Learn Hardcore Korean: nagal ttae hyeongwan mun kkok jamga.

Here 꼭 means “for sure/without fail,” adding emphasis like “make sure to.” It can also mean “tightly/firmly” in other contexts (e.g., 뚜껑을 꼭 닫아), and “exactly/just” (e.g., 너랑 꼭 닮았어). In this sentence, it’s the “be sure to” meaning.

Can I say 잠궈 instead of 잠가?

Yes. With 잠그다, both forms are accepted in modern standard Korean:

잠가 / 잠가요 / 잠갔어
잠궈 / 잠궈요 / 잠궜어 In writing or textbooks you’ll often see 잠가, but 잠궈 is very common in speech. With -(으)세요, keep the stem: 잠그세요 (not “잠가세요/잠궈세요”).

What’s the difference between 잠그다 and 잠기다?

잠그다 = transitive “to lock” (you lock something): 문을 잠갔어.
잠기다 = intransitive/passive “to be locked” (something is locked): 문이 잠겼어. / 문이 잠겨 있어. Use 잠가/잠그세요 to tell someone to lock; don’t use 잠겨 for that.

Why is it 나갈 때 and not 나가면, 나갔을 때, or 나가면서?

-(으)ㄹ 때 marks the time “when (you) do/will do” something: 나갈 때 = when leaving (now/next time).
나갔을 때 = when (I/you) went out (specific past time).
나가면 = if/whenever you go out (conditional/general rule).
나갈 때마다 = every time you go out.
나가기 전에 = before going out.
나가면서 = while going out (simultaneous action).

Do I need a space between 현관 and 문? Should it be 현관문?

Both 현관문 (closed compound) and 현관 문 (separated) are seen. Many style guides prefer the closed compound 현관문 in formal writing. In casual text, both appear. Do keep a space in 나갈 때; 때 is a dependent noun, so write 나갈 때 (not “나갈때”).

What’s the difference between 현관문 and 대문?

현관문: the front door at the entrance of a house/apartment (the door to the living space).
대문: the main gate to the property/yard (common in standalone houses). In apartments, you typically use 현관문, not 대문.

Can I move 꼭 somewhere else in the sentence?

Yes. Natural options include:

꼭 현관문 잠가.
현관문 꼭 잠가.
현관문을 꼭 잠가. Positioning slightly changes focus, but all are fine. Putting 꼭 right before the verb (꼭 잠가) is the most neutral.

How do I say the negative (“don’t lock it”)?

Use -지 마:

Casual: 나갈 때 현관문 잠그지 마.
Polite: 나갈 때 현관문 잠그지 마세요. You can also add emphasis: 꼭 잠그지 마 = “make sure not to lock it.”

How can I make the request softer or more indirect?

Casual softening: 나갈 때 현관문 꼭 잠가 줘. / 잠가 줄래?
Polite request: 나갈 때 현관문 꼭 잠가 주시겠어요?
Very polite/formal: 나갈 때 현관문을 꼭 잠가 주시면 감사하겠습니다.

Why not 잠가라 at the end?

잠가라 is the plain-style imperative, often used in instructions, writing, or to someone younger/subordinate; it can sound stern. In everyday banmal, 잠가 is the common spoken command.

Who is the subject here?

It’s omitted. Because this is an imperative, the understood subject is you. You can add a topic for a general rule: 나갈 때는 현관문 꼭 잠가. You can also say 너 나갈 때… for emphasis, but it’s usually unnecessary.

Why 나가다 instead of 나오다?

나가다: go out/leave (movement away from the speaker’s/current location). Used for house rules like this.
나오다: come out (movement toward the speaker). If the speaker is outside and the listener is inside, they might say 나올 때.

Any quick pronunciation tips?

현관 문 is pronounced as if one word (현관문) due to liaison.
꼭 uses a tense k-sound (like “kkok”).
잠가 sounds like “jam-ga” (not “jam-gwo”).
때 is a strong “ttae” sound.

What’s the nuance difference between 꼭, 반드시, and 꽉?

꼭: “for sure/without fail” (neutral, common) or “tightly” (contextual).
반드시: “without fail” but more formal/emphatic.
꽉: only “tightly/firmly” (e.g., 문을 꽉 닫아). You wouldn’t use 꽉 for “be sure to.”

How would this look on a sign or note?

Friendly note: 나갈 때 현관문 잠그기! (using -기 as a to-do reminder)
Formal sign: 나갈 때에는 현관문을 반드시 잠그십시오. or 퇴실 시 현관문을 반드시 잠그세요.

Can I say 나갈 때에 instead of 나갈 때?

Yes. 나갈 때에 is acceptable but sounds more formal/literary. In everyday speech, 나갈 때 is preferred. You can also add a topic marker for a rule-of-thumb feel: 나갈 때는 ….