-요

Etymology 1
First widely attested in late eighteenth- and nineteenth-century novels intended for popular consumption. Stems from a contraction of, from +. The suffix itself goes back to, though the exact derivation is unclear, and ultimately to. Compare,. Compare also which has the same function.

Usage notes

 * is the traditional, prescriptive pronunciation; is a common alternative pronunciation by young South Koreans.
 * For the copula and, the form is irregularly.
 * For the honorific, the form is irregularly.
 * In the polite style, there is no explicit marker to distinguish between indicative, interrogative, imperative, and hortative moods. The distinction is made only by pitch in speech (e.g. rising pitch for questions), and by punctuation in writing.
 * For the second definition, it was considered prescriptively incorrect to add the allomorphic form to words ending in a consonant, even though that it was common in usage; however, this was updated on February 3, 2021 to where  may be used after words ending in a consonant.  Nonetheless, it is still prescriptively correct to add -요 after words ending in both vowels and consonants.

Etymology 2
See. The semivowel is introduced to break hiatus.