Mastering Korean Past Tense: How to Conjugate -았/었어요 and Irregular Verbs

Have you ever tried having a conversation in Korean, only to realize you can only talk about what is happening right now?

In beginner Korean, learning the present tense (-아/어요) is thrilling because it lets you say "I eat" (먹어요), "I go" (가요), and "I study" (공부해요). But real human connection happens through storytelling:

• "What did you do yesterday?"
• "Where did you travel last summer?"
• "How was that new K-drama episode you watched last night?"

To share your memories, tell stories, and answer everyday questions, you need the Korean past tense (-았/었어요).

The great news? The Korean past tense follows the exact same vowel harmony rules as the present tense (-아/어요). Once you grasp the underlying logic of vowel harmony and vowel contraction, you will be able to conjugate nearly any Korean verb or adjective into the past tense with automatic confidence.

In this comprehensive masterclass, we will explore:

1. The 3 core vowel harmony conjugation rules (-았어요, -었어요, -했어요).
2. Crucial vowel contraction and merger rules (why 가다 becomes 갔어요, not 가았어요).
3. How to conjugate descriptive verbs (adjectives) into the past tense.
4. The 5 essential irregular verb families (ㄷ, ㅂ, ㅅ, 르, ㅡ).
5. Two ways to express past negation ("didn't" vs "couldn't").
6. 3 multi-turn natural dialogues from daily Seoul life.
7. 5 common traps English speakers fall into and how to avoid them.
8. A 5-question practice quiz with comprehensive grammatical breakdowns.

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1. The Core Architecture of the Korean Past Tense

Unlike English, which relies on hundreds of unpredictable irregular past tense forms (eat → ate, buy → bought, go → went, think → thought), the Korean past tense is built around a single, highly logical grammatical suffix:

📌 Core Past Tense Infix:
-았- / -었- / -했-

To create the standard polite informal past tense ending (the primary and most widely used past tense form in daily spoken Korean), we attach the polite sentence ending -어요 to the past tense infix:

💡 Formal Register Note:
If you are speaking in formal settings (such as TV news, military, job interviews, or formal presentations), the polite ending changes from -어요 to -습니다:

• -았- + -습니다 → -았습니다
• -었- + -습니다 → -었습니다
• -했- + -습니다 → -했습니다

The stem conjugation rules remain 100% identical across both speech registers.

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2. The 3 Golden Rules of Vowel Harmony

To determine whether a verb or adjective takes -았어요 or -었어요, look at the last vowel of the verb stem (the base form after dropping -다).

Rule 1: Bright Vowels (ㅏ, ㅗ) → Add -았어요

If the final vowel of the verb stem is either ㅏ (a) or ㅗ (o), it is classified as a "bright vowel" in Korean linguistic harmony. Attach -았어요:

📌 Example Sentences:

• 어제 친구에게서 생일 선물을 받았어요.
  (Yesterday, I received a birthday gift from my friend.)
• 지난 주말 날씨가 정말 좋았어요.
  (The weather was really nice last weekend.)

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Rule 2: Dark / Neutral Vowels (ㅓ, ㅜ, ㅣ, ㅐ, ㅔ, ㅡ) → Add -었어요

If the final vowel of the verb stem is ANY vowel other than ㅏ or ㅗ (such as ㅓ, ㅜ, ㅣ, ㅐ, ㅔ, or ㅡ), attach -었어요:

📌 Example Sentences:

• 아침에 사과와 토스트를 먹었어요.
  (I ate an apple and toast this morning.)
• 어젯밤에 재미있는 소설책을 읽었어요.
  (I read an interesting novel last night.)

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Rule 3: Any Verb Ending in 하다 → Conjugates to -했어요

Any verb or adjective ending in 하다 (such as Sino-Korean action verbs or descriptive states) automatically changes to -했어요.

Technically, 하- combines with -였- to form 하였어요, which contracts into the universal spoken form 했어요:

📌 Example Sentences:

• 어제 도서관에서 한국어를 3시간 동안 공부했어요.
  (Yesterday, I studied Korean for 3 hours at the library.)
• 지난주는 회사 일이 너무 바빠서 정말 피곤했어요.
  (Last week was so busy at work that I was really tired.)

