In Christian Delacampagne reviews the discipline's divergent and dramatic course and shows that its greatest figures, even the most unworldly among them, were deeply affected by events of their time. From Ludwig Wittgenstein, whose famous Tractatus was actually composed in the trenches during World War I, to Edmund Husserl and Martin Heidegger—one who found himself barred from public life with Hitler's coming to power, the other a member of the Nazi party who later refused to repudiate German war crimes. From Bertrand Russell, whose lifelong pacifism led him to turn from logic and mathematics to social and moral questions, and Jean-Paul Sartre, who made philosophy an occasion for direct and personal political engagement, to Rudolf Carnap, a committed socialist, and Karl Popper, a resolute opponent of Communism. From the Vienna Circle and the Frankfurt School to the contemporary work of philosophers as variously minded as Jacques Derrida, Jürgen Habermas, and Hilary Putnam. The thinking of these philosophers, and scores of others, cannot be understood without being placed in the context of the times in which they lived.