The structure of scientific revolutions – the 1967 postscript

September 11, 2008

Below is my page-by-page summary of Kuhn’s 1967 postscript to The Structure of Scientific Revolutions.

The following points seem to me to contain the essence of Kuhn’s thesis:

Exemplars:

  1. Exemplars (solved problems) are an important component of any specific scientific world-view. Without exemplars the laws and theories have little empirical content. The exemplars teach practitioners how to attach the relevant abstractions to elements of particular problems and how to see a variety of situations as being alike.
  2. The intuitive knowledge of which situations are alike is analyzable but not by specifying rules since it is perceptual rather than interpretive knowledge. It is similar to other knowledge of perception: e.g., identifying certain light patterns as all representing swans. Perceptual knowledge is selected for “success” – success in survival in the primitive case, success in puzzle solving in the scientific case.
  3. The situation may be similar in non-scientific schools (e.g., art).

Revolutions:

  1. Scientific revolutions – “a special sort of change in scientific thinking involving a certain sort of reconstruction of group commitments” – occur regularly on the smaller scale (within communities of dozens to hundreds).
  2. Crisis is the usual mechanism inducing revolutions. Crises supply a self-correcting mechanism which ensures that the rigidity of normal science will not forever go unchallenged.
  3. Judgments of scientific values – simplicity, consistency and compatibility – can vary greatly from individual to individual. Therefore, debates on theory-choice cannot be decided in a formal way. Still, those values constrain the dominant group view. This explains why competing world-views are rare in science but are common in other human activities.

Scientific progress:

  1. Because the commitment by scientists to puzzle-solving success shapes the long-term structure of scientific development (even if the application of this commitment in any particular case is ambiguous and subjective), scientific development, like biological development, is unidirectional and irreversible. When comparing scientific theories held by various scientific specialties to theories held by the specialty from which the former had their origins, “an uncommitted observer” would be able to consistently distinguish the newer theories from the older. The newer theories will enable more accurate, quantitative, predictions, in a wider variety of situations and they will be more esoteric. Differences in simplicity, scope and compatibility with other specialties are not as telling.
  2. Scientific progress is therefore well defined, but, like biological progress, it cannot be said that science comes closer and closer to a certain goal – “reality”. There is no objective reality which stands outside a specific scientific world-view.

Detailed summary

Page references are to the 1970 University of Chicago Press edition (published as v. 2, no. 2 in the International Encyclopedia of Unified Science series).

