Skepticism

The Scottish philosopher David Hume responded to the skeptical challenge in ways that made him central to philosophical discussion up to the twenty-first century. His Treatise of Human Nature (1739–1740) argued for skepticism about both facts and reason. His critique of causation reduces it to little more than a habit based on constant conjunction. And yet in typical skeptical fashion he showed people how to live with skepticism on the basis of probabilities and custom.

The Prussian philosopher Immanuel Kant (1724–1804) was called the "all-destroyer" because of his rejection of many other dogmatic philosophies. He adopted skeptical Greek vocabulary when he argued that one could have no knowledge of the noumena—the reality behind appearances—but only of the phenomena. He saved free will and morality from scientific determinism by reducing human knowledge of them to faith rather than knowledge. Other skeptics writing in German in his time included Salomon Maimon and Gottlob Ernst "Aenesidemus" Schulze. When Carl Friedrich Stäudlin's Geschichte und Geist des Skepticismus (History and spirit of skepticism) of 1794 showed Hume facing Kant on the title page, it was clear that these two thinkers had posed the skeptical challenge for the age. Stäudlin denounced unphilosophical skepticism even as he demonstrated that philosophical skepticism could not be refuted.

In the nineteenth century, the German philosopher Georg Wilhelm Friedrich Hegel (1770–1831) believed that ancient skepticism was of great philosophical importance while modern skepticism had little merit. The Danish philosopher Søren Kierkegaard (1813–1855) incorporated skepticism into his theology. One of the prize questions of the Royal Academy in Paris concerned the failure of all answers to skepticism. The Swiss philologist and philosopher Friedrich Nietzsche (1844–1900) made skepticism a significant part of his philosophy. Karl Marx (1818–1883) and Sigmund Freud (1856–1939) followed in a long-established tradition of using various skepticisms against their opponents but then claiming dogmatic truth for their own positions. Their practice reflected the important distinction between partial skepticism (e.g., of claims in one domain, such as religion, or the claims of an opposing political party) and global or universal skepticism, which suspends judgment about everything.

In the twentieth century Jean Grenier (1898–1971) translated Sextus into French. His student Albert Camus (1913–1960) drew on skepticism in his work as one of the founders of existentialism. In Germany, Odo Marquard (1928–) led a self-consciously skeptical charge against the dogmatisms of thinkers such as Jürgen Habermas. Also in the same century, some analytical philosophers developed their own ahistorical definitions of skepticism and debated them with little if any reference to the traditions of skepticism. Revisionists such as Stephen Toulmin (1922–) then interpreted one of their heroes, Ludwig Wittgenstein (1889–1951), as following in the footsteps of the ancient skeptics.