Bertrand Russell

Russell, with Whitehead, tried in Principia Mathematica (1910–1913) to derive mathematics from logic, and his theory of descriptions and logical atomism made him a founder of analytic philosophy. The Problems of Philosophy (1912) defended a realism about universals and a correspondence theory of truth against pragmatism; in religion he was an agnostic who found every proof of God wanting, called the doctrine of hell cruel, and in “A Free Man's Worship” (1903) built a stoic ethic on the ruins of a purposeless cosmos. He went to prison as a pacifist in 1918, supported the war against Hitler, led the campaign against nuclear weapons, and wrote Marriage and Morals (1929), A History of Western Philosophy (1945) and the Nobel-winning essays that made him the century's best-known skeptic.

Why he matters: The Russell–Copleston debate is still the clearest short exchange between the Thomist arguments and analytic doubt, and Copleston's History of Philosophy was written partly to correct Russell's. “Why I Am Not a Christian” set the terms of popular unbelief for two generations, and the questions it presses (the first cause, the moral argument, hell, the character of Christ) are exactly those apologetics has to answer.