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Thomas Kuhn challenged the view of science as gradual accumulation of knowledge. He argued that science alternates between 'normal science' (puzzle-solving within an accepted framework) and 'revolutionary science' (periods of crisis leading to paradigm shifts). A paradigm is a shared set of theories, methods, standards, and exemplars that define a scientific community. When anomalies accumulate and the paradigm enters crisis, a new paradigm may be adopted, involving incommensurable standards and worldviews.
Study detailed historical case studies: Ptolemaic to Copernican astronomy, Newtonian to Einsteinian physics, or phlogiston to oxygen chemistry. Analyze how scientists resisted paradigm shifts and how new paradigms gained acceptance.
From your introduction to philosophy of science, you are familiar with the received view: science advances by accumulating confirmed facts, eliminating false hypotheses, and converging on truth through careful observation and reasoning. Thomas Kuhn's *The Structure of Scientific Revolutions* (1962) challenged this picture so fundamentally that it changed how historians, philosophers, and scientists themselves think about what science does.
A paradigm is more than just a theory. It is the entire package of commitments shared by a scientific community: exemplary solved problems (the "exemplars" that teach practitioners what good science looks like), accepted methods and instruments, background assumptions about what phenomena need explaining, and standards for what counts as a satisfactory explanation. Normal science operates within a paradigm — it is not testing the paradigm but extending and applying it, like solving puzzles whose form is already determined. A physicist working within Newtonian mechanics does not question Newton's laws; she uses them to handle new problems. The paradigm defines which problems are worth solving and what solutions look like.
Inevitably, anomalies accumulate — observations that resist solution within the paradigm's framework. For a while, the community sets them aside: every paradigm has unresolved puzzles, and anomalies don't automatically trigger crisis. But when anomalies proliferate and touch core commitments, crisis ensues. Practitioners begin to question foundations they previously took for granted. Alternative frameworks emerge. Eventually — and this is Kuhn's most controversial claim — the scientific community undergoes a paradigm shift: the new framework is adopted, the old one abandoned, and the community reconstitutes itself around new exemplars and standards. Classic cases include the Ptolemaic-to-Copernican shift in astronomy, the phlogiston-to-oxygen shift in chemistry, and the Newtonian-to-Einsteinian shift in physics.
The philosophically charged concept is incommensurability: Kuhn argued that successive paradigms are not straightforwardly comparable, because the meaning of key terms shifts and the standards of success change. Scientists in different paradigms literally see the world differently — they are solving different problems by different standards. This does not mean, as critics charged, that paradigm choice is irrational or arbitrary. Kuhn acknowledged that new paradigms typically solve more problems, generate more precise predictions, and open new research avenues. But there is no paradigm-neutral vantage point from which to make the comparison, which complicates the simple story of science as converging on a fixed truth about the world.
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