783A new theory, however special its range of application, is seldom or never just an increment to what is already known. Its assimilation requires the reconstruction of prior theory and the re-evaluation of prior fact, an intrinsically revolutionary process that is seldom completed by a single man and never overnight.
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784Aristotle's Physica, Ptolemy's Almagest, Newton's Principia and Optiks, Franklin's Electricity, Lavoisier's Chemistry, and Lyell's Geology--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 the redefined group of practitioners to resolve.
784
785The study of paradigms, including many that are far more specialized than those named illustratively above, is what mainly prepares the student for membership in the particular scientific community with which he will later practice. Because he there joins men who learned the bases of their field from the same concrete models, his subsequent practice will seldom evoke overt disagreement over fundamentals. Men whose research is based on shared paradigms are committed to the same rules and standards for scientific practice.
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786To be accepted as a paradigm, a theory must seem better than its competitors, but it need not, and in fact never does, explain all the facts with which it can be confronted.
18
787Truth emerges more readily from error than from confusion. Francis Bacon.
18
788Rules, I suggest, derive from paradigms, but paradigms can guide research even in the absence of rules.
42
789Normal science can be determined in part by the direct inspection of paradigms, a process that is often aided by but does not depend upon the foundation of rules and assumptions. Indeed, the existence of a paradigm need not even imply that any full set of rules exist.
44
790Footnote 1. Michael Polanyi has brilliantly developed a very similar theme, arguing that much of the scientist's success depends upon "tacit knowledge" i.e. upon knowledge that is acquired through practice and that cannot be articulated explicitly.
44
791Scientists work from models acquired through education and through subsequent exposure to the literature often without quite knowing or needing to know what characteristics have given these models the status of community paradigms. And because they do so, they need no full set of rules. The coherence displayed by the research tradition in which they participate may not imply even the existence of an underlying body of rules and assumptions that additional historical or philosophical investigation might uncover. That scientists do not usually ask or debate what makes a particular problem or solution legitimate tempts us to suppose, at least intuitively, they know the answer. But it may only indicate that neither the question nor the answer is felt to be relevant to their research. Paradigms may be prior to, more binding, and more complete than any sort of rules for research that could be unequivocally abstracted from them.
46
792Discovery commences with the awareness of anomaly, i.e. with the recognition that nature has somehow violated the paradigm-induced expectations that govern normal science. It then combines with a more or less extended exploration of the area of anomaly. And it closes only when the paradigm theory has been adjusted so that the anomalous has become the expected.
53
793That proliferation of versions of a theory is a very usual symptom of crisis.
71
794These three examples are almost entirely typical. In each case a novel theory emerged only after a pronounced failure in the normal problem-solving activity. Furthermore, except for the case of Copernicus in which factors external to science played a particularly large role, that breakdown and the proliferation of theories that is its sign occurred no more than a decade or two before the new theory's enunciation. The novel theory seems a direct response to crisis.
75
795Let us then assume that crises are a necessary precondition for the emergence of novel theories and ask next how scientists respond to their existence.
77
796Scientists never do when confronted by severe and prolonged anomalies: They do not remove the paradigm that has led them into crisis. They do not treat anomalies as counterinstances.
77
797Once it has achieved the status of a paradigm, a scientific theory is declared invalid only if an alternate candidate is available to take its place.
77
798One perceptive historian, viewing a case of science's reorganization by paradigm change recently described it as "picking up the other end of the stick," a process that involves "handling the same bundle of data as before, but placing them in a new system of relations with one another by giving them a different framework."
85
799As in political revolutions, so in paradigm choice--there is no standard higher than the assent of the relevant community.
94
800Normal research, which is cumulative, owes its success to the ability of scientists regularly to select problems that can be solved with conceptual and instrumental techniques close to those already in existence. Et seq.
96
801There are only three types of phenomena about which a new theory might be developed.
1. Provided by existing paradigms
2. Indicated by incomplete paradigms
3. Unaddressed by existing paradigms
97
802Interpretation can only articulate a paradigm, not correct it. Paradigms are not corrigible by normal science at all. Et seq. Normal science-Recognition of anomalies & Crisis.
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803Verification is like natural selection. It picks out the most viable among the actual alternatives in a particular historical situation. Whether that choice is the best that could have been made if still other alternatives had been available or if the data had been if another sort is not a question that can usefully be asked. There are no tools to employ in seeking answers to it.
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804A very different approach to this whole network of problems has been developed by Karl R. Popper who denounces the existence of any verification process at all. Instead he emphasizes the importance of falsification, i.e. of the test that [...] necessitates the rejection of an established theory.
145
805Why should [scientific revolution] move steadily ahead in ways that say art, political theory, or philosophy does not? Why is progress a perquisite reserved almost exclusively for the activities we call science? [...] We must conclude it by asking whether a substitute can be found.
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