The Past Tense -았/었어요

Korean marks the past with a single infix, -았- / -었-, that slots in between the verb stem and the ending. In the polite 해요체 that yields 갔어요, 먹었어요, 좋았어요; in the formal 합니다체 it's 갔습니다, 먹었습니다. Two facts make this one of the friendliest corners of Korean grammar: the choice between 았 and 었 follows the exact same vowel harmony you already learned for the present, and there is only one past marker for every person — no I/you/he agreement to juggle. This page gives you the mechanics and, more importantly, the shortcut that makes the past nearly free once you can form the present.

The marker and its harmony

The past infix comes in two shapes, selected by the last vowel of the stem — the same ㅏ/ㅗ harmony that governs the present:

• Stem's last vowel is ㅏ or ㅗ → -았-: 가다 → 갔-, 좋다 → 좋았-, 오다 → 왔-.
• Anything else (ㅓ, ㅜ, ㅡ, ㅣ, ㅔ …) → -었-: 먹다 → 먹었-, 읽다 → 읽었-, 마시다 → 마셨-.

Then the polite ending -어요 attaches on top, and the two ㅆ+어 come together as ㅆ어요.

The shortcut: 해요-form, minus 요, plus ㅆ어요

Here is the highest-value trick in the whole Korean tense system. You do not need to re-derive the past from scratch. Take the verb's present 해요체 form, drop the 요, and glue on ㅆ어요:

The payoff is huge: every vowel contraction you already fought through for the present carries over unchanged. 마시다 already contracts to 마셔요 in the present; the past is just 마셔 + ㅆ어요 → 마셨어요. You never re-contract. If you can say it in the present polite, you can say it in the past.

하다 verbs and one marker for all persons

The endlessly common 하다 ("do") follows the shortcut perfectly: its present is 해요, so its past is 했어요. Every 하다-verb inherits this — 공부하다 → 공부했어요, 사랑하다 → 사랑했어요. (Full detail on the past of 하다.)

And remember: there is exactly one past form for every subject. 갔어요 covers "I went," "you went," "she went," "they went" — Korean verbs don't agree with the subject. Whoever the topic is, the verb is identical.

The formal past: -았/었습니다

In the formal 합니다체, the same -았/었- infix takes the ending -습니다 instead: 갔습니다, 먹었습니다, 했습니다. The harmony choice is identical; only the politeness shell changes.

Adjectives and the copula take the very same marker

The past infix is not just for action verbs. Descriptive verbs (adjectives) and the copula 이다 use -았/었- with the identical harmony rule: 좋다 → 좋았어요, 바쁘다 → 바빴어요, 크다 → 컸어요. The copula has its own past shape — 이었어요 after a consonant, 였어요 after a vowel — and the existence verbs give 있었어요 / 없었어요. So once you own the marker, the whole predicate system inflects the same way.

The details — including why an adjective's own stem carries the past rather than a copula — are on the past of adjectives and the copula.

Common Mistakes

1. Wrong harmony — reaching for 았 after a ㅓ/ㅜ/ㅣ stem. 먹 has ㅓ, so it must take 었.

2. Failing to contract a vowel stem. 가 + 았 fuses into a single 갔; you never write both blocks out.

3. Conjugating 하다 regularly. 하다's past is the irregular 했 (from 하 + 여 → 해), not ×하았어요.

4. Over-marking simple past as -았었-. For a plain "I went," use one past marker (갔어요). The double past 갔었어요 means "had gone (and am no longer there)" — a discontinued or remote past, not a neutral one.

(For when the double past is right, see the -았었- discontinued past.)

Key Takeaways

• The past marker is -았- / -었-, chosen by the same ㅏ/ㅗ harmony as the present: 갔어요, 먹었어요, 좋았어요.
• Shortcut: take the 해요-form, drop 요, add ㅆ어요. All present-tense contractions carry over free (마셔요 → 마셨어요).
• 하다 → 했어요, and every 하다-verb follows (공부했어요).
• One marker for all persons — no subject agreement. 갔어요 = "I/you/he/she/we/they went."
• Formal past is -았/었습니다 (갔습니다); the double past -았었- is a different, discontinued meaning, not a stronger "simple past."