Kant famously claims that pure reason is subject to a transcendental illusion in which the subjective validity and the regulative use of a principle of reason are conflated with its objective validity and constitutive use. His doctrine of transcendental illusion is puzzling for he insists that this illusion is natural as well as necessary. The two dominant interpretation strategies cannot make sense of this puzzle because they turn out to be either too strong or too weak: they either struggle to (...) account for the legitimate, regulative use of the transcendental principle of reason or fall short of explaining the necessity of the transcendental illusion. In contrast, I shall argue that it is possible to account for the fact that the transcendental illusion is natural and necessary because it has its source in the discursive form of our human understanding, and that this illusion can nevertheless be known to be illusory because our discursive nature can be recognised as a merely particular form of understanding by comparing it with a possible, intuitive form of understanding in an act of critical self-reflection. (shrink)