The basis of modern idealism is Kant’s doctrine of the Transcendental Ego of Apperception… Kant abstracted and depersonalized it, and made it the most universal of all his categories.
James traces the philosophical genealogy of modern idealism from Kant’s Transcendental Ego through its conversion by post-Kantian successors into a world-soul, and interrogates whether this tradition can supply faith with a firmer warrant than theology.
, The Varieties of Religious Experience Amazon, 1902thesis