~어서/아서

Both express reason, but ~기 때문에 is more formal, can take past/future tense in the first clause, and does not have the sequential action meaning.

Both express reason. ~(으)니까 often implies a discovered reason, can be used with imperatives/propositives, and allows tense in the first clause.

Both can connect sequential actions. ~고 simply lists actions without implying cause or prerequisite, and tense can be expressed in the first clause.

Many English speakers find ~어서/아서 confusing because it has two main uses that seem unrelated: expressing a reason ('because, so') and expressing a sequential action ('and then, after doing'). The context usually makes it clear, but it takes practice to get comfortable with both.

When ~어서/아서 indicates a reason, it explains why something happened or is the case. For sequential actions, it shows that the first action is completed before the second one starts, and often that the first action is a prerequisite for the second. Unlike other 'and' conjunctions, the subject of both clauses linked by ~어서/아서 is usually the same, and the tense is only expressed in the final verb.

날씨가 좋아서 산책했어요. (The weather was good, so I took a walk.) - Reason 밥을 먹어서 배불러요. (I ate, so I'm full.) - Reason 집에 와서 바로 잤어요. (I came home and then slept right away.) - Sequential Action 학교에 가서 공부했어요. (I went to school and then studied.) - Sequential Action

This is another way to say 'because' or 'due to,' and learners often wonder when to use it instead of ~어서/아서. While both express reason, they aren't always interchangeable.

~기 때문에 is generally more formal and emphasizes the reason more strongly. It can also be used with verbs ending in past tense (~았/었기 때문에) or future tense (~(으)ㄹ 것이기 때문에), which ~어서/아서 cannot. ~어서/아서 also has the sequential action meaning, which ~기 때문에 does not.

비가 오기 때문에 경기가 취소되었어요. (Because it's raining, the game was canceled.) 늦잠을 잤기 때문에 지각했어요. (Because I overslept, I was late.)

This also translates to 'because' or 'since,' adding to the confusion of how to express reasons in Korean.

Similar to ~어서/아서, ~(으)니까 can express a reason. However, it often implies that the speaker discovered the reason *after* doing something or after a situation became clear. It's frequently used with imperative (commands) or propositive (suggestions) sentences in the second clause, which ~어서/아서 cannot do. The tense can be expressed in the first clause with ~(으)니까.

밖에 비가 오니까 우산을 가져가세요. (Since it's raining outside, take an umbrella.) 배가 고프니까 밥 먹으러 가자. (Since I'm hungry, let's go eat.)

Like ~어서/아서, ~고 can connect two actions, making learners wonder which one to use for 'and then.'

~고 simply lists actions in chronological order or lists items. The first action doesn't necessarily cause or enable the second action. There's no implication of a causal relationship or that the first action *must* be completed before the second. Tense can be expressed in the first clause with ~고.

책을 읽고 음악을 들었어요. (I read a book and listened to music.) - Simple sequence 밥을 먹고 커피를 마셨어요. (I ate and drank coffee.) - Simple sequence

While often translated as 'but' or 'however,' this conjunction also introduces background information or a preceding situation, which can sometimes feel like a reason or context for the following clause.

~는데/은데/ㄴ데 sets the scene or provides background information for the following clause. It can express contrast ('but'), introduce a new topic, or provide context. It's not a direct 'because' in the same way ~어서/아서 is, but the background information it provides can often imply a reason.

비가 오는데 우산이 없어요. (It's raining, but I don't have an umbrella.) 저는 학생인데 한국어를 공부해요. (I am a student, and I study Korean.)