A paradigm shift (or revolutionary science) is, according to Thomas Kuhn, in his influential book The Structure of Scientific Revolutions (1962), a change in the basic assumptions, or paradigms, within the ruling theory of science. It is in contrast to his idea of normal science. According to Kuhn, "A paradigm is what members of a scientific community, and they alone, share" (The Essential Tension, 1977). Unlike a normal scientist, Kuhn held, "a student in the humanities has constantly before him a number of competing and incommensurable solutions to these problems, solutions that he must ultimately examine for himself" (The Structure of Scientific Revolutions).
Once a paradigm shift is complete, a scientist cannot, for example, reject the germ theory of disease to posit the possibility that miasma causes disease or reject modern physics and optics to posit that ether carries light. In contrast, a critic in the humanities can choose to adopt an array of stances (e.g., Marxist criticism, Freudian criticism, Deconstruction, 19th-century-style literary criticism), which may be more or less fashionable during any given period but which are all regarded as legitimate. Since the 1960s, the term has also been used in numerous non-scientific contexts to describe a profound change in a fundamental model or perception of events, even though Kuhn himself restricted the use of the term to the hard sciences. Compare as a structured form of Zeitgeist.
Kuhnian paradigm shifts 
A scientific revolution occurs, according to Kuhn, when scientists encounter anomalies that cannot be explained by the universally accepted paradigm within which scientific progress has thereto been made. The paradigm, in Kuhn's view, is not simply the current theory, but the entire worldview in which it exists, and all of the implications which come with it. This is based on features of landscape of knowledge that scientists can identify around them.
There are anomalies for all paradigms, Kuhn maintained, that are brushed away as acceptable levels of error, or simply ignored and not dealt with (a principal argument Kuhn uses to reject Karl Popper's model of falsifiability as the key force involved in scientific change). Rather, according to Kuhn, anomalies have various levels of significance to the practitioners of science at the time. To put it in the context of early 20th century physics, some scientists found the problems with calculating Mercury's perihelion more troubling than the Michelson-Morley experiment results, and some the other way around. Kuhn's model of scientific change differs here, and in many places, from that of the logical positivists in that it puts an enhanced emphasis on the individual humans involved as scientists, rather than abstracting science into a purely logical or philosophical venture.
When enough significant anomalies have accrued against a current paradigm, the scientific discipline is thrown into a state of crisis, according to Kuhn. During this crisis, new ideas, perhaps ones previously discarded, are tried. Eventually a new paradigm is formed, which gains its own new followers, and an intellectual "battle" takes place between the followers of the new paradigm and the hold-outs of the old paradigm. Again, for early 20th century physics, the transition between the Maxwellian electromagnetic worldview and the Einsteinian Relativistic worldview was neither instantaneous nor calm, and instead involved a protracted set of "attacks," both with empirical data as well as rhetorical or philosophical arguments, by both sides, with the Einsteinian theory winning out in the long-run. Again, the weighing of evidence and importance of new data was fit through the human sieve: some scientists found the simplicity of Einstein's equations to be most compelling, while some found them more complicated than the notion of Maxwell's aether which they banished. Some found Eddington's photographs of light bending around the sun to be compelling, while some questioned their accuracy and meaning. Sometimes the convincing force is just time itself and the human toll it takes, Kuhn said, using a quote from Max Planck: "a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."
After a given discipline has changed from one paradigm to another, this is called, in Kuhn's terminology, a scientific revolution or a paradigm shift. It is often this final conclusion, the result of the long process, that is meant when the term paradigm shift is used colloquially: simply the (often radical) change of worldview, without reference to the specificities of Kuhn's historical argument.
Science and paradigm shift 
A common misinterpretation of paradigms is the belief that the discovery of paradigm shifts and the dynamic nature of science (with its many opportunities for subjective judgments by scientists) are a case for relativism: the view that all kinds of belief systems are equal. Kuhn vehemently denies this interpretation and states that when a scientific paradigm is replaced by a new one, albeit through a complex social process, the new one is always better, not just different.
These claims of relativism are, however, tied to another claim that Kuhn does at least somewhat endorse: that the language and theories of different paradigms cannot be translated into one another or rationally evaluated against one another — that they are incommensurable. This gave rise to much talk of different peoples and cultures having radically different worldviews or conceptual schemes — so different that whether or not one was better, they could not be understood by one another. However, the philosopher Donald Davidson published a highly regarded essay in 1974, "On the Very Idea of a Conceptual Scheme" (Proceedings and Addresses of the American Philosophical Association, Vol. 47, (1973-1974), pp. 5–20) arguing that the notion that any languages or theories could be incommensurable with one another was itself incoherent. If this is correct, Kuhn's claims must be taken in a weaker sense than they often are. Furthermore, the hold of the Kuhnian analysis on social science has long been tenuous with the wide application of multi-paradigmatic approaches in order to understand complex human behaviour (see for example John Hassard, Sociology and Organization Theory: Positivism, Paradigm and Postmodernity. Cambridge University Press, 1993, ISBN 0521350344.)