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3. Essential Vowel Contraction Rules (축약 규칙)

When a verb stem does NOT end in a consonant (batchim / 받침), the vowel of the stem merges directly with the past tense suffix (-았- or -었-).

Native speakers naturally blend these adjacent vowel sounds together to make speech smoother and faster. Master these 5 vowel mergers:

📌 Core Contraction Formula:
[Stem Vowel without Consonant] + [Past Suffix] → [Contracted Sound]

1. ㅏ + 았- → 았- (Vowel Absorption)

When the stem vowel is ㅏ, adding -았- creates two identical a sounds back-to-back. The two vowels collapse into a single syllable:

• 가다 (to go): 가- + 았어요 → 갔어요 (NOT 가았어요)
• 만나다 (to meet): 만나- + 았어요 → 만났어요 (NOT 만나았어요)
• 자다 (to sleep): 자- + 았어요 → 잤어요 (NOT 자았어요)
• 사다 (to buy): 사- + 았어요 → 샀어요 (NOT 사았어요)

2. ㅗ + 았- → 왔- (Compound Diphthong ㅘ)

When the stem vowel is ㅗ, it combines with -았- to form the diphthong ㅘ (wa):

• 오다 (to come): 오- + 았어요 → 왔어요
• 보다 (to see/watch): 보- + 았어요 → 봤어요

3. ㅜ + 었- → 웠- (Compound Diphthong ㅝ)

When the stem vowel is ㅜ, it combines with -었- to form ㅝ (wo):

• 배우다 (to learn): 배우- + 었어요 → 배웠어요
• 주다 (to give): 주- + 었어요 → 줬어요
• 바꾸다 (to exchange/change): 바꾸- + 었어요 → 바꿨어요

4. ㅣ + 었- → 였- (Glide Diphthong ㅕ)

When the stem vowel is ㅣ, it blends with -었- into ㅕ (yeo):

• 마시다 (to drink): 마시- + 었어요 → 마셨어요
• 기다리다 (to wait): 기다리- + 었어요 → 기다렸어요
• 가르치다 (to teach): 가르치- + 었어요 → 가르쳤어요
• 빌리다 (to borrow): 빌리- + 었어요 → 빌렸어요

5. ㅡ Deletion (탈락)

When a verb stem ends in the vowel ㅡ (without a final consonant), the ㅡ drops completely. The vowel in the preceding syllable then dictates whether you add -았어요 or -었어요:

• 크다 (to be big): 크- + 었어요 → The ㅡ drops, leaving ㅋ + 었어요 → 컸어요
• 쓰다 (to write / use): 쓰- + 었어요 → ㅆ + 었어요 → 썼어요
• 바쁘다 (to be busy): 바ㅃ- (preceding vowel is ㅏ → bright!) → 바ㅃ + 았어요 → 바빴어요
• 예쁘다 (to be pretty): 예ㅃ- (preceding vowel is ㅔ → dark!) → 예ㅃ + 었어요 → 예뻤어요
• 아프다 (to be sick / hurt): 아ㅍ- (preceding vowel is ㅏ → bright!) → 아ㅍ + 았어요 → 아팠어요

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4. Descriptive Verbs (Adjectives) in the Past Tense

In Korean grammar, adjectives function as "descriptive verbs." This means they conjugate into the past tense using the exact same mechanisms as action verbs.

When you describe how something felt, looked, or tasted in the past, always use the past tense:

📌 Natural Context Comparison:

• 영화가 정말 재미있었어요!
  (The movie was really fun!)
• 어제 저녁에 먹은 비빔밥이 아주 맛있었어요.
  (The bibimbap I ate yesterday evening was very delicious.)
• 한국어 시험이 조금 어려웠어요.
  (The Korean exam was a little difficult.)

