Sun refused at least three official court positions offered to him: by the Emperor Wendi of the Sui Dynasty and by the Emperors Taizong and Gaozong of the Tang Dynasty. He preferred to provide treatment for ordinary people in the rural setting, though he accompanied Emperor Gaozong for a time. His medical orientation was described in an official history of the Tang Dynasty, as relayed by Paul Unschuld (3): "His biography describes him as an extraordinarily talented man, who devoted himself to the teachings of the Yi Jing [I-Ching], of Lao Zi [Lao-tzu; author of the Dao De Jing], and of the yin-yang philosophers, and he also took an interest in the magical calculation of numbers." His work emphasized the five elements and yin-yang systems of influences that are based on correspondences between features of the external environment and the internal structures and workings of the body. He is considered the first to have presented issues related to ethics of medical treatment, depicting the characteristics of a great physician and cautioning physicians about behavior that was inappropriate to their profession. He was especially concerned, as emphasized in Taoist philosophy, about physicians being influenced by a desire for rewards, including financial rewards, fame, or favors granted to them: they should not have these as their goal. Patients should be treated equally, regardless of rank, wealth, age, or beauty.