Thomas Kuhn

Kuhn was born in Cincinnati to an engineer, studied physics at Harvard, graduated summa cum laude in 1943, worked in a radar laboratory and in Europe during the war, and took his doctorate in physics in 1949. In 1947 Harvard's president Conant asked him to teach history of science to non-scientists, and while preparing Aristotle's physics he had an 'epiphany': Aristotle was not a bad Newton; his physics was coherent within its own framework, using wholly different concepts. He turned to the history of science.

After some years as a Harvard fellow reading Koyré, Piaget, Wittgenstein and Fleck, he went to Berkeley in 1956 and published The Copernican Revolution in 1957. The Structure of Scientific Revolutions appeared in 1962 as a volume of the International Encyclopedia of Unified Science, a project of logical positivism that the book proceeded to bury. Mature science, it argued, works under a 'paradigm', a community's shared exemplars, theory, methods and standards; 'normal science' is puzzle-solving within it; accumulated anomalies produce 'crisis'; then a new paradigm replaces the old in a 'revolution', a shift like a Gestalt switch that evidence and logic cannot compel, the old and new being 'incommensurable'. After a revolution scientists 'work in a different world'.

The book sold over a million copies, 'paradigm shift' entered ordinary speech, and the social sciences, humanities and business all borrowed it. Philosophers accused him of reducing science to irrational 'mob psychology', and at a London conference in 1965 he debated Popper, Lakatos and Feyerabend in a famous exchange. He answered with a Postscript, splitting 'paradigm' into 'disciplinary matrix' and 'exemplar' and insisting he was no relativist: there are reasons for choosing paradigms, only no algorithm.

He moved to Princeton in 1964 and to MIT in 1979, wrote a history of black-body radiation and the quantum revolution, and spent his last thirty years on a philosophical work about incommensurability and change in scientific vocabulary, revised repeatedly and unfinished at his death. He disliked most of what 'Kuhnians' made of him, saying 'I am not a Kuhnian'. He died of lung cancer. His book changed how people talk about science and remains the starting point of every discussion of scientific change.