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.^[2]

Seo was a great scholar of the day. He counted among his students the famed gisaeng Hwang Jini, for whom he wrote this sijo:

Other works:

• Hwadamjip (화담집; 花潭集) - collection of his writings
• Woniki (원이기; 原理氣) - About origin of Qi
• Igiseol (이기설; 理氣說) - about processing of Qi
• Taeheoseol (태허설; 太虛說) - About Mu of Qi
• Gwisin sasaengnon (귀신사생론; 鬼神死生論) - about spirit of soul and life and death.

• Hwang Jin-yi - Korean poet and artist
• Heo Gyun - Korean novelist, philosopher, and politician
• Yi Ji-ham (이지함) - Korean astrologer, diviner, and politician
• Heo Nanseolheon - Korean poet
• Han Baek-gyeom (한백겸) - Geographer and philosopher
• Park Sun (박순) - Philosopher and politician

• Father - Seo Ho-beon (서호번; 徐好蕃)
• Mother - Lady Han of the Boan Han clan (보안 한씨; 保安 韓氏)
• Sibling(s)
  • Younger brother - Seo Sung-deok (서숭덕; 徐崇德)
• Wives and their issue
  • Lady Yi of the Taein Yi clan (태안 이씨; 泰安 李氏); daughter Yi Gye-jong (이계종; ? – 7 January 1561)
    • Son - Seo Eung-ga (서응가; 徐應暇)
    • Son - Seo Eung-gi (서응기; 徐應麒)
    • Daughter - Lady Seo of the Dangseong Seo clan (당성 서씨)
  • Unnamed concubine
    • Son - Seo Eung-bong (서응봉; 徐應鳳)
    • Son - Seo Eung-gu (서응구; 徐應龜)