Contents
Introduction
Origin of both 어서 and 니까
Where 어서 is strongly preferred
Where 니까 is strongly preferred
Comparing 어서 and 니까
Additional details
Associated grammar
See also
Bibliography
User examples
Introduction
A common problem faced by Korean learners is discerning between 어서 and 니까 in causation expressions. This is because both 어서 and 니까 translate to ‘because’ in English. However, Korean learners must learn their nuances because choosing the wrong ending can be highly impolite.
There have been many linguistic frameworks explaining 어서 VS 니까 and they all have similar explanations of these endings. They only differ in their reasoning for how 어서 and 니까 differences occur.
Linguistic frameworks (for the nerds)
| Paper | 어서 VS 니까 framework |
|---|---|
| Lee (2002) | Continuum model: 어서 serves for basic temporal/causal links, while 니까 extends into inferential and speech act functions. |
| Oh (2005) | A multi‑level semantic approach: 어서 is mainly used at the content level, while 니까 spans epistemic, illocutionary, and discourse functions. |
| Kwon (2012) | 어서 marks content (real‑world) causality with the cause in the first clause; 니까 marks epistemic/speech act causality with the speaker’s judgment in the second clause. |
| 황화상 (2008) | Functional distinction: 어서 expresses reason, whereas 니까 indicates a trigger or opportunity, making it suitable for imperatives and suggestions. |
| Hoe (2016) | Syntactic and mood-based distinctions: 어서 (subjunctive with 1st‑person restrictions under CT-marking) versus 니까 (indicative without such restrictions). |
| Hwang (2023) | Differentiates usage domains: native speakers show a clear division (어서 for content and 니까 for epistemic/speech act contexts), whereas learners tend to use both forms interchangeably. |
| 박정순 (2023) | Not a framework, but takes a pedagogical approach showing: 어서 is used in polite, non‑imperative expressions; 니까 is reserved for subjective, directive contexts and carries a [+당연성] (obviousness) nuance that may sound impolite. |
| 정예은 (2024) | Not a framework, but using Searle’s “Direction of Fit” argues that 니까 with its uncertain causality is preferred to mitigate face-threatening acts, in contrast to 어서 which conveys established causality. |
Across all these frameworks is the theme of 어서 expressing direct cause, and 니까 expressing judgments. This is the basis for my framework of Neutral Causation VS Speaker’s Judgment which will be explained throughout this GRD entry.
Neutral Causation VS Speaker’s Judgment
• Use 어서 when you’re simply stating a direct cause:
내가 열심히 공부해서 시험에 합격했어.
I studied hard, so I passed the test.
Here, 어서 simply states a cause-and-effect relationship: that studying led directly to passing the exam.
• Use 니까 when you’re making a judgment or concluding something:
내가 열심히 공부하니까 시험에 합격했지.
Because I studied hard, I (of course) passed the test.
Here, 니까 emphasizes a personal judgment: passing the exam was an outcome of studying hard.
Origin of both 어서 and 니까
First of all, let’s see how these two forms evolved.
The reason/cause meaning of 어서 comes from its original role as a sequential connector. Historically, 어서 was mainly used to show sequence, but over time, it took on a significant causal meaning (see 어서 origin for more details).
On the other hand, 니까 (originally 니) was the most common causal connector in Middle Korean (15th–16th century). Back then, just like today, 니 was used to express the speaker’s strong conviction about a statement.
This difference in origins explains how 어서 and 니까 are used today: 어서 retains its sense of sequence, while 니까 emphasizes the speaker’s reasoning.
Where 어서 is strongly preferred
어서 is strongly preferred when expressing simple cause-and-effect relationships, without suggesting personal judgment. It indicates a straightforward, objective connection between events.
달이 예뻐서 전화했어.
The moon looked pretty, so I called you.
Here, the prettiness of the moon is given as a direct, factual reason for making the phone call. There is no suggestion of a drawing conclusion; it’s a straightforward cause-effect scenario.
영희를 사랑해서 철수가 돌아왔다.
철수 came back because he loves 영희.
Once again, the speaker presents a simple real-world fact (철수’s love for 영희) that led directly to the result (his return). We are not focusing on the speaker’s reasoning.
옷을 사러 갔는데 비싸서 그냥 왔어요.
I went to buy clothes, but just came back because it was expensive.
Here, the speaker is making a neutral, factual statement. There is no additional inference that the listener is expected to share.
Basic thanks/apology
In basic expressions of thanks and apology, there is a strong preference for 어서. Such expressions are factual acknowledgments without involving subjective judgment.
무거운 물건을 들어줘서 고마워요.
Thank you for lifting these heavy objects.
Here, the cause is treated as an already recognized fact. The speaker is simply reporting “You did X, so I feel Y”. The gratitude expressed is a natural consequence without additional judgment.
More examples:
늦어서 죄송합니다.
I’m sorry for being late.
불러주셔서 감사합니다.
Thank you for inviting me.
