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Notes: Kuhn2012-qo The structure of scientific revolutions



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Kuhn, T. S. (2012). The structure of scientific revolutions (4th ed.). Chicago, IL: University of Chicago Press. Retrieved from






A footnote encountered by chance led me to the experiments by which Jean Piaget has illuminated both the various worlds of the 2growing child and the process of transition from one to the next.2 One of my colleagues set me to reading pape rs in the psychology of perception, my colleagues set me to reading pape rs in the psychology of perception, particularly the Gestalt psychologists ; another introduced me to B. L. particularly the Gestalt psychologists ; another introduced me to B. L. Whorf ’s speculations about the effect of language on world view; and W. V. O . Q u i n e o p e n e d f o r m e t h e p h i l o s o p h i c a l p u z z l e s o f t h e a n a l y t i c -3synthetic distinction.3 That is the sort of random exploration that the Society of Fellows permits, and only through it could I have encountered Society of Fellows permits, and only through it could I have encountered Ludwik Fleck’s almost unknown monograph, Entstehung und Entwicklung einer wis- (p. 6)

composed predominantly of social scientists confronted me with unanticipated problems about the differences between such communities and those of the natural scientists among whom I had been trained. Particularly, I was struck by the number and extent of the overt disagreements between social scientists about the nature of fi (p. 8)

physics, chemistry, or biology normally fails to evoke the controversies over fundamentals that today often seem endemic among, say, over fundamentals that today often seem endemic among, say, psychologists or sociologists. Attempting to discover the source of that psychologists or sociologists. Attempting to discover the source of that difference led me to recognize the role in scientific research of what I have since called “paradigms.” (p. 8)

I. Introduction: A Role for History (p. 13)

That image has previously been drawn, even by scientists themselves, mainly from the study of finished scientific achievements as these are recorded in the classics and, more (p. 13)

This essay attempts to show that we have been misled by them in (p. 13)

Those texts have, for example, often seemed to imply that the content of science is uniquely exemplified by the observations, laws, and theories described in their pages. (p. 13)

teaching only through textbooks is doing injustice to science learning. (p. 13)

If science is the constellation of fa cts, theories, and methods collected in current texts, then scientists ar e the men who, successfully or not, have striven to contribute one or another element to that particular have striven to contribute one or another element to that particular constellation. Scientific development becomes the piecemeal process by constellation. Scientific development becomes the piecemeal process (p. 13)

In recent years, however, a few historians of science have been finding it more and more difficult to fulfil the functions that the concept of development-by-accumulation assigns to them. As chroniclers of an development-by-accumulation assigns (p. 14)

individual discoveries and inventions. Simultaneously, these same historians confront growing difficultie s in distinguishing the “scientific” component of past observation and belief from what their predecessors had readily labeled “error” and “supe (p. 14)

If these out-ofdate beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scienti fic knowledge. If, on the other hand, they are to be called science, then science has included bodies of belief quite incompatible with the ones we hold today. Given these alternatives, the historian must choose the latter. (p. 14)

unscienti fic because they have been ficult to see scientific discarded. That choice, however, makes it difficult to see scientific development as a process of accretion. displays the difficulties in isolating indi (p. 15)

What aspects of science will emerge to prominence in the course of this effort? First, at least in order of presentation, is the insufficiency of methodological directives, by themselves, to dictate a unique substantive conclusion to many sorts of scientifi (p. 15)

What differentiated these various schools was not one or anothe r failure of method— they were all “scientific”—but what we shall come to call their incommensurable ways of seeing the world and of practici (p. 16)

incommensurable ways of seeing the world and of practicing science in it – a beautiful way of describing the issue here.

