 Jaspers’s metaphysical reconstruction of Kantian idealism has been denounced by other philosophers, most notably those in the broad milieu of the Frankfurt School, as a stage in a wider course of cognitive degeneration, which falsely translates absolute metaphysical contents into moments of human inner experience. Despite this, there are good grounds for arguing that Jaspers’s metaphysics is an important critique of the fully autonomist accounts of rationality proposed by neo-Kantianism, and it even coincides with the critiques of Kantian formalism which underpinned the philosophies widely associated with the Frankfurt School. Jaspers intuited that Kantian transcendentalism suppressed a deep-lying impulse for transcendence, and this aspect of Kant’s thought was badly neglected by interpreters who saw Kant’s philosophy as a doctrine of pure immanence or autonomy. Adorno’s later argument that Kant’s transcendental idealism always contains a lament over the closure of reason against transcendence was thus anticipated by Jaspers, albeit in subjectivist terms, and Jaspers and Adorno—for all their political differences—can be placed close together as thinkers who endeavoured to revitalize the metaphysical traces in idealism. In any case, Jaspers’s insistence, contra Kant and the neo-Kantians, that reason itself is not the sole source of knowledge, and that the task of reason is not proscriptively to circumscribe the sphere of its validity against transcendence, but to overcome its cognitive limits and to envision contents which cannot be generated by its own autonomous functions, deserves to be rehabilitated as an abidingly significant contribution to modern debates on metaphysics and epistemology.