The Sasang typology (Hangul: 사상의학. Hanja: 四象醫學) is a traditional Korean medical typology, which was systematically theorized by Lee, Jae-ma and his book, "The Principal of Life Preservation in Oriental Medicine" (東醫壽世保元, 동의수세보원) in 1894. This medical typology divides people in four types based on their biopsychosocial traits; Tae-Yang(Greater Yang), So-Yang(Lesser Yang), Tae-Eum(Greater Yin) and So-Eum(Lesser Yin) types.