The Structure of Scientific Revolutions
The Structure of Scientific Revolutions (
Thomas Kuhn,
1962) is an analysis of the
history of science. Its publication was a landmark event in the
sociology of knowledge, and popularized the terms
paradigm and
paradigm shift.
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Cover of 3rd edition, paperback |
The work was first published as a
monograph in the
International Encyclopedia of Unified Science, then as a book by
University of Chicago Press in
1962 (ISBN 0-226-45808-3). (All page numbers below refer to the third edition of the text, published in
1996). In
1969, Kuhn added a postscript to the book in which he replied to critical responses to the first edition of the book.
Kuhn dated the genesis of his book to
1947, when he was a graduate student at
Harvard University and had been asked to teach a
science class for humanities undergraduates with a focus on historical case studies. Kuhn later commented that until then, "I'd never read an old document in science."
Aristotle's
Physics was astonishingly unlike
Isaac Newton's work in its concepts of matter and motion. Kuhn concluded that Aristotle's concepts were not "bad Newton", just different.
Basic approach
Kuhn's approach to the history and philosophy of science has been described as focusing on conceptual issues: what sorts of ideas were thinkable at a particular time, what sorts of intellectual options and strategies were available to people during a given period, and the importance of not attributing modern modes of thought to historical actors. Taking this general stance, Kuhn's book argues that the evolution of scientific theory does not emerge from the straightforward accumulation of facts, but rather from a set of changing intellectual circumstances and possibilities.
Historical examples
Kuhn explains his ideas using examples taken from the
history of science.
For instance, at a particular stage in the
history of chemistry, some chemists began to explore the idea of
atomism. When many substances are heated they have a tendency to decompose into their constituent elements, and often (though not invariably) these elements can be observed to combine only in set proportions. At one time, a
mixture of
water and
alcohol was generally classified as a
compound. Nowadays it is considered to be a mixture, but there was no reason then to suspect that it was not a compound. Water and alcohol would not separate spontaneously, but they could be separated when heated. Water and alcohol can be combined in any proportions.
Now, a chemist favoring
atomic theory would view all compounds whose elements combine in fixed proportions as exhibiting normal behavior, and all known exceptions to this pattern would be regarded as anomalies whose behavior would probably be explained at some time in the future.
On the other hand, if a chemist believed that theories of the atomicity of matter were erroneous, then all compounds whose elements combined in fixed proportions would be regarded as anomalies whose behavior would probably be explained at some time in the future, and all those compounds whose elements are capable of combining in any ratio would be seen as exhibiting the normal behavior of compounds.
Nowadays the consensus is that the atomists' view was correct. But if one were to restrict oneself to thinking about chemistry using only the knowledge available at the time, either point of view would be defensible.
The Copernican Revolution
What is arguably the most famous example of a revolution in scientific thought is the
Copernican Revolution. In
Ptolemy's school of thought,
cycles and epicycles (with some additional concepts) were used for modeling the movements of the
planets in a cosmos that had a stationary Earth at its center. Given the knowledge available at the time, this approach was the most plausible. As the accuracy of celestial observations increased, the complexity of the Ptolemaic cyclical and epicyclical mechanisms had to increase in step with the increased accuracy of the observations, in order to maintain the calculated planetary positions close to the observed positions.
Copernicus proposed a cosmology in which the
Sun was at the center and the
Earth was one of the planets revolving around it. For modeling the planetary motions, Copernicus used the tools he was familiar with, namely the cycles and epicycles of the Ptolemaic toolbox. But Copernicus' model needed more cycles and epicycles than existed in the then-current Ptolemaic model. Copernicus' contemporaries rejected his
cosmology, and Kuhn asserts that they were quite right to do so: Copernicus' cosmology lacked credibility.
Thomas Kuhn illustrates how a paradigm shift later became possible when
Galileo Galilei introduced his new ideas concerning motion. Intuitively, when an object is set in motion, it soon comes to a halt. A well-made cart may travel a long distance before it stops, but unless something keeps pushing it, it will eventually stop moving. Presumably, Aristotle argued, this is a fundamental property of
nature: in order for the motion of an object to be sustained, it must continue to be pushed. Given the knowledge available at the time, this represented sensible, reasonable thinking.
