The ㄷ Irregular Rule
Some Korean verbs ending in the consonant ㄷ change their shape when they meet certain endings.
When a ㄷ irregular verb is followed by an ending that starts with a vowel (like -아요/-어요 or -(으)면 ), the ㄷ changes to ㄹ .
Examples
듣다 + 어요 → 들어요
걷다 + 어요 → 걸어요
Core takeaway: ㄷ changes to ㄹ before a vowel
Before Consonants
The stem does not change if the ending starts with a consonant (like -고 or -지만 ). The ㄷ remains exactly as it is.
Examples
듣다 + 고 → 듣고
걷다 + 고 → 걷고
싣다 + 고 → 싣고
Comparing Endings
Let's see how the same verb behaves differently depending on what attaches to it.
듣다
Ending Type · Rule · Result
+ 고 · Starts with consonant (No change) · 듣고
+ 어요 · Starts with vowel (ㄷ → ㄹ) · 들어요
+ 으면 · Starts with vowel (ㄷ → ㄹ) · 들으면
Regular ㄷ Verbs
Not all verbs ending in ㄷ are irregular. Some common verbs are regular and never change their ㄷ, even before a vowel.
Common Regular Verbs
받다 + 아요 → 받아요
닫다 + 아요 → 닫아요
믿다 + 어요 → 믿어요
Note: You cannot tell if a word is irregular just by looking at its dictionary form. You must memorize these common regular verbs as you learn them.
Common Learner Mistake
Because the ㄷ irregular is so common, learners sometimes apply it to regular verbs by mistake.
❌ Wrong
받다 + 아요 → 발아요 (Incorrect)
닫다 + 아요 → 달아요 (Incorrect)
✅ Correct
받다 + 아요 → 받아요
닫다 + 아요 → 닫아요
Watch out: Do not change regular ㄷ verbs