"To 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."
"Truth emerges more readily from error than from confusion." Francis Bacon, op. cit., p. 210 The Works of Francis Bacon, Ed. J. Spedding, R. L, Ellis, & D. D. Heath (New York, 1896)
"Paradigms gain their status because they are more successful than their competitors in solving a few problems that the group of practitioners has come to recognize as acute. To be more successful is not, however, to be either completely successful with a single problem or notably successful with any large number. The success of a paradigm is at the start largely a promise of success discoverable in selected and still incomplete examples."
"Mopping-up operations are what engage most scientists throughout their careers. ... Nor do scientists normally aim to invent new theories, and they are often intolerant of those invented by others."
"The pre-paradigm period ... is regularly marked by frequent and deep debates over legitimate methods, problems, and standards of solution, though these serve rather to define schools than produce agreement. ... (p. 48) "Although almost non-existent during periods of normal science, they recur regularly just before and during scientific revolutions, the periods when paradigms are first under attack and then subject to change."
"Novelty ordinarily emerges only for the man who, knowing with precision what he should expect, is able to recognize that something has gone wrong. Anomaly appears only against the background provided by the paradigm ... In the normal mode of discovery, even resistence to change has a use ... By ensuring that the paradigm will not be easily surrendered, resistance guarantees that scientists will not be lightly distracted and that the anomalies that lead to paradigm change will penetrate existing knowldege to the core."
"So long as the tools a paradigm supplies continue to prove capable of solving the problems it defines, science moves fastest and penetrates most deeply through confident employment of the tools. The reason is clear. As in manufacture so in science - retooling is an extravagance to be reserved for the occasion that demands it. The significance of crises is the indication they provide that an occasion for the retooling has arrived."
"Once it has achieved the status of paradigm, a scientific theory is declared invalid only if an alternative candidate is available to take its place. ... The decision to reject one paradigm is always simultaneously the decision to accept another ... that decision involves the comparison of both paradigms with nature and with each other."
"if an anomaly is to evoke a crisis, it must usually be more than just an anomaly. There are always difficulties somewhere in the paradigm-nature fit ... The scientist who pauses to examine every a nomaly he notes will seldom get significant work done."
"When the transition [to the new paradigm] is complete, the profession will have changed its view of the field, its methods, and its goals. ... [some who] have noted this aspect of scientific advance have emphasized its similarity to a change in visual gestalt: the marks on paper that were first seen as a bird are now seen as an antelope, or vice-versa. ... the switch of gestalt ... is a useful elementary prototype for what occurs in full-scale paradigm shift."
"It is ... particularly in periods of acknowledged crisis that scientists have turned to philosophical analysis as a device for unlocking the riddles of their field."
"Nor is it an accident that the so-called thought experiement should have played so critical a role in the progress of research."
"Almost always the men who achieve these fundamental inventions of a new paradigm have been either very young or very new to the field whose paradigm they change."
"Like the choice between competing political institutions, that between competing paradigms proves to be a choice between incompatible modes of community life. Because it has that character, the choice is not and cannot be determined merely by the evaluative procedures characteristic of normal science, for those depend in part upon a particular paradigm and that paradigm is at issue. When paradigms enter, as they must, into a debate about paradigm choice, their role is necessarily circular. Each group uses its own paradigm to argue in that paradigm's defense."
"...this issue of paradigm choice can never be unequivocally settled by logic and experiment alone."
"since no paradigm ever solves all the problems it defines and since no two paradigms leave all the same problems unsolved, paradigm debates always involve the question: Which problems is it more significant to have solved. Like the issue of competing standards, that question of values can be answered only in terms of criteria that lie outside of normal science altogether, and it is that recourse to external criteria that most obviously makes paradigm debates revolutionary."
"It is as elementary prototypes for these transformations of the scientific world that the familiar demonstrations of a switch in visual gestalt prove so suggestive. What were ducks in the scientist's world before the revolution are rabbits afterwards. The man who first saw the exterior of the box from above later sees its interior from below. Transformations like these, though usually more gradual and almost always irreversible, are common concomitants of scientific training."
"Surveying the rich experimental literature from which these examples are drawn makes one suspect that something like a paradigm is prerequisite to perception itself. What a man sees depends both upon what he looks at and also upon what his previous visual-conceptual experience has taught him to see. In the absence of such training there can only be, in William James' phrase, "a bloomin' buzzin' confusion.""
"The competition between paradigms is not the sort of battle that can be resolved by proofs."
"the proponents of competing paradigms practice their trades in different worlds. ... Practicing in different worlds, the two groups of scientists see different things when they look from the same point in the same direction."
"Just because it is a transitiion between incommensurables, the transition between competing paradigms cannot be made a step at a time, forced by logic and neutral experience. Like the gestalt switch, it must occur all at once (though not necessarily in an instant) or not at all."
Max Planck: "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. (1947 Scientific Autobiography and Other Papers. Trans. F. Gaynor, New York, pp 33-34.)
"if a new candidate for paradigm had to be judged from the start by hard-headed people who examined only the relative problem-solving ability, the sciences would experience very few major revolutions. But paradigm debates are not really about relative problem-solving ability ... Instead, the issue is which paradigm should in the future guide research on problems many of which neither competitor can yet claim to resolve completely. A decision between alternate ways of practicing science is called for, and in the circumstances that decision must be based less on past achievement than on future promise. ... A decision of that kind can only be made on faith.
"Something must make at least a few scientists feel that the new proposal is on the right track, and sometimes it is only personal and inarticulate aesthetic considerations that can do that."