Galilei put forward a bold alternative conjecture: suppose, he said, that we always observe objects coming to a halt simply because some
friction is always occurring. Galilei had no equipment with which to objectively confirm his conjecture, but he suggested that without any friction to slow down an object in motion, its inherent tendency is to maintain its
speed without the application of any additional
force.
The Ptolemaic approach of using cycles and epicycles was becoming strained: there seemed to be no end to the mushrooming growth in complexity required to account for the observable phenomena.
Johannes Kepler was the first person to abandon the tools of the Ptolemaic paradigm. He started to explore the possibility that the planet
Mars might have an
elliptic orbit rather than a
circular one. Clearly, the
angular velocity could not be constant, but it proved very difficult to find the formula describing the rate of change of the planet's angular velocity. After many years of ceaseless but fruitless calculations, Kepler arrived at what we now know as
law of equal areas.
Galilei's conjecture was merely that — a conjecture. So was Kepler's cosmology. But each conjecture increased the credibility of the other, and together, they changed the prevailing perceptions of the scientific community. Later,
Newton showed that Kepler's three laws could all be derived from a single theory of motion and planetary motion. Newton solidified and unified the paradigm shift that Galilei and Kepler had initiated.
Coherence
One of the aims of science is to find models that will account for as many observations as possible within a coherent framework. Together, Galilei's rethinking of the nature of motion and
Keplerian cosmology represented a coherent framework that was capable of rivalling the Aristotelian/Ptolemaic framework.
Once a paradigm shift has taken place, the textbooks are rewritten. Often the
history of science too is rewritten, being presented as an inevitable process leading up to the current, established framework of thought. There is a prevalent belief that all hitherto-unexplained phenomena will in due course be accounted for in terms of this established framework. Kuhn states that scientists spend most (if not all) of their careers in a process of puzzle-solving. Their puzzle-solving is pursued with great tenacity, because the previous successes of the established paradigm tend to generate great confidence that the approach being taken guarantees that a solution to the puzzle exists, even though it may be very hard to find. Kuhn calls this process
Normal science.
As a paradigm is stretched to its limits,
anomalies — failures of the current paradigm to take into account observed phenomena — accumulate. Their significance is judged by the practitioners of the discipline. Some anomalies may be dismissed as errors in observation, others as merely requiring small adjustments to the current paradigm that will be clarified in due course. Some anomalies resolve themselves spontaneously, having increased the available depth of insight along the way. But no matter how great or numerous the anomalies that persist, Kuhn observes, the practicing scientists will not lose faith in the established paradigm for as long as no credible alternative is available; to lose faith in the solubility of the problems would in effect mean ceasing to be a scientist.
In any community of scientists, Kuhn states, there are some individuals who are bolder than most. These scientists, judging that a
crisis exists, embark on what Thomas Kuhn calls
revolutionary science, exploring alternatives to long-held, obvious-seeming assumptions. Occasionally this generates a rival to the established framework of thought. The new candidate paradigm will appear to be accompanied by numerous anomalies, partly because it is still so new and incomplete. The majority of the scientific community will oppose any conceptual change, and, Kuhn emphasizes, so they should. In order to fulfill its potential, a scientific community needs to contain both individuals who are bold and individuals who are conservative. There are many examples in the history of science in which confidence in the established frame of thought was eventually vindicated. Whether the anomalies of a candidate for a new paradigm will be resolvable is almost impossible to predict. Those scientists who possess an exceptional ability to recognize a theory's potential will be the first whose preference is likely to shift to the challenging paradigm. There typically follows a period in which there are adherents of both paradigms. In time, if the challenging paradigm is solidified and unified, it will replace the old paradigm, and a
paradigm shift will have occurred.
Three phases
Chronologically, Kuhn distinguishes three phases.The first phase, which is undergone only once, is the
pre-scientific phase, in which there is no consensus on any
theory. This phase is characterized by several incompatible and incomplete theories. If this pre-scientific community eventually gravitates to one of these frames of thought, leading to wide-spread consensus on choice of
methods,
terminology, recognition of what kind of
experiment is likely to contribute to sharpening the
insights, then the second phase, normal science begins. From time to time, a science may go through a phase of revolutionary science.
Transition period
The transition period between paradigms is neither quick nor calm. Sometimes, as
Max Planck observed, and Kuhn quoted (SSR, p. 151):
"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."
