-어

• (SK Standard/Seoul) IPA^(key): [ʌ̹]
• Phonetic hangul: [어]

From Middle Korean 어〮 (Yale: -é), from Old Korean 良 (*-a), the vowel shift presumably informed by vowel harmony. In Old and Middle Korean, the suffix was solely a connective one and could not be used to end a sentence.

Modern sentence-final usage emerged at some point in Early Modern Korean. Indisputable examples of the infinitive serving as an informal imperative, one given below, are found by the eighteenth century. This innovation was probably extended from a practice in which the auxiliary or other subsequent verb was omitted to be determined by context in colloquial speech, transforming the infinitive into a sentence-ending suffix.[1][2]

어 • (-eo)

1. The "infinitive" suffix, connecting verbs and adjectives.
   1. Joins the main verb or adjective to its auxiliary.

      해는 저물어 간다. ― Hae-neun jeomur-eo ganda. ― The sun is setting.

      저거 한 번 먹어 봐. ― Jeo-geo han beon meog-eo bwa. ― Have a taste of that.

      그는 죽어 있다. ― Geu-neun jug-eo itda. ― He is dead.

      날이 더워진다. ― Nari deow-o-jinda ― It's getting hot.

   2. and, by; expresses a sequence of actions made by the same subject. There is a nuance that the first action is impacting or enabling the second; compare 고 (-go), which lacks this nuance.

      Synonym: 어서 (-eoseo)

      옷을 벗어 침대에 던졌다. ― Os-eul beos-eo chimdae-e deonjyeotda. ― I took off my clothes and threw them on the bed.

      의자에 앉아 글을 쓸 것이다. ― Uija-e anj-a geur-eul sseul geosida. ― I will sit on a chair and write.

      종이를 접어 학을 만들었다. ― Jong'i-reul jeob-eo hag-eul mandeureotda. ― I made cranes by folding paper.

   3. since, because; expresses causation.

      Synonyms: 어서 (-eoseo), 니까 (-nikka)

      꽃이 피어 기분이 좋다. ― Kkoch-i pi-eo gibun-i jota. ― I feel happy since the flowers bloomed.

2. In the "intimate" speech level used between friends, by superiors to inferiors, etc., a general-purpose sentence-ending suffix attached to verbs and adjectives:
   1. Marks the declarative or indicative mood.

      나 점심 먹고 있어. ― Na jeomsim meokgo iss-eo. ― I'm having lunch.

   2. Marks the interrogative mood.

      너는 점심 먹었어? ― Neo-neun jeomsim meogeoss-eo? ― Did you have lunch?

   3. Marks the imperative mood.

      얼른 점심 먹어. ― Eolleun jeomsim meog-eo. ― Go have lunch soon.

      • 1728, 珍(진)本(본)靑(청)丘(구)永(영)言(언) (Jinbon Cheongguyeong'eon) [Songs from the Green Hills]:

        日(일)中(듕)三(삼)足(죡)烏(오)야 가지 말고 내 말 드러

        Ildyung samjyogo-ya gaji malgo nae mal deur-eo

        Three-legged Crow inside the sun, don't go; listen to what I have to say.

   4. (uncommon) Marks the hortative mood.

      Synonym: (more common) 자 (-ja)

(connective suffix):

• The verb or adjective to which 어 (-eo) attaches cannot take tense or aspect markers such as 었 (-eot-) or 겠 (-get-); these must occur at the main verb.
• It does not normally occur after a verb negated with 안 (an, “not”), though it does occur with one negated by 못 (mot, “cannot”).

(sentence-final suffix):

• The distinct moods are distinguished by intonation, e.g. a rising intonation for a question.

(vowel harmony)

• Most stems whose final vowel is a yang vowel take the 아 (-a) form. Other stems take 어 (-eo). Note that stems ending in ㅐ (ae), if not elided as a contraction, take 어 (-eo); hence the infinitive of 새다 (saeda, “to leak”) is 새어 (saeeo).
• Multisyllabic stems with irregular conjugation of ㅂ (b) take 어 (-eo), even if the final vowel is a yang vowel. Hence the infinitive of 사납다 (sanapda, “to be fierce”) is 사나워 (sanawo).
• Younger speakers often use 어 (-eo) for verb stems which have ㅏ (a) followed by a consonant. For instance, they may use 막어 (mag-eo) as the infinitive of 막다 (makda, “to block”) rather than traditional 막아 (mag-a). This is considered prescriptively incorrect.

(contractions and allomorphy)

• The infinitive is elided before a stem ending in ㅏ (a) or ㅓ (eo). The exception is the extremely common verb 하다 (hada), whose infinitive is the irregular 하여 (hayeo) or 해 (hae), with the former being formal.
• The infinitive elides a stem ending in ㅡ (eu), so that the infinitive of 쓰다 (sseuda) is 써 (sseo).
• In certain verbs, younger speakers generally front 아 (-a) to 애 (-ae), realized as /e/. This is most common for 같다 (gatda, “to be the same”), whose infinitive tends to be 같애 (gat-ae) for young South Koreans. This is also considered prescriptively incorrect.
• 어 (-eo) is possible, but rare, after the copula 이다 (-ida, “to be”) and 아니다 (anida, “to not be”); the common equivalents are 라 (-ra) for the connective suffix and 야 (-ya) for the sentence-final suffix.

Sino-Korean suffix; see the main entry.

어 • (-eo)

1. See the entry at 어(語) (eo, “language”).