  1. (p. 175) Two senses of “paradigm”: (a) entire constellation of beliefs, values, techniques, and son shared by the members of a given community, (b) one element in the constellation – the concrete puzzle-solution which, employed as models or examples can replace explicit rules as a basis for the solution of the remaining puzzles of normal science.
  2. (p. 176-177) Community is prior to paradigm(a). Practicing scientists respond at once to questions about their community affiliations. A scientific community consists of the practitioners of a scientific specialty, sharing similar education and professional initiations using standard literature. Competing scientific communities are rare. The members of a community see themselves and are seen by others as uniquely responsible for the pursuit of shared goals.
  3. (p. 177-178) Various sizes of communities: At top, all natural scientists, at bottom, formal and informal communication networks with about 100 members, occasionally significantly fewer. Usually scientists belong to more than one.
  4. (p. 179) Transition from “pre-paradigm” to “post-paradigm” is not marked by presence of paradigm(a) (which exists always), but its nature [emergence of paradigm(b)?].
  5. (p. 180) A community can share a paradigm(a) but remain uncommitted, as a community, or other matters. Those remain outside the paradigm(a).
  6. (p. 180-181) A revolution is a special sort of change involving a certain sort of reconstruction of group commitments. Need not be large, need not seem revolutionary to those outside a community, consisting perhaps of fewer than 25 people. Occurs regularly on the smaller scale.
  7. (p. 181) Crisis is the usual mechanism inducing revolutions, but not necessarily the only one. Crises supply a self-correcting mechanism which ensures that the rigidity of normal science will not forever go unchallenged.
  8. (p. 182) Paradigm(a) may be called “disciplinary matrix”.
  9. (p. 182-183) One element in paradigm(a) is “symbolic generalizations” (f=ma, I = V/R, H = RI^2). These may describe laws of nature, when the quantities are known in advance, but usually define some of the symbols employed. The balance in these two functions changes over time.
  10. (p. 184) Another component in paradigm(a) is “beliefs in particular models”. For example “heat is kinetic energy of the constituent parts of bodies” or “molecules of a gas behave like tiny elastic billiard balls in random motion”. These supply the community with preferred or permissible analogies and metaphors. They thus determine what is accepted as a puzzle solution – and what is accepted as a puzzle and its importance.
  11. (p. 184-185) “Values” are also a part of paradigm(a): accurate prediction are desirable, preferably quantitative. Theories must permit puzzle-formation and solution. They should be simple, self consistent and compatible with other theories.
  12. (p. 185-186) Judgments of simplicity, consistency and compatibility can vary greatly from individual to individual. Still, those values constrain the dominant group view.
  13. (p. 187-191) Paradigms(b) – exemplars – are another component of paradigm(a). These are the central element of what is most novel about the book. Exemplars were traditionally seen as examples of application of rules of a theory, and thus secondary to the rules. The book claims that without exemplars the laws and theories have little empirical content. The exemplars teach practitioners how to attach the relevant abstractions to elements of particular problems. The ability to see a variety of situations as like each other is the main thing a student acquires by doing exemplary problems.
  14. (p. 191-195) The intuitive knowledge of which situations are alike is shared by the practitioners in a community. It is analyzable but not by specifying rules since it is perceptual rather than interpretive knowledge. It is similar to other knowledge of perception: e.g., identifying certain light patterns as all representing swans.
  15. (p.195-196) Perceptual knowledge is selected for “success” – success in survival in the primitive case, success in puzzle solving in the scientific case.
  16. (p. 199-200) Debates on theory-choice cannot be decided in a formal way. The decision depends on shared values judged differently by different people.
  17. (p. 200-203) Communication between proponents of different theories is made difficult by the fact that the groups use the same language to describe different notions, since the similarity relations are different in different theories. Communication by-passing those differences in notions would be cumbersome but possible.
  18. (p. 203-204) Most new theories will have some difficulties with some matters that are handled well by the established theory, providing grounds for preferring the established theory. Counter-arguments, in any case, are always available, and no rules prescribe how the balance must be struck. Nevertheless, as argument piles on argument and as challenge after challenge is successfully met, only blind stubbornness can at the end account for continued resistance.
  19. (p. 204) Veteran practitioners will be unable to use the new way of thinking mandated by the new theory, even if they are persuaded that it is successful.
  20. (p. 205-206) The commitment by scientists to puzzle-solving success shapes the long-term structure of scientific development even if the application of this commitment in any particular case is ambiguous and subjective. This makes scientific development, like biological development, unidirectional and irreversible. When comparing scientific theories held by various scientific specialties to theories held by the specialty from which the former had their origins, “an uncommitted observer” would be able to consistently distinguish the newer theories from the older. The newer theories will enable more accurate, quantitative, predictions, in a wider variety of situations and they will be more esoteric. Differences in simplicity, scope and compatibility with other specialties are not as telling.
  21. (p. 206) Scientific progress is well defined in the sense of 20., but, like biological progress, it cannot be said that science comes closer and closer to a certain goal – “reality”. There is no objective reality which stands outside a paradigm(a).
  22. (p. 207-208) The way scientists actually carry out science is a good indication of what they should be doing, since they are experts in this craft. Their behavior therefore is evidence supporting a theory of science that explains their behavior as reasonable rather than as an anomaly.
  23. (p. 208-209) It is long known that many non-scientific communities experience revolutions. It may be useful to analyze those in terms of paradigms(b) instead of changes of rules. Science, however, is materially different than the activities of other groups: characteristics such as scarcity of competing paradigms(a), focus on puzzle solving, and scientific communities addressing only themselves set the scientific activity apart.
  24. (p. 210) Scientific knowledge is a characteristic of the community.
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