Thomas Samuel Kuhn (18 July 1922 - 17 June 1996) was an American historian and philosopher of science whose 1962 work The Structure of Scientific Revolutions fundamentally altered how scholars understand the development of scientific knowledge. Kuhn argued that science does not progress through simple accumulation of facts but through periodic revolutionary shifts he called “paradigm shifts” - episodes in which an established framework of assumptions collapses under the weight of anomalies and is replaced by a new one. His work introduced or popularized terms now common in both academic and popular discourse, including paradigm, paradigm shift, normal science, and incommensurability.

Kuhn was trained as a physicist at Harvard University, earning his Ph.D. in 1949. While teaching a general education course on science history, he encountered the work of Aristotle and was struck by how radically different Aristotelian physics was from Newtonian physics - not merely wrong by modern standards, but operating within an entirely different conceptual framework. This observation became the seed of his mature philosophy of science. His historical study of the Copernican Revolution, published in 1957, provided an extended case study for ideas he would later systematize in The Structure of Scientific Revolutions.

Kuhn spent much of his career at Harvard, Berkeley, Princeton, and MIT. He died in Cambridge, Massachusetts on 17 June 1996.

Normal science refers, in Kuhn's framework, to the routine activity of scientists working within an accepted paradigm - solving puzzles defined by the paradigm's assumptions rather than questioning those assumptions. Paradigms are the shared exemplars, values, and theoretical commitments that define what counts as legitimate science within a given community at a given time. Anomalies are observations or results that resist explanation within the reigning paradigm; when anomalies accumulate beyond a threshold, the field enters a crisis. A scientific revolution occurs when the community abandons the old paradigm and adopts a new one that resolves (or dissolves) the crisis. The new paradigm does not simply extend or correct the old one; it reconstitutes the field on new conceptual foundations.

Incommensurability is Kuhn's claim that competing paradigms cannot always be evaluated against a shared neutral standard, because the meaning of key terms shifts between paradigms. Critics have argued this entails relativism; Kuhn disputed this characterization while acknowledging the interpretive difficulty.

The Structure of Scientific Revolutions is among the most cited academic works of the 20th century and had significant impact outside philosophy of science, influencing sociology, literary criticism, political theory, and economics. Within philosophy of science, responses have ranged from substantial incorporation of his historical methods to sharp criticism of his epistemological commitments. Karl Popper, Imre Lakatos, Paul Feyerabend, and Israel Scheffler each engaged critically with Kuhn's framework, and the resulting debates shaped the field for decades.

Kuhn revised his views in response to critics, particularly on incommensurability and the role of values in theory choice, in essays collected in The Essential Tension (1977) and in his posthumously published The Road Since Structure (2000).

There is broad consensus in the history and philosophy of science that Kuhn's work permanently altered the field's methods and questions, particularly by making historical case studies central to philosophical argument. The normative implications of his framework - especially whether incommensurability entails relativism about scientific truth - remain actively contested. See Philosophy of Science Consensus.

• Kuhn as historian of science - Kuhn's historical methodology is widely respected as a model for grounding philosophical claims in detailed case studies rather than rational reconstruction alone. Kuhn as Historian Viewpoint

• Kuhn as relativist - Critics including Popper and Scheffler argued that incommensurability and the social account of paradigm change imply that science cannot claim objective progress, reducing scientific choice to sociology or rhetoric. Note that Feyerabend's critique ran in the opposite direction: he considered Kuhn too conservative and insufficiently relativist, faulting him for not abandoning methodological norms altogether. The Relativism Charge Viewpoint

• Kuhn as anti-relativist - Kuhn himself rejected the relativist label, arguing that paradigm choice is guided by shared epistemic values (accuracy, consistency, scope, simplicity, fruitfulness) and that later paradigms genuinely improve on earlier ones in solving puzzles. Kuhn's Anti-Relativist Defense Viewpoint

• Kuhn and social constructivism - Later scholars in science and technology studies (STS), including David Bloor and members of the Edinburgh School, invoked Kuhn in support of strong social constructivist accounts of scientific knowledge. Kuhn distanced himself from these readings. Kuhn and Social Constructivism Viewpoint

• Kuhn and cumulative progress - Some philosophers of science argue that Kuhn's revolution model, while illuminating, understates genuine cumulative and progressive elements of scientific development that persist across paradigm changes. Cumulative Progress Viewpoint

• Thomas Kuhn - History
• Thomas Kuhn - Debate
• Philosophy of Science Consensus
• Copernican Revolution
• Paradigm Shift
• Philosophy of Science
• Scientific Realism
• Incommensurability
• Normal Science
• Karl Popper
• Imre Lakatos
• Paul Feyerabend

1. Kuhn, Thomas S. The Structure of Scientific Revolutions. University of Chicago Press, 1962. (2nd ed. 1970, 3rd ed. 1996, 4th ed. 2012.)
2. Kuhn, Thomas S. The Copernican Revolution: Planetary Astronomy in the Development of Western Thought. Harvard University Press, 1957.
3. Kuhn, Thomas S. The Essential Tension: Selected Studies in Scientific Tradition and Change. University of Chicago Press, 1977.
4. Kuhn, Thomas S. The Road Since Structure. Eds. James Conant and John Haugeland. University of Chicago Press, 2000.
5. Hoyningen-Huene, Paul. Reconstructing Scientific Revolutions: Thomas S. Kuhn's Philosophy of Science. University of Chicago Press, 1993.
6. Lakatos, Imre, and Alan Musgrave, eds. Criticism and the Growth of Knowledge. Cambridge University Press, 1970. (Contains responses to Kuhn by Popper, Lakatos, Feyerabend, and others.)
7. Scheffler, Israel. Science and Subjectivity. Bobbs-Merrill, 1967.
8. Fuller, Steve. Thomas Kuhn: A Philosophical History for Our Times. University of Chicago Press, 2000.