Reflecting on many debates in ed research, are we isolating us in our own incommensurable ways of seeing the world? (p. 16)

An apparently arbitrary element, compounded of personal and historical accident, is always a formative ingredient of the beliefs espoused by a given scienti fic community at a given time. community at a given time. (p. 16)

That element of arbitrariness does not, however, indicate that any entific group could practice its trade without some set of received scientific group could practice its trade without some set of received beliefs. Nor does it make less consequential the particular constellation (p. 16)

research scarcely begins before a scientific community thinks it has acquired firm answers to questions like the following: What are the acquired firm answers to questionfundamental entities (p. 16)

examining normal science in Sections III, IV, and V, we shall want finally to describe that research as a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education. Simultaneously, we shall wonder whether research could proceed without such boxes, whatever the element of arbitrariness in their historic origins and, occasionally, in their subsequent development. historic origins and, occasionally, in their subsequent development. (p. 17)

fundamental novelties because they are necessarily subversive of its basic commitments. Nevertheless, so long as those commitments retain an element of the arbitrary, the very nature of normal research ensures an element of the arbitrary, the very nature of normal research ensures that novelty shall not be suppressed for very long. Sometimes a normal that novelty shall not be suppressed for very long. (p. 17)

these and other ways besides, normal science repeatedly goes astray. And when it does—when, that is, the profession can no longer evade And when it does—when, that is, the profession can no longer evade anomalies that subvert the existing tradition of scientific practice—then anomalies that subvert the existing tradition of scientific practice—then begin the extraordinary investigations th at lead the profession at last to a new set of commitments, a new basis for the practice of science. The extraordinary episodes in which that shift of professional commitments occurs are the ones known in this essay as scientific revolutions. They are the tradition-shattering complements to the tradition-bound activity are the tradition-shattering complements to the tradition-bound activity of normal science. of normal science. (p. 18)

necessitated the community’s rejection of one time-honored scientific theory in favor of another incompatible with it. Each produced a consequent shift in the problems available for scientific scrutiny and in the standards by which the profession determined what should count as an admissible problem or as a legitimate problem-solution. And each transformed the scientific imagination in ways that we shall ultimately need to describe as a transformation of the world within which scientific work was done. Such changes, together with the controversies that almost always accompany them, are the de fining characteristics of scientific revolutions. (p. 18)

new theories regularly, and appropriately, evokes the same response from some of the specialists on whose area of special competence they from some of the specialists on whose area of special competence they impinge. For these men the new theory implies a change in the rules impinge. For these men the new theory implies a change in the rules governing the prior practice of normal science. Inevitably, therefore, it reflects upon much scientific work they have already successfully completed. That is why a 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 in trinsically revolutionary process that (p. 19)

a new theory is seldom or never just an increment to what is already know! (p. 19)

That is why the unexpected discovery is not simply factual in its import and why the scientist’s world is qualitatively transformed as well as quantitatively enriched by fundamental novelties of either fact or theory. (p. 19)

descriptive discipline. The theses suggested above are, however, often (p. 20)

II. The Route to Normal Science (p. 22)

‘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 scientific community acknowledges for a time as supplying the foundation for its further practice (p. 22)

AKA textbook science; canons (p. 22)

accepted theory, illustrate many or a ll of its successful applications, and compare these applications with exemplary observations and compare these applications with exemplary observations and experiments. Before such books became popular early in the nineteenth experiments. (p. 22)

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. (p. 22)

fruitfulness (p. 22)

Achievements that share these two characteristics I shall henceforth refer to as ‘paradigms,’ a term that relates closely to ‘normal science.’ (p. 22)

particular coherent traditions of scientific research (p. 22)

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 later practice. (p. 23)

scientific community – mentioning it is important. Link with identity (p. 23)

research is based on shared paradi gms are committed to the same rules and standards for scientific practice. That commitment and the apparent consensus it produces are prerequisites for normal science, i.e., for the genesis and continuation of a particular research tradition. i.e., for the genesis and continuation of a particular research tradition. (p. 23)

what sense is the shared paradigm a fundamental unit for the student of scientific development, a unit that cannot be fully reduced to logically (p. 23)

paradigm and of the more esoteric type of research it permits is a sign of maturity in the development of any given scientific field. (p. 23)

These transformations of the paradigms of physical optics are scientific revolutions, and the successive transition from one paradigm to another via revolution is the usual developmental pattern of mature science. (p. 24)

