[This excerpt is from Chapter 2 of Explaining Postmodernism: Skepticism and Socialism from Rousseau to Foucault]
Kant’s skeptical conclusion
Immanuel Kant is the most significant thinker of the Counter-Enlightenment. His philosophy, more than any other thinker’s, buttressed the pre-modern worldview of faith and duty against the inroads of the Enlightenment; and his attack on Enlightenment reason more than anyone else’s opened the door to the nineteenth-century irrationalists and idealist metaphysicians. Kant’s innovations in philosophy were thus the beginning of the epistemological route to postmodernism.
Kant is sometimes considered to be an advocate of reason. Kant was in favor of science, it is argued. He emphasized the importance of rational consistency in ethics. He posited regulative principles of reason to guide our thinking, even our thinking about religion. And he resisted the ravings of Johann Hamann and the relativism of Johann Herder. Thus, the argument runs, Kant should be placed in the pantheon of Enlightenment greats. That is a mistake.
The fundamental question of reason is its relationship to reality. Is reason capable of knowing reality—or is it not? Is our rational faculty a cognitive function, taking its material from reality, understanding the significance of that material, and using that understanding to guide our actions in reality—or is it not? This is the question that divides philosophers into pro- and anti-reason camps, this is the question that divides the rational gnostics and the skeptics, and this was Kant’s question in his Critique of Pure Reason.
Kant was crystal clear about his answer. Reality—real, noumenal reality—is forever closed off to reason, and reason is limited to awareness and understanding of its own subjective products. Reason has “no other purpose than to prescribe its own formal rule for the extension of its empirical employment, and not any extension beyond all limits of empirical employment.” Limited to knowledge of phenomena that it has itself constructed according to its own design, reason cannot know anything outside itself. Contrary to the “dogmatists” who had for centuries held out hope for knowledge of reality itself, Kant concluded that “[t]he dogmatic solution is therefore not only uncertain, but impossible.”
Thus Kant, that great champion of reason, asserted that the most important fact about reason is that it is clueless about reality.
Part of Kant’s motivation was religious. He saw the beating that religion had taken at the hands of the Enlightenment thinkers, and he agreed strongly with them that religion cannot be justified by reason. So he realized that we need to decide which has priority—reason or religion. Kant firmly chose religion. This meant that reason had to be put in its proper, subordinate, place. And so, as he stated famously in the Second Preface to the first Critique, “I here therefore found it necessary to deny knowledge in order to make room for faith.” One purpose of the Critique, accordingly, was to limit severely the scope of reason. By closing noumenal reality off to reason, all rational arguments against the existence of God could be dismissed. If reason could be shown to be limited to the merely phenomenal realm, then the noumenal realm—the realm of religion—would be off limits to reason, and those arguing against religion could be told to be quiet and go away.
 E.g., Höffe 1994, 1.
 Kant 1781, A686/B714.
 Kant 1781, B512/A484.
 Kant 1781, Bxxx.
 Kant 1781, Bxxxi.
[This is an excerpt from Stephen Hicks’s Explaining Postmodernism: Skepticism and Socialism from Rousseau to Foucault (Scholargy Publishing, 2004, 2011). The full book is available in hardcover or e-book at Amazon.com. See also the Explaining Postmodernism page.]