약속 시간을 못 지켜서 죄송합니다.
I’m sorry for failing to keep the appointment time.
However, there are times when speakers wish to express thanks/apologies with a more evaluative stance.
매번 이렇게 무거운 물건을 들어주시니까 감사합니다.
Thank you for always lifting these heavy objects.
Here, the speaker goes beyond stating a recognized fact, and expresses their gratitude informed by their judgment. 니까 is used to give the nuance of “Look, you always do this, and I feel really grateful”.
Where 니까 is strongly preferred
니까 is strongly preferred when the speaker emphasizes their own judgment about the causal relationship. This emphasizes a conclusion drawn from the cause rather than simply describing an objective connection.
그 여자는 내 누나하고 같이 학교에 다녔으니까 마흔이다.
She should be forty because she went to school with my sister.
Here, the speaker draws a conclusion (the woman’s age) based on the fact (she attended school long ago). It’s not a simple, neutral event. Rather, it’s an expression of the speaker’s reasoning process. Using 어서 would be unnatural here because attending school together doesn’t objectively force someone to be forty.
얼음이 녹았으니까 냉장고가 고장난 게 틀림없다.
The refrigerator must be broken because the ice melted.
Here, ice melting is evidence leading the speaker to conclude that the fridge must be broken. The speaker is making an inference, rather than stating a simple X → Y causation.
물이 얼었으니까 0도가 된거네.
It’s zero degrees because the water’s frozen.
Here, ice is a clue the speaker uses to conclude that the temperature is below zero. Rather than making a neutral cause-effect connection, the speaker is expressing their judgment of the situation.
Making commands, suggestions, promises
Since commands, suggestions and promises are expressions of what should/will happen, the speaker must logically connect the cause to a not-yet-realized effect. This inferential step is exactly why 니까 is used in these expressions.
너는 똑똑하니까 잘 생각해봐.
Since you’re smart, you try to solve it!
Here, the speaker expresses their reasoning with 니까, and this reasoning is used to justify the command (“You figure it out”).
내게 우산이 있으니까 같이 가자.
Since I have an umbrella, let’s go together.
Here, “having an umbrella” justifies the speaker’s proposal “to walk together”. It’s not just, “I have an umbrella, so (as a natural consequence) we walk together”. Rather, 니까 expresses the sense of logical reasoning leading to the suggestion.
보고 싶으니까 곧바로 갈게.
I want to see you, so I’ll go right away.
Here, the speaker’s desire is not just a factual cause. Rather, it’s a personal motive that justifies a future action. 니까 expresses the nuance of “I want to see you (and therefore, of course) I’m going right away”.
More examples:
더우니까 에어컨을 켜 줘.
Turn on the air conditioner because it’s hot.
비가 오니까 집에 일찍 오세요.
Because it’s raining, please come home early.
우리 파리에 왔으니까 뭐부터 할까?
Since we’re in Paris, what shall we do first?
내일 시험이 있으니까 공부 열심히 해.
Study hard because you have an exam tomorrow.
방을 깨끗이 청소했으니까 맛있는 걸 사줄게.
I’ll buy you something delicious because you cleaned your room.
Spontaneous discoveries by the speaker
니까 is preferred in cases where speakers suddenly notice something and immediately draw conclusions. This is because “Aha!” or “Now I see…” moments are inferred judgments. Rather than simply stating “I did X and then Y happened”, 니까 signals the discovery as the speaker’s realization.
운동을 하고 나니까 기분이 상쾌한 거 있지.
It’s surprising how refreshed I feel after working out.
Here, the speaker finishes working out and suddenly realizes how refreshed they feel. 니까 expresses how the speaker is slightly surprised/impressed by the workout causing a feeling of refreshment.
빵 냄새를 맡으니까 갑자기 배가 고파진다.
Smelling the bread, I suddenly feel hungry.
Here, 니까 expresses the speaker’s realization of the cause-effect relationship. That is, smelling the bread causes hunger.
More examples:
이제 차를 샀으니까 주말마다 여행 다닐 거야.
Now that I’ve bought a car, I’ll go on trips every weekend.
책장을 정리하다 보니까 옛날 사진이 생각난다.
While organizing my bookshelf, old photos suddenly come to mind.
이제 시간이 많아졌으니까 취미를 시작해야겠어.
Now that I have more time, I should start a hobby.
Comparing 어서 and 니까
To illustrate when to use 어서 and 니까, here are some comparative examples.
Difference in nuance
눈이 와서 행복했다.
It snowed so I felt happy.
VS
눈이 오니까 행복했다.
I felt happy because it snowed.
Both 어서 and 니까 are very similar in the above example, but they do have different nuances. In the 어서 sentence, the speaker states an objective cause-effect connection: “Snow fell and that makes me happy”. In the 니까 sentence, the speaker highlights their subjective realization: “Snow fell, so that makes me happy”.
아내: 왜 늦었어요?
Wife: Why are you late?
