Core Grammar Rule: -(으)니까
-(으)니까 is a connective ending used to express a reason or cause for the following clause. It's often used when the reason is a logical basis for a command, suggestion, or a statement of the speaker's will.
Meaning & Usage
Meaning: It translates to "because," "since," or "so." It connects two clauses, where the first clause [Reason] is the cause for the second clause [Result/Action]
When to use: Use it when the reason in the first clause leads to a suggestion (~하자/~합시다), a command (제발/~하세요), or a statement of intention (~합니다/~할게요). It can also be used to state a reason for a fact that has already occurred.
Conjugation Rules
Rule: The form depends on whether the verb or adjective stem ends in a vowel or a consonant.
Vowel or ㄹ: Attach ~니까 directly to the stem. For stems ending in ㄹ, the ㄹ is dropped. (e.g., 가다 → 가니까 / 놀다 → 노니까)
Consonant: Attach ~으니까` to the stem. (e.g., 먹다 → 먹으니까 / 좋다 → 좋으니까)
Vowel/ㄹ: ~니까 / Consonant: ~으니까
Synonyms & Differences: -(으)니까 vs. -아/어서
While both -(으)니까 and -아/어서 mean "because" or "so," they are not always interchangeable. The key difference lies in the type of sentence that can follow.
Commands & Suggestions
Context: When the main clause is a command (e.g., ~(으)세요) or a suggestion (e.g., ~(으)ㅂ시다, ~(으)ㄹ까요?), you must use -(으)니까. Using -아/어서 in this context is grammatically incorrect.
Example: 날씨가 좋으니까 공원에 갑시다. (Let's go to the park since the weather is good.) (O) / 날씨가 좋아서 공원에 갑시다. (X)
Expressing Gratitude or Apology
Context: When expressing a reason for gratitude or an apology, -아/어서 is the natural choice. Using -(으)니까 in these situations can sound unnatural or even slightly arrogant, as if you're justifying your reason for being thanked or for apologizing.
Example: 도와주셔서 감사합니다. (Thank you for helping me.) (O) / 늦어서 죄송합니다. (I'm sorry for being late.) (O) / 늦었으니까 죄송합니다. (X)
`-(으)니까`: Use with commands/suggestions / `-아/어서`: Use for general reasons & thanks/apologies
Native Nuance & Mistakes: ~거든요
~거든요 is used to provide a reason or background information that the speaker assumes the listener does not know. It has a friendly, explanatory tone, but its nuance can be tricky.
Providing New Information
Context: Use ~거든요 when you're explaining the "why" behind something, almost like you're letting the listener in on a secret or a piece of background info. It adds a nuance of "..., you see." or "..., because...".
Example: 왜 이렇게 피곤해 보여요? — 어제 잠을 거의 못 잤거든요. (Why do you look so tired? — It's because I barely slept last night, you see.)
Sounding Defensive
Context: Be careful, as ~거든요 can sometimes sound like you're making an excuse or being slightly defensive, especially if your tone is sharp. It can imply "Well, the reason is THIS (so you should understand)."
Example: In the dialogue, "얼룩이 생각보다 너무 심했거든요" (The stain was much worse than I thought, you see) works well as a polite explanation. However, if said with a frustrated tone, it could sound like an excuse.
Do: Use to share new background info. (O) / Don't: Use with a sharp tone, as it can sound defensive. (X)
Common Endings with `~(으)니까`
The grammar ~(으)니까 is often followed by specific types of sentence endings, particularly suggestions, commands, or statements of the speaker's intention.
Suggestions & Commands
Because ~(으)니까 establishes a logical reason, it naturally leads to telling someone what to do (or not do) as a result.
Common endings include ~(으)세요 (please do), ~지 마세요 (please don't), ~(으)ㅂ시다/~자 (let's), and ~(으)ㄹ까요? (shall we?).
Example: 거의 다 됐으니까요. 잠시만 앉아서 기다려 주세요. (It's almost done. Please have a seat and wait for just a moment.)
Statements of Will or Future Plans
You can also use ~(으)니까 to explain the reason behind your own decision, necessity, or a future plan.
Common endings include ~(으)ㄹ게요 (I will...), ~해야 해요 (I must...), and ~(으)ㄹ 거예요 (I'm going to... / It will probably...).
Example: 제가 내일 아침에 중요한 면접이 있으니까 꼭 오늘 받아야 해요. (I have an important interview tomorrow morning, so I must get it today.)
~하세요 / ~합시다 / ~할게요
Responding to a Reason
When someone gives you a reason using ~(으)니까 or ~거든요, your response should acknowledge their point and move the conversation forward.
Acknowledge and Agree
First, show you've heard and understood the reason. You can use expressions like 진짜요? (Really?), 아, 그렇군요 (Oh, I see), or 알겠어요 (I understand).
Then, you can state your resulting action, often starting with 그럼 (then / in that case).
Example: In response to 거의 다 됐으니까요. 잠시만 앉아서 기다려 주세요, the customer says, 그럼 기다릴게요. (I'll wait then.)
Propose the Next Step
After acknowledging the reason, you can ask a follow-up question or suggest a new plan.
Example: After Sujin explains they can't go hiking (비 오니까 등산은 못 가잖아), Yuna accepts this and asks, 그럼 우리 뭐 해? (Then what do we do?).
Example: When the customer explains why he needs the suit (면접이 있으니까...), the owner responds with a solution: 정말요? 그럼 최대한 빨리 해 드릴게요. (Oh, really? Then I'll do it as fast as possible for you.)
진짜요? 그럼... / 그럼 기다릴게요.