De Casu Diaboli

Anselm of Canterbury's De Casu Diaboli represents a pivotal exploration of divine justice and evil within the medieval philosophical framework, addressing the fundamental theological problem of how evil originated in a universe created by an omnipotent and perfectly good God. Written as a dialogue between a teacher and student, this work extends Anselm's systematic approach to rational theology, employing his characteristic method of faith seeking understanding to illuminate one of Christianity's most challenging doctrines.

The treatise confronts the paradox of angelic fall: how could beings created good by God, possessing perfect knowledge and dwelling in divine presence, choose evil? Anselm's solution hinges on his sophisticated analysis of free will and justice. He argues that the devil's sin originated not from any positive evil—which would implicate God as its creator—but from the absence of perseverance in righteousness. This privation theory of evil, while drawing on Augustinian foundations, receives distinctive treatment through Anselm's rigorous dialectical method.

Central to Anselm's argument is his distinction between two forms of will: the will for happiness and the will for justice. Angels, like rational creatures generally, possess both inclinations. The devil's fall resulted from prioritizing happiness over justice, desiring something beyond what God had granted—specifically, to be like God. This analysis allows Anselm to maintain divine innocence while preserving genuine creaturely freedom. God gave angels the capacity for justice and happiness but not the perseverance to maintain their original righteousness indefinitely without divine assistance.

The work's philosophical significance extends beyond its immediate theological context. Anselm's treatment of modal concepts—necessity, possibility, and contingency—in relation to free will anticipates later medieval debates about divine foreknowledge and human freedom. His insistence that the devil's choice was neither necessary nor impossible but genuinely free establishes important groundwork for subsequent discussions of libertarian freedom in Scholastic thought.

De Casu Diaboli demonstrates how rational analysis can illuminate revealed truths without diminishing their mystery. By showing that the origin of evil involves no logical contradiction with divine perfection, Anselm strengthens the coherence of classical theism against potential objections. The work exemplifies the Anselmian project of demonstrating Christianity's rational foundations, contributing to the broader medieval synthesis of faith and reason that would influence centuries of theological reflection on the problem of evil.