Though there had been dissident voices, it had been taken for granted that the sciences grew by the accumulation of accredited "facts". Adding new facts had no effect on those already accumulated. Laws of nature were drawn from regularities among these facts by induction.
Drawing on the pioneering work of Ludwik Fleck, Kuhn proposed a very different picture. He was struck by the wholesale transformation that took place in the beliefs of a scientific community when some revolutionary development occurred. In giving up an earth-centred picture of the solar system for a sun-centred cosmology, the astronomers of the 16th century not only changed the factual basis of astronomy but the entire framework of thought in which the old beliefs had been framed. This transformation he called a paradigm shift. It was so drastic a change that Kuhn sometimes used the metaphor of "different worlds" to express the radical shift in perspective that a paradigm change brought about. It was almost as if those who lived within the old paradigm and those in the new were cut off from one another by a chasm of mutual unintelligibility.
The key notion of paradigm did duty, in Kuhn's most influential writings, for a variety of features of the coherent world view of a community of scientists. These included a general conception of the nature of the material world, a cluster of accredited methods and a concrete exemplar of good work to which aspirants to membership of a scientific circle could be directed for guidance. Despite philosophical criticisms of the details of Kuhn's use of the term "paradigm", it has continued to be a valuable tool for characterising large-scale changes in some scientific field.
How did paradigm change occur? How did one paradigm come to replace another, creating a new scientific community? The rational picture of a logically ordered accumulation of facts inductively giving rise to laws left no room for what had evidently happened in history. Paradigm change, or "revolutionary science" as Kuhn called it, was more a matter of persuasion, personal influence, indirect influences from social changes and even propaganda, than it was a matter of logic. Once a revolution had occurred, then the pattern of "normal science", the painstaking accumulation of detailed knowledge within the new paradigm, was resumed.
Kuhn's work was so influential in so many fields partly because of his historical verisimilitude, and partly because, in the spirit of the times, it opened a space for the sociology of knowledge to find a serious role in philosophy of science, hitherto very much the province of those with a predominantly logical interest.
Kuhn himself did not carry these ideas to a fully radical conclusion, as did some philosophers and historians influenced by him. In his later writings he repudiated the extreme historical dislocation that others had taken him to be claiming to divide paradigms from one another. In his "Postscript" to the 1969 edition of The Structure of Scientific Revolutions he explicitly disavowed the strong "incommensurability thesis", the idea that there was a sharp, unbridgeable gap between successive paradigm-governed discourses and even views of the world.
To combat some of the misunderstandings and indeed vagueness of his original use of the word "paradigm" he came to favour the expression "disciplinary matrix". But "paradigm", for all its ambiguity, has stuck. In response to radical interpretations of his incommensurability thesis, he argued for the commonsense and indeed plausible idea that when scientists become aware of a paradigm difference between two communities they "become translators" working on ways of making the two world views mutually intelligible, while they remain distinct and separate.
Kuhn was born in Cincinnati, Ohio, in 1922. He studied physics at Harvard, and began his academic career there, first as a Junior Fellow and then from 1952 to 1956 as an assistant professor. In 1957 he moved to Berkeley before taking up a senior post at Princeton in 1964. The final part of his career took him to MIT in 1979. He was married twice and had two daughters and a son. Though not a recluse he was not often seen at large international gatherings. He was an amiable man of considerable personal charm, and with little of the combativeness that is not uncommon in academic circles. He had a quirkish sense of humour, for instance in one autobiographical piece he listed among his hobbies "riding roller-coasters".
Kuhn's moderation in thought and modesty in personal style militated against his later writing on the history of quantum theory and other topics in the development of physics having the same impact as The Structure of Scientific Revolutions. His essays published as The Essential Tension in 1977 were widely read, but contained nothing essentially new. Though Kuhn was not alone in advocating a transformational theory of the development of science, nor indeed in the use of the word "paradigm" for the cluster of very different aspects that the science of an epoch displayed, there was something about the way he presented the case at a moment when logicism was beginning to be looked on with less enthusiasm that ensured that his work took centre stage and will be looked back on as a turning point in our understanding of science.
Thomas Samuel Kuhn, philosopher of science: born Cincinnati, Ohio 18 July 1922; Fellow, Harvard 1948-51, Instructor and Assistant Professor 1951-56; Assistant Professor, Associate Professor and Professor, University of California (Berkeley) 1957-64; Professor and M. Taylor Pine Professor, Princeton University 1964-79; Professor, MIT 1979-83, Laurance S. Rockefeller Professor of Philosophy 1983-91 (Emeritus); married 1948 Kathryn Muhs (one son, two daughters; marriage dissolved 1978), 1982 Jehane Burns; died Cambridge, Massachusetts 17 June 1996.