Kant's critique of rational psychology is a thought experiment that targets no individual or school, but rather the natural tendency of human reason to “hypostatize” the highest intellectual condition of all cognition (the pure ‘I think’) as though it were itself a cognition of the ‘I.’ To do so is to violate the very anti-circularity stricture also at work in Kant's better-known transcendental critiques of Locke and Hume. Along with a new type of circularity (level circularity), this article proposes a conception of transcendental arguments different from that of most contemporary debates regarding empiricism, naturalism, and Cartesian foundationalism.