~어/아/여서 VS ~(으)니까 – Differences and important rules

These two – ~어/아/여서 and ~(으)니까 – are probably two of the most commonly confused grammar expression. To be very honest, I’m not sure about the difference at times. I’ll list some very important rules down (with much research) because the difference can’t be easily explained through mere differences. There are very specific situations where they can be used.

Important rules about using ~어/아/여서 and ~(으)니까

1. ~어/아/여서 cannot be used for propositive, imperative situations or expressing one’s intent

~어/아/여서 cannot be used in situations where the speaker is suggesting/requesting/demanding/commanding the listener to do something or if the speaker is expressing his/her own intention to do something.

This means that in any sentences that you’ll end with a ~(으)세요, ~ㅂ시다, ~자, ~ㄹ까, ~겠, ~ㄹ게 you absolutely cannot use ~어/아/여서 and absolutely must use ~(으)니까.

Examples:

오늘 추우니까 따뜻하게 입으세요. (O)
오늘 추워서 따뜻하게 입으세요. (X)
Because/Since today is cold, please wear warmly.

오늘 추우니까 매운 음식을 먹읍시다/먹자. (O)
오늘 추워서 매운 음식을 먹읍시다/먹자. (X)
Because/Since today is cold, let’s eat spicy food.

오늘 추우니까 집에서 영화를 볼까(요)? (O)
오늘 추워서 집에서 영화를 볼까(요)? (X)
Because/Since today is cold, shall we watch a movie at home?

오늘 추우니까 장갑을 입고 나가겠어요. (O)
오늘 추워서 장갑을 입고 나가겠어요. (X)
Because/Since today is cold, I’ll wear gloves and go out.

2. ~(으)니까 cannot be used in speeches of greetings/apologies/gratitude

This means that in any sentence that you’re greeting, apologising, thanking, or any other similar situations that involve some sort of emotions, you cannot use ~(으)니까.

Examples:

만나서 반갑습니다/반가워요. (O)
만나니까 반갑습니다/반가워요. (X)
We met so I’m pleased/glad/Nice to meet you.

늦어서 죄송합니다/미안해요. (O)
늦으니까 죄송합니다/미안해요. (X)
I’m late so I’m sorry.

초대해 주셔서 감사합니다/고마워요. (O)
초대해 주니까 감사합니다/고마워요. (X)
You invited us so thank you/I’m thankful.

그동안 많이 챙겨서 항상 감사합니다/고마워요. (O)
그동안 많이 챙기니까 항상 감사합니다/고마워요. (X)
You’ve taken good care of me so thank you/I’m thankful.

선물을 좋아해서 다행이에요/다행이야. (O)
선물을 좋아하니까 다행이에요/다행이야. (X)
You like this gift so it’s fortunate.

사랑하는 사람은 떠나가서 슬픕니다/슬퍼요. (O)
사랑하는 사람은 떠나가니까 슬픕니다/슬퍼요. (X)
The person whom I love left so I’m sad.

3a. ~어/아/여서 is used in situations where you want to explain cause and effect.

In other words, ~어/아/여서 is usually used when recounting past experiences/happenings. Because something happened, that led to another thing. Their causal relationship is also usually of some natural consequence that anyone can relate to and not something that requires some sort of justification.

*~어/아/여서 places emphasis on the clause after it, essentially placing more focus on the effect instead of the cause. This is also because both of the clauses have already happened (past).

Examples:

배고 너무 파서 많이 먹었어요. (O)
배고 너무 프니까 많이 먹었어요. (X)
I was really hungry so I ate a lot.

비가 와서 학교에 늦게 도착했어요. (O)
비가 오니까 학교에 늦게 도착했어요. (X)
It rained so I reached school late.

열심히 공부해서 시험을 잘 봤어요. (O)
열심히 공부하니까 시험을 잘 봤어요. (X)
I studied diligently so I did well for the test.

As you can see from the examples above, those are considered “matter of facts”. Therefore, it is not appropriate to use ~(으)니까, unless the context calls for it.

Also, the emphasis is on the second clause, which is the cause/action that follows the reason.

For example, unless (and this is very rare that it’s case) the situation in the first sentence is known to both the speaker and listener that “eating a lot” is not a natural consequence of “being very hungry”.

3b. ~(으)니까 is used in situations where you want to justify an action/thought/request/etc.

In other words, ~(으)니까 is usually used when explaining the motivation or reason behind a certain action. Most of the time, you would want to use ~(으)니까 if a justification is needed for a certain action.

