A professor of philosophy at the University of California, San Diego (1963–73), and Washington University, St Louis, Missouri (1973–86), Richard Popkin was best known for his work on scepticism, notably for his classic study The History of Scepticism from Erasmus to Descartes (1960). This revolutionised the received picture of both the history of philosophy and the history of science, by demonstrating the influence, in the century before Descartes, of ancient Greek sceptical arguments, deriving ultimately from Pyrrho, about the impossibility of knowing God and the world. Instead of treating the history of science and philosophy as a series of breakthroughs by canonical figures, Popkin viewed the thought of the past from within its own framework.