Learn Hardcore Korean: gapjagi iri saenggyeoseo yaksogeul mirwosseoyo. - Something suddenly came up, so I postponed the appointment.

It literally means “a matter/event occurred.” In everyday English it maps to “something came up.” So 갑자기 일이 생겨서 = “because something suddenly came up.”

Why is it 생겨서 and not 생겼어서?

With the reason connector -어서/아서 (-서), Korean normally doesn’t put the past marker before the connector. You just use the connective form (생겨서), and the past relationship is understood from context. 생겼어서 is widely treated as nonstandard/unnatural. If you really want an explicit past feel, use 생겼기 때문에 or make two sentences: 갑자기 일이 생겼어요. 그래서…

What does the -어서/아서 (-서) connector mean in this sentence?

It marks cause/reason or a natural sequence: “because/since” → result. Here: (갑자기 일이 생겨서) → (약속을 미뤘어요). Note: for making requests/commands based on a reason, Korean tends to prefer -으니까/니까 over -어서/아서.

Why is 일이 marked with -이 instead of -를? Could I say 일을 생겨서?

No—생기다 is intransitive, and the thing that arises is the subject. So it’s the fixed collocation 일이 생기다 (not 일을). 일이 uses the subject marker -이 because 일 ends in a consonant.

Can I move 갑자기? Is 일이 갑자기 생겨서 okay?

Yes. Both are natural:

갑자기 일이 생겨서… (the whole situation occurred suddenly)
일이 갑자기 생겨서… (the act of arising was sudden) The nuance difference is tiny in most contexts.

Does 일 here mean “work (my job)” or just “something”?

Here 일 means “a matter/issue/something” rather than your job duties. 갑자기 일이 생기다 is a set phrase meaning “something came up (unexpectedly).”

What’s the difference between 일이 생겨서 and 일이 있어서?

일이 생겨서 implies something arose, often unexpectedly.
일이 있어서 is more neutral: “I have something (to do/going on).” Both can explain a change of plans; 생겨서 sounds more sudden.

How is 미뤘어요 formed from 미루다? Why does it have ㅝ?

Stem 미루- + vowel 어 → ㅜ + 어 contracts to ㅝ → 미뤄-. Add past -었- + polite -어요 → 미뤘어요. Present is 미뤄요. Pronunciation tip: 미뤘어요 is pronounced roughly [미뤄써요].

What politeness level is this? How would it change in casual or formal speech?

-었어요 is polite informal. Variants:

Casual: 미뤘어.
Polite formal: 미뤘습니다.
Very casual text/chat: 미뤘어용/미뤘어요~ (informal, playful).

What’s the nuance difference among 미루다, 연기하다, 취소하다, 늦추다, 당기다, 옮기다?

미루다: postpone/push back (everyday, colloquial). Works well with 약속.
연기하다: postpone/defer (more formal/journalistic; used for events, deadlines). Note: 연기 also means “smoke” and “acting” (different characters), so rely on context.
취소하다: cancel.
늦추다: make something later; often used with 시간/일정 (e.g., 시간을 늦추다). Less common with 약속 directly.
당기다/앞당기다: move earlier.
옮기다: move/shift (time or place). 약속 시간을/날짜를 옮기다 is natural; 약속을 옮기다 is heard, but specifying what you moved (time/date) is clearer.

Is 약속 the right word here? How is it different from 예약?

약속: a promise/plan/appointment with a person.
예약: a reservation/booking with a service/business (restaurant, hospital). So you usually 약속을 미루다 (postpone meeting someone) vs 예약을 변경/취소하다 (change/cancel a reservation).

Do I need the object marker 를 on 약속? Can I say 약속 미뤘어요?

In speech, dropping object particles is common, so 약속 미뤘어요 is fine. In careful/written Korean, keep 약속을 미뤘어요.

Could I use -으니까 or 그래서 instead of -어서?

Yes.

갑자기 일이 생겼으니까 약속을 미룰게요. (often used for suggestions/decisions)
갑자기 일이 생겼어요. 그래서 약속을 미뤘어요. (two-sentence cause → result) All are natural; -어서 is the most compact/explanatory.

Do I need to say “I” (저는/제가) explicitly?

No. Korean often omits obvious subjects. If needed for clarity or contrast, you can say 제가 갑자기 일이 생겨서… or 저는 약속을 미뤘어요.

How can I make this more polite when rescheduling?

Some polite templates:

죄송하지만, 갑자기 일이 생겨서 약속을 미뤄도 될까요?
불편을 드려 죄송합니다. 갑작스럽게 일이 생겨서 약속을 다음으로 미뤄도 될지 여쭙습니다.
Propose alternatives: 혹시 내일이나 모레로 시간을 옮겨도 될까요?

Are there other natural substitutes for 일이 생겨서?

Yes, e.g.:

사정이 생겨서 (some circumstances came up; slightly formal)
급한 일이 생겨서 (something urgent came up)
개인적인 일이 생겨서 (a personal matter came up)
급히 처리할 일이 생겨서 (something I must handle urgently came up)

Any collocation pitfalls like 사고가 생기다 vs 나다?

Prefer set pairings:

사고가 나다 (an accident happened) is the default; 사고가 생기다 is less common.
문제가 생기다/발생하다 are both fine.
일이 생기다 is the idiomatic one for “something came up.”

If I mean I’m going to postpone now (not already did), should I still use 미뤘어요?

Use a prospective form:

Decision now: 약속을 미룰게요.
Intention/plan: 약속을 미루려고 해요.
Requesting permission: 약속을 미뤄도 될까요? 미뤘어요 states it’s already been postponed.