Kuhn, Thomas

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Kuhn, Thomas 1922-1996


Thomas Kuhn was the author of five works in the history of science, of which the most influential, The Structure of Scientific Revolutions, explores the character of scientific change. On its appearance in 1962 it became the central document for attacks on the logical empiricist account of science as the progressive accumulation of objective knowledge controlled by experimental and observational methods. Though Kuhn regretted and rejected the radical interpretation of this book, this interpretation was natural and served as the starting point for one side in a generation-long culture war between exponents and detractors of sciences claim to objectivity.

Kuhns ostensible topic was scientific change, how the broadest theories replace one another during periods of scientific revolution. Among the most important of these was the shift from Aristotelian physics to Newtonian mechanics, from phlogiston chemistry to Lavoisiers theories of reduction and oxidation, from nonevolutionary biology to Darwinism, and from Newtonian mechanics to relativistic and quantum mechanics. Periods of revolutionary change in science alternate with periods of what Kuhn called normal science, during which the direction, methods, instruments, and problems that scientists face are all fixed by what he called a paradigm (the term has gone into common usage). Paradigms are more than just equations, laws, statements encapsulated in the chapters of a textbook. The paradigm of Newtonian mechanics was not just Newtons laws of motion, it was also the model or picture of the universe as a deterministic clockwork in which the fundamental properties of things were their position and momentum from which all the rest of their behavior could eventually be derived when Newtonian science was completed. The Newtonian paradigm also included apparatus, a methodology, indeed an entire metaphysics. Paradigms drive normal science, and normal science dictates the direction of scientific progress by determining what counts as science altogether.

During normal science, three sorts of empirical enquiries flourish: redetermining previously established observational claims to greater degrees of precision; the establishment of facts without significance themselves but which vindicate the paradigm; experiments undertaken to solve problems to which the paradigm draws ones attention. Failure to accomplish any of these three aims reflects on the scientist attempting them, not the paradigm employed.

Naturally, some disciplines are, as Kuhn put it, in pre-paradigm states, as evinced for example by the lack of textbook uniformity. These disciplines are ones, like many of the social sciences, where the lack of commonality among the textbooks reveals the absence of consensus on a paradigm. At some points in the histories of each of the mature sciences, a ruling paradigm emerged. But it could not have done so owing to its correctness or empirical warrant. Apparently, its ascendancy must have a social explanation.

According to Kuhn, once established, the paradigm determined the outcome of empirical inquiry. It is not empirical inquiry that determines the paradigms scientists embrace. Independent of paradigms there are no empirical facts to observe. To illustrate and support this claim Kuhn cited evidence from psychological experiments about optical illusions, gestalt-switches, expectation-effects, and the unnoticed theoretical commitments of many apparently observational words we incautiously suppose to be untainted by presuppositions about the world. Here was Kuhns most forceful direct attack on the theoretical/observational distinction that underwrites logical empiricisms account of scientific knowledge.

As normal science progresses, its puzzles succumb to what Kuhn called the articulation of the paradigm. A small number of puzzles continue to be recalcitrant: phenomena that the paradigm cannot explain, or phenomena the paradigm leads us to expect but that do not turn up, discrepancies in the data beyond the margins of error, or major incompatibilities with other paradigms. In each case, there is within normal science a rational explanation for these anomalies; and eventually further work turns an anomaly into a solved puzzle. Revolutions occur when an anomaly resists solution long enough to produce a crisis. As more scientists attach paramount importance to the problem, the entire disciplines research program begins to be focused around the unsolved anomaly. At some point a (usually younger) scientist formulates a new paradigm, which turns the anomaly into a solved puzzle. But revolutionaries are not behaving in the most demonstrably rational way; nor are their (usually elderly) establishment opponents who defend the ruling paradigm against their approach acting irrationally.

During these periods of competition between old and new paradigms, nothing between them can be settled by observation or experiment. Often there is little or no difference between the competing paradigms when it comes to predictive accuracy, and often the new paradigm fails to solve puzzles solved in the old one. A new paradigm disagrees radically with its predecessor. Sometimes new paradigms are advanced by scientists who do not realize their incompatibility with ruling ones. But the new paradigm must be radically different from its predecessor just insofar as it can treat as a mere puzzle what the previous one found an increasingly embarrassing recalcitrant anomaly. Paradigms are so all encompassing, and the difference between paradigms is so radical, that Kuhn wrote that scientists embracing differing paradigms find themselves literally in different worlds. Paradigms are, in Kuhns words, incommensurable with one another, in the sense of not being translatable one into the other, as poems in one language are untranslatable into another. And this sort of radical incommensurability underwrites the further claim that paradigms do not improve on one another, and that therefore science does not cumulate in the direction of successive approximation to the truth. Thus the history of science is like the history of art, literature, religion, politics, or culture, a story of changes, but not over the long haul a story of progress.

Because a new paradigm is literally a change in world-view, and at least figuratively a change in the world in which the scientist lives, it is often too great a shift for well-established scientists. These scientists, wedded to the old paradigm, will not just resist the shift to the new one, they will be unable to make the shift; what is more, their refusal will be rationally defensible. Or at any rate, arguments against their view will be question-begging because they will presume a new paradigm they do not accept. What is more, there is, recall, no neutral ground on which competing paradigms can be compared. When allegiance is transferred from one paradigm to another, the process is more like a religious conversion than a rational belief shift supported by relevant evidence. Old paradigms fade away as their exponents die off, leaving the proponents of the new paradigm in command of the field.

Progress is to be found in science, according to Kuhn, but like progress in evolution, it is always a matter of increasing local adaptation. In one of the last pages of his book Kuhn wrote, We may, to be more precise, have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth (1962, p.170).

The consequences of this account for skepticism about sciences epistemic status were evident to Kuhn. He spent much of his career after the appearance of The Structure of Scientific Revolutions trying to reconcile its account of scientific change with the objectivity and cumulation of scientific knowledge.



Kuhn, Thomas. 1962. The Structure of Scientific Revolutions. Chicago: University of Chicago Press.

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

Alex Rosenberg