Sunday, September 9, 2007

Thomas Kuhn (1922-)

Sierra Club


It is, I think, particularly in periods of acknowledged crisis that scientists have turned to philosophical analysis as a device for unlocking the riddles of their field. Scientists have not generally needed or wanted to be philosophers.


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Thomas Samuel Kuhn (1922-1996) wrote extensively on the history of science, and developed several important notions in the philosophy of science. He is most famous for his book The Structure of Scientific Revolutions in which he presented the idea that science does not "evolve gradually toward truth", but instead undergoes periodic revolutions which he calls paradigm shifts. Kuhn's analysis of the history of science suggests to him 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 of explanation. This phase is generally characterized by several incompatible and incomplete theories.

Eventually one of these theories "wins" and this ushers in the second of Kuhn's phases: Normal Science. A scientist working within this phase has an overriding theory (or set of theories) which Kuhn calls a paradigm. Within normal science, the scientist's job is to elaborate, expand, and further justify the paradigm. Eventually, however, problems arise, 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 or group thereof, and someone proposes a replacement or redefinition of the theory. This is what Kuhn calls a paradigm shift, ushers in a new period of revolutionary science. Kuhn believes that all scientific fields go through these 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) revolved around the Earth. Prior to Copernicus there was an elaborate set of epicycles (circles on top of circles) which were used to predict the movements of the 'heavenly bodies'. Ptolmey'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. Of course, 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 '30s and Suess and Wegener's plate tectonics the 1960's by geologists.

According to Kuhn, the science before and after a paradigm shift are so much 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. It is important to understand that Kuhn's contribution to the philosophy of science is more precisely an observation about the sociology of science as practiced by humans. We can imagine a practice of science by Little Green Men somewhere whose characteristic way of handling science, changes in theory, new data, etc do not work the way Kuhn suggested in Structure. Thus we can see that a philosophy of science which applies to both human practice and to LGM practice could not be as it is said, by many, that Kuhn claimed. A reading of Structure makes clear that he, himself, was not making such a claim about the nature of science. There is an old observation (by Planck) that science progresses when the old guys die off and take their outmoded beliefs with them. A prematurely Kuhnian comment, perhaps, but not germaine to fundamental questions about the nature of science and scientific method. Popper's falsifiability is a much better candidate for a characteristic of science which will be invariant across all those doing science (ie, both us and the LGM and everyone else will have to do it the same way). Kuhn is very often misunderstood to have said something 'post-modern' about the nature of science. That is -- approximately -- that he showed that scientific truth changes with the scientist or the group of scientists doing it. This is further extended, in further misunderstanding, to suggest that such things as cultural relativity, prejudice, and so on are at the heart of science. This deconstruction of science has become common among some observers, but cannot be extended very far since science differs in fundamental ways from other intellectual enterprises. It is fundamentally a misunderstanding of the nature of science and, under the best conditions, its practice.

Like all human endeavors, science has shown itself fully susceptible to fad, fashion, delusion, and prejudice -- in every case, pernicious, trivial, and everything in between. S. J. Gould's Mismeasure of Man is a booklength exposure of this regrettable fact in regard to claims -- 'scientific' claims -- about the relative intelligence of groups based on ethnicity, gender, etc. This intrusion of human concerns into the practice of an intellectual effort is not, or should not be, surprising. However, regrettable.

Unlike other human endeavors, science has, at least in theory (however little actually resorted to in actual practice), a method of distinguishing between scientific claims based on fad, fashion, etc and scientific claims which can actually survive experimental testing and so require no support from fads, fashion, faith, etc. It is this, not always promptly applied, potential for correction which distinguishes 'science' from 'non-science', together with a certain consistency and methodical quality in the reasoning. It should also rescue Kuhn's account of the sociology of human science from its too common misunderstandings, but too often doesn't. [This article is licensed under the GNU Free Documentation License and uses material adapted in whole or in part from the Wikipedia article on Thomas Kuhn.]

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