Kant on Wheels

Peter Lipton

  • The Road since Structure: Philosophical Essays, 1970-93 by Thomas Kuhn, edited by James Conant and John Haugeland
    Chicago, 335 pp, £16.00, November 2000, ISBN 0 226 45798 2
  • Thomas Kuhn: A Philosophical History for Our Times by Steve Fuller
    Chicago, 472 pp, £24.50, June 2000, ISBN 0 226 26894 2

At a New York cocktail party shortly after the war, a young and insecure physics postgraduate was heard to blurt out to a woman he had met there: ‘I just want to know what Truth is!’ This was Thomas Kuhn and what he meant was that specific truths such as those of physics mattered less to him than acquiring metaphysical knowledge of the nature of truth. Soon afterwards, he gave up physics, but rather than take up philosophy directly, he approached it by way of the history of science. The work that followed, especially The Structure of Scientific Revolutions, published in 1962 and now with sales of well over a million copies, makes his the most important contribution to the history and philosophy of science of the 20th century.

Kuhn was struck by the consensus among those working in particular disciplines during periods of what he came to call ‘normal science’. It isn’t just that they accept the same theories and data, they also have a shared conception of how to proceed in their research, a tacit agreement about where to look next. There is agreement about which new problems to tackle, what techniques to try and what count as good solutions. It is rather as if new practitioners in a particular discipline are covertly given copies of a book of rules, the secret guide to research in their field. But no such rulebooks exist. Kuhn wanted to find out what does the job of the rules that aren’t there.

What he found was that scientists learn to proceed by example rather than by rule. They are guided by what Kuhn called their exemplars, or certain shared solutions to problems in their speciality, like the problem sets that science students are expected to work through. (‘Exemplar’ captures the most important sense of Kuhn’s famous multivalent term, ‘paradigm’.) The function of problem sets is not to test students’ knowledge but to engender it. Similarly, exemplars guide research scientists in their work, for although, unlike rules, they are specific in content, they are general in their import. Scientists will choose new problems that seem similar to the exemplary ones, will deploy techniques similar to those that worked in the exemplars, and will judge their success by the standards the exemplars exemplify.

This idea of the co-ordinating and creative power of exemplars provided Kuhn with the basis for his general model of how sciences develop. Any new area of scientific inquiry must do without exemplars to start with and hence without the co-ordination of normal science. If suitable exemplars are eventually found, normal science can proceed. But exemplars sow the seeds of their own destruction, since they will eventually suggest problems that are not soluble by the exemplary techniques. This leads to a state of crisis and in some cases to a scientific revolution, where new exemplars replace the old ones and another period of normal science begins.

A scientific revolution is more disruptive than a simple replacement of one theory by a better one, because the theories held on either side of it are not just incompatible, they are ‘incommensurable’. In Structure, Kuhn used that term to refer to various factors that make the evaluation of competing theories problematic. Scientific revolutions are not irrational episodes, they are stages of enquiry where rationality becomes a much more complex and messy business than during periods of normal science. This is so in part because straightforward argument requires many shared premises, which are what normal scientists enjoy and revolutionary scientists lack.

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