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5. The 5 Major Irregular Past Tense Families

Just like in the present tense, five primary irregular stem behaviors apply in the past tense when followed by vowels. Learn these patterns once, and you will never stumble over an irregular verb again:

1. ㄷ Irregular (ㄷ → ㄹ Mutation)

When certain verbs ending in the final consonant ㄷ meet a vowel, the ㄷ changes to ㄹ:

• 듣다 (to listen / hear): 듣- + 었어요 → 들었어요 (NOT 듣었어요)
• 걷다 (to walk): 걷- + 었어요 → 걸었어요 (NOT 걷었어요)
• 묻다 (to ask): 묻- + 었어요 → 물었어요 (NOT 묻었어요)

⚠️ Regular Exceptions:
A few common verbs are regular and keep their ㄷ:

• 닫다 (to close) → 닫았어요
• 받다 (to receive) → 받았어요
• 믿다 (to believe) → 믿었어요

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2. ㅂ Irregular (ㅂ → 우 Transformation)

Most descriptive verbs (and a few action verbs) ending in ㅂ drop the ㅂ and transform it into 우. When 우 meets -었어요, it contracts into -웠어요:

• 춥다 (to be cold): 추- + 우 + 었어요 → 추웠어요
• 덥다 (to be hot): 더- + 우 + 었어요 → 더웠어요
• 어렵다 (to be difficult): 어려- + 우 + 었어요 → 어려웠어요
• 쉽다 (to be easy): 쉬- + 우 + 었어요 → 쉬웠어요
• 고맙다 (to be thankful): 고마- + 우 + 었어요 → 고마웠어요

💡 Special Exception (돕다 & 곱다):
For the verbs 돕다 (to help) and 곱다 (to be delicate/fine), the ㅂ transforms into 오 instead of 우, resulting in -왔어요:

• 돕다 → 도- + 오 + 았어요 → 도왔어요 (helped)

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3. ㅅ Irregular (ㅅ Deletion)

For certain verbs ending in ㅅ, the ㅅ drops out when followed by a vowel, but the vowels do not contract together:

• 낫다 (to recover / be better): 나- + 았어요 → 나았어요 (NOT 났어요)
• 짓다 (to build / compose): 지- + 었어요 → 지었어요 (NOT 졌어요)
• 붓다 (to swell / pour): 부- + 었어요 → 부었어요

⚠️ Regular Exceptions:

• 웃다 (to smile/laugh) → 웃었어요 (regular)
• 씻다 (to wash) → 씻었어요 (regular)
• 벗다 (to take off clothes) → 벗었어요 (regular)

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4. 르 Irregular (Doubling the ㄹ)

When a verb ending in 르 meets -았/었어요, the vowel ㅡ drops, and an additional ㄹ attaches as a batchim to the preceding syllable:

• 빠르다 (to be fast): 빠- adds ㄹ batchim → 빨- + 라 + 았어요 → 빨랐어요
• 모르다 (to not know): 모- adds ㄹ batchim → 몰- + 라 + 았어요 → 몰랐어요
• 다르다 (to be different): 다- adds ㄹ batchim → 달- + 라 + 았어요 → 달랐어요
• 부르다 (to sing / call / be full): 부- adds ㄹ batchim → 불- + 러 + 었어요 → 불렀어요
• 고르다 (to choose / pick): 고- adds ㄹ batchim → 골- + 라 + 았어요 → 골랐어요

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5. ㅎ Irregular (Adjectives in ㅎ)

Color and descriptive adjectives ending in ㅎ drop both the ㅎ and the vowel, merging into -앴어요 or -했어요:

• 그렇다 (to be so): 그렇- → 그랬어요
• 어떻다 (to be how): 어떻- → 어땠어요 (How was it?)
• 이렇다 (to be like this): 이렇- → 이랬어요
• 빨갛다 (to be red): 빨갛- → 빨갰어요
• 파랗다 (to be blue): 파랗- → 파랬어요

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6. Past Tense Negation: Two Ways to Say "Didn't"

Just as we explored in our foundational guide on Korean Negation: 안 vs -지 않아요, there are two distinct ways to make a past tense sentence negative.

