Karl Popper Built Modern Philosophy of Science to Tell Marxism From Relativity

In 1919, the 17-year-old Karl Popper attended a lecture in Vienna by a follower of Marxism, sat through Adlerian psychoanalysis sessions for a few months on a related research project, and read about Eddington's eclipse expedition that had just confirmed an Einstein prediction by photographing starlight bending around the sun. He came away with what would become the question of his life: why did one of these three intellectual frameworks feel different from the other two?

Popper's answer, refined for the rest of his career, was about risk. Marxism and psychoanalysis, in his telling, could explain everything that happened. A worker's strike confirmed the dialectic; a worker's docility confirmed false consciousness; both moved as predicted. A boy who pushed another into a river was acting out an Oedipal anxiety; a boy who saved another was sublimating one. There was no observation that could, in principle, count as evidence against the theory. Einstein's general relativity, by contrast, made a specific quantitative prediction — light bending by a precise angle around the sun — that could have been falsified by Eddington's measurement and would have been falsified if the angle had come out wrong. The willingness of a theory to put itself at risk, Popper argued, was the dividing line between science and pseudoscience.

He published Logik der Forschung in Vienna in 1934, fled to New Zealand in 1937, wrote The Open Society and Its Enemies there during the war, and spent the rest of his life at the LSE. He was knighted in 1965 and elected to the Royal Society in 1976. The falsifiability criterion has been picked at by philosophers for decades — most modern philosophers of science consider it incomplete — but it remains the layperson's working definition of "science."