Published in the thirties, Feng You-lan’s History of Chinese Philosophy systematically introduced neo-realism to explain Cheng Yi’s and Zhu Xi’s thoughts—the universe of li, the relationship between li and qi, the relationship between mind and nature, the acquirement of knowledge through the study of phenomena, and taichi—while refereeing to the distinctions between Zhu and Lu (Lu Xiang-shan) along with the differences between Zhu and Wang (Wang Yang-ming). Illustrating Zhu Xi’s philosophy with neo-realism, Feng argued that Zhu Xi’s conception of li was metaphysical and transcendental, while mind was the most sensitive perception, faculty, and entity. Zhu Xi’s distinction between li and mind became a strong dogma. Actually, Zhu Xi’s thoughts were quite complicated. What he meant by “mind” was not only the mind of cognition or a function or attribute of perception, gbut also the essential mind and the mind of morality and justice. Nature as li is equivalent to the mind as li; according to Lu Xiang-shan, what differentiates them was the distinction between formality and practice. Zhu Xi and Lu Xiang-shan, though different in their cosmologies and in the hierarchies of li and qi, had matching ideas about the origin of morality. Zhu Xi believed in the will of nature; his thoughts were under the powerful influence of Buddhism and distinct from realism or neo-realism, which Feng simply ignored. Therefore we can’t overlook the fact that Feng’s analyses of the distinction between Zhu and Lu along with the differences between Zhu and Wang must have been partial. Feng proposed his ideas in 1930s, but in the new edition published in 1980s, he still asserted the same claims. Thus with the discussion about these questions, this article still has its significance.