The Structure of Scientific Revolutions

Kuhn states that the practice of science comes in 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. One theory eventually becomes sufficiently accepted that scientists begin to successfully use it methodically. Other knowledge, such as common terminology, common experimental methods and equipment and, to a greater or lesser degree, a common interpretation of scientific phenomena, develops into a paradigm.

After this occurs, normal science begins. Kuhn explains that normal science is what scientists spend most of their careers doing. It can only be performed under a specific paradigm, and its goal is to explain and expand the paradigm. Kuhn explained normal science as a process of puzzle solving: armed with knowledge provided by a paradigm, scientists can begin to make well-founded and trusted assumptions about what they are studying. This may seem to violate long held ideals about objectivity in science, but it is extremely difficult to study anything without making at least a few basic assumptions (see Naive Empiricism). The challenge of normal science is to see how well one can apply all one's knowledge and assumptions to a certain problem.

It is important to note that there are advantages and disadvantages to using a paradigm to make assumptions about a particular topic. The advantage is that if all scientists are using similar assumptions, then their methods, terminology, and analyses will all be very homogenous and easily compared; it allows for greater communication and cooperation between people. However, if many scientists use similar assumptions which are not entirely correct, they may be led astray for a very long time before an anomaly occurs which brings attention to the problem. When this happens there is usually a period of disagreement between scientists, and the theory is modified in an ad hoc way to accommodate experimental evidence which might seem to contradict the original theory.

Eventually, the current explanatory theory fails to explain some phenomenon, and someone proposes a replacement or redefinition of the theory. This is what Kuhn calls a paradigm shift, which ushers in a new period of revolutionary science; all scientific fields go through paradigm shifts multiple times as new theories supplant the old.

One well-known Kuhnian example involves Copernicus' suggestion that the Earth revolves around the Sun, rather than the Ptolemaic suggestion that the Sun (and the other planets and stars) revolves around the Earth. The Ptolemaic theory used an elaborate set of epicycles (circles on top of circles) which were used to predict the movements of the heavenly bodies. Ptolemy's original epicyclic combinations were, by the Middle Ages, becoming noticeably less adequate, and fixes by later astronomers were more and more elaborate. Copernicus offered a return to an alternative view (suggested by many in antiquity) but with rather better data to support it; this new account decreased the complexity of theory necessary to account for the available observations. Once Copernicus' theory was accepted by other astronomers, it ushered in a new period of normal science. Refinements added by Kepler and Newton adhered to the new paradigm.

Other more recent examples are the acceptance of Einstein's general relativity to replace Newton's account of gravity in the 1920s and 1930s and of Suess and Wegener's plate tectonics in the 1960s by geologists.

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.

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.

This has important implications for other attempts to explain scientific progress. 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. Advocates of such 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 attributes the success of science to the way in which scientists are able to work within a paradigm, removing the need to repeatedly work from first principles. For Kuhn, it is that scientists work within a particular kind of community that explains the astonishing success of science: "The scientific community is a supremely efficient instrument for maximising the number and precision of the problem solved through paradigm change." (SSR, p. 169).

As Max Planck observed, before Kuhn:

"An important scientific innovation rarely makes its way by gradually winning over and converting its opponents ... What does happen is that its opponents gradually die out, and that the growing generation is familiarised with the idea from the beginning."

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 critical 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 idealised 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.

Thomas S. Kuhn, The Structure of Scientific Revolutions, University of Chicago Press, Chicago, 1962 - ISBN 0-226-45808-3

External links

• Summary of book by the author

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