Definition from Wiktionary, the free dictionary
는 • (neun)
- (semantic) marks the topic of the sentence. (not to be confused with the subject of the sentence)
- (semantic) depending on context, shows contrast with or adds emphasis to the preceding word or phrase in a sentence.
- (topic marker): The topic is what is being talked about in the sentence; it is the main point. This, however, is different in meaning from the subject which the predicate directly refers to. The topic and subject may be the same in a sentence.
- 매리는 나의 친구다 ― maerineun naui chin-guda ― Mary is my friend.
- (Complete form) 이 반에 있는 학생들은 똑똑하다.
- I bane inneun haksaengdeureun ttokttokhada.
- The students that are in this class are smart.
- (Shortened form) 이 반은 학생들이 똑똑하다.
- I baneun haksaengdeuri ttokttokhada.
- The students in this class are smart.
- Compare the complete and shortened form. Here, the topic/subject distinction is a pseudo-grammatical distinction. All sentences that use both 은/는 and 이/가 can derive its expletive form as shown above.
- In the shortened form, the topic is "This class" while the subject is "the students".
- In cases like this, the topic can often be thought of as a range, or to what extent the sentence is applicable. In the example above, if "speaking of this class" was removed, the sentence would not be limited to "this class", and would talk about all students in general.
- Grammatically, this phenomenon is explained by the concept of predicate clause; that is, the sentence "학생들이 똑똑하다" (The students are smart) wholly works as an adjective (This class is 'student-smart.", so to speak).
- (Contrast/emphasis marker): 는 (neun), can be placed after most case markers (including 가 (ga), 를 (reul), 에 (e), 에게 (ege), 에서 (eseo), 로 (ro), 과 (gwa)) to show contrast between two or more choices or add emphasis to a word or phrase, depending on the context. If used after 가 (ga) or 를 (reul), the 가 (ga) or 를 (reul) are deleted leaving only 은 (eun).
- 서울은 한국의 수도다.
- Seoureun han-gugui sudoda.
- Seoul is the capital city of South Korea.
- If 은 (eun) is stressed, it might suggest "other cities are not."
- 여름에는 덥다.
- Yeoreumeneun deopda.
- It is hot during the summer.
- If 는 (neun) is stressed, it might suggest "during other seasons, it's not."
- 그는 나에게 책을 주었다.
- Geuneun na-ege chaegeul jueotda.
- He gave me the book. (He gave the book to me.)
- If 는 (neun) is stressed, it might suggest "other people may have not."
- Variants: 그가 나에게는 책을 주었다.
- Geuga na-egeneun chaegeul jueotda.
- I'm sure that he gave the book to me, but I'm not certain if he gave it to others as well.
- 그가 나에게 책은 주었다.
- Geuga na-ege chaegeun jueotda.
- I'm sure that he gave me the book, but I'm not certain if he gave me other things, too.
- 그가 나에게 책을 주기는 했다/주기는 주었다.
- Geuga na-ege chaegeul jugineun haetda/jugineun jueotda.
- He gave me the book, but I'm uneasy about the way he did. (It was too late/seriously damaged/not the one I wanted/just half of it/etc.)
- 서울은 한국의 수도다.
- 은 (eun) (after a consonant)
는 • (-neun-)
- a suffix indicating the present tense, appearing directly after a stem of a verb, ending in a consonant other than ㄹ (l), which is at the end of a declarative or exclamatory sentence or an indirect quotation clause.
- 깨어나지 않다 (kkaeeonaji anta, “not to awake”) → 환자가 아직도 깨어나지 않는다./않는구나! (Hwanjaga ajikdo kkaeeonaji anneunda./anneun-guna!, “The patient doesn't awake yet.”) → 환자가 아직도 깨어나지 않는다는 말에 가슴이 답답해져 온다. (Hwanjaga ajikdo kkaeeonaji anneundaneun mare gaseumi dapdaphaejyeo onda., “Hearing that the patient doesn't awake yet, I'm getting to feel heavy.”)
- -ㄴ- (-n-)
는 • (-neun)
- a present tense suffix used to help a verb or one of two adjectives 있다 (itda, “existing”) and 없다 (eopda, “not existing”) to act like a determiner.
- 딸이 책을 읽는다. (Ttari chaegeul ingneunda., “My daughter reads a book.”) → 딸이 읽는 책 (ttari ingneun chaek, “the book my daughter reads”)
- 내가 이곳에 산다. (Naega igose sanda., “I live in this place.”) → 내가 사는 곳 (naega saneun got, “the place I live in”)
- 호랑이가 동물원에 있다. (Horang-iga dongmurwone itda., “A tiger is in a zoo.”) → 동물원에 있는 호랑이 (dongmurwone inneun horang-i, “a tiger which is in a zoo”)
- 우리는 그곳에 갈 수 없다. (Urineun geugose gal su eopda., “We can't go to the place.”) → 우리는 갈 수 없는 그곳 (urineun gal su eomneun geugot, “the place we can't go to”)
- E.g.이기다 (igida, “to win”) → 이기는 놈 (igineun nom, “the one who wins”)