Also, when you use ~(으)니까, you’re essentially making it clear to the listener(s) that the justification is being emphasised on.

*~(으)니까 places emphasis on the clause before it, essentially placing more focus on the reason instead of the action. This is also because the action is usually not carried out yet (present or future).

Examples:

높은 성적을 얻고 싶으니까 지금부터 드라마 안 보고 끝까지 열심히 공부할게요. (O)
높은 성적을 얻고 싶어서 지금부터 드라마 안 보고 끝까지 열심히 공부할게요. (X)
Because/Since I want to get a high grade, from now on, I won’t watch dramas and study hard until the end.

엄마는 장미꽃을 아주 좋아하시니까 꽃집이 멀어도 꼭 샀다 올게요. (O)
엄마는 장미꽃을 아주 좋아해서 꽃집이 멀어도 꼭 샀다 올게요. (X)
Because/Since my Mum really loves roses, no matter how far the florist is, I will surely buy it back.

보무님은 많이 힘들어도 우리를 잘 키우니까 이제 우리가 보무님을 돌보자. (O)
보무님은 많이 힘들어도 우리를 잘 키워서 이제 우리가 보무님을 돌보자. (X)
Because/Since our parents brought us up well despite that it was very tough, let’s take good care of them now.

As you can see from the examples above, the speaker is justifying why he/she is intending to do something. There is no cause and effect relationship in those examples, simply because the action in the second clause hasn’t happened yet (the speaker’s intent).

Like in the examples above, the speaker is talking about something that has already happened in the first clause (and emphasising it), which is essentially the justification for the intent/request in the second clause.

4a. ~어/아/여서 is usually used to describe cause and effect (past) but the past tense is placed at the back of the sentence. You absolutely cannot attach ~어/아/여서 to a past tense verb/descriptive verb (adjective).

Examples:

배고 너무 파서 많이 먹었어요. (O)
배고 너무 팠어서 많이 먹었어요. (X)
I was really hungry so I ate a lot.

비가 와서 학교에 늦게 도착했어요. (O)
비가 왔어서 학교에 늦게 도착했어요. (X)
It rained so I reached school late.

열심히 공부해서 시험을 잘 봤어요. (O)
열심히 공부했어서 시험을 잘 봤어요. (X)
I studied diligently so I did well for the test.

4b. ~(으)니까 is usually used to justify an action in the present or intent to carry out an action in the future; the justification can be either something that is happening (present) or has happened (past). The present/future tense is placed at the back of the sentence (action/intent/suggestion/request/etc). You can attach ~(으)니까 to a past tense verb/descriptive verb (adjective).

Examples:

오늘 아침은 회사에 늦게 왔으니까 늦게 퇴근할게요. (O)
Because/Since I came to the office late this morning, I’ll be leaving office late.

아침은 항상 회사에 늦게 오니까 늦게 퇴근해요. (O)
Because/Since I always come to office late, I leave office late.

어제 이 영화를 봤으니까 다른 영화를 볼까? (O)
Because/Since I watched this movie yesterday, shall we watch other movies?

친구는 이 영화를 보고 재미 없다고 하니까 다른 영화를 볼까? (O)
Because/Since my friend watched this movie and said that it’s not interesting, shall we watch other movies?

Summary

~어/아/여서

  • cannot be used for propositive, imperative situations or expressing one’s intent (eg. ~(으)세요, ~ㅂ시다, ~자, ~ㄹ까, ~겠, ~ㄹ게)
  • ~어/아/여서 is used in situations where you want to explain cause and effect
  • ~어/아/여서 is usually used to describe cause and effect (past) but the past tense is placed at the back of the sentence
  • You absolutely cannot attach ~어/아/여서 to a past tense verb/descriptive verb (adjective)

~(으)니까

  • ~(으)니까 cannot be used in speeches of greetings/apologies/gratitude (eg. …반갑습니다, 감사합니다, 고맙습니다, 죄송합니다, 미안합니다, 기쁩니다, 슬픕니다, etc.)
  • ~(으)니까 is used in situations where you want to justify an action/thought/request/etc.
  • ~(으)니까 is usually used to justify an action in the present or intent to carry out an action in the future; the justification can be either something that is happening (present) or has happened (past).
  • The present/future tense is placed at the back of the sentence (action/intent/suggestion/request/etc).
  • You can attach ~(으)니까 to a past tense verb/descriptive verb (adjective).

References

Kimchicloud

Reddit

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