Paradigm shifts tend to be most dramatic in sciences that appear to be stable and mature, as in physics at the end of the 19th century. At that time, physics seemed to be a discipline filling in the last few details of a largely worked-out system. In 1900, Lord Kelvin famously told an assemblage of physicists at the British Association for the Advancement of Science, "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement." Five years later, Albert Einstein published his paper on special relativity, which challenged the very simple set of rules laid down by Newtonian mechanics, which had been used to describe force and motion for over two hundred years.
In The Structure of Scientific Revolutions, Kuhn wrote, "Successive transition from one paradigm to another via revolution is the usual developmental pattern of mature science." (p. 12) Kuhn's idea was itself revolutionary in its time, as it caused a major change in the way that academics talk about science. Thus, it could be argued that it caused or was itself part of a "paradigm shift" in the history and sociology of science. However, Kuhn would not recognise such a paradigm shift. In the social sciences, people can still use earlier ideas to discuss the history of science.
Philosophers and historians of science, including Kuhn himself, ultimately accepted a modified version of Kuhn's model, which synthesizes his original view with the gradualist model that preceded it.
Examples of paradigm shifts in 
Natural sciences 
Some of the "classical cases" of Kuhnian paradigm shifts in science are:
- The transition in cosmology from a Ptolemaic cosmology to a Copernican one.
- The transition in optics from geometrical optics to physical optics.
- The transition in mechanics from Aristotelian mechanics to classical mechanics.
- The acceptance of the theory of biogenesis, that all life comes from life, as opposed to the theory of spontaneous generation, which began in the 17th century and was not complete until the 19th century with Pasteur.
- The acceptance of the work of Andreas Vesalius, whose work De humani corporis fabrica corrected the numerous errors in the previously-held system created by Galen.
- The transition between the Maxwellian Electromagnetic worldview and the Einsteinian Relativistic worldview.
- The transition between the worldview of Newtonian physics and the Einsteinian Relativistic worldview.
- The development of quantum mechanics, which replaced classical mechanics at microscopic scales.
- The acceptance of plate tectonics as the explanation for large-scale geologic changes.
- The development of absolute dating.
- The acceptance of Lavoisier's theory of chemical reactions and combustion in place of phlogiston theory, known as the Chemical Revolution.
- The acceptance of Mendelian inheritance, as opposed to pangenesis in the early 20th century
Social sciences 
In Kuhn's view, the existence of a single reigning paradigm is characteristic of the sciences, while philosophy and much of social science were characterized by a "tradition of claims, counterclaims, and debates over fundamentals." Others have applied Kuhn's concept of paradigm shift to the social sciences.
- The movement, known as the Cognitive revolution, away from Behaviourist approaches to psychological study and the acceptance of cognition as central to studying human behaviour.
- The Keynesian Revolution is typically viewed as a major shift in macroeconomics. According to John Kenneth Galbraith, Say's Law dominated economic thought prior to Keynes for over a century, and the shift to Keynesianism was difficult. Economists who contradicted the law, which implied that underemployment and underinvestment (coupled with oversaving) were virtually impossible, risked losing their careers. In his magnum opus, Keynes cited one of his predecessors, John Atkinson Hobson, who was repeatedly denied positions at universities for his heretical theory.
- Later, the movement for Monetarism over Keynesianism marked a second divisive shift. Monetarists held that fiscal policy was not effective for stabilizing inflation, that it was solely a monetary phenomenon, in contrast to the Keynesian view of the time was that both fiscal and monetary policy were important. Keynesians later adopted much of the Monetarists view of the quantity theory of money and shifting Philips curve, theories they initially rejected.
In the later part of the 1990s, 'paradigm shift' emerged as a buzzword, popularized as marketing speak and appearing more frequently in print and publication. In his book Mind The Gaffe, author Larry Trask advises readers to refrain from using it, and to use caution when reading anything that contains the phrase. It is referred to in several articles and books as abused and overused to the point of becoming meaningless.
Other uses 
The term "paradigm shift" has found uses in other contexts, representing the notion of a major change in a certain thought-pattern — a radical change in personal beliefs, complex systems or organizations, replacing the former way of thinking or organizing with a radically different way of thinking or organizing:
- M. L. Handa, a professor of sociology in education at O.I.S.E. University of Toronto, Canada, developed the concept of a paradigm within the context of social sciences. He defines what he means by "paradigm" and introduces the idea of a "social paradigm". In addition, he identifies the basic component of any social paradigm. Like Kuhn, he addresses the issue of changing paradigms, the process popularly known as "paradigm shift." In this respect, he focuses on the social circumstances which precipitate such a shift. Relatedly, he addresses how that shift affects social institutions, including the institution of education.
