Choosing Endings That Change and Don't Change

Many learners think irregular verbs change every time they are used.

In Korean, an irregular verb stem typically only changes when it meets specific endings. The first letter of the ending determines if the stem stays the same or transforms. Learning to check the ending will help you conjugate correctly every time.

Endings that start with consonants like ㄱ or ㅈ generally do not trigger ㄷ, ㅂ, 르, or ㅎ irregular changes.

When you attach -고 (and) or -지만 (but), the dictionary stem usually remains exactly the same.

Dictionary Form · With -고 / -지만

듣다 · 듣고

춥다 · 춥지만

모르다 · 모르고

빨갛다 · 빨갛지만

Endings that start with a vowel typically trigger the irregular changes we learned in previous lessons.

If the ending starts with -아/어 or -(으)면 , you generally must apply the transformation to ㄷ, ㅂ, 르, and ㅎ stems.

Dictionary Form · With -아요 / -(으)면

듣다 · 들어요

춥다 · 추우면

모르다 · 몰랐어요

빨갛다 · 빨개요

Words ending in ㄹ follow a different pattern.

The ㄹ stays in place before vowel endings and most consonant endings (like -고 or -면). However, it drops completely when it meets an ending starting with ㅅ, ㅂ, or ㄴ (like -세요).

살다 → 살고 (keeps ㄹ before ㄱ)

살다 → 살면 (keeps ㄹ before ㅁ)

살다 → 사세요 (drops ㄹ before ㅅ)

A frequent beginner mistake is changing the stem even when the ending doesn't require it.