Contrary to the classic picture of scientists as dispassionate, objective investigators following the empirical evidence wherever it leads, Kuhn argued cogently that scientific theories are held dogmatically, often for reasons that have nothing to do with the evidence and sometimes even in spite of the evidence, and are overturned only when a new generation of scientists arises which has no particular allegiance to the old view. It's only when the old guard fades away and a younger cohort of independent thinkers arises that a paradigm shift, a term coined by Kuhn, occurs.
In recognition of Kuhn's achievement Matthew Rees at The New Atlantis has a feature story on his book. Here are some highlights:
The argument of Structure is not especially complicated. Kuhn held that the historical process of science is divided into three stages: a “normal” stage, followed by “crisis” and then “revolutionary” stages. The normal stage is characterized by a strong agreement among scientists on what is and is not scientific practice. In this stage, scientists largely agree on what are the questions that need answers. Indeed, only problems that are recognized as potentially having solutions are considered scientific. So it is in the normal stage that we see science progress not toward better questions but better answers. The beginning of this period is usually marked by a solution that serves as an example, a paradigm, for further research. (This is just one of many ways in which Kuhn uses the word “paradigm” in Structure.)This leads to the emergence of a new competing paradigm:
A crisis occurs when an existing theory involves so many unsolved puzzles, or “anomalies,” that its explanatory ability becomes questionable. Scientists begin to consider entirely new ways of examining the data, and there is a lack of consensus on which questions are important scientifically. Problems that had previously been left to other, non-scientific fields may now come into view as potentially scientific.
Eventually, a new exemplary solution emerges. This new solution will be “incommensurable” — another key term in Kuhn’s thesis — with the former paradigm, meaning not only that the two paradigms are mutually conflicting, but that they are asking different questions, and to some extent speaking different scientific languages. Such a revolution inaugurates a new period of normal science. Thus normal science can be understood as a period of “puzzle-solving” or “mopping-up” after the discovery or elucidation of a paradigm-shifting theory. The theory is applied in different contexts, using different variables, to fully flesh out its implications. But since every paradigm has its flaws, progress in normal science is always toward the point of another crisis.Kuhn was accused of being a post-modern relativist because he didn't think that science progresses toward truth and didn't seem quite sure whether there even was a final, complete "truth" about the world at all.
Kuhn quotes Max Planck, who famously wrote that “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.”
Over time, there again comes to be almost unanimous agreement on the validity of the predominant theory — it achieves paradigmatic status. Scientists tacitly assume agreement on the meanings of technical terms, and develop a shared and specialized technical vocabulary to facilitate data accumulation and organization. They establish journals dedicated to their scientific field, begin to cross-reference one another, and scrutinize each other’s work according to whether or not it conforms to the theory. Their students, likewise, learn to approach problems in the same way they do, much as an apprentice learns from a master. Normal science has resumed and the cycle begins anew.
It was important for Kuhn that his conception of the history and process of science was not the same as that of scientific progress. He maintained that the process of science was similar to biological evolution — not necessarily evolution toward anything, only away from previous error. In this way, Kuhn was rather skeptical about the idea of progress at all. This was the most controversial aspect of his thesis, the one that most concerned the contemporary critics of Structure, on the basis of which they accused — or celebrated — Kuhn as a champion of relativism. As University of Toronto philosophy professor Ian Hacking notes in an introductory essay prepended to the new fiftieth-anniversary edition of Structure, Kuhn’s notion that science moves away from previous error:Rees talks about the extent of Kuhn's indebtedness to Michael Polyani and also compares and contrasts him to Karl Popper. He also gives a great deal of space to Kuhn's impact on the social sciences, a discussion which should be of interest to those in these fields.seems to call in question the overarching notion of science as aiming at the truth about the universe. The thought that there is one and only one complete true account of everything is deep in the Western tradition.... In popular versions of Jewish, Christian, and Muslim cosmology, there is one true and complete account of everything, namely what God knows. (He knows about the death of the least sparrow.)
This image gets transposed to fundamental physics, many of whose practitioners, who might proudly proclaim themselves to be atheists, take for granted that there just is, waiting to be discovered, one full and complete account of nature. If you think that makes sense, then it offers itself as an ideal towards which the sciences are progressing. Hence Kuhn’s progress away from will seem totally misguided.
Rees also mentions that Kuhn, who was a physicist by training, doesn't talk much about the Darwinian revolution in biology. I thought the point was apt, but I wonder if the more interesting point isn't that biology seems to be in the midst now of a Kuhnian crisis of its own wherein the anomalies of the Darwinian claim that high levels of complexity and information are the products of blind, purposeless forces are piling up. Perhaps we're witnessing a paradigm shift in our own time in biology.