- The concept has been developed for technology and economics in the identification of new techno-economic paradigms as changes in technological systems that have a major influence on the behaviour of the entire economy (Carlota Perez; earlier work only on technological paradigms by Giovanni Dosi). This concept is linked to Joseph Schumpeter's idea of creative destruction. Examples include the move to mass production and the introduction of microelectronics.
- In the arena of political science, the concept has been applied to the ethos of war. Evolutionary biologist Judith Hand, in a paper entitled "To Abolish War," argued that a paradigm shift is possible from a global ethos that operates on the assumption that war is an inevitable aspect of human nature to a global ethos that rejects war under any circumstances.
- Two photographs of the Earth from space, "Earthrise" (1968) and "The Blue Marble" (1972), are thought to have helped to usher in the environmentalist movement which gained great prominence in the years immediately following distribution of those images.
- Hans Küng applies Thomas Kuhn's theory of paradigm change to the entire history of Christian thought and theology. He identifies six historical "macromodels": 1) the apocalyptic paradigm of primitive Christianity, 2) the Hellenistic paradigm of the patristic period, 3) the medieval Roman Catholic paradigm, 4) the Protestant (Reformation) paradigm, 5) the modern Enlightenment paradigm, and 6) the emerging ecumenical paradigm. He also discusses five analogies between natural science and theology in relation to paradigm shifts. Küng addresses paradigm change in his books, Paradigm Change in Theology and Theology for the Third Millennium: An Ecumenical View.
See also 
- Accelerating change
- Attitude polarization
- Buckminster Fuller
- Cognitive bias
- Confirmation bias
- Cultural bias
- Disruptive technology
- Don Tapscott (author of Paradigm Shift)
- Gaston Bachelard
- Epistemological break
- Human history
- Infrastructure bias
- Kondratiev wave
- Ludwik Fleck
- Systemic bias
- Teachable moment
- World view
- Quoted in Thomas Kuhn, The Structure of Scientific Revolutions (1970 ed.): p. 150.
- Sankey, Howard (1997) "Kuhn's ontological relativism," in Issues and Images in the Philosophy of Science: Scientific and Philosophical Essays in Honour of Azarya Polikarov, edited by Dimitri Ginev and Robert S. Cohen. Dordrecht: Kluwer Academic, 1997. Boston studies in the philosophy of science, vol. 192, pp. 305-320. ISBN 0792344448
- Weisstein, Eric W.. "Eric Weisstein's World of science". Wolfram Research. Retrieved January 2, 2013.
- Kuhn, Thomas N. (1972) . "Logic of Discovery or Psychology of Research". In Lakatos, Imre; Musgrave, Alan. Criticism and the Growth of Knowledge (second ed.). Cambridge: Cambridge University Press. p. 6. ISBN 0-521-09623-5
- David Laidler. Fabricating the Keynesian Revolution.
- Galbraith, John Kenneth. (1975). Money: Whence It Came, Where It Went, p. 223. Houghton Mifflin.
- Keynes, John Maynard. The General Theory of Employment, Interest, and Money, p. 366. "Mr. Hobson has flung himself with unflagging, but almost unavailing, ardour and courage against the ranks of orthodoxy. Though it is so completely forgotten to-day, the publication of this book marks, in a sense, an epoch in economic thought."
- Bordo, Michael D., Schwartz, Anna J. (2008). Monetary Economic Research at the St. Louis Fed During Ted Balbach's Tenure as Research Director. The Federal Reserve Bank of St. Louis Review.
- Robert Fulford, Globe and Mail (June 5, 1999). http://www.robertfulford.com/Paradigm.html Retrieved on 2008-04-25.
- Cnet.com's Top 10 Buzzwords
- "The Complete Idiot's Guide to a Smart Vocabulary" p142-143, author: Paul McFedries publisher: Alpha; 1st edition (May 7, 2001), ISBN 978-0-02-863997-0
- Hand, Judith L. (2010). "To Abolish War". Journal of Aggression, Conflict, and Peace Research 2 (4): 44–56. doi:10.5042/jacpr.2010.0536.
- Schroeder, Christopher H. "Global Warming and the Problem of Policy Innovation: Lessons from the Early Environmental Movement". 2009. http://www.lclark.edu/org/envtl/objects/39-2_Schroeder.pdf
- See also Stewart Brand#NASA image of Earth
- Kung, Hans & Tracy, David (ed). Paradigm Change in Theology. New York: Crossroad, 1989.
- Küng, Hans. Theology for the Third Millennium: An Ecumenical View. New York: Anchor Books, 1990.
- MIT 6.933J - The Structure of Engineering Revolutions. From MIT OpenCourseWare, course materials (graduate level) for a course on the history of technology through a Kuhnian lens.