According to Kuhn, the scientific paradigms before and after a paradigm shift are so different that their theories are incomparable. The paradigm shift does not just change a single theory, it changes the way that words are defined, the way that the scientists look at their subject and, perhaps most importantly, the questions that are considered valid and the rules used to determine the truth of a particular theory. Kuhn observes that they are
incommensurable — literally, lacking comparison, untranslatable. New theories were not, as they had thought of before, simply extensions of old theories, but radically new worldviews.This incommensurability applies not just before and after a paradigm shift, but between conflicting paradigms. It is simply not possible, according to Kuhn, to construct an impartial language that can be used to perform a neutral comparison between conflicting paradigms, because the very terms used belong within the paradigm and are therefore different in different paradigms. Advocates of mutually exclusive paradigms are in an insidious position:
"Though each may hope to convert the other to his way of seeing science and its problems, neither may hope to prove his case. The competition between paradigms is not the sort of battle that can be resolved by proof." (SSR, p. 148).
Kuhn (SSR, section XII) points out that the probabilistic tools used by
verificationists are in themselves inadequate to the task of deciding between
conflicting theories, since they are a component of the very paradigms they seek to compare. Similarly, observations intended to
falsify a statement will be part of one of the paradigms they seek to compare, and so inadequate to the task. According to Kuhn, the concept of falsifiability does not help in understanding why and how science has developed the way it did. In the actual practice of science, scientists will only consider the possibility that a theory is falsified if an alternative that they judge as credible is available. If there isn't, the scientist will trust the established frame of thought. If a paradigm shift has taken place, the schoolbooks are rewritten, stating that the previous theory is falsified.
In the postscript in the 3rd edition, in section 6, Kuhn writes about his opinion on the matter of scientific progress. He describes the thought experiment of an observer, who gets to inspect a collection of theories that have been stages in a succession of theories. What if the observer is presented with these theories without explicit indications of their chronological order? Kuhn expects that it will be possible to reconstruct the original chronology on the basis of the content and scope of the theories, because the more recent theories will be better instruments for solving the kind of puzzles that scientists aim to solve. Kuhn writes:
That is not a relativist's position, and it displays the sense in which I am a convinced believer in scientific progress.SSR is interpreted by
postmodern and
post-structuralist thinkers as having undermined the enterprise of science by showing that scientific knowledge is dependent on the
culture of groups of scientists rather than on adherence to a specific, definable method. In this regard, Kuhn is considered a precursor to the more radical thinking of
Paul Feyerabend. Kuhn's work has also been interpreted as blurring the
demarcation between scientific and
non-scientific enterprises because it describes scientific progress without reference to an idealized
scientific method that can be used to distinguish science from non-science. In the years after the publication of
The Structure of Scientific Revolutions, debate raged with adherents of
Popper's falsificationism such as
Imre Lakatos.
On the one hand,
logical positivists and many scientists criticize Kuhn's "humanizing" of the scientific process going too far, while the postmodernists in line with Feyerabend have criticized Kuhn for not going far enough. SSR was also embraced by those wishing to discredit or attack the authority of science, such as
creationists and
radical environmentalists, and the changing national attitudes about science which occurred at the same time of the book's publication (
Rachel Carson's
Silent Spring was released in the same year), and modern scholars have wondered whether Kuhn himself would have made more explicit that he meant not to create a tool with which to undermine science had he seen what was coming down the pipe.
Outside of the history and philosophy of science, the book's basic tenets have been adopted and co-opted by a variety of fields and disciplines.
Changes in
politics,
society, and
business are often expressed in Kuhnian terms, however poor their analog to science may seem to scientists and historians. The terms
paradigm and "
paradigm shift" have become such notorious buzzwords that in many circles they are considered hollow and empty, and rarely have any strong connection to Kuhn's original text.
In
1987, Kuhn's work was reported as the most heavily cited book of the
20th century, and the
Times Literary Supplement labeled it as one of "The Hundred Most Influential Books Since the Second World War."
