Karl Popper

Karl Raimund Popper was born in Vienna in 1902. As a teenager he briefly considered himself a communist in 1919, but turned away from Marxism after a deadly street clash and later abandoned socialism as incompatible with individual liberty. Best known for his philosophy of science and the idea of falsifiability, he wrote The Open Society and Its Enemies (1945) while teaching in New Zealand during the Second World War. He moved to the London School of Economics in 1946, took British citizenship, was knighted in 1965 and died in 1994.

The Open Society and Its Enemies became one of the best known defenses of liberal democracy of the 20th century, and its attack on Plato, Hegel and Marx as forerunners of closed societies shaped Cold War liberalism. His paradox of tolerance is still widely cited in debates about free speech and extremism. Admirers on both the center left and center right claim him, from social democrats to market liberals influenced by his friend Friedrich Hayek. Critics argue that his readings of Plato and Hegel were unfair or inaccurate, that piecemeal engineering offers little guidance on larger questions of justice, and that his use of the paradox of tolerance is easily stretched to justify censorship.