Kuhn, Thomas (1922–1996)

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Educated at Harvard University (SB, 1943; PhD in physics, 1949), Thomas Kuhn taught at Harvard (19511956), University of California, Berkeley (19561964), Princeton University (19641979), and Massachusetts Institute of Technology (19791991). His book The Structure of Scientific Revolutions, first published in 1962 (2nd. ed., 1970), continues to stimulate discussion among historians and philosophers of science even as its concepts of "paradigm" and "paradigm shift" have been adopted by a great diversity of writers, often at some remove from their source in Kuhn's book.

Conceptual Schemes, Paradigms, and Normal Science

At Harvard Kuhn became the protégé of its president, James B. Conant, to whom he dedicated the first edition of Structure of Scientific Revolutions. Conant's concept of "conceptual scheme," applied especially to the chemical revolution's phlogiston and oxygen theories, reappeared in Kuhn's first book, The Copernican Revolution: Planetary Astronomy in the Development of Western Thought (1957), and was one of the principal sources of Kuhn's all-important paradigm concept. His evolving understanding of that concept also reflected a pivotal experience in 1947, in which he suddenly appreciated that Aristotle could not properly be understood from the perspective of post-Galilean physics, but only from within Aristotle's own context of problems, concepts, and assumptions. Kuhn's early conviction that such systems of scientific thought can only be understood holistically and that a scientist's appreciation for a radically new system comes in a flash of insight underlay his notions of the incommensurability of paradigms and of the gestalt switch that marks the transition from one paradigm to another.

Kuhn announced his central problem as "the nature of science and the reasons for its special success" (1970, p. v). He forged his concept of "paradigms"glossed here as "universally recognized scientific achievements that for a time provide model problems and solutions to a community of practitioners" (p. viii)in part as a way to understand why there is less disagreement among natural scientists over fundamentals than there is among social scientists and psychologists. Kuhn rejected the view that scientific knowledge grows incrementally through the accumulation of individual facts, laws, and theories. He linked his rejection of demarcationist issueswhat distinguishes good science from error or superstitionto his insistence that superseded conceptual systems like Aristotelian dynamics and phlogistic chemistry were, in their context, no less scientific than currently accepted science.

Kuhn applied the term "normal science" to "research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice" (1970, p. 10). Paradigm-defining works like Aristotle's Physics, Isaac Newton's Principia, and Antoine Lavoisier's Chemistry were "sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity" and "sufficiently open-ended to leave all sorts of problems for the redefined group of practitioners to resolve" (p. 10). Subsequent scientists (and students of science) study such works as "concrete models," whereby they become "committed to the same rules and standards for scientific practice" (p. 11). Strong commitment and broad consensus characterize the practitioners of Kuhnian normal science. The paradigm that defines that practice limits the questions worth asking and the experiments worth performing as it specifies the entities the world is composed of and the relevance of putative facts.

For Kuhn, most scientists are engaged in "mopping-up operations" resembling "an attempt to force nature into the preformed and relatively inflexible box that the paradigm supplies" (p. 24). Kuhn likened normal science to "puzzle-solving": a solution must be assumed to exist for any problem worth addressing, and one knows ahead of time the general form the solution will take. Kuhn insisted that paradigms guide research not via rules and definitions but as models (later called "exemplars") of proper scientific practice. He associated his understanding with Michael Polanyi's concept of tacit knowledge and Ludwig Wittgenstein's notion that one can employ words without having reduced their meaning to some putative essence.

In the context of his discussion of anomalies and the emergence of scientific discoveries, Kuhn began to employ the terms "paradigm" and "paradigm change" in a broader sense closer to his and Conant's earlier "conceptual scheme," whereby his central example was the chemical revolution associated with Lavoisier's oxygen theory. Kuhn here insisted that unanticipated discoveries of new sorts of phenomena typically occur in response to the perception of anomaly with regard to the expectations of normal science. Kuhn likened scientists' response to anomalies to subjects in an experiment with playing cards who are asked to identifyamong normal cardsblack hearts and red spades, and who typically try unconsciously to assimilate those anomalies to the expected categories: "In science, as in the playing card experiment, novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation" (1970, p. 64).

