Paul Karl Feyerabend was born in Vienna in 1924. He served in the German army’s Pioneer Corps during the second world war and in 1944 he received the Iron Cross. In 1946 he chose to study history and sociology at the University of Vienna’s Institut für Österreichische Geschichtsforschung, thinking that history, unlike physics, was concerned with real life. But he became dissatisfied with the study of history, and returned to theoretical physics. Together with a group of science students, Feyerabend infiltrated philosophy lectures and seminars. He later recalled that in all interventions he took the radical ‘positivist’ line that science is the basis of all knowledge; that it is empirical; and that non-empirical enterprises are either formal logic (which includes mathematics) or nonsense. This is the view associated with the Logical Positivists, a group of philosophers and scientists comprising the ‘Vienna Circle’, which flourished in Austria from the early 1920s. In 1948, Feyerabend met the philosopher Karl Popper, who was to be the largest single influence (first positive, then negative) on his work. In 1949 Feyerabend set up the Kraft Circle, a university philosophy club centred around Viktor Kraft, the last member of the Vienna Circle remaining in Vienna. The Kraft Circle’s main concern was the question of the existence of the external world, a question which positivists had traditionally rejected as being ‘metaphysical’. Modelled on the Vienna Circle, the Kraft Circle ‘set itself the task of considering philosophical problems in a non-metaphysical manner and with special reference to the findings of the sciences’. Feyerabend then studied the philosophy of quantum mechanics under Popper at the London School of Economics between 1952 and 1953. Having been convinced by Popper’s and Duhem’s critiques of inductivism (the positivist view that science proceeds via generalization from facts recorded in basic sentences), he came to consider Popper’s philosophy a real option and he applied falsificationism, the view that good science is distinguished by the theorist’s production of and determination to test highly testable theories, in his papers and lectures. Feyerabend returned to Vienna in the summer of 1953 as an assistant to Arthur Pap, who was trying to reinvigorate the doctrines of the Vienna Circle. From 1955 onwards he published many articles, mostly on philosophy of quantum mechanics and general philosophy of science. The early ones strongly reflected the influence of Popper, Kraft and Wittgenstein. Feyerabend attempted to combine falsificationism with the ‘contextual’ theory of meaning which he read into Wittgenstein’s Philosophical Investigations. Feyerabend emigrated to the USA in 1959, becoming Professor of Philosophy at the University of California, Berkeley, in 1962. No longer under the direct influence of Popper, he began to extend, and eventually to slough off, the falsificationist philosophy. A gradual but fundamental reorientation in his attitude towards philosophy of science saw him align himself increasingly with the outwardly historical approach of T. S. Kuhn, and against what he came to think of as ‘rationalism’, the tendency to find within or impose upon all worthwhile scientific activity a single ‘scientific rationality’. Undoubtedly, student radicalism and the Free Speech movement were among his other influences at the time. He lectured also at University College London (1966–9), where he met and befriended another major influence on his work, Imre Lakatos, who genuinely admired Popper and sought to liberalize the falsificationist philosophy of science. The liberalization that Lakatos had in mind was pushed to its extreme by Feyerabend: he came to embrace the relativist views that there is no single rationality, no unique way of attaining knowledge, and no single body of truth to be thereby attained. He became intensely sceptical about the ambitions and achievements of ‘Western rationalism’, suspecting it to be the willing tool of Western imperialism. His sympathies came to lie firmly with people marginalized by this intellectual tradition, and he sought to show that many of its greatest intellectual heroes did not play by the standards which the tradition’s self-appointed ambassadors advertise. He also sought to downgrade the importance of empirical arguments by suggesting that aesthetic criteria, personal whims and social factors have a far more decisive role in the history of science than rationalist or empiricist historiography would indicate. His 1975 and 1978 books Against Method and Science in a Free Society famously gave expression to these anti-rationalist themes, and garnered an audience far wider than books in philosophy of science usually have. He came to be seen as a leading cultural relativist, not just because he stressed that some theories are incommensurable, but also because he defended relativism in politics as well as in epistemology. He died in Switzerland in 1994.