Past Tense: 았/었어요
Turn present tense sentences into past tense using 았/었어요.
Past tense in Korean is formed by inserting -았/었- between the verb stem and the polite ending -어요. The vowel choice follows the same harmony rule as the present: ㅏ/ㅗ stems take -았어요, everything else takes -었어요. 하다 verbs become 했어요.
Examples: 먹다 (eat) → 먹었어요 (ate), 가다 (go) → 갔어요 (went — the ㅏ of 가 fuses with the 았 of -았어요 to produce 갔), 마시다 (drink) → 마셨어요 (drank), 공부하다 (study) → 공부했어요 (studied). The past tense in Korean is just one tense — there is no distinction between 'I ate' / 'I have eaten' / 'I was eating' the way English makes. Context tells you which English equivalent fits. This makes Korean past tense easier than English past tense for once.
Past Tense: 았/었어요
Same vowel rule as present: if stem vowel is ㅏ/ㅗ → 았어요, otherwise → 었어요, 하다 → 했어요. Just replace 아요/어요 with 았어요/었어요.
Time Words for Past Tense
Common time words: 어제 (yesterday), 지난주 (last week), 지난달 (last month), 작년 (last year), 아까 (a while ago), 방금 (just now).
Cultural & Language Note
Korean past tense is marked once, on the verb at the end of the sentence, and time words like 어제 do not need to agree with it. This is the same economy Japanese has. English, by contrast, forces agreement across the clause. The practical upshot is that once you attach 았/었, the rest of the sentence needs no adjustment.
Common Mistakes to Avoid
The vowel rule from the present tense carries over: stems with ㅏ or ㅗ take 았어요, everything else takes 었어요, and 하다 becomes 했어요. Learners often default to 었어요 for everything. Another frequent slip is doubling the past marker in compound expressions — once is enough, on the final verb.