-어

Etymology 1
From, from , 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.

Suffix

 * 1) and, by;
 * 2) since, because;
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * 1) and, by;
 * 2) since, because;
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * 1) and, by;
 * 2) since, because;
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * 1) since, because;
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * 1) since, because;
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]
 * [[File:소년이 벽에 페인트를 칠하고 있어요.ogg]]

Usage notes

 * The verb or adjective to which attaches cannot take tense or aspect markers such as  or ; these must occur at the main verb.
 * It does not normally occur after a verb negated with, though it does occur with one negated by.


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


 * Most stems whose final vowel is a yang vowel take the form. Other stems take . Note that stems ending in, if not elided as a contraction, take ; hence the infinitive of  is.
 * Multisyllabic stems with irregular conjugation of take, even if the final vowel is a yang vowel. Hence the infinitive of  is.
 * Younger speakers often use for verb stems which have  followed by a consonant. For instance, they may use  as the infinitive of  rather than traditional . This is considered prescriptively incorrect.


 * The infinitive is elided before a stem ending in or . The exception is the extremely common verb, whose infinitive is the irregular  or , with the former being formal.
 * The infinitive elides a stem ending in, so that the infinitive of is.
 * In certain verbs, younger speakers generally front to, realized as . This is most common for , whose infinitive tends to be  for young South Koreans. This is also considered prescriptively incorrect.
 * is possible, but rare, after the copula and ; the common equivalents are  for the connective suffix and  for the sentence-final suffix.

Etymology 2
Sino-Korean suffix; see the main entry.