Lo Ch'in-shun, who inherited from Chu Hsi his theory of human nature, was a prominent scholar at the middle of the Ming Dynasty. In his well-known book, Knowledge Painfully Acquired, he criticized Ch'an and regarded the theories of Lu Hsiang-shan, Ch'en Pai-sha and Wang Yang-ming as Ch'an. In Lo's book, “Ch'an” was usually used to indicate a way of thinking. As a result, Lo's criticism of Ch'an, in fact, included Lu, Ch'en and Wang. To some extent, Lo's criticism on Ch'an's theory of mind reflected the different ways of understanding mind in Confucianism at that time. Lo believed that the Ch'eng-Chu theory of human nature completely corresponded to the teachings of Confucius and Mencius, and insisted that the sensible function of mind should not be considered as its substance. The reason Lo criticized Ch'an so sharply was that he hoped to ensure the purity of Confucianism, especially with respect to the theory of human nature. As a result, as indicated above, Lu, Ch'en and Wang were not regarded as legitimate Confucians. In short, though the validity of Lo's criticism perhaps still remained questionable, yet at the time when Ch'en's and Wang's thought prevailed, his achievement showed the special significance of the Ch'eng-Chu theory. From the historical point of view, Lo's criticism of Ch'an also played an important role at the middle of the Ming Dynasty.