Karl Jaspers' concept of philosophical faith is a notion he developed in the latter part of his career, and it has been most carefully expressed in the work of Leonard H. Ehrlich. Jaspers struggled with the perennial dichotomy between reason and faith, and, in the face of modern perils, provided a rationale, and—more importantly—an example, of how one might live both. He does so with a sympathetic critique of science, and with an intuitive awareness of both the power of reason and the demands of emotion. Jaspers tried to combine Kant, Kierkegaard, and science as he developed his own belief system about existence.