Anomalies, Crises, and Paradigm Shifts

The point is of crucial importance. Anomalies enable scientists to isolate weaknesses within the dominant paradigm and to devise a solution that ultimately induces the scientific community to embrace a new and more effective paradigm. These are the "paradigm shifts" associated with the Copernican, Newtonian, and chemical revolutions. In Kuhn's view awareness of serious anomalyalways with regard to internal, technical issues, not to any of various external factorsleads to a period of crisis characterized by "the proliferation of competing articulations, the willingness to try anything, the expression of explicit discontent, the recourse to philosophy and to debate over fundamentals" (1970, p. 91)that is, by what he termed "extraordinary science."

Although Kuhn recognized that "every problem that normal science sees as a puzzle can be seen, from another viewpoint, as a counterinstance and thus as a source of crisis" (p. 79), he offered no satisfactory explanation for why only some unsolved problems are perceived as anomalies, and why only some anomalies lead to crises. In his view no fundamental changes to a paradigm can come from the resources of normal science itself. The transition from one paradigm to another constitutes "a reconstruction of the field from new fundamentals, a reconstruction that changes some of the field's most elementary theoretical generalizations as well as many of its paradigm methods and applications" (p. 85). Kuhn likened such a paradigm shift to "a change in visual gestalt" (p. 84) and defined the associated "scientific revolutions" as "those non-cumulative developmental episodes in which an older paradigm is replaced in whole or in part by an incompatible new one" (p. 92).

Incommensurability and Relativism

In elaborating parallels between scientific and political revolutions, Kuhn introduced a number of ideas that would prove controversial. He argued that because they recognize no common higher authority, "the parties to a revolutionary conflict must finally resort to the techniques of mass persuasion, often including force" (1970, p. 93).

Like the choice between competing political institutions, that between competing paradigms proves to be a choice between incompatible modes of community life. Because it has that character, the choice is not and cannot be determined merely by the evaluative procedures characteristic of normal science, for these depend in part upon a particular paradigm. As in political revolutions, so in paradigm choicethere is no standard higher than the assent of the relevant community. (p. 94)

Such assertions led many to accuse Kuhn of making science a matter of might makes right, of mob psychology, where the techniques of political persuasion replace those of evidence and rational argument.

Because different paradigms make different ontological claims, define different problems as significant, and employ different standards of what properly belongs to science, "the normal-scientific tradition that emerges from a scientific revolution is not only incompatible but often actually incommensurable with that which has gone before" (1970, p. 103). Hence defenders of opposing paradigms, absent a shared set of values, "will inevitably talk through each other when debating the relative merits of their respective paradigms" (p. 109). Although Kuhn resisted the charge of relativism, his position clearly relativizes scientific knowledge to the paradigm-dependent standards enforced by particular scientific communities, not to ostensibly objective experimental tests.

That implicit relativism was reinforced by Kuhn's insistence that scientists working within different paradigms see the world in profoundly different ways, that they effectively live in different worlds. Again, analogiesgestalt switches and experiments with inverting lenses and anomalous playing cardswere invoked to enhance the claim's plausibility. The transformation of vision that students undergo as they learn to read bubble-chamber photographs parallels "the shifts in scientific perception that accompany paradigm change" (1970, p. 117). The sudden and unstructured gestalt switch that accompanies a paradigm shift thrusts scientists into a world "incommensurable" with the one they had inhabited before. Kuhn's insistence that such transformations of vision are not reducible to a reinterpretation of individual stable data derived from his rejection of the possibility of a neutral observation language for science. In speaking of the "flashes of intuition through which a new paradigm is born" (p. 123), Kuhn transformed the gestalt switch from a metaphor to an operative element in the dynamics of scientific change. And in shifting the locus of conceptual change from the ostensibly objective externalities of experiment and argument to the psychological internality of a holistically unanalyzable gestalt switch, he seemed to many to undercut the epistemological legitimacy of science. Kuhn likened a revolutionary paradigm shift to a conversion experience that cannot be forced by logic and neutral experience. "Persuasion" and "conversion" are the terms that dominate Kuhn's discussion of paradigm shift.

