are wrong. Write 나아요 and 지어요.
• Dropping the ㅅ before a consonant. 나고 for "recovers and" is wrong. Write 낫고.
• Dropping the ㅅ from regular verbs. 우어요 is wrong. 웃다 gives 웃어요.
• Mixing 낫다 and 낮다. 낮아요 means "it is low". 나아요 means "it gets better".
• Merging the two vowels. Say 나-아-요 as three syllables.

What Should You Learn after the Korean ㅅ Irregular?

Learn the larger classes next. The full word list for this class sits on the ㅅ irregular verbs hub, and the other six classes are collected in Korean irregular verbs. The step that follows this lesson in the sequence is the irregular verbs chart.

The Korean ㅅ irregular is small, with few members and one rule. If you remember that 낫다 becomes 나아요 and 짓다 becomes 지어요, you have learned nearly all of it.

For the pairs that look irregular but are not, read regular verbs that look irregular.

What this page does not cover. It does not cover the ㅂ, ㄷ, 르, ㅎ, ㅡ and ㄹ classes, the formal and casual speech levels beyond the past forms above, or every sense of 짓다 and 붓다. About this page. Last updated 2026-10-09. The Korean text and spoken forms on this page were machine-generated and reviewed and signed off by Min-ji Park on 15 October 2026. Forms were cross-checked with the site's rule-based conjugation engine. Romanization follows the Revised Romanization of Korean and is shown only as a learning aid.

Frequently Asked Questions

Why is 낫다 나아요 and not 낫아요? The ending -아요 starts with a vowel, and a stem-final ㅅ in this class drops before any vowel. So 낫 + 아요 becomes 나아요, with two vowels side by side. The same drop happens before 으 in -(으)면 and -(으)세요: 나으면 and 나으세요. Consonant endings keep the ㅅ: 낫고 and 낫습니다.

Is 웃다 irregular? No. 웃다 ("to laugh, to smile") is a regular verb, because its ㅅ stays before vowels: 웃어요, 웃었어요, 웃으면. Only a short closed list of verbs drops ㅅ, and 웃다 is not on it. A quick test is to form the polite present. If the ㅅ is still there, the verb is regular.

What is the past tense of 낫다? The polite past of 낫다 is 나았어요, from 낫 + 았 + 어요 with the ㅅ dropped before 았. The formal past is 나았습니다 and the casual past is 나았어. It is pronounced in four syllables, [나아써요]. The future is 나을 거예요, because -(으)ㄹ also starts with a vowel sound.

What is the past tense of 짓다? The polite past of 짓다 is 지었어요, from 짓 + 었 + 어요 with the ㅅ dropped. The formal past is 지었습니다 and the casual past is 지었어. The vowel harmony choice is 었, not 았, because the stem vowel is ㅣ. Pronounce 지었어요 as [지어써요], with the ㅆ of 었 sounding tense.

Which ㅅ irregular verbs should a beginner learn? Learn 낫다 and 짓다 first, because they are the ones that appear in everyday speech and writing: 감기가 나았어요 and 집을 지어요. Add 붓다 for pouring and swelling and 잇다 for connecting when you reach intermediate texts. 긋다 and 젓다 are rarer. Spend more of your time on the ㅂ, ㄷ and 르 classes.