本文試圖探討唐君毅《生命存在與心靈境界》一書中關於「惡」的論點。首先，我們發現唐君毅晚期對「惡」的說明，是圍繞著「自我封閉」這一概念來展開的。其次，唐君毅認為：如果人習慣於某一種思考與行動模式，他自然會傾向維持同一種模式；這種傾向在道德上是中性的。但是，如果這種傾向成為行動者實踐道德的阻礙，我們才可將此傾向稱為「封閉」。再者，透過對「自我封閉」的討論，我們發現在道德情境中，主體若拒絕面對當下的具體情境，則道德動力可能不會在他身上發揮作用。最終，我們認為人亦可能藉由「手段／目的式」的思考，來拒絕道德的要求。在此情況下，主體僅依據原本預設的目的而行動，將道德價值與事物之內在價值，視作達到此預設目的的手段。

This paper attempts to analyze Tang Chun-I's theory of “evil” in Life Existence and the States of the Mind. Firstly, I discover that “self-enclosure” is the core concept to understand the cause of evil in Tang Chun-I's late philosophy. Secondly, Tang Chun-I argues that if a person is accustomed to a certain pattern of thinking and acting, he will naturally tend to maintain the same pattern. This tendency is morally neutral. However, we only call this tendency “self-enclosure” if it prevents the agent from doing moral practice. Thirdly, through the discussion of “self-enclosure,” I find that moral motivation may not move him to act in moral situations if the agent refuses to face the concrete situation of the moment. Finally, I argue that people may also reject moral commands through “means-and-end reasoning.” In this case, the agent acts only because of the originally presupposed purpose and regards the moral value and the intrinsic value as the means to achieve his presupposed purpose.