Human beings uniquely act with knowledge of their own mortality. What does that knowledge do to moral choice? Why do people create, sacrifice, preserve institutions, and pursue consequences they know they will never live to see? Why do some responses to mortality produce constructive legacies while others become destructive? And how can moral systems persist, fail, and correct themselves across generations of finite agents? DEFIANCE approaches these questions by distinguishing fear-driven avoidance of mortality from active resistance to its consequences. It introduces “Oblivion” as a broader category encompassing death, erasure, loss of identity, insignificance, and collapse of meaning, and “Defiance” as the opposing motivational response: action undertaken despite recognition that Oblivion cannot ultimately be defeated. What makes such Defiance morally constructive or destructive? How does an individual action become Legacy? What responsibilities do agents have toward consequences extending beyond their own lifetimes? DEFIANCE develops an account of Legacy as consequence extending beyond the individual and examines virtue and vice through constructive and destructive forms of Defiance. The analysis then moves from individuals to moral systems. How can a moral system preserve Moral capacity while remaining capable of change? How do such systems become corrupted, rigid, or self-defeating? What mechanisms allow them to identify and repair their own failures? And what happens when the interests of present Agency conflict with the Legacy being transmitted to future agents? Through these questions, DEFIANCE treats mortality not merely as a source of fear to be managed, but as a structural condition of moral life: finite agents know they will disappear, yet continue to create consequences, institutions, values, and obligations that outlive them.