At various times all these schools made signi ficant contributions to the body of concepts, phenomena, and techniques from which Newton drew the first nearly uniformly accepted paradigm for physical optics. (p. 25)

physical optics before Newton may well conclude that, though the field’s practitioners were scientists, the net result of their activity was something less than science. Being able to take no common body of belief for granted, each writer on phys ical optics felt forced to build his field anew from its foundations. In doing so, his choice of supporting observation and experiment was relatively free, for there was no standard set of methods or of phenomena that every optical writer felt forced to employ and explain. Under these circumstances, the dialogue of the resulting books was often directed as much to the members of other schools as it was to nature. That pattern is not unfamiliar in a number of creative fields today, nor is it incompatible with significant discovery and invention. It is not, however, the pattern of development that physical optics acquired af ter Newton and that other natural sciences make familiar today. (p. 25)

interesting. So the establishment of a paradigm benefits continual growth of a body of work. (p. 25)

Only through the work of Franklin and his immediate successors did a theory arise that could account with something like equal facility for very nearly all th ese effects and that therefore could and did provide a subsequent gene ration of “electricians” with a common paradigm for its research. common paradigm for its research. Excluding those fields, like math (p. 27)

NA (p. 27)

question what parts of social science have yet acquired such paradigms at all. History suggests that the road to a firm research consensus is extraordinarily arduous. the road to a firm research consensus is extraordinarily arduous. (p. 27)

candidate for paradigm, all of the facts that could possibly pertain to the development of a given science are likely to seem equally relevant. As a result, early fact-gathering is a far more nearly random activity than the one that subsequent scientific development makes familiar. (p. 27)

Because the crafts are one readily accessible source of facts that could not have been casually discovered, technology (p. 27)

has often played a vital role in the emergence of new sciences. (p. 28)

No natural history can be interpreted in the absence of at least some implicit body (p. 28)

of intertwined theoretical and me thodological belief that permits selection, evaluation, and criticism. If that body of belief is not already implicit in the collection of facts—in which case more than “mere facts” are at hand—it must be externally supplied, perhaps by a current metaphysic, by another science, or by personal and historical accident. (p. 29)

fluid and therefore gave particular emphasis to conduction provide an excellent case in point. Led by this belief, which could scarcely cope with the known multiplicity of attractive and repulsive effects, several of them conceived the idea of bottling the electrical fluid. The immediate fruit of their efforts was the Leyden jar, a device which might never have been discovered by a man exploring nature casually or at random, but which was in fact independently developed by at least two investigators in the 7early 1740’s. (p. 29)

To be accepted as a paradigm, a etitors, but theory must seem better than its competitors, but (p. 29)

it need not, and in fact never does, explain all the facts with which it can be confronted. What the fluid theory of electricity did for the subgroup that held it, the Franklinian paradigm later did for the entire group of electricians. It suggested which experiments would be worth performing and which, because directed to secondary or to overly complex manifestations of (p. 30)

Freed from the concern with any and all electrical phenomena, the united group of electricians could pursue selected phenomena in far more detail, designing much special equipment for the task and employing it more designing much special equipment for the task and employing it more stubbornly and systematically than electricians had ever done before. stubbornly and systematically than electricians had ever done before. Both fact collection and theory arti culation became highly directed (p. 30)

promisingness judgments become easier (p. 30)

emergence of a paradigm affects the structure of the group that practices the field. When, in the development of a natural science, an individual or group first produces a synthesis able to attract most of the next generation’s practitioners, the older schools gradually disappear. (p. 30)

gm implies a new and more rigid definition of the field. Those unwilling or unable to accommodate their work to it must proceed in isolation or attach themselves to some other work to it must proceed in isolation or attach themselves to some other group.11 Historically, they have often simply stayed in the departments group.11 Historically, they have often simply stayed in the departments of philosophy from which so many of the special sciences have been of philosophy from which so many of the special sciences have been spawned. As these indications hint, it is sometimes just its reception of a paradigm that transforms a group previously interested merely in the paradigm that transforms a group previously interested merely in the study of nature into a profession or, at least, a discipline. In the sciences study of nature into a profession or, at least, a discipline. (p. 31)

interesting.. so we are heading to the philosophy department if we are deemed useless in our own professions. Haha. (p. 31)

