Learn Hardcore Korean: jeonwon beoteuneul gilge nulleoya hwamyeoni kyeojyeo. - You need to press and hold the power button for the screen to turn on.

It marks a necessary condition: only if/when you press (and hold), then the result happens. With a following clause, it means “only if X, Y.” Compare:

Necessary condition: 전원 버튼을 길게 눌러야 화면이 켜져요.
Obligation (must): 전원 버튼을 길게 눌러야 해요/돼요. (Here, -아/어야 combines with 하다/되다 to mean “have to.”)

Why not use 눌러서 instead of 눌러야?

-아서/어서 presents cause/sequence (“press and then it turns on”), often describing a one-time sequence. -아/어야 emphasizes necessity/condition (“only if you press and hold, it will turn on”). For general instructions or rules, -아/어야 is the natural choice.

What exactly is 켜져?

It’s the informal present of the passive/inchoative verb 켜지다 (“to be/get turned on”). Morphology:

켜다 (to turn on something) → 켜지다 (it turns on / gets turned on)
켜지 + 어 → 켜져 (contraction of 지어 → 져) Meaning here: an event/result (“it turns on”), not an action you actively do.

Why is it 화면이 and not 화면은 or 화면을?

화면이: subject marker; the screen is what turns on (with passive 켜지다).
화면은: topic; would sound like “as for the screen, it turns on,” often contrastive.
화면을: object; would pair with the active verb 켜다 (e.g., 화면을 켜다).

What’s going on with 누르다 → 눌러야? Is that irregular?

Yes, 르- irregular. When adding endings beginning with -아/어, 르 becomes ㄹㄹ:

누르 + 어요 → 눌러요
누르 + 었어요 → 눌렀어요
누르 + 어야 → 눌러야

Why 길게? Could I say 오래 or 꾹 instead?

길게 누르다 is the standard collocation in device instructions.
오래 누르다 also means “press for a long time,” but is less manual-like.
꾹 adds the nuance “firmly/steadily.” You’ll also hear combinations: 꾹 길게 누르다.

Can I drop particles in casual speech?

Yes, in conversation you may hear: 전원 버튼 길게 눌러야 화면 켜져. Object/subject markers (을/를, 이/가) often drop when the meaning is clear. Keep them in writing or formal contexts.

Could I reverse or rephrase the sentence?

Common alternatives:

화면이 켜지려면 전원 버튼을 길게 눌러야 해요. (“If you want the screen to turn on, you have to press and hold the power button.”)
전원 버튼을 길게 눌러야만 화면이 켜져요. (-야만 adds “only if,” with stronger emphasis.)

Is 켜져 polite enough?

켜져 is casual/informal. More polite or formal:

Polite: 켜져요
Formal: 켜집니다 Choose register to match your audience (friends vs. customers/manuals).

Could I use the active verb 켜다 instead of passive 켜지다?

Yes, but then the screen becomes the object:

화면을 켜려면 전원 버튼을 길게 눌러야 해요. Using 켜지다 focuses on the screen’s change of state; both are natural, with a slight nuance difference.

Does 눌러야 by itself mean “you must press it”?

Not by itself. If there’s no following result clause, add 하다/되다:

Obligation: 눌러야 해요/돼요. With a result clause (as in your sentence), 눌러야 means “only if (you) press...”.

How should I pronounce the sentence naturally?

전원 → [저눤]
버튼 → [버튼]
길게 → [길게]
눌러야 → [눌러야]
화면이 → [화며니]
켜져 → [켜저] Note: 켜져 is pronounced [켜저] but spelled with 져 (ㅕ), not 저.

Any common spelling pitfalls here?

Write 켜져, not “켜저.”
눌러야 is one word; don’t split it as “눌러 야.”
Spacing: 전원 버튼을 (space between the nouns), particles attach with no space.

Why use the passive-like 켜지다 at all?

Korean often uses -아/어지다 (or -이/히/리/기) to describe things changing state without focusing on an agent. With devices, saying the screen “gets turned on” (켜지다) is idiomatic and sounds natural.

What’s the difference between event vs. state for 켜져?

Event/result (your sentence): after the condition, it turns on.
State: use -아/어 있다 → 화면이 켜져 있어요 (“the screen is on” as a current state).

Are there synonyms for 전원 버튼? And doesn’t 전원 also mean “everyone”?

Synonyms: 전원 버튼, 전원 키, 파워 버튼. 스위치 can work for toggles.
Homonym: 전원(電源) = power; 전원(全員) = everyone. Context (…버튼) makes it clear this is “power.”