First-millennium Old Korean also featured the locative particle 中(*-kuy). The two particles were compounded as 良中(*-a-kuy) as early as the seventh century. The compounded form becomes predominant in the corpus after the eleventh century, after which 良 *-a in isolation is not encountered. The compounded form eventually fused into a single morpheme, becoming the Middle Korean locative particle 애 (Yale: -ay).
After the fourteenth century, Korean scribes occasionally reused the character 良 to write 애 (Yale: -ay). This is a feature of Middle Korean writing, not Old Korean.
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이승재 (Lee Seung-jae) (2000) , “Chaja pyogi jaryo-ui gyeokjosa yeon'gu [Study of case markers in the Chinese-based orthography [of Korean]]”, in Gugeo Gukmunhak, volume 127, pages 107–132
Hwang Seon-yeop (2006). "Godae gugeo-ui cheogyeok josa" 고대국어의 처격조사] ["The locative case markers of Old Korean"]. Hanmal Yeon'gu Hakhoe Jeon'guk Haksul Daehoe (conference). Seongnam, South Korea. pp. 35–48.
Nam Pung-hyun (2012) , “Old Korean”, in The Languages of Japan and Korea, Routledge, →ISBN, pages 41–72