The more rigid definition of the scienti fic group has other consequences. When the individual scientist can take a paradigm for granted, he need no longer, in his major works, attempt to build his fi eld anew (p. 31)

Given a textbook, however, the creative scientist can begin his research where it leaves off and thus concentrate exclusively upon the subtlest and most esoteric aspect s of the natural phenomena that subtlest and most esoteric aspect s of the natural phenomena that concern his group. And as he does this, his research communiqués will begin to change in (p. 32)

To d a y i n t h e s c i e n c e s , b o o k s a r e u s u a lly either texts or retrospective reflections upon one aspect or another of the scientific life. (p. 32)

guide the whole group’s research. Except with the advantage of hindsight, it is hard to find another criterion that so clearly proclaims a field a science. (p. 34)

III. The Nature of Normal Science (p. 35)

In a sc ience, on the other hand, a paradigm is rarely an object for replication. Instead, like an accepted judicial decision in the common law, it is an object for further articulation and specification under new or more stringent conditions. (p. 35)

he success of a paradigm—whether Aristotle’s analysis of motion, Ptolemy’s computations of planetary position, Lavoisier’s application of the balance, or Maxwell’s mathematization of the electromagnetic field—is at the start largely a promise of success discoverable in selected and (p. 35)

still incomplete examples. (p. 36)

Normal science consists in the actualization of that promise, an actualization achieved by extending the knowledge of those facts that the paradigm displays as particularly revealing, by increasing the extent of the match between those facts and the paradigm’s predictions, and by further articulation of the paradigm itself. (p. 36)

Mop-ping-up operations are what engage most scientists throughout their careers. They constitute what I am here calling normal science. (p. 36)

Nor do scientists normally aim to invent new theories, and they are often intolerant of those invented by others.1 Instead, normal-scientific research is directed to the articulation of those phenomena and theories that the paradigm already supplies. (p. 36)

On what aspects of nature do scientists ordinarily report? What determines their choice? And, since most scientific observation consumes much time, equipment, and money, what motivates the scientist to pursue that choice to a conclusion? (p. 37)

Attempts to increase the accuracy and scope with which facts like these are known occupy a significant fraction of the literature of experimental and observational science. (p. 37)

some scientists have acquired great reputations, not from any novelty of their discoveries, but from the precision, reliability, and scope of the methods they developed for the redetermination of a previously known sort of fact. (p. 38)

apparatus (p. 38)

The existence of the paradigm sets the problem to be solved; often the paradigm theory is implicated directly in the design of apparatus able to solve the problem (p. 39)

A third class of experiments and observations exhausts, I think, the fact-gathering activities of normal science. It consists of empirical work undertaken to articulate the paradigm theory, resolving some of its residual ambiguities and permitting the solution of problems to which it had previously only drawn attention. This class proves to be the most important of all, and its description demands its subdivision (p. 39)

experimentalists (p. 40)

great stories about theoretical physicists working with experimental physicists etc (p. 40)

Coulomb’s success depended upon his constructing special apparatus to measure the force between point charges (p. 40)

But that design, in turn, depended upon the previous recognition that every particle of electric fluid acts upon every other at a distance. (p. 40)

A part of normal theoretical work, though only a small part, consists simply in the use of existing theory to predict factual information of intrinsic value. (p. 42)

The need for work of this sort arises from the immense difficulties often encountered in developing points of contact between a theory and nature. (p. 42)

Even in the mathematical sciences there are also theoretical problems of paradigm articulation; and during periods when scientific development is predominantly qualitative, these problems dominate. (p. 45)

More than any other sort of normal research, the problems of paradigm articulation are simultaneously theoretical and experimental; (p. 45)

They were working both with fact and with theory, and their work produced not simply new information but a more precise paradigm, obtained by the elimination of ambiguities that the original from which they worked had retained. In many sciences, most normal work is of this sort. (p. 46)

