Korean Casual Speech Deepened: -자, -니?, -구나, and 아/야
Korean casual speech (반말): -자 means 'let's' (영화 보자), -니?
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Written by Alvin Lim Certified Korean Language Teacher (Level 2)
Korean casual speech runs on four moves: -자 is the casual “let’s” (영화 보자 — let’s watch a movie), -니? asks a friendly casual question (어디 가니? — where ya going?), -는구나/-구나 voices a realization (벌써 끝났구나 — oh, it’s already over!), and 아/야 calls someone by name (민수야!, 지은아!).
You met 반말 (casual speech) in Level 1 as bare verb stems. Now we deepen it — and, just as importantly, learn the social ritual of agreeing to drop formalities.
You just finished telling travel stories in polite speech. But with close friends and 동갑 (same-age peers), Koreans don’t stay formal forever.
At some point one person says 우리 말 놓자 (let’s speak casually), and the whole register shifts. This lesson gives you the four endings that make 반말 sound natural — plus the etiquette of when to use it.
Ten words for going casual
These come up exactly when two people decide to drop the formalities.
The four casual endings — -자, -니?, -구나
Three of the four moves attach straight to a verb or adjective stem. -자 turns a sentence into a casual suggestion (“let’s”), -니? turns it into a friendly casual question, and -는구나/-구나 voices a sudden realization or exclamation.
우리 영화 보자 = let’s watch a movie (-자, let’s) 이제 말 놓자 = let’s drop the formal speech (-자) 어디 가니? = where are you going? (-니?, casual question) 밥 먹었니? = did you eat? (-니?) 벌써 끝났구나 = oh, it’s already over! (-는구나, realization) 아, 그렇구나 = ah, I see / so that’s how it is (-구나)
Note the small differences: -자 is the casual partner of polite 봐요/봅시다. -니? is softer and warmer than a bare 어디 가? — it often carries a caring or gentle tone.
For -구나, verbs take -는구나 (먹는구나) while adjectives and 이다 take plain -구나 (예쁘구나, 학생이구나); past tense always uses -구나 (끝났구나).
Calling a name — 아/야
To call out to someone in casual speech, add the vocative particle 아 or 야 to their name. The choice follows the name’s final sound — exactly the vowel/consonant logic behind 이/가 and 을/를.
민수야, 어디 가? = Minsu, where are you going? (민수 ends in a vowel → 야) 지은아, 밥 먹었어? = Jieun, did you eat? (지은 ends in a consonant → 아) 동혁아, 같이 가자! = Donghyeok, let’s go together! (consonant → 아)
So vowel-final names take 야 (민수야, 영희야) and consonant-final names take 아 (지은아, 동혁아). This particle is strictly for close, equal, or younger people — you would never tack 아/야 onto an elder’s or a boss’s name.
Agreeing to go casual
Watch two same-age people drop 존댓말 and try out 반말 on the spot:
All four moves in one exchange: 말 놓자 and 가자 use -자 (let’s), 어디 가니? uses -니? (casual question), 잘하는구나 uses -구나 (realization), and 민수야 / 지은아 show 아/야 in action. Notice how the speakers ask first (말 놓을까요?) before switching — that consent ritual is the real lesson.
⚡ 2-Minute Check
Q 1 / 5Frequently asked questions
When is it actually okay to switch to 반말?
반말 (casual speech) is for people you're close to and roughly equal or younger: close friends, 동갑 (same-age peers), younger siblings, or someone clearly junior who's agreed to it. The crucial rule is that you don't just drop into it — you ask or agree first: 우리 말 놓을까요?
or 말 놓자 (let's speak casually). Using 반말 with a stranger, someone clearly older, or in a formal setting sounds rude, so when in doubt, stay in 존댓말 (polite speech) until both sides agree to switch.
Among 동갑 friends, switching to 반말 is a warm sign you've become close.
What's the difference between -니? and just dropping the ending in a casual question?
Both are casual, but they feel different. -니?
(어디 가니? 밥 먹었니?
) is a softer, warmer, slightly caring question ending — common from parents, older friends, or anyone being gentle. Simply dropping the ending with rising intonation (어디 가?
밥 먹었어? ) is the most everyday casual question and sounds very natural among close friends.
-니? can sound a touch old-fashioned or affectionate depending on who says it, while bare 어디 가?
is neutral casual. Both are correct 반말 — pick -니?
when you want a softer, kindlier tone.
How do I know whether to add 아 or 야 to someone's name?
Look at the last sound of the name. If it ends in a vowel, add 야: 민수 → 민수야, 영희 → 영희야.
If it ends in a consonant (a 받침), add 아: 지은 → 지은아, 동혁 → 동혁아. This vocative particle is only for casual address among close, equal, or younger people — you'd never call an elder or boss with 아/야.
Note this is the same vowel/consonant logic behind many Korean particles (이/가, 을/를): consonant-final words take the form with a vowel up front.