Jacob Conrad
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Thomas S. Kuhn, _The Structure of Scientific Revolutions_, 2nd edition, U. of Chicago Press, 1970
Ch. II, "The Route to Normal Science", pp. 10 - 11
In this essay, "normal science" means research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice. Today, such achievements are recounted, though seldom in their original form, by science textbooks, elementary and advanced. These textbooks expound the body of accepted theory... Before such books became popular...many of the famous classics of science fulfilled a similar function. Aristotle's Physica, Ptolemy's Almagest...these and many other works served for a time implicitly to define the legitimate problems and methods of a research field for succeeding generations of practitioners. They were able to do so because they shared two essential characteristics. Their achievement was sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity. Simultaneously, it was sufficiently open-ended to leave all sorts of problems for...practitioners to resolve.
Achievements that share these two characteristics I shall henceforth refer to as "paradigms," a term that relates closely to "normal science."... These are the traditions which the historian describes under such rubrics as "Ptolemaic astronomy"...and so on. The study of paradigms...is what mainly prepares the student for membership in the particular scientific community with which he [sic] will later practice... Men [sic] whose research is based on shared paradigms are committed to the same rules and standards for scientific practice.