These three classes of problems—determination of significant fact, matching of facts with theory, and articulation of theory-exhaust, I think, the literature of normal science, both empirical and theoretical. (p. 46)

Inevitably, therefore, th e overwhelming majority of the problems undertaken by even the very best scientists usually fall into one of the three categories outlined above. Work under the paradigm can be conducted in no other way, and to desert the paradigm is to cease practicing the science it defines. We shall shortly discover that such desertions do occur. They are the pivots about which scientific revolutions turn. (p. 46)

IV. Normal Science as Puzzle-solving (p. 47)

Perhaps the most striking feature of the normal research problems we have just encountered is how little they aim to produce major novelties, conceptual or phenomenal. (p. 47)

Because they yielded neit her consistent nor simple results, they could not be used to articulate the paradigm from which they derived. Therefore, they remained mere facts, unrelated and unrelatable to the continuing progress of electrical research. (p. 47)

But if the aim of normal science is not major substantive novelties—if failure to come near the anticipated result is usually (p. 47)

failure as a scientist—then why are these problems undertaken at all? (p. 48)

Bringing a normal research pr oblem to a conclusion is achieving the anticipated in a new way, and it requires the solution of all sorts of complex instrumental, conceptual, and mathematical puzzles. The man who succeeds proves himself an expert puzzle-solver, and the challenge of the puzzle is an important part of what usually drives him on. (p. 48)

It is no criterion of goodness in a puzzle that its outcome be intrinsically interesting or important. (p. 48)

n e o f t h e t h i n g s a s c i e n t i fic community acquires with a paradigm is a criterion for choosing problems that, while the paradigm is taken for granted, can be assumed to have solutions. (p. 49)

Other problems, including many that had previously been standard, are rejected as metaphysical, as the concern of another discipline, or sometimes as just too problematic to be worth the time. (p. 49)

A man may be attracted to science for all sorts of reasons. Among them are the desire to be useful, the excitement of exploring new territory, the hope of finding order, a n d t h e d r i ve t o t e s t e s t a b l i s h e d knowledge. (p. 49)

the rules that govern jigsaw-puzzle solutions (p. 50)

Only a change in the rules of the game could have provided an alternative. (p. 52)

While they continue to be honored, such statements help to set puzzles and to limit acceptable solutions. (p. 52)

Less local and temporary, though still not unchanging characteristics of science, are the higher level, quasi-metaphysical commitments that historical study so regularly displays. (p. 53)

after the appearance of Descartes’s immensely influential scientific writings, most physical scientists assumed that the universe was composed of microscopic corpuscles and that all natural phenomena could be explained in terms of corpuscular shape, size, motion, and interaction. That nest of commitments proved to be both metaphysical and methodological. As metaphysical, it told scientists what sorts of entities the universe did and did not contain: there was only shaped matter in motion. As methodological, it told them what ultimate laws and fundamental explanations must be like: laws must specify corpuscular motion and interaction, and explanation must reduce any given natural phenomenon to corpuscular action under these laws. (p. 53)

Finally, at a still higher level, there is another set of commitments without which no man is a scientist. The scientist must, for example, be concerned to understand the world and to extend the precision and scope with which it has been ordered. That commitment must, in turn, lead him to scrutinize, either for himself or through colleagues, some aspect of nature in great empirical detail. And, if that scrutiny displays pockets of apparent disorder, then these must challenge him to a new refinement of his observational techniques or to a further articulation of his theories. (p. 54)

The existence of this strong network of commitments—conceptual, theoretical, instrumental, and methodological—is a principal source of the metaphor that relates normal science to puzzle-solving. Because it provides rules that tell the practitioner of a mature specialty what both the world and his science are like, he can concentrate with assurance upon the esoteric problems that these rules and existing knowledge define for him. (p. 54)

ules, I suggest, derive from paradigms, but paradigms can guide research even in the absence of rules. (p. 54)

V. T h e P r i o r i t y o f P a r a d i g m s (p. 55)

Nevertheless, if the coherence of the research tradition is to be understood in terms of rules, some specification of common ground in the corresponding area is needed. As a result, the search for a body of rules competent to constitute a given normal research tradition becomes a source of continual and deep frustration. (p. 56)

