FromMiddle Korean-어〮 (Yale:-é), fromOld Korean良(*-a), the vowel shift presumably informed byvowel 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]
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.
In the"intimate" speech level used between friends, by superiors to inferiors, etc., a general-purpose sentence-ending suffix attached to verbs and adjectives:
The verb or adjective to which어(-eo) attachescannot 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 with안(an,“not”), though it does occur with one negated by못(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 ayang vowel take the-아(-a) form. Other stems take어(-eo). Note that stems ending inㅐ(ae), if not elided as a contraction, take어(-eo); hence the infinitive of새다(saeda,“to leak”) is새어(saeeo).
Multisyllabic stems with irregular conjugation ofㅂ(b) take어(-eo), even if the final vowel is a yang vowel. Hence the infinitive of사납다(sanapda,“to be fierce”) is사나워(sanawo).
Younger speakers often use어(-eo) for verb stems which haveㅏ(a) followed by a consonant. For instance, they may use막어(mag-eo) as the infinitive of막다(makda,“to block”) rather than traditional막아(mag-a). This is considered prescriptively incorrect.
(contractions and allomorphy)
The infinitive is elided before a stem ending inㅏ(a) orㅓ(eo). The exception is the extremely common verb하다(hada), whose infinitive is the irregular하여(hayeo) or해(hae), with the former being formal.
The infinitive elides a stem ending inㅡ(eu), so that the infinitive of쓰다(sseuda) is써(sseo).
In certain verbs, younger speakers generallyfront-아(-a) to-애(-ae), realized as/e/. This is most common for같다(gatda,“to be the same”), whose infinitive tends to be같애(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”) and아니다(anida,“to not be”); the common equivalents are-라(-ra) for the connective suffix and-야(-ya) for the sentence-final suffix.
^고광모 [gogwangmo] (2001), “반말체의 등급과 반말체 어미의 발달에 대하여 [banmalche'ui deunggeupgwa banmalche eomiui baldare daehayeo,On the level of the intimate style and the development of intimate-style suffixes]”, inEoneohak, volume30, pages3—27
^장윤희 [jang'yunhui] (2012), “국어 종결어미의 통시적 변화와 쟁점 [gugeo jonggyeoreomiui tongsijeok byeonhwawa jaengjeom,A general survey of diachronic change of Korean sentence-terminating endings]”, inGugeosa yeon'gu, volume14, pages63—99
