But the philosophical trend was already moving in an opposite direction. By the time of Immanuel Kant (late eighteenth century), reason had fallen out of favor and Plato's ideas were enshrined in a new form. The ultimate practical consequences of Kant's philosophy appeared in the twentieth century, in totalitarian Nazi and Communist regimes as well as increasing statism in other countries, in a widespread popular distrust of science and technology, in a repudiation of the liberal ideas of the Enlightenment—and in a widespread rebellion against reason, material progress, and even the human species, a rebellion which has now spread beyond the ivory tower to pervade popular culture.

Human progress depends on our use of reason to apprehend objective reality. Although reason and reality may be "common sense" concepts, they evidently involve some subtleties that have eluded many philosophers. In Section 1 we therefore look more closely at these concepts.