Core Pattern Rule: -(으)니까 (Reason & Discovery)
-(으)니까 is a versatile connector that primarily serves two functions: giving a reason for a subsequent suggestion or command, and indicating a discovery made after performing an action.
Meaning & Usage
Reason for Suggestion/Command: The first clause states the reason or cause, and the second clause provides a suggestion, command, or proposal. It's the natural choice when you want to say, "Because of X, let's do Y" or "Since X is the case, please do Y."
Discovery: The first clause describes an action, and the second clause reveals what the speaker discovered or realized upon completing that action. It translates to "When I did X, I found that Y..."
Formation
This pattern attaches to verb and adjective stems, as well as nouns.
Vowel or ㄹ ending stem + -니까:
가다 (to go) → 가니까
만들다 (to make) → 만드니까
Consonant ending stem + -으니까:
먹다 (to eat) → 먹으니까
좋다 (to be good) → 좋으니까
Nouns + -(이)니까:
학생 (student) → 학생이니까
너 (you) → 너니까
더우니까 에어컨 켜자. / 냉장고를 열어 보니까 없더라. / 너니까 봐주는 거야.
Synonyms & Differences: -(으)니까 vs. -아/어서
Both -(으)니까 and -아/어서 can mean "because" or "so," but they are not interchangeable. The key difference lies in what kind of clause can follow them.
Suggestions & Commands
-(으)니까: This is the correct choice when the second clause is a suggestion (-자, -ㄹ까요?), a command (-세요, -지 마세요), or a proposal (-ㅂ시다).
날씨가 좋으니까 산책하자. (The weather is nice, so let's go for a walk.) - Correct
-아/어서: Cannot be followed by suggestions or commands. It's used for general statements of fact or reason.
날씨가 좋아서 산책하자. - Incorrect/Unnatural
Tense
-(으)니까: Can be used with past tense markers (-았/었-).
늦었으니까 택시 타자. (We're late, so let's take a taxi.)