In this chapter, I examine the metaphysical systems that Kant so sharply criticized, using Crusius’s approach as a case study. I argue that these systems leave no conceptual room for a robust notion of deceptive appearance. Instead, what might seem like deceptive appearance ultimately reduces to the limitations of human understanding, whose restricted scope leads to error. This is because the principles of logic, as rules of thought, and the very possibility of attaining certain knowledge, are grounded in the nature and authority of a perfect divine intellect. Consequently, in Crusius’s view, error arises not from an appearance of truth, but from a misplaced sense of indubitability. More broadly, my aim is to shed light on the challenges posed by Kant’s attempt to abandon theologically grounded metaphysics—an endeavor that necessitated the emergence of new conceptual space, now occupied by notions such as appearance and negativity, which were previously reducible within earlier systems.