Seo Gyeong-deok (Korean: 서경덕; Hanja: 徐敬德; 18 March 1489 – 13 August 1546[1]) was a Korean Neo-Confucianist philosopher during the Joseon period.
His philosophy studied materialism and phenomenology based on ancient taoist philosophy theories absorbed by neoconfucianism, like Yin and Yang and Ki.
He counted among his students the famed gisaeng Hwang Jini, for whom he wrote this sijo:
마음이 어린 후이니 하는 일이 다 어리다 만중운산(萬重雲山)에 어느 님 오리마는 지는 잎 부는 바람에 행여 귄가 하노라 My heart is young so I act young all the time.
Clouds hide this distant mountain: who would ever visit me here?