남편1: 길이 많이 막혀서, 늦었어.
Husband 1: The traffic was heavy, so I was late.
VS
남편2: 길이 많이 막히니까, 늦었지.
Husband 2: Since the traffic was heavy, I was late.
In the 어서 response, the husband simply states the cause as a direct factual reason for being late. It’s a neutral report of what happened. On the other hand, in the 니까 response, the speaker implies the traffic as an obvious reason for lateness and that creates the nuance of justification: “I shouldn’t have to say this”. This nuance is further compounded by the conviction ending 지.
A1: 일을 그르쳐서 죄송합니다.
A1: Sorry I made a mistake.
VS
A2: 매번 중요한 일을 {그르쳐서/그르치니까} 죄송합니다.
A2: Sorry for always making important mistakes.
VS
A3: (비꼬듯이) 일을 그르치니까 아주 죄송해 죽겠네요.
A3: (Sarcastically) I made a mistake, so I’m just oh-so sorrry.
• In A1, the cause (making mistakes) is a shared awareness between speakers, so 어서 is strongly preferred over 니까.
• In A2, the speaker’s need to express justification with “important every time” makes 니까 a more acceptable option.
• In A3, the speaker uses the “of course” nuance inherent in 니까 to express insincerity. In the speaker’s mind, they don’t really think they made a mistake.
Answering questions
A common mistake made by Korean learners, and one which easily offends, is using 니까 in response to ‘why’ questions. Since ‘speaker’s judgment’ gives 니까 a nuance of “of course”, it can be very impolite when spoken to superiors.
Take for instance a visit to the dentist:
Dentist: 어떻게 오셨어요?
Dentist: How can I help you?
Patient: 이가 아파서요.
Patient: I came because my tooth hurts.
VS
Patient: 이가 아프니까요.
Patient: I’m here because my tooth hurts (obviously).
Here, 니까 is very impolite since it conveys the tone of “obviously (you should have known this)”. 어서 on the other hand is polite because it simply states a direct cause. One must always consider social hierarchy in the choice between 어서 and 니까.
Even between friends, 니까 can have a combative tone:
A: 왜 또 먹어?
A: You’re eating again?
B: 배가 고파서.
B: Because I’m hungry.
VS
B: 배가 고프니까.
B: Because I’m obviously hungry… (you got a problem with that?)
Here, 어서 calmly explains why the speaker is eating again, while 니까 expresses a belligerent justification.
Note that in contexts where it’s natural to provide additional justification, 니까 is perfectly polite. In such cases, there is no implication that the listener already knows.
On a blind date:
A: 어떤 음식 드시겠어요?
A: What kind of food would you like?
B: 저는 매운 음식을 좋아하니까 짬뽕 먹을게요.
B: I like spicy food, so I’ll have Jjamppong.
Here, the speaker is providing a reason for their choice. There is no rude or presumptuous justification. Rather, the new acquaintance simply learns about the preference in a casual, natural way.
Bibliography
— Choo, M., & Kwak, H. (2008). Using Korean: A Guide to Contemporary Usage. New York: Cambridge University Press.
— King, R., Yeon, J., & Lee, I. (2015) Continuing Korean. Boston: Tuttle Publishing.
— Kwon, I. (2012). Forward causality in basic communicative spaces networks: The-ese and-nikka constructions in Korean. Discourse and Cognition, 19(1), 1-27.
— Lee, H. K. (2002). Towards a new typology of connectives with special reference to conjunction in English and Korean. Journal of pragmatics, 34(7), 851-866.
— Hoe, S., & Park, Y. (2016). A Syntactic Approach to the 1st Person Restriction of Causal Clauses in Korean. In Proceedings of the 30th Pacific Asia Conference on Language, Information and Computation (pp. 287-295). Waseda University.
— Hwang, S. H. (2023). Exploring the Use of -ese and -nikka by English-Speaking Learners on the Basis of Corpus-Based Learner Data. 언어학, 31(3), 195-215.
— Oh, S. (2005). A multi-level semantic approach to Korean causal conjunctive suffixes-(e) se and-(u) nikka: A corpus-based analysis. International journal of corpus linguistics, 10(4), 469-488.
— Yeon, J., & Brown, L. (2008). Korean: A Comprehensive Grammar. New York: Routledge.
— 박정순. (2023). 한국어 초급 학습자를 위한 이유·원인의 연결어미 교육 방안 연구 – ‘-어서, -니까’의 의미·기능 분석을 중심으로 –. 문화와융합, 45(7), 711-722.
— 정예은. (2024). ‘-니까’의 불확정적 인과성과 공손성. 한국어 의미학, 86, 1-29.
— 황화상. (2008). 연결어미 ‘-어서’, ‘-니까’의 의미 기능과 후행절 유형. 國語學, 51, 57-88.
— 조규태. (2006). 중세 국어의 선어말 어미 ‘-으니-’에 대하여. 배달말, 39, 347-370.