Method 1: Short Negation (안 + Past Tense Verb)

Simply place the negative adverb 안 (short for 아니) directly in front of the conjugated past tense verb:

• 가다 → 안 갔어요 (I didn't go)
• 먹다 → 안 먹었어요 (I didn't eat)
• 보다 → 안 봤어요 (I didn't watch it)

⚠️ Critical Word Order Rule for 하다 Verbs:
For compound verbs made of [Noun] + 하다 (like 공부하다, 운동하다, 일하다), the negative adverb 안 must be placed between the noun and the verb:

• 공부 안 했어요 (Correct ✅)
• 안 공부했어요 (Incorrect / Unnatural ❌)
• 운동 안 했어요 (Correct ✅)
• 안 운동했어요 (Incorrect / Unnatural ❌)

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Method 2: Long Negation (Verb Stem + -지 않았어요)

For a slightly more formal, emphatic, or written style, attach -지 않았어요 directly to the verb stem:

• 가다 → 가- + -지 않았어요 → 가지 않았어요
• 먹다 → 먹- + -지 않았어요 → 먹지 않았어요
• 공부하다 → 공부하- + -지 않았어요 → 공부하지 않았어요

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💡 "Didn't" (안) vs "Couldn't" (못)

Be careful not to confuse a lack of willingness (didn't) with a lack of ability or circumstantial impossibility (couldn't):

• 안 갔어요: I didn't go. (By choice / intent)
• 못 갔어요: I couldn't go. (Due to sickness, traffic, work, or lack of ability)

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7. Real-Life Dialogue Masterclass

Let us examine how native speakers in Seoul utilize the past tense across three everyday conversational situations.

Dialogue 1: Talking About Yesterday's Weekend (주말 이야기)

상황: Minho and Sarah meet on Monday morning near Hongik University Station and talk about what they did over the weekend.

• 민호: 사라 씨, 주말에 뭐 했어요?
  (Sarah, what did you do over the weekend?)
• 사라: 토요일에 친구들과 한강공원에 갔어요. 자전거를 탔어요.
  (On Saturday, I went to Han River Park with friends. We rode bicycles.)
• 민호: 와, 날씨가 좋아서 정말 재미있었겠네요! 맛있는 것도 먹었어요?
  (Wow, the weather was nice so it must have been fun! Did you eat something delicious too?)
• 사라: 네! 편의점에서 한강 라면을 끓여서 먹었어요. 정말 맛있었어요. 민호 씨는 주말에 뭐 했어요?
  (Yes! We cooked and ate Han River instant ramen at the convenience store. It was delicious. Minho, what did you do over the weekend?)
• 민호: 저는 집에서 넷플릭스로 한국 드라마를 봤어요. 하루 종일 쉬어서 피로가 다 풀렸어요.
  (I watched Korean dramas on Netflix at home. I rested all day, so my fatigue was completely relieved.)

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Dialogue 2: Reviewing a Meal at a Restaurant (식당 후기)

상황: Jiwon and Alex are discussing a new restaurant that recently opened in Gangnam.

• 지원: 알렉스 씨, 어제 새로 생긴 삼겹살집에 다녀왔어요?
  (Alex, did you go to that newly opened samgyeopsal restaurant yesterday?)
• 알렉스: 네, 퇴근하고 동료들과 갔어요. 고기가 정말 신선하고 좋았어요.
  (Yes, I went with my colleagues after work. The meat was really fresh and good.)
• 지원: 손님이 많아서 웨이팅이 길지 않았어요?
  (Weren't there a lot of customers, so the wait wasn't long?)
• 알렉스: 30분 정도 기다렸어요. 그렇지만 된장찌개도 서비스로 주셨어요.
  (We waited for about 30 minutes. But they also gave us soybean paste stew on the house.)
• 지원: 가격은 어땠어요? 비쌌어요?
  (How was the price? Was it expensive?)
• 알렉스: 아니요, 생각보다 전혀 안 비쌌어요. 다음 회식 때 꼭 다시 가기로 했어요.
  (No, it wasn't expensive at all compared to what I expected. We decided to go again for our next team dinner.)

