After the fall of the Han dynasty (202 B.C.-220 A.O.), Confucian thought did not become influential again until the end of the T'ang dynasty (618-907) and the beginning of the Sung dynasty (960-1279). Its resurgence in the Sung was accompanied by, if not completely driven by a newly conceived system of metaphysics. Although Sung Confucians honored and frequently referred to Confucius and Mencius, metaphysics was their central concern. Lo Ch'in-shun, a Confucian in the Ming dynasty (1368-1644), saw inconsistencies between traditional Confucian thought and the thought of Sung Confucians. He viewed himself as orthodox and thought it was his duty as a Confucian to fight heterodox thought, and to resolve the inconsistencies within Confucian thought and return it to unity. His philosophy was a product of his approach to these duties and is the subject of this study. Lo's efforts to return to unity can be seen in his work Knowledge Painfully Acquired (K'un-chih chi). After discussing Lo's social context, the following four questions provide a framework to examine his philosophy: !)Given that there is only one Way, what is the Way that runs through the realms of heaven-and-earth and man? 2)Of what does human nature consist? 3)How is it that Mencius said that human nature is good and yet there is evil in the world? and 4)What is the mind(hsin), and how does a man cultivate it to enable him to become a sage? Comparing Lo's views with Confucian thinkers who preceded him provides answers to the questions, and assists in defining Lo's thought. These answers and comparisons show the significant shifts away from Sung Confucian thought contained in Lo's philosophy, but they also show his desire to return to unity. He strove to return to unity not only for himself, but more importantly, for the ultimate good of Confucianism and society.