休謨的道德學是其人學思想的重要內容之一，國內外學者以往都立足於人的能力的知─情─意之區分，將之視為與知識論和心理學相對應的部分，從而導致了某些嚴重誤解，並忽略了對作為《人性論》「論道德」之改寫的《道德原則研究》作應有的研究。本文通過對比研究這兩書，認為，休謨否定意志自由，突破了人的能力的傳統劃分模式，其道德學乃直接屬於心理學，並以此為基礎，比較和分析了這兩書的思路和觀點，指出了後書對前書的許多重要的發展，揭示出了後書中深刻隱藏力圖將道學系統化的旨趣和線索。

Hume’s doctrine of morals is an integral part of his science of man. Both local and foreign scholars used to see it as the corresponding part between epistemology and psychology, which caused some serious misunderstanding and ignored the proper study of An Enquiry Concerning the Principles of Morals, which is the re-write of “Of Morals” in A Treatise of Human Nature. Via a comparative study of the two books, this paper contends that Hume denied the freedom of will and broke the traditional categorization of human capabilities. His doctrine of morals is a part of psychology. Based on such a thesis, this paper compares and analyzes the thoughts and views of the two books; it also points out many important developments of A Treatise of Human Nature in An Enquiry Concerning the Principles of Morals and shows the topics and clues in the latter book about how Hume strove to systemize his doctrine of morals.