Thought that...

This pattern is used to express something you believed to be true, which has now been proven false. It carries the nuance of "I thought X... but I was wrong." It's a way to explain a misunderstanding or a past assumption.

Formation Rules

The ending -줄 알았어 attaches to a descriptive clause. The form of that clause changes depending on the word type and tense.

Nouns: Add -(이)ㄴ

Vowel-ending noun + ㄴ 줄 알았어 (e.g., 의사 -> 의사인 줄 알았어)

Consonant-ending noun + 인 줄 알았어 (e.g., 학생 -> 학생인 줄 알았어)

Adjectives / Descriptive Verbs: Add -(으)ㄴ

Vowel stem + ㄴ 줄 알았어 (e.g., 예쁘다 -> 예쁜 줄 알았어)

Consonant stem + 은 줄 알았어 (e.g., 괜찮다 -> 괜찮은 줄 알았어)

Action Verbs (Present Tense): Add -는

Verb stem + 는 줄 알았어 (e.g., 자다 -> 자는 줄 알았어, 먹다 -> 먹는 줄 알았어)

Action Verbs (Past Tense): Add -(으)ㄴ (same as adjectives)

Vowel stem + ㄴ 줄 알았어 (e.g., 가다 -> 간 줄 알았어)

Consonant stem + 은 줄 알았어 (e.g., 먹다 -> 먹은 줄 알았어)

네가 범인인 줄 알았어. / 자는 줄 알았어. / 집에 간 줄 알았어. / 괜찮은 줄 알았어.

The most important nuance of -줄 알았어 is that it always implies the speaker's assumption was incorrect. The phrase carries an unspoken "...but I was wrong" or "...but it turns out that's not the case."

Context is Key

Explaining a Mistake: You might say 이거 공짜인 줄 알았어요 (I thought this was free) to a cashier when you're surprised at being asked to pay. The implied meaning is, "...but I see now that it isn't."

Expressing Surprise: Seeing a friend you thought had left, you might say 집에 간 줄 알았어! (I thought you went home!). This expresses your surprise at seeing them still there.

This pattern isn't just a neutral statement of a past thought; it's used specifically in the moment of realizing that thought was mistaken.

끝난 줄 알았어. / 아무도 없는 줄 알았어. / 진짜인 줄 알았어. / 연예인인 줄 알았어.