Why the Moral Law Must be Formal: Kiesewetter’s Case for Kant

Why the Moral Law Must be Formal: Kiesewetter’s Case for Kant

This paper examines Johann Gottfried Carl Christian Kiesewetter’sÜber den ersten Grundsatz der Moralphilosophie (1790/91) as a systematic defence and development of Kant’s formal principle of morality. I argue that Kiesewetter articulates a distinctive interpretation of the categorical imperative by identifying three essential marks of any genuine moral principle－universality, necessity, and primacy－and by showing that only Kant’s formal law satisfies all three. The paper first reconstructs Kiesewetter’s account of these criteria and his arguments for the apriority and formality of the moral law. It then analyzes his negative project: a comprehensive critique of rival‘material’principles, including those grounded in happiness, moral feeling, education and custom, perfection, and divine command. I show how Kiesewetter exposes the heteronomy and contingency implicit in each alternative. The third part discusses his replies to major objections against Kantian ethics, ranging from experiential and epistemic worries to concerns about motivation and competing goals. Finally, the paper considers Kiesewetter’s attempt to reconcile Kantian duty with Christian love in response to J. L. Ewald, arguing that practical love can be understood as reason-governed beneficence without reducing it to mere sentiment. Kiesewetter’s treatise thus offers an early and philosophically rich model for integrating formal Kantian ethics with broader existential and religious concerns.