Kuhn was trained as a physicist; after his PhD, reading Aristotelian physics for a history of science course at Harvard, he had the conceptual shock that became the starting point of this book. Aristotle struck him at first as 'wholly wrong'; but weeks later he realised that Aristotle had in fact reasoned coherently inside a very self-consistent system — only the basic assumptions of that system (its concepts, its questions, its rules for what counts as evidence) differed radically from modern physics. That realisation became the kernel of the book.

Kuhn's term is 'paradigm.' A paradigm is the basic shared concepts of a scientific community, its accepted exemplary problems and their solutions, its agreement about what is important and what is not — in short, the entire background of research. 'Normal science' is done within a paradigm: scientists work on the puzzles the paradigm defines. Anomalies accumulate over time; when their number and severity cross a threshold, a 'crisis' begins. A new paradigm emerges as a rival; the scientific community's generational shift to it completes the 'revolution.'

Examples: Copernicus (from Ptolemy to heliocentrism), Newton (from Aristotelian physics), Einstein (from Newtonian physics), Darwin (from creation to evolution), Lavoisier (from phlogiston to oxidation). At each transition 'observation' is not neutral — what is seen under the old paradigm and what is seen under the new are not the same, because the paradigm determines what is visible. Kuhn calls this 'incommensurability'; it is one of his most contested concepts and remains a live debate in philosophy of science.

The book provoked strong reaction. The Popper school (Popper, Lakatos, Watkins) accused Kuhn of 'irrationalism' and 'relativism' — if paradigms are incommensurable, how can we say one science is 'better' than another? Kuhn responded in 1969 with a 'Postscript' that softened some terms. The debate continues.

The book's true historical effect may be outside philosophy of science: 'paradigm shift' has become a stock phrase across management theory, political analysis, and popular culture — a success Kuhn himself viewed with discomfort. In academia, it stands as the heaviest blow yet to the classical positivist image of science as 'a-historical, asocial, purely rational'; the sociology of science (the Edinburgh school, Bruno Latour) and science studies as a field were built directly on this ground.