The Story of Philosophy: The Lives and Opinions of the Greater Philosophers

Kant’s philosophy dominated the thought of the 19th century, and Durant admits he towers above the 19th-century thinkers he will later cover. The transition from Voltaire to Kant is one “from theoretical reason without religious faith, to religious faith without theoretical reason” (277). The animating conviction of the Enlightenment was in the power of human reason to transform nature, both in terms of physical reality and human society. The first sign of dissent was the question of whether it was possible for reason to triumph over superstition and other irrational forces, especially once philosophers like John Locke and David Hume developed theories of psychology which highlighted the inherent limits of human perception.

Hume’s skepticism regarding the inability of human beings to detect the real laws of the universe threatened science no less than religion. Rousseau took this even further by arguing that reason-driven material progress had ruined mankind’s primordial state, where they lived simple and happy lives according to instinct. Rousseau argued that even education, which the Enlightenment had held up as the key to humanity’s liberation, “does not make a man good, it only makes him clever—usually for mischief” (284). Kant’s mission was to “save science from skepticism” (285) and to place it on sturdier foundations than the Enlightenment had left it.

Born in Prussia in 1724, Kant grew up in a strictly religious household during the reign of Frederick the Great, an enthusiastic supporter of philosophy (he had provided a home for Voltaire). He was a professor of logic and metaphysics in his native Königsberg, with many of his early writings focusing on natural phenomena. Known for his daily walks through the neighborhood, he was 57 when he produced his first great work, The Critique of Pure Reason. The term “critique” means a “critical analysis” (289) rather than a criticism, and it challenges Locke and Hume’s contention that all knowledge is processed through the senses.

Mathematics, for example, contains absolute truths that do not depend upon perception or experience at all—two plus two simply is four. Through “transcendental philosophy” (291), a person can access the logical propositions that lie beyond the senses, just as one learns the nature of what they see, hear, or taste beyond what that sensation alone conveys. The senses are ultimately subordinate to mental processes of categorization, informing concepts such as space and time that do not cease to be real for not being subject to direct perception. The skeptics who would limit human consciousness to the senses have grossly underestimated the power of the mind to organize the aggregate knowledge of the senses into something the senses alone could never have understood. Physics points the way to metaphysics.

Kantian “Idealism” thus affirms that the “thing-in-itself” (297)—the purest representation of an object—does in fact exist, and can be grasped by the human mind, however imperfectly. Informing this ultimate reality is a “necessary being” (299) akin to God, although here also it lies beyond perception and even reason. In Kant’s next book, The Critique of Practical Reason, he sought to base religion on morality alone. This moral law, which derives from duty rather than reason, postulates that every human being must treat every other human being as an end unto themselves, and not a means to some other end. Sensibility is enough for a person to know that no social life is possible without this principle, and that social life would achieve its best form if everyone obeyed this principle all the time. To base such a principle on morality, rather than science or reason, is to affirm human freedom and the ability to choose their path rather than searching for dictates of nature. This freedom in turn serves as proof of the existence of God, a supreme moral will that does not and need not make itself manifest to the senses.

Kant also wrote a book criticizing the manipulation of the church for political ends, a controversial move in a Prussia which branded itself as the center of Lutheranism. Kant agreed to cease speaking on religious matters until the end of his life, yet he had one more controversy up his sleeve: a brief essay on the achievement of perpetual peace, which among other things called for the abolition of standing armies and the disavowal of a prince’s personal sovereignty over a parcel of land. He called for every state to adopt a “republican constitution” (310), at the same moment that the ostensibly democratic armies of the French Revolution were waging war against Europe’s monarchies, including Prussia. He died in 1804, at the age of 79, just as the French Republic was rebranded as an Empire under Napoleon I.

Among the many philosophers who followed in Kant’s footsteps, the most significant was Georg W. F. Hegel, who was a student at Jena when Napoleon scored his crushing victory over the Prussian army near the town. This formative event led Hegel to think of history itself as a dialectic: a clash of opposites that must produce a final synthesis. The human mind is charged with detecting these vast historical forces, to order social life accordingly, while religion preaches belief in an ultimate resolution. While Hegel inspired many revolutionaries (including Marx) with his belief in grand historical change upending what one era used to regard as the nature of things, Hegel himself was a conservative who regarded the state as the only proper custodian of historical evolution. The clash between these Hegelian factions would have a massive impact on philosophy and the politics of Europe in the second half of the 20th century.