Intermediate · Korean Grammar
Give reasons in Korean: -아/어서 and -(으)니까 in context
Move beyond isolated sentences by choosing a reason ending that fits the result, suggestion, or request you want to express.
Start here if you can already form polite sentences
This intermediate lesson assumes you can read Hangul, find a verb stem, and recognise everyday polite endings such as -아요/어요 and -(으)세요. If those are unfamiliar, return to the beginner sentence guide first. The goal is not to collect another translation for “because.” It is to choose an ending that fits what the second half of your sentence is doing.
We will compare two useful reason constructions: -아/어서 and -(으)니까. They can both connect a reason with a following idea, but they are not interchangeable in every context. In particular, pay attention to whether you are reporting a result or recommending an action.
The examples here are original practice situations. Read both clauses together before you decide which pattern you need. A single English word such as “so” is not enough to select the Korean grammar.
Compare a result with a suggestion
In the first example, 비가 와서 connects the rain with the reported result: staying home. The past ending is on 있었어요. In the second, 비가 오니까 presents the rain as a reason for the listener to take an umbrella. 가져가세요 is the polite request that follows.
For a standard learner pattern, use -(으)니까 when the reason is followed by a command or suggestion. Do not mechanically replace it with causal -아/어서 before -(으)세요 or -자. This restriction concerns the reason use: -아/어서 also has other meanings, including sequences of related actions, which need their own explanation.
Build the forms from stems you know
| Dictionary form | Reason with -아/어서 | Reason with -(으)니까 |
|---|---|---|
| 오다 | 와서 | 오니까 |
| 먹다 | 먹어서 | 먹으니까 |
| 하다 | 해서 | 하니까 |
| 살다 | 살아서 | 사니까 |
For -아/어서, use the familiar vowel choice from the -아요/어요 family, then the connecting form: 오다 becomes 와서, 먹다 becomes 먹어서, and 하다 becomes 해서. This is a reminder of the pattern, not a complete irregular-conjugation chart.
For -(으)니까, add -니까 after a vowel-ending stem and -으니까 after most consonant-ending stems. A stem ending in ㄹ drops that ㄹ before -니까: 살다 becomes 사니까. That form can look identical to a form of 사다, “buy,” so the whole sentence supplies the meaning.
Other irregular stems need separate care. Do not add an ending to a dictionary form including 다, as in 먹다으니까. First identify the stem, then apply the appropriate form.
Choose the pattern by the job of the second clause
| What the speaker is doing | Example | Meaning |
|---|---|---|
| Reporting a result | 길이 막혀서 늦었어요. | The traffic was heavy, so I was late. |
| Making a suggestion | 시간이 있으니까 같이 걸을까요? | We have time, so shall we walk together? |
| Explaining a feeling | 다시 만나서 기뻐요. | I’m glad to see you again. |
| Making a request | 잘 안 들리니까 조금 크게 말해 주세요. | I can’t hear well, so please speak a little louder. |
The final example gives a practical reason, but tone still matters. A grammatically correct reason can sound abrupt if it is delivered as a complaint. You can begin with 죄송하지만, “I’m sorry, but,” when that fits the interaction.
Do not assume -(으)니까 always sounds rude or always sounds more polite than -아/어서. The speaker’s attitude, relationship and full sentence matter. The contrast taught here is the relationship between the clauses, not a ranking of which ending is “nicer.”
Let the time reference make sense across the sentence
In 바빠서 전화를 못 했어요, “I was busy, so I could not call,” the past ending on 했어요 places the situation in the past. You do not need to put a past marker on every clause just because both events happened yesterday.
-(으)니까 can follow a past marker when you are explicitly referring to a completed situation: 숙제를 끝냈으니까 이제 쉬어도 돼요. — “You have finished the homework, so you may rest now.” The reason is something already completed.
For an initial controlled exercise, use a simple stem before causal -아/어서 and put the required tense in the final clause. More specialised discussions of tense and -아/어서 should not distract you from the common patterns here. Focus first on making the intended timeline and the second clause’s purpose clear.
Explain your choice
- Complete the advice: 비가 오___ 우산을 가져가세요.
- Connect a cause and reported result: 길이 막히다 + 늦었어요.
- Make the -(으)니까 form of 살다.
- Complete a suggestion: 시간이 있___ 같이 걸을까요?
- Why is “because” alone not enough to choose the ending?
Check the answers and explanations
- 비가 오니까 우산을 가져가세요. The reason supports a request or advice.
- 길이 막혀서 늦었어요. 막히다 becomes 막혀서.
- 사니까. Drop ㄹ before -니까.
- 시간이 있으니까 같이 걸을까요? The second clause suggests an action together.
- You also need to know what the following clause does, such as reporting a result or asking someone to act.
Now write two sentences about the same weather: one describing what you did, and one suggesting what to do next. Compare the two endings. You are practising a communicative choice, not replacing a single English connector mechanically.
A small listening check
Pronunciation help: Listen across the clause boundary
Keep 비가 오니까 together as the reason, then give the following advice. A short natural pause can help the listener follow the structure; avoid pausing after every syllable.
Listen and choose
Play the sound, then select the Korean you heard. The answer buttons unlock after playback. This is one short practice item, not a pronunciation assessment.
Listen before choosing.
Reference and further study
The examples and practice tasks in this guide were written for Korean With a Local. For reference and further study:
- National Institute of Korean Language: causal connections — Official discussion of restrictions on the following clause, in Korean.
- University of British Columbia: -(으)니(까) — Teaching notes on reasons and the suggestion or command that may follow.
Reviewed September 3, 2026. Found a mistake? Send a correction.