July 28, 1902 - September 17, 1994. Austrian-born, British thinker, widely viewed as one of the twentieth century's greatest philosophers of science. He was also a social and political philosopher of considerable stature, a staunch defender of liberal democracy and the principles of social criticism upon which it is based, and an implacable opponent of authoritarianism. He is best known for his repudiation of the classical observationalist-inductivist account of science, his espousal of falsifiability as a criterion of demarcation between science and non-science, and his defence of the Open Society.
Born in Vienna in 1902 to middle-class parents of Jewish origins, Karl Popper was educated at the University of Vienna. He took a Ph.D. in philosophy in 1928, and taught in secondary school from 1930-1936. In 1937, concerns about the growth of Nazism led him to emigrate to New Zealand, where he became lecturer in philosophy at Canterbury University College, Christchurch. In 1946, he moved to England to become reader in logic and scientific method at the London School of Economics, where he was appointed professor in 1949. He was knighted in 1965, and was elected Fellow of the Royal Society in 1976. He retired from academic life in 1969, though he remained intellectually active until his death in 1994.
Popper coined the term critical rationalism to describe his philosophy. This designation is significant, and indicates his rejection of classical empiricism, and of the observationalist-inductivist account of science that had grown out of it. Popper argued strongly against the latter, holding that scientific theories are universal in nature, and can be tested only indirectly, by references to their implications. He also held that scientific theory, and human knowledge generally, is irreducibly conjectural or hypothetical, and is generated by the creative imagination in order to solve problems that have arisen in specific historico-cultural settings. Logically, no number of positive outcomes at the level of experimental testing can confirm a scientific theory, but a single genuine counter-instance is logically decisive: it shows the theory, from which the implication is derived, to be false. Popper's account of the logical asymmetry between verification and falsification lies at the heart of his philosophy of science. It also inspired him to take falsifiability as his criterion of demarcation between what is and is not genuinely scientific: a theory should be accounted scientific if and only if it is falsifiable. This led him to attack the claims of both psychoanalysis and contemporary Marxism to scientific status, on the basis that the theories enshrined by them are not falsifiable.
In The Open Society and It's Enemies and The Poverty of Historicism, Popper developed a powerful critique of historicism and a defence of the Open Society, liberal democracy. Historicism is the theory that history develops inexorably and necessarily according to knowable general laws towards a determinate end. Popper considered this view to be the principal theoretical presupposition underpinning most forms of authoritarianism and totalitarianism. He accordingly attacked it, arguing that it is founded upon mistaken assumptions regarding the nature of scientific law and prediction. Since the growth of human knowledge is a causal factor in the evolution of human history, and since no society can predict, scientifically, it's own future states of knowledge, it follows, he argued, that there can be no predictive science of human history. For Popper, metaphysical and historical indeterminism go hand in hand.
Popper has a significant number of critics. On the one hand, there are those who seek to vindicate the claims of historicism or holism to intellectual respectability, or psychoanalysis or Marxism to scientific status. On the other, there are those who argue that, in principle or in point of detail, his philosophy of science is mistaken. Few, however, would deny his influence or importance, and there would be considerable support for the view of Popper as one of the foremost critics of authoritarianism in the twentieth century, yet also arguably the premier philosopher of science during a century of unparalleled scientific discovery.