beginner
Makes a noun plural. Often optional but clarifies multiple items.
Usage
Often omitted unless referring to people.
In Context
학생들이 공부해요.
Students are studying.
새들이 날아요.
Birds are flying.
들: the plural marker Korean mostly doesn't need
English forces you to choose. Every countable noun is either singular or plural and there's no way to dodge it. Korean doesn't work that way, and 들 is optional almost everywhere.
The default is no marker at all
- 펜을 샀어요. (pen-eul sasseoyo) — "I bought a pen." Or pens. Both.
Nothing is missing from that sentence. Korean leaves number unmarked and lets context handle it, the same way English leaves out politeness level and nobody complains.
When 들 shows up
Mostly with people, and mostly when the plurality matters.
- 학생들이 왔어요. (haksaengdeur-i wasseoyo) — "The students came."
- 사람들 (saramdeul) — "people"
- 친구들하고 갔어요. (chingudeul-hago gasseoyo) — "I went with my friends."
With objects it's rare and can sound clumsy. 책들 is grammatical but a Korean speaker would usually just say 책.
Where it's actually wrong
Don't use it with a number or counter. The number already tells you there's more than one, so 들 becomes redundant and sounds off.
- 학생 세 명이 왔어요. (haksaeng se myeong-i wasseoyo) — "Three students came." ✓
- 학생들 세 명이 왔어요. ✗
If you want more on the counter half of that sentence, the counters page covers all of them.
Don't use it with mass nouns. 물들 or 공기들 makes as little sense as "waters" and "airs" do in English.
The strange one: 들 on things that aren't nouns
This catches people who are already fairly advanced. Korean can stick 들 onto adverbs, verb endings, even whole phrases, to signal that the listeners are plural.
- 안녕히 가세요들. (annyeonghi gaseyo-deul) — "Goodbye, all of you."
- 많이 드세요들. (mani deuseyo-deul) — "Eat up, everyone."
The 들 isn't making anything plural in that sentence. It's marking that you're addressing a group. You don't need to produce this, but recognizing it explains a lot of otherwise baffling sentences.
The short version
Leave it out unless you're talking about people and the plurality is the point. Korean tolerates ambiguity about number in a way English can't, and over-marking is a more obvious learner tell than under-marking.