I want to address a vexed question in this essay: does Kant really need a transcendental deduction to justify his claim “man is evil by nature”? Transcendental deductions, Kant is the first to admit it, are notoriously difficult. In the case of the Religion within the Boundaries of Mere Reason, whose transcendental argument (if there is one) must be assembled through careful detective work, the difficulty is clearly compounded. I take up the gauntlet here because much of the current debate on this question is fueled, I suspect, by an insufficient grasp of the systematic character of Kant's doctrine of radical evil. Triggered by Kant's own lack of expository clarity at crucial passages, interpreters have tended to conflate the different notions of an “evil disposition” (böse Gesinnung) and a “propensity to evil” (Hang zum Bösen). A reader of the acuity of Henry E. Allison, for instance, says:

But surely this cannot be Kant's considered view. For he cannot possibly mean that the individual's choice of Gesinnung is equivalent to the species's choice of propensity. Otherwise, our personal wrongdoing would be explicated (and exculpated) by sheer membership in humanity.

Contemporary debates in moral philosophy have primarily been focused on meta-ethical questions about the justification of morality, disregarding the ease with which perfectly justified norms are displaced by non-moral considerations. Given the scope, magnitude, and inventiveness of human wrongdoing, this philosophical trend seems utterly misguided. The challenge does not lie so much in how to justify morality, but in understanding how perfectly justified judgments are so easily disregarded by self-serving calculations.

Kant's doctrine of radical evil has much to tell us about this. Against the widespread tendency to explain evil in terms of the pernicious power of natural inclinations, Kant believed that evil represented “an invisible enemy, one who hides behind reason and hence [is] all the more dangerous” (R 6: 57). The enemy is invisible, for “no matter how far back we direct our attention to our moral state, we find that this state is no longer res integra” (R 6: 58n.). And it is exceptionally dangerous, for the corruption in question is self-imposed: “genuine evil consists in our will not to resist the inclinations when they invite transgression” (ibid.). Since this type of volition rests on a maxim, and maxim formation in Kant always takes place under the constraints of the categorical imperative, evil hides at the heart of practical reason: it is the deliberate attempt to subordinate what we ought to do in favor of what pleases us.