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Dialogue 3: Asking About a Trip to Jeju Island (제주도 여행)

상황: Yuna is asking Chris about his vacation to Jeju Island.

• 유나: 크리스 씨, 지난주에 제주도 여행 잘 다녀왔어요?
  (Chris, did you have a good trip to Jeju Island last week?)
• 크리스: 네, 바다가 너무 아름다워서 정말 행복했어요. 사진도 많이 찍었어요.
  (Yes, the ocean was so beautiful that I was truly happy. I took a lot of photos too.)
• 유나: 한라산 등산도 했어요?
  (Did you hike Hallasan Mountain too?)
• 크리스: 날씨가 갑자기 흐려지고 비가 와서 정상까지는 못 올라갔어요. 백록담은 못 봤어요.
  (The weather suddenly turned cloudy and it rained, so I couldn't climb to the summit. I couldn't see Baengnokdam Lake.)
• 유나: 아이고, 조금 아쉬웠겠어요. 그래도 흑돼지 구이는 먹었어요?
  (Oh dear, that must have been a bit disappointing. But did you eat black pork barbecue?)
• 크리스: 물론이죠! 정말 꿀맛이었어요. 다음 봄에 꼭 다시 가고 싶어졌어요!
  (Of course! It was absolute heaven. It made me want to go back next spring!)

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8. 5 Common Traps & Mistakes English Speakers Make

Trap 1: Forgetting Vowel Contraction (가았어요 vs 갔어요)

• ❌ Incorrect: 어제 학교에 가았어요.
• ✅ Correct: 어제 학교에 갔어요.
• Why it happens: Beginners often follow the formula mechanically (가- + -았어요) without collapsing the two identical vowels. Whenever a verb stem ends in a vowel, check if it can merge into a single syllable.

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Trap 2: Misplacing 안 in 하다 Action Verbs

• ❌ Incorrect: 어제 안 공부했어요. / 주말에 안 운동했어요.
• ✅ Correct: 어제 공부 안 했어요. / 주말에 운동 안 했어요.
• Why it happens: In English, "didn't" always precedes the entire verb (didn't study, didn't exercise). In Korean, 공부하다 is literally "study-doing". The negative adverb 안 modifies the active verb 하다, resulting in [명사] + 안 + 했어요.

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Trap 3: Over-conjugating Clauses with -아/어서

• ❌ Incorrect: 어제 피곤했어서 일찍 잤어요.
• ✅ Correct: 어제 피곤해서 일찍 잤어요.
• Why it happens: English speakers want to mark both clauses in the past tense ("Because I was tired, I went to bed early"). But in Korean, the causal connective ending -아/어서 NEVER accepts tense markers! The past tense is marked only once, at the very end of the final sentence predicate. (See our deep dive in Expressing Reasons: -아/어서 vs -(으)니까).

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Trap 4: Confusing 안 (Didn't) with 못 (Couldn't)

• ❌ Incorrect: 어제 아파서 회사에 안 갔어요. (Sounds like you willfully boycotted work because you were sick)
• ✅ Correct: 어제 아파서 회사에 못 갔어요. (I was physically unable to go to work because I was sick)
• Why it happens: English speakers often casually say "I didn't go" when they actually mean "I couldn't go." In Korean, using 안 implies your personal choice, whereas 못 implies external obstacles or physical incapacity.

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Trap 5: Confusing 이/그/저렇다 Adjectives

• ❌ Incorrect: 영화가 어떠았어요? / 어떻었어요?
• ✅ Correct: 영화가 어땠어요? (How was the movie?)
• Why it happens: The ㅎ irregular adjectives drop the ㅎ and fuse the vowel into ㅐ. Always remember the trio:
  • 어떻다 → 어땠어요? (How was it?)
  • 그렇다 → 그랬어요. (It was like that.)
  • 이렇다 → 이랬어요. (It was like this.)

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9. Interactive Practice Quiz

Test your mastery of the Korean past tense with these 5 practical, exam-style questions.

