(으)니까 connective ending (because, since)

You use (으)니까 to connect two clauses. The first clause provides the reason. The second clause provides the result, a command, or a suggestion. It is like a bridge between a fact and an action. One cool thing about this grammar is its flexibility. It works with verbs, adjectives, and even the copula 이다 (to be). Unlike some other endings, it also plays well with tenses. You can use it to talk about the past, present, or future. It is like a multi-tool in your grammar kit. Use it when you want the listener to understand your specific reasoning. It is the "logic bridge" of the Korean language.

1. 1Check the verb or adjective stem.
2. 2If the stem ends in a vowel, add 니까. For example, 가다 (to go) becomes 가니까.
3. 3If the stem ends in a consonant (except ㄹ), add 으니까. For example, 먹다 (to eat) becomes 먹으니까.
4. 4If the stem ends in ㄹ, drop the ㄹ and add 니까. For example, 살다 (to live) becomes 사니까. This is a classic Korean irregular move. Think of it as the ㄹ taking a quick vacation.
5. 5For the past tense, attach it to 았/었. So, 갔다 becomes 갔으니까.
6. 6For the future tense, use (으)ㄹ 거니까. For example, 갈 거니까 (because I will go).
7. 7With nouns, use 이니까 after a consonant and 니까 after a vowel. 학생 (student) becomes 학생이니까.

First, use it when giving a command or making a suggestion. This is its superpower. If you say "It is raining, so take an umbrella," you must use (으)니까. Phrases ending in -(으)세요 or -(으)ㅂ시다 love this grammar. Second, use it for personal discoveries. Imagine you opened the fridge and saw no milk. "I opened the fridge, and (since) there was no milk, I went out." Third, use it when the reason is already known to the listener. It is like saying, "As you already know, since it is late, let's go." It feels very natural in social settings. Use it when ordering a second round of drinks because the first was so good. It is the ultimate social connector.

Do not use (으)니까 in very formal writing like news reports or academic papers. In those cases, 기 때문에 is the safer, more professional bet. Also, avoid using it for general, objective facts that everyone knows. For example, "The sun rises because it is morning" sounds a bit weird with 니까. It is also not the best choice for simple greetings. If you want to say "Thank you for the gift," do not use 니까. It sounds like you are giving a logical lecture on why you are thankful. Nobody wants a lecture with their thank-you note! Keep it for situations where your personal opinion or a specific action matters.

Many learners try to use 니까 with simple greetings. They say 만나니까 반가워요 for "Nice to meet you." This is a big no-no. It sounds like "Because I met you, I am happy (as a logical result)." Use 만나서 반가워요 instead. Another mistake is forgetting the ㄹ irregular rule. Saying 살으니까 will make native speakers tilt their heads. Remember, the ㄹ disappears! Also, do not use it for apologies. 늦으니까 죄송합니다 sounds like you are making an excuse. It is like saying "Since I am late (and that is just how it is), I am sorry." Stick to 늦어서 죄송합니다 to sound truly sincere. Even native speakers might slip up, but you can be better!

The biggest rival is 아/어서. Think of 아/어서 as the "natural cause" and (으)니까 as the "subjective reason." 아/어서 is for general facts, feelings, and chronological events. You cannot use commands or suggestions after 아/어서. This is the golden rule. If the sentence ends in "Let's..." or "Please...", (으)니까 is the winner. Another contrast is with 기 때문에. 기 때문에 is very formal and strong. It is like a legal document. (으)니까 is much more conversational and light. It is the difference between a textbook and a chat with a friend. Choosing the right one is like picking the right shoes for an outfit.