This essay tries to lay the transcendental foundations to a notion of “pure evil”, pure in the Kantian sense of the term, which means to find the necessary conditions for the concept and establish which criteria must be in place for such a concept to be justified. This essay tries to show the importance of thinking evil on its own terms instead as a secondary concept derived from ”the Good”. The prevailing philosophical stance from Platon until Kant has been to treat evil as either privation or unreason; this paper instead seeks to formulate a substantive notion of evil as pure evil, showing how it can be thought in its own right as an independent and self-sufficient concept. From a Kantian perspective it is only practical reason that can ground a moral action or maxim as free and self-determined, therefore a true concept of evil is only possible at level of the moral law i.e. the source of reason itself. Hence this paper argues that pure evil is intimately linked to the functioning of pure reason itself. In contrast to the traditional thinking regarding the issue of evil, I argue that reason is the sole source of pure evil and that no other factors such as pathology, affect or bad faith can account for events or actions that demonstrates the characteristics of pure evil. With help from the groundbreaking work of Kant, Arendt, Lacan and Sade I hope to point towards a new understanding of the concept of evil as a product of reason itself. Hopefully this work manages to show how and why such a perspective is needed and makes clear what we might gain from such an analysis.