Karl Popper, who died in 1994, was one of the most influential philosophers of the twentieth century—as much outside the profession of philosophy as within it (Chancellor Helmut Schmidt, Sir Peter Medawar, and Sir Ernst Gombrich were ardent Popperians). An emigrant from Vienna in 1937, who had fled the Nazis, Popper spent his early academic years in New Zealand before obtaining a post at the London School of Economics in 1945, where he taught until he re-tired. (Popper’s early years are comprehensively covered in Malachi Haim Hacohen’s The Formative Years.) Polymathic, prolific, strong-willed, he made his mark in both the philosophy of science and political philosophy, later developing distinctive views in the philosophy of mind and even Greek philosophy.
His initial philosophical impetus came from the Vienna Circle, a group of scientifically inclined philosophers and scientists who flourished in the interwar years and who espoused the philosophy that came to be known as “logical positivism”—a view best defined as against religion and traditional metaphysics and for empir-ical science (A.J. Ayer’s Language, Truth and Logic introduced this philosophy to the English-speaking world in 1946). However, Popper said that he diverged profoundly from the Vienna Circle, particularly over the nature of scientific method: while they took empirical verifiability as the touchstone of science (and hence intellectual respectability), Popper took the notion of falsification as the essential mark of scientific discourse. This key idea was to have a large impact on the philosophy of science, as well as on the whole issue of what constituted reputable discourse. The recent books devoted to Popper attest to the vitality of the ideas he introduced. While not being a guru within the narrow confines of analytical philosophy, when compared, say, to Wittgenstein, he continues to be a major intellectual figure in the world beyond.
There is an impressive and attractive unity to Popper’s thought. In his philosophy of science, his general theory of knowledge, his philosophy of biology, and his political philosophy the same basic ideas recur. For Popper, everything revolves around the solving of problems by means of the critical elimination of attempted solutions. In “The Logic and Evolution of Scientific Theory,” the first essay in the aptly named All Life Is Problem Solving, a collection of his later lectures and essays, Popper offers us a three-stage model of learning, which he takes to apply to animal learning as well as to the upper reaches of scientific research: first there is the problem (Popper is very fond of the emphatic use of italics); then there are the attempted solutions; finally there is the elimination of those solutions. Epistemic progress works by trial and error.
In the case of scientific knowledge this three-stage model assumes the familiar Popperian form: the scientist is confronted by a problem in accepted theory, occasioned by a faulty prediction or explanatory weakness, which leads to the need for a new theory; she generates, by means of imaginative creativity, a range of conjectures or …