Kant, Immanuel - Critique of Pure Reason - Heuristics and the systems of the universes
Type of spiritual experience
A description of the experience
Critique of Pure Reason – Transcendental Doctrine of Elements: Transcendental Logic
Many forces of Nature, which manifest their existence by certain effects, remain perfectly inscrutable to us, because we cannot follow them up far enough by observation.
The transcendental object, which forms the foundation of all appearances and with it the ground of our sensibility, having these rather than any other supreme conditions, is and always will be inscrutable.