으 drop pattern (not really irregular)

In Korean, vowels love to flow together. When a verb or adjective stem ends in ㅡ, it is a bit shy. If the next part of the word starts with a consonant, ㅡ stays put. For example, 아프다 becomes 아프고 (sick and...). But if the next part starts with a vowel, like -아 or -어, the ㅡ panics and disappears. It's like ㅡ is the introvert of the alphabet. As soon as a loud vowel shows up, it sneaks out the back door. Once the ㅡ is gone, the remaining part of the word has to decide which vowel to pair with. This choice depends on what came before the ㅡ. It is all about vowel harmony. If there is no syllable before it, we have a default rule. It sounds complex, but it is actually very consistent.

1. 1Follow these steps to master the vanishing ㅡ act:
2. 2Find the verb or adjective stem by dropping 다. Example: 아프다 becomes 아프.
3. 3Check if there is a syllable before the ㅡ.
4. 4If there is NO syllable before it (like 쓰다 -> 쓰), always add 어. Result: 써요.
5. 5If there IS a syllable before it, look at that syllable's vowel.
6. 6If the previous vowel is ㅏ or ㅗ, add 아. Example: 바쁘다 -> 바빠요.
7. 7If the previous vowel is anything else (ㅓ, ㅜ, ㅣ, etc.), add 어. Example: 예쁘다 -> 예뻐요.
8. 8Combine the new vowel with the remaining consonant of the dropped syllable.

Use this pattern whenever you attach a suffix starting with a vowel. The most common scenarios are the polite present tense (-아/어요) and the past tense (-았/었어여). You will also need it for the "because" connector (-아서/어서). Imagine you are at a cafe and want to say you are busy. You use 바쁘다. Since you are talking to a barista, you need the polite form. 바쁘 + 어/아 요 becomes 바빠요. Or maybe you are at a job interview and need to say you wrote a report. 쓰다 (to write) + 았어요 becomes 썼어요. It is essential for describing feelings too. If you are happy (기쁘다), you say 기뻐요. If you are sad (슬프다), you say 슬퍼요. These are everyday words you cannot avoid.

Do not drop the ㅡ if the suffix starts with a consonant. This is a very common trap! If you want to say "I am sick, but...", you use 아프지만. The ㅡ stays because 지 starts with a consonant. If you want to say "Please write", you say 쓰세요. The ㅡ stays because 세 starts with a consonant. Think of consonants as a protective shield for the ㅡ. It only disappears when it faces another vowel directly. Also, do not use this for nouns. This rule only applies to verbs and adjectives. Some learners try to apply it to words like 음식 (food), but that will just lead to confusion.

Yes, even native speakers mess this up sometimes when typing fast! The biggest mistake is forgetting to "look back." Learners often see 아프다 and think it should be 아퍼요 because they forget the ㅏ in the first syllable. Remember the rule: ㅏ and ㅗ are "bright" vowels and they want to hang out together. Another mistake is over-applying the rule. Some people try to drop the ㅡ even when a consonant follows. Saying 바빠고 instead of 바쁘고 is a classic A2-level slip-up. Finally, don't forget the single-syllable words. 쓰다 should never be 싸요 (that means "it's cheap"). It must be 써요. One tiny vowel change can change the whole meaning of your sentence!

This pattern is often confused with the ㅂ irregular or the ㄹ irregular. In the ㅂ irregular (like 덥다 -> 더워요), the ㅂ actually changes into a 우. In our ㅡ pattern, the vowel just vanishes entirely. It doesn't transform into something else; it just leaves a seat open for the next vowel. Also, unlike the ㄹ irregular which happens before ㄴ, ㅂ, or ㅅ, the ㅡ drop *only* cares about vowels. If you see a vowel, the ㅡ is gone. If you see a consonant, it stays. It is much more predictable than the ㄷ irregular (like 듣다 -> 들어요), which is why some teachers say it isn't even truly "irregular." It is just a phonological rule of thumb.