Kuhn's SSR was soon criticized by his colleagues in the history and philosophy of science. In 1965, a special symposium on Kuhn's SSR was held at an International Colloquium on the Philosophy of Science was held at Bedford College, London, chaired by Sir
Karl Popper. The symposium led to the publication of the presentations and other essays, most of them critical, which were ultimately published in an influential volume of essays that went through 21 printings by 1999. Kuhn expressed the opinion that his critics' readings of his book were so inconsistent with his understanding of it that he was "tempted to posit the existence of two Thomas Kuhns," one the author of his book, the other the person who was being criticized in the symposium by "Professors Popper,
Feyerabend,
Lakatos,
Toulmin and Watkins."
[Imre Lakatos and Alan Musgrave, eds. Criticism and the Growth of Knowledge: Volume 4: Proceedings of the International Colloquium in the Philosophy of Science, London, 1965, (Cambridge: Cambridge University Press, 1970), pp. 231.]Margaret Masterman, a computer scientist working in computational linguistics, provided a critique of Kuhn's definition of "paradigm", noting that Kuhn uses the word in at least 21 subtly different ways. She claimed that this ambiguity contributed to misunderstandings by philosophically inclined critics of his book, thereby undermining the effectiveness of his argument with which she generally agreed. Kuhn responded to Masterman's criticisms in his postscript in the third edition, using the word "disciplinary matrix" to refer to a set of concepts, values, techniques, and methodologies rather than the word "paradigm."
[Margaret Masterman, "The Nature of a Paradigm," pp. 59-89 in Lakatos and Musgrave, eds. Criticism and the Growth of Knowledge.]C.R. Kordig, in a series of texts published in the early 1970's, asserted a position somewhere between that of Kuhn and the older philosophy of science. The crucial point of Kordig's analysis centered around the existence of observational invariance and his criticism of the Kuhnian position was that the incommensurability thesis was too radical, rendering it impossible to explain the confrontation of scientific theories which actually takes place. According to Kordig, it is possible to admit the existence of revolutions and paradigm shifts in science while still recognizing that theories which belong to different paradigms can be compared and confronted on the plane of observation.Those who accept the incommensurability thesis do not do so because they admit the discontinuity of paradigms, but because they attribute as an effect of such shifts a radical change in meanings.
[Kordig, C.R. (1973), Discussion:Observational Invariance in "Philosophy of Science", 40, pp. 558-69]Kordig maintains, in the first place, that there is a common observational plane.
Kepler and
Tycho Brahe, for example, when trying to explain the relative variation of the distance of the sun from the horizon at sunrise, both see the same thing (the same configuration is designed on the retina of each individual). This is but one example of the fact that "rival scientific theories share some observations, and therefore some meanings." Kordig suggests that, with this approach, he is not reintroducing the distinction between observations and theory, where the former is assigned a privileged and neutral status, but that one can affirm more simply that, even if there is no sharp distinction between theory and observations, this does not imply that at the two extremes of this polarity there are no comprehensible differences.
On a second level, there is, for Kordig, a common plane of inter-paradigmatic standards or shared normswhich permit the effective confrontation of rival theories.
In 1973, Hartry Field published an article which also sharply criticized Kuhn's idea of incommensurability. In particular, he took issue with this passage from Kuhn:
"Newtonian mass is immutably conserved; that of Einstein is convertible into energy. Only at very low relative velocities can the two masses be measured in the same way, and even then they must not be conceived as if they were the same thing." (Kuhn 1970).
Field takes this idea of incommensurability between the same terms in different theories one step further, transforming the entire nature of the discussion. Instead of attempting to identify a persistence of the reference of terms in different theories, Field's analysis results in the recognition of the indeterminacy of reference even within single theories. Field takes up the example of the term "mass" and asks what exactly does "mass" mean in modern post-relativistic physics. He finds that there are at least two different definitions:
1) Relativistic mass: the mass of a particle is equal to the total energy of the particle divided by the speed of light squared. Since the total energy of a particle in relation to one system of reference differs from the total energy in relation to other systems of reference, while the speed of light remains constant in all systems, it follows that the mass of a particle has different values in different systems of reference.
2) "Real" mass: the mass of a particle is equal to the non-kinetic energy of a particle divided by the speed of light squared. Since non-kinetic energy is the same in all systems of reference, and the same is true of light, it follows that the mass of a particle has the same value in all systems of reference.
