Learn Hardcore Korean: jungyohan geon memojange jeogeo. - Write important things in the notepad.

More formal or written: bold 중요한 것은
Natural everyday speech: bold 중요한 건
Very casual colloquial: bold 중요한 거는 (bold 거 is the spoken form of bold 것; adding bold 는 makes it topical too)

Why use the topic marker (bold 건) instead of the object marker (bold 걸)?

Using bold 건 topicalizes the phrase: “As for the important stuff, …” It makes the sentence feel like general advice or a rule. bold 중요한 걸 메모장에 적어 is also correct, but it sounds like a direct instruction about a specific object. With bold 건, the object of bold 적어 is understood from context (the topicalized “important stuff”) and omitted, which is very natural in Korean.

What politeness level is bold 적어, and what are safer polite alternatives?

bold 적어 is informal banmal imperative, used to close friends, younger people, or yourself (as a reminder). Alternatives:

Plain/blunt: bold 적어라 (can sound commanding or textbook)
Polite: bold 적어요 (soft request/statement)
Polite honorific imperative: bold 적으세요 (safest to people you don’t know well)
Softened requests: bold 메모장에 좀 적어 줘 (casual), bold 메모장에 좀 적어 주세요 (polite)

What’s the difference between bold 적다 and bold 쓰다?

bold 적다: to jot down/record information (notes, lists, short items). Think “write down.”
bold 쓰다: to write/compose (letters, essays) or to “use.” In this sentence, bold 적어 is perfect because you’re telling someone to note something down. You could also say bold 메모해 (from bold 메모하다), which emphasizes “make a memo.”

What does bold 메모장 refer to exactly—paper notebook or phone app?

bold 메모장 can mean either a physical memo pad/notepad or a digital notepad/Notes app. Context decides. Related words:

bold 수첩: pocket notebook
bold 노트: school/spiral notebook
bold 메모 앱 / 노트 앱: notes app on a phone
On Windows, bold 메모장 often refers to Notepad

Why bold 메모장에 and not bold 메모장에서 or bold 메모장으로?

bold 에 marks the destination/target medium: you’re putting the content into the notepad.
bold 에서 marks the place where an action occurs (e.g., “write at the library”), not the container you write into.
bold 으로 means “toward/as/into (as a means)”; it’s not used for the recording medium here. You can also say bold 메모장에다(가) 적어, which colloquially emphasizes “onto there.”

Is bold 중요한 건 singular or plural? How do I say “all the important things”?

Korean often leaves number unmarked. bold 중요한 건 can mean “the important thing” or “important things (in general).”

To make it clearly plural: bold 중요한 것들
To say “all the important things”: bold 중요한 건 다 메모장에 적어 or bold 중요한 것들은 다 메모장에 적어

Can I drop particles, like say bold 중요한 거 메모장에 적어?

Yes. In casual speech, the object marker is frequently dropped, so bold 중요한 거 메모장에 적어 is natural. The topicalized bold 건 is common, but a bare bold 거 (no particle) also works in everyday conversation. Keep bold 에 on bold 메모장에 because it marks the target location.

Is bold 적어 here definitely an imperative, or could it also mean “and write”?

As a standalone sentence with that intonation, bold 적어 is an imperative (“Write it down”). It can also function as the connective “write and …” only if another clause follows (e.g., “… 적어 놓고 확인해”). Here, with a period and no following clause, it’s an instruction.

How can I make it sound like advice: “Make sure you write important things down”?

Add an emphasis word or a keep-it-for-later helper:

bold 중요한 건 꼭 메모장에 적어.
Polite: bold 중요한 건 꼭 메모장에 적어 두세요 / 적어 두세요. Words like bold 꼭 / bold 반드시 make it feel like “make sure.”

What about bold 적어 둬 or bold 적어 놔? How do bold -둬 and bold -놔 change the nuance?

bold -둬 (from bold 두다): “do it and keep it that way (for future use).” bold 메모장에 적어 둬 = “write it down and leave it there.”
bold -놔 (from bold 놓다): very similar in casual speech, often a bit more colloquial. Both imply writing it so it’ll be available later, which fits note-taking well.

Is there any ambiguity with bold 적어 meaning “few”?

bold 적다 also means “to be few.” Context resolves it:

bold 사람이 적어 = “There are few people.”
bold 메모장에 적어 = “Write (it) in the notepad.” Here, the location particle bold 에 and the verb-object pattern make “write (down)” the only sensible reading.

What’s the grammar of bold 중요한? Why not bold 중요하는?

bold 중요하다 is a descriptive verb (“to be important”). Its attributive (modifier) form is bold 중요한 (“important”). bold 중요하는 is ungrammatical because bold 중요하다 is not an action verb that takes bold -는 to modify nouns.

Can I change the word order?

Yes, Korean word order is flexible. The original focuses the topic first. Variants:

bold 메모장에 중요한 건 적어. (OK; now the location is fronted)
bold 중요한 건 메모장에 꼭 적어. (adds emphasis) The topicalized phrase typically comes early, which is why bold 중요한 건 … feels natural.

How do you pronounce the sentence naturally?

Roughly: jung-yo-han geon me-mo-jang-e jeo-geo.

bold 적어 sounds like “jeo-geo” [저거].
bold 건 is “geon” [건]. Keep a smooth flow without stressing each syllable too much.

Any spacing or spelling gotchas?

Standard spacing is bold 중요한 건 (space). Writing bold 중요한건 is common online but nonstandard.
Particles attach without a space: bold 메모장에, not bold 메모장 에.
The contraction bold 건 is standard; it replaces bold 것은 as a unit.

Would bold 중요한면 메모장에 적어 be okay?

Slight correction: it should be bold 중요하면 메모장에 적어 (“If it’s important, write it down”). That’s a very natural way to express the same idea with a conditional.

What would a fully explicit version with all particles look like?

bold 중요한 것을 메모장에 적어. (keeps the object marker)
If you want plural/emphasis: bold 중요한 것들을 다 메모장에 적어. Topicalizing with bold 건 is just more colloquial and advice-like.

How do I say it politely about a phone’s Notes app?

bold 중요한 건 메모 앱에 적어 두세요.
iPhone context: bold 중요한 건 메모에 적어 두세요.
Galaxy context: bold 중요한 건 삼성 노트에 적어 두세요. Using bold 적어 두세요 keeps the “write it and keep it” nuance.