  His biography (in both of the two Standard Histories of the Tang Dynasty, trans. Sivin 1968, 81–144) emphasizes his interests in philosophy, noting his particular study of the Yi jing, Daode jing, works concerned with yin-yang theory, and shu shu numerical calculations. His work reflected these interests in yin-yang and wuxing theory and macrocosm-microcosm correspondences between the body and cosmos.  He is also the first Chinese physician to write extensively on medical ethics.