Now projecting this distinction backward in time onto Newtonian dynamics, we can formulate the following two hypotheses:
HR: the term "mass" in Newton denotes relativistic mass.
Hp: the term "mass" in Newton denotes "real" mass.
And, according to Field, it is impossible to decide which of these two affermations is true. Before the discovery of the theory of relativity, the term "mass" was referentially indeterminate. But this doesn't mean that the term mass did not have a different meaning than that which it now has. The problem is not with meaning but with reference. The reference of such terms as mass is only partially determined: we don't really know how Newton intended his use of this term. On this basis, we can reformulate the two hypotheses above:
HR*: the term "mass" in Newton partially denotes the relativistic mass.
HP*: the term "mass" in Newton partially denotes the "real" mass.
As a consequence, neither of the two terms fully denotes (refers). The conseqeunce of this result is that it is improper to maintain that a term has changed its reference during the course of a scientific revolution. It is more appropriate to describe the process of development of such terms as "mass" as "having undergone a denotional refinement" during the course of a scientific revolution.[ Field, H. (1973), Theory Change and the Indeterminacy of Reference, in "The Journal of Philosophy", 70, pp. 462-81]
In his 1970, Steven Toulmin argued that a more realistic picture of science than that presented in SSR would admit the fact that revisions in science take place much more frequently and are much less dramatic than can be explained by the revolution/normal science model. Such revisions occur, in Toulmin's view, quite often during periods of what Kuhn would call "normal science." In order for Kuhn to explain such revisions in terms of the non-paradigmatic puzzle-solutions of normal science, he would need to delineate a, perhaps implausibly, sharp distinction between paradigmatic and non-paradigmatic science.[Toulmin, S. (1958), The Uses of argument. Camridge University Press, London.]
The tight relation between the interpretationalist hypothesis and a holistic conception of beliefs is at the base of the idea of the dependence of perception on theory, a central concept in Kuhn's Structure of Scientific Revolutions. Kuhn (1962), Norwood Hanson (1958) and Nelson Goodman (1968) have all maintained that the perception of the world depends on how the percipient conceives the world: two individuals (two scientists) who witness the same phenomenon and are steeped in two radically different theories will see two radically different things. It is our interpretation of the world, in this view, which determines that which we see.[ Ferretti, F. (2001) Jerry A. Fodor. Rome:Editori Laterza. ISBN 8842062200 ]
Jerry Fodor attempts to establish that this theoretical paradigm is fallacious and misleading by demonstrating the impenetrability of perception to the background knowledge of subjects. The strongest case can be based on the evidence from experimental cognitive psychology itself: the persistence of perceptual illusions. Just knowing that the two horizontal lines in the Muller-Lyer illusion are equal does not prevent one from continuing to see them as one being longer than the other. It is this impenetrability of the information elaborated by the mental modules (informationally encapsulated) which limits the extent of interpretationalism.
In epistemology, for example, the criticism of, what Fodor calls, the interpretationalist hypothesis accounts for the common sense intuition (at the base of naïve physics) of the independence of reality from the conceptual categories of the epistemic subject. If the processes of elaboration of the mental modules are independent of the background theories, in fact, then it is possible to maintain the realist view that two scientists who embrace two radically diverse theories see the world exactly in the same manner even if they interpret it differently. The point is that is necessary to distinguish between observations and the perceptual fixation of beliefs. While it is beyond doubt that the second process involves the holistic relation between beliefs, the first is largely independent of the background beliefs of individuals.
Other critics, such as Israel Sheffler, Hilary Putnam and Saul Kripke, have focused on the Fregean distinction between sense and reference in order to defend a position of scientific realism. Sheffler contends that Kuhn confuses the meanings of terms such as "mass" with their reference. While their meanings may very well differ, their reference (the object or entity to which they correspond in the external world) remains fixed. Putnam and Kripke developed a causal theory of reference which does away with the idea of meaning altogether. These ideas of reference anchor theories to the external world and thus make it possible to measure their progress toward the truth about the external world, contrary to the view of Kuhn.* Important publications in philosophy of science
* Exemplar* Summary of book by Frank Pajares
* Text of chapter 9 and a postscript at Marxists.org
*Thomas Kuhn, 73; Devised Science Paradigm (obituary by Lawrence Van Gelder, New York Times, 19 June 1996)