Although he appealed to the greater problem-solving ability of postrevolution theories, Kuhn had no paradigm-independent way to define scientific progress and no way at all to address the question of the truth value of particular scientific claims. He sought to make this stance acceptable by appealing to an analogy between the historical development of science and Charles Darwin's rejection of the goal-directedness of evolution. The process by which one paradigm wins out over its competitors "is the selection by conflict within the scientific community of the fittest way to practice future science. Successive stages in that developmental process are marked by an increase in articulation and specialization. And the entire process may have occurred, as we now suppose biological evolution did, without benefit of a set goal, a permanent fixed scientific truth, of which each stage in the development of scientific knowledge is a better exemplar" (1970, pp. 172173). But goal-directedness is not the same thing as correspondence to the physical world, and although this may be a viable way to account for the history of science, it does not address the underlying epistemological question concerning the truth-likeness of scientific theories. In asking why scientific communities are able to reach consensus at all, Kuhn failed to assign a principal role to inputs from the physical world as he increasingly appealed to the sociology of scientific communities.

Scientific and Linguistic Communities

In the postscript appended to the second edition of Structure of Scientific Revolutions, Kuhn defended his original claims while effectively abandoning the term "paradigm." One important amplification was his appeal to the analogy between members of scientific and linguistic communities, whereby he urged "that men who hold incommensurable viewpoints be thought of as members of different language communities and that their communication problems be analyzed as problems of translation" (1970, p. 175). Like the acceptance of a new paradigm, Kuhn saw the transition accompanying translation into a new language as a qualitatively discontinuous conversion experience: "The conversion experience that I have likened to a gestalt switch remains, therefore, at the heart of the revolutionary process" (p. 204).

See also Aristotle; Galileo Galilei; Lavoisier, Antoine; Newton, Isaac; Paradigm-Case Argument; Philosophy of Science, Problems of; Wittgenstein, Ludwig Josef Johann.


works by kuhn

The Copernican Revolution: Planetary Astronomy in the Development of Western Thought. Cambridge, MA: Harvard University Press, 1957. Rev. ed., 1979.

The Structure of Scientific Revolutions. 1962. 2nd ed. with postscript. Chicago: University of Chicago Press, 1970. 3rd ed. with index, 1996.

The Essential Tension: Selected Studies in Scientific Tradition and Change. Chicago: University of Chicago Press, 1977.

The Road since Structure: Philosophical Essays, 19701993, with an Autobiographical Interview, edited by James Conant and John Haugeland. Chicago: University of Chicago Press, 2000. Contains a complete bibliography of Kuhn's publications.

works about kuhn

Barnes, Barry. T. S. Kuhn and Social Science. New York: Columbia University Press, 1982.

Buchwald, Jed Z., and George E. Smith. "Thomas S. Kuhn, 19221996." Philosophy of Science 64 (1997): 361376.

Caneva, Kenneth L. "Possible Kuhns in the History of Science: Anomalies of Incommensurable Paradigms." Studies in History and Philosophy of Science 31 (1) (March 2000): 87124.

Gutting, Gary, ed. Paradigms and Revolutions: Appraisals and Applications of Thomas Kuhn's Philosophy of Science. Notre Dame, IN: University of Notre Dame Press, 1980.

Hoyningen-Huene, Paul. Reconstructing Scientific Revolutions: Thomas S. Kuhn's Philosophy of Science. Translated by Alexander T. Levine. Chicago: University of Chicago Press, 1993.

Lakatos, Imre, and Alan Musgrave, eds. Criticism and the Growth of Knowledge. Cambridge, U.K.: Cambridge University Press, 1970.

Nickles, Thomas, ed. Thomas Kuhn. Cambridge, U.K.: Cambridge University Press, 2003. Contains a short bibliography of important studies on Kuhn and his influence.

Kenneth L. Caneva (2005)