Korean verb conjugation follows predictable patterns based on vowel harmony. This guide covers the two most essential conjugation forms: past tense and the polite ~요 form.

The Basic Rule: Vowel Harmony

Before conjugating, identify the vowel before 다 in the verb’s dictionary form:

Vowel Type Vowels Connecting Vowel
Bright ㅏ, ㅗ 아
Dim/Neutral ㅓ, ㅜ, ㅡ, ㅣ 어

Past Tense Formation (ㅆ다)

Formula: Verb stem + connecting vowel + ㅆ다

The past tense marker ㅆ needs a vowel to attach to, so we use the connecting vowel.

Bright Vowels (ㅏ, ㅗ) → 았다

Dictionary Form Conjugation Result
가다 (go) 가 + 았다 갔다
오다 (come) 오 + 았다 왔다
보다 (see) 보 + 았다 봤다

Note: When 오 meets 았, the sounds naturally combine to make 왔다 (not 오았다).

Dim/Neutral Vowels (ㅓ, ㅜ, ㅡ, ㅣ) → 었다

Dictionary Form Conjugation Result
얼다 (freeze) 얼 + 었다 얼었다
주다 (give) 주 + 었다 줬다
들다 (hold) 들 + 었다 들었다
밀다 (push) 밀 + 었다 밀었다

Exceptional Cases

하다 → 했다 (not 핬다)

This is an irregular form that must be memorized.

Polite Form (~요)

Formula: Verb stem + connecting vowel + 요

The same vowel harmony rules apply.

Bright Vowels → 아요

Dictionary Form Conjugation Result
가다 (go) 가 + 아요 가요
오다 (come) 오 + 아요 와요
보다 (see) 보 + 아요 봐요

Dim Vowels → 어요

Dictionary Form Conjugation Result
두다 (put) 두 + 어요 둬요
벌다 (earn) 벌 + 어요 벌어요

Neutral Vowels → 어요

Dictionary Form Conjugation Result
기다리다 (wait) 기다리 + 어요 기다려요
시다 (sour) 시 + 어요 시어요
이쁘다 (pretty) 이쁘 + 어요 이뻐요

Exceptional Case

하다 → 해요 (not 하어요)

Why Use a Connecting Vowel?

For nouns, we can simply add 요 directly:

  • 물 + 요 = 물요 (water, politely)

But for verbs, we add a connecting vowel to differentiate them from nouns. This helps listeners immediately recognize whether a word is a noun or verb.

Exceptional Consonant Changes

Some verbs have consonant changes during conjugation:

ㄷ → ㄹ (before vowels)

Dictionary Form ~어요 Form Reason
묻다 (ask) 물어요 ㄷ changes to ㄹ
걷다 (walk) 걸어요 ㄷ changes to ㄹ

Why does this happen?

  • When pronouncing ㄷ and ㄹ, the tongue touches the same position (back of upper teeth)
  • ㄷ stops the sound abruptly, making continuous pronunciation difficult
  • ㄹ allows sound to flow smoothly
  • This makes pronunciation easier and more natural

Not all ㄷ verbs change:

  • 받다 (receive) → 받아요 (stays as ㄷ)

Summary Table

Verb Past Tense ~요 Form
가다 (go) 갔다 가요
오다 (come) 왔다 와요
먹다 (eat) 먹었다 먹어요
하다 (do) 했다 해요
걷다 (walk) 걸었다 걸어요
묻다 (ask) 물었다 물어요

Quick Reference

  1. Identify the vowel before 다
  2. Choose connecting vowel: 아 (bright) or 어 (dim/neutral)
  3. Add ending: ㅆ다 (past) or 요 (polite)
  4. Check for exceptions: 하다 → 했다/해요, ㄷ → ㄹ changes