對休謨來說，人具有理性能辨別真假之事實，此雖不容否定，但「道德」只源自於「情感」（passion）。善惡是基於與激情有關的道德情感而來，道德判定奠定在快樂與否之情感，人之理性應該聽從於情感。儘管理性推理對於修正情感有其重要性，但理性終究由情感所推動，亦即，理性雖能提示何種行為具有最大效益，卻無法喚起快樂與痛苦的感受，從理性之「真」即「是」，不必然得出道德之「善」與「應該」，從事實領域的實然到價值領域的應然，兩者橫亙一條鴻溝，此不會因理性而消弭。因為驅使我們行動的力量是情感，理性不能對情感作任何層面的批判。道德的形成，源自於主體之情感，倘若少了情感之指引，理性活動之目的亦不復存在。因著對情感的關注，休謨對人之探究，細膩的深入情感範疇，由心理活動及機制來觀察，為人性的多元面貌，歸納普遍而基本的傾向與原則，也為道德價值之實現，開闢了廣闊的情感之路。本文擬透過休謨學說，探討在道德判斷的進程上，理性與情感之彼此消長，所呈現的微妙關係，以進一步闡析道德、情感和理性之關聯。

The Scottish philosopher and historian David Hume (1711-1776) believed that human beings possess the attribute of reason, which enables them to distinguish between truth and falsehood. More specifically, he asserted that morality originates only from passion, that good and evil emanate from perception, and that decisions concerning the morality or immorality of an action depend on whether the agent senses a positive (or happy) passion. Therefore, Hume insisted that human reason ought to be submitted to passion. Although the existing critical literature contains much discussion of Hume's concept of the complementarity between reason and passion, little attention has been directed toward his theory of moral sentimentalism. Hence, my descriptive-analytical study of selected philosophical writings by Hume focuses on this aspect of his thought.
According to Hume, although judgment or inference by reason plays a significant role in correcting passion, reason is ultimately powered by passion. Hence, reason does not possess the ability to allow feelings of happiness and pain, although it may be capable of reminding a person of
the best benefit of an action. If it is the nature of reason to always be required to pursue “truth” and“righteousness,” such pursuit does not always result in “being good” and “ought to be” propositions Hume perceived a large gap between “it is” and “it should be” which cannot be bridged by merely“being reasonable.” If passion is the power that drives human actions, then reason gains no ground in the criticism of passion in any of its aspects. Furthermore, any activity powered by reason would
become purposeless if no passion is involved. By observing human mental and psychological activities, Hume inductively proposed a general principle for realizing the value of morality and broadening a way to enjoy passion.