As you know

The -잖아 ending is used to state a fact that you believe the listener already knows. It's like adding "as you know," "you know," or "c'mon" to your sentence, confirming a piece of shared information.

Formation

This pattern attaches directly to verb and adjective stems, or to nouns.

Verbs & Adjectives: Attach -잖아(요) directly to the stem, regardless of whether it ends in a vowel or a consonant. This also applies to past tense stems.

가다 (to go) → 가잖아

먹다 (to eat) → 먹잖아

예쁘다 (to be pretty) → 예쁘잖아

말했다 (spoke) → 말했잖아

Nouns:

If the noun ends in a consonant, add -이잖아(요).

학생 (student) → 학생이잖아

If the noun ends in a vowel, add -잖아(요).

친구 (friend) → 친구잖아

내가 말했잖아. / 우린 친구잖아. / 오늘 일요일이잖아.

The feeling of -잖아 depends heavily on context and intonation. Getting it right is key to sounding natural.

Tone is Everything

-잖아 can be a friendly reminder, but it can also sound like you're scolding, complaining, or being condescending if used improperly.

Friendly Reminder (rising intonation): 오늘 우리 약속 있잖아? (We have plans today, remember?)

Frustration/Scolding (strong, falling intonation): 내가 하지 말라고 했잖아! (I told you not to do that!)

Common Mistake: Using it for New Information

The core of this pattern is shared knowledge. Never use -잖아 to introduce a fact the listener doesn't know. For example, if you tell a new acquaintance, 저는 학생이잖아요 ("I'm a student, as you know"), it sounds strange and presumptuous, as if they were supposed to know that already. Stick to 저는 학생이에요 for new information.

위험하잖아. / 바쁘잖아. / 약속했잖아. / 춥잖아.

When someone uses -잖아 on you, your response usually acknowledges the information they're reminding you of.

Agreement or Realization

If you genuinely forgot or just realized something, you can agree.

아, 맞다. (Oh, right.)

그렇네. (That's true.)

그러게. (I know, right? / Tell me about it.)

Acknowledging a Mistake

If the -잖아 felt like a gentle scolding, you can apologize for forgetting.

미안, 깜빡했어. (Sorry, I forgot.)

알아, 미안해. (I know, I'm sorry.)

Example Dialogue:

A: 왜 아직 안 자? 내일 일찍 일어나야 하잖아. (Why aren't you sleeping yet? You have to wake up early tomorrow, you know.)

B: 아, 맞다. 지금 잘게. (Oh, right. I'll go to sleep now.)

A: 오늘 일요일이잖아요. / B: 아, 그렇네요! 깜빡했어요. / A: 이거 네 거잖아. / B: 아, 맞다. 고마워.

Like many Korean endings, -잖아 has a casual form and a standard polite form, which you can switch between depending on the listener.

Casual Form: -잖아

This is the base form (반말). Use it with close friends, family members, or people who are younger than you. It creates a familiar, informal, and direct tone.

너도 알잖아. (You know it too.)

배고프잖아. (I'm hungry, you know.)

Polite Form: -잖아요

Simply add 요 to make the pattern polite (해요체). Use this with people you don't know well, colleagues, older acquaintances, or in any situation where you would normally use polite speech. It softens the tone while still conveying the "as you know" meaning.

호리 씨도 알잖아요. (Hori, you know it too.)

배고프잖아요. (I'm hungry, you know.)

맛있잖아. / 맛있잖아요. / 학생이잖아. / 학생이잖아요.