Cause and Reason: 아/어서, 니까, 때문에, 덕분에, 탓에

Core examples: 비가 와서; 바쁘니까; 사고 때문에; 선생님 덕분에; 내 탓에; 늦어서 죄송합니다.

“Because” is too blunt

English because is useful, but Korean reason expressions divide the work more finely. A reason can be natural sequence, speaker’s ground, neutral cause, positive attribution, blame, apology explanation, instruction basis, or formal causal link.

Compare:

• 비가 와서 못 갔어요.
• 바쁘니까 나중에 전화해.
• 사고 때문에 길이 막혔어요.
• 선생님 덕분에 많이 배웠어요.
• 제 탓에 늦었어요.
• 늦어서 죄송합니다.

They all explain why. They do not have the same tone. Korean cause expressions tell you not only the reason, but the speaker’s stance toward the reason.

아/어서: natural reason or sequence

아/어서 often presents the first clause as the natural reason or preceding condition for the second.

• 비가 와서 못 갔어요.
• 배가 아파서 쉬었어요.
• 늦어서 죄송합니다.
• 만나서 반가워요.
• 도와주셔서 감사합니다.

It is common with apologies and thanks because it naturally links the speaker’s feeling or expression to the reason.

In many standard teaching contexts, 아/어서 is not the usual choice before commands or suggestions. For commands and suggestions, 니까 is usually safer.

Less natural as a basic learner pattern:

비가 와서 우산 가져가세요.

Better:

비가 오니까 우산 가져가세요.

니까: reason, ground, or speaker basis

니까 often gives a reason that supports a command, suggestion, decision, or conclusion.

• 바쁘니까 나중에 전화해.
• 비가 오니까 우산 가져가세요.
• 시간이 없으니까 빨리 갑시다.
• 지금 출발하니까 기다려 주세요.
• 제가 확인했으니까 걱정하지 마세요.

니까 can feel more explicit, speaker-grounded, or directive than 아/어서. It is useful when the second clause is an instruction or proposal.

때문에: noun-based cause

때문에 attaches to nouns or nominalized clauses:

• 사고 때문에 길이 막혔어요.
• 비 때문에 경기가 취소됐어요.
• 일정 때문에 참석하기 어렵습니다.
• 건강 문제 때문에 쉬고 있습니다.
• 네가 늦은 것 때문에 문제가 생겼어.

때문에 can be neutral, formal, or blame-oriented depending on context. It often sounds heavier than 아/어서 in conversation.

덕분에: positive attribution

덕분에 marks a beneficial cause: thanks to.

• 선생님 덕분에 많이 배웠어요.
• 친구 덕분에 해결했어요.
• 날씨 덕분에 여행이 즐거웠어요.
• 여러분 덕분입니다.

It gives credit and is common in thanks, success stories, and polite appreciation. Sarcastic uses exist, but learners should first master the positive use.

탓에: blame or negative attribution

탓에 frames the cause negatively, often as fault or blame.

• 제 탓에 늦었어요.
• 비 탓에 경기가 취소됐어요.
• 부주의 탓에 사고가 났어요.
• 누구 탓을 하지 마세요.

탓 carries evaluation. It is not neutral because. Use it when blame, fault, or negative responsibility is intended.

Reason expressions and politeness

Reasons can soften or harden a message.

Soft apology:

늦어서 죄송합니다.

Directive reason:

시간이 없으니까 빨리 가 주세요.

Formal explanation:

내부 사정 때문에 일정이 변경되었습니다.

Appreciation:

도와주신 덕분에 잘 마무리했습니다.

Blame:

제 실수 탓에 문제가 생겼습니다.

Choosing the reason form changes the social effect of the sentence.

A reason-choice routine

1. Is the reason a natural sequence or personal explanation? Consider 아/어서.
2. Does the reason support a command, suggestion, or decision? Consider 니까.
3. Is the cause a noun or formal explanation? Consider 때문에.
4. Is the cause positive and credit-giving? Use 덕분에.
5. Is the cause negative and blame-oriented? Use 탓에.
6. Is this an apology, thank-you, complaint, instruction, news report, or workplace explanation?
7. Does the reason sound too blunt for the relationship?

Technical-review guardrail: reason forms carry stance and compatibility

The article keeps the core distinction among natural reason, speaker-grounded premise, explicit cause, positive credit, and blame. The upgraded caution is that 때문, 덕분, and 탓 are evaluative noun-based choices, while 아/어서 and 니까 are connective choices whose fit depends on the following clause. The 아/어서 + command warning remains a learner default, not a claim that context never licenses exceptions.

Mini practice: choose the cause expression

Suggested functions:

1. Reason input: user enters a cause and result.
2. Stance selector: neutral, directive, positive, blame, apology, formal.
3. Pattern output: 아/어서, 니까, 때문에, 덕분에, 탓에.
4. Command warning: flags common 아/어서 + command problems.
5. Politeness meter: blunt, neutral, softened, formal, appreciative, blame-oriented.
6. Rewrite practice: same reason across apology, workplace email, complaint, and advice.

Final rule

Do not translate every English “because” the same way. Choose the Korean reason form by logic and stance: natural reason, speaker ground, formal cause, positive credit, or blame.

• Inkuntri Korean Article Outlines — First 100, especially articles 061–080.

Technical-review checklist applied in v2

• Confirmed that the file contains articles 061–080 exactly once and preserves the original order.