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Question 1: Basic Vowel Harmony

Choose the correct past tense form for the verb 마시다 (to drink):

• ① 마시었어요
• ② 마셨어요
• ③ 마샸어요
• ④ 마시았어요

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Question 2: Irregular Verb Conjugation

Which sentence correctly conjugates the irregular verb 듣다 (to listen) into the past tense?

• ① 어제 신나는 K-pop 음악을 듣았어요.
• ② 어제 신나는 K-pop 음악을 들었어요.
• ③ 어제 신나는 K-pop 음악을 듣었어요.
• ④ 어제 신나는 K-pop 음악을 들았어요.

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Question 3: ㅂ-Irregular Adjective

Complete the blank with the correct past tense form of 춥다 (to be cold):

어제 서울은 날씨가 정말 [              ].

• ① 춥었어요
• ② 추웠어요
• ③ 추왔어요
• ④ 춥았어요

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Question 4: Natural Negative Word Order

Choose the most natural Korean sentence meaning: "I didn't exercise yesterday."

• ① 어제 안 운동했어요.
• ② 어제 운동을 안 했어요.
• ③ 어제 운동을 못 했어요.
• ④ 어제 운동하안 였어요.

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Question 5: Situational Comprehension

Read the dialogue below and choose the most appropriate question for the blank:

민수: 지난 주말에 제주도로 혼자 여행을 다녀왔어요.
유진: 와, 좋았겠네요! 제주도 여행은 [              ]?
민수: 날씨도 맑고 바다도 깨끗해서 정말 최고였어요!

• ① 어디였어요
• ② 누구였어요
• ③ 어땠어요
• ④ 뭐였어요

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👉 Click here to check the Official Answers & Detailed Explanations

1. Answer: ② 마셨어요

• Explanation: The stem of 마시다 is 마시-. Since the final vowel is ㅣ (not ㅏ or ㅗ), it takes -었어요. When 시 meets -었-, the vowels contract into ㅕ: 마시- + 었어요 → 마셨어요.

2. Answer: ② 어제 신나는 K-pop 음악을 들었어요.

• Explanation: 듣다 is a ㄷ-irregular verb. When followed by a vowel suffix (-었-), the ㄷ changes to ㄹ: 듣- + 었어요 → 들었어요. ① and ③ keep the unmutated ㄷ incorrectly; ④ uses the incorrect vowel harmony suffix -았어요.

3. Answer: ② 추웠어요

• Explanation: 춥다 is a ㅂ-irregular descriptive verb. The batchim ㅂ drops and transforms into 우. Then, 우 + 었어요 contracts into 워: 추- + 우 + 었어요 → 추웠어요.

4. Answer: ② 어제 운동을 안 했어요.

• Explanation: For action verbs formed by [Noun] + 하다, the negative adverb 안 must be placed immediately before 하다: 운동(을) 안 했어요. ① places 안 before the noun (unnatural); ③ changes the meaning to "couldn't exercise"; ④ is gibberish.

5. Answer: ③ 어땠어요

• Explanation: Minsu explains that the trip was "the absolute best because the weather was clear and the sea was clean." Therefore, Yujin asked "How was your trip?" which is 어땠어요? (the past tense of 어떻다). ① Where was it?, ② Who was it?, ④ What was it?

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10. Summary Cheatsheet & What's Next

📋 The Ultimate Past Tense Quick Reference

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🚀 Up Next in Lesson 17: The Complete Korean Future Tense Guide

Now that you can vividly narrate everything that happened in your past, it is time to look ahead into the future!

In Lesson 17: Korean Future Tense Guide (-(으)ㄹ 거예요 vs -(으)ㄹ게요 vs -겠어요), we will master the Korean Future Tense and untangle the number one confusion point for global learners:

• -(으)ㄹ 거예요: The standard objective future prediction ("I will / It will...")
• -(으)ㄹ게요: The conversational promise and consideration for the listener ("I'll do it for you / as promised!")
• -겠어요: Expressing firm determination, intent, or polite conjecture ("I will definitely...")

👉 Click here to start Lesson 17: Korean Future Tense Guide

Keep practicing by conjugating three things you did yesterday into the past tense, and see you in Lesson 17!