Inevitably, the first effect of those statements is to raise problems. In the absence of a competent body of rules, what restricts the scientist to a particular normal-scientific tradition? What can the phrase ‘direct inspection of paradigms’ mean? Partial answers to questions like these were developed by the late Ludwig Wittgenstein (p. 56)

What need we know, Wittgenstein asked, in order that we (p. 56)

apply terms like ‘chair,’ or ‘leaf,’ or ‘game’ unequivocally and without provoking argument?2 (p. 57)

That question is very old and has generally been answered by saying that we must know, consciously or intuitively, what a chair, or leaf, or game is. We m u s t , t h a t i s , g r a s p s o m e s e t of attributes that all games and that only games have in common. Wittgenstein, however, concluded that, given the way we use language and the sort of world to which we apply it, there need be no such set of characteristics. (p. 57)

Scientists 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. (p. 58)

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. (p. 58)

o far this p oint has been entirely theoretical: paradigms could determine normal science without the intervention of discoverable rules. (p. 58)

The first, which has already been discussed quite fully, is the severe difficulty of discovering the rules that have guided particular normal-scientific traditions. (p. 58)

The second, to which the first is really a corollary, i s r o o t e d i n t h e n a t ure of scientific education. Scientists, it should already be clear, never learn concepts, laws, and theories in the abstract and by themselves. Instead, these intellectual tools are from the start encountered in a historically and pedagogically prior unit that displays them with and through their applications. (p. 58)

But they continue to be closely modeled on previous achievements as are the problems that normally occupy him during his subsequent independent scientific career. One is at liberty to suppose that somewhere along the way the scientist has intuitively abstracted rules of the game for himself, but there is little reason to believe it. (p. 59)

they are little better than laymen at characterizing the established bases of their field, its legitimate problems and methods. (p. 59)

A fourth reason for granting paradigms a status prior to that of shared rules and assumptions (p. 61)

The introduction to this essay suggested that there can be small revolutions as well as large ones, that some revolutions affect only the members of a professional subspecialty, and that for such groups even the discovery of a new and unexpected phenomenon may be revolutionary. (p. 61)

If normal science is so rigid and if scientific communities are so close-knit as the preceding discussion has implied, how can a change of paradigm ever affect only a small subgroup? What has been said so far may have seemed to imply that normal science is a single monolithic and unified enterprise that must stand or fall with any one of its paradigms as well as with all of them together. But science is obviously seldom or never like that. Often, viewing all fields together, it seems instead a rather ramshackle structure with little coherence among its various parts. (p. 61)

On the contrary, substituting paradigms for rules should make the diversity of scientific fields and specialties easier to understand. Explicit rules, when they exist, are usually common to a very broad scientific group, but paradigms need not be. (p. 61)

In short, though quantum mechanics (or Newtonian dynamics, or electromagnetic theory) is a paradigm for many scientific groups, it is not the same paradigm for them all. (p. 62)

VI. Anomaly and the Emergence of Scientific Discoveries (p. 64)

Normal science, the puzzle-solving activity we have just examined, is a highly cumulative enterprise (p. 64)

Yet one standard prod uct of the scientific enterprise is missing. Normal science does not aim at novelties of fact or theory and, when successful, finds none. (p. 64)

History even suggests that the scientific enterprise has developed a uniquely powerful technique for producing surprises of this sort. (p. 64)

That distinction between discovery and invention or between fact and theory will, however, immediately prove to be exceedingly artificial. Its artificiality is an important clue to several of this essay’s main theses. (p. 64)

Discovery commences with the awareness of anomaly, i.e., with the recognition that nature has somehow violated the paradigm-induced (p. 64)

expectations that govern normal science. It then continues 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. Assimilating a new sort of fact demands a more than additive adjustment of theory, and until that adjustment is completed—until the scientist has learned to see nature in a different way—the new fact is not quite a scientific fact at all. (p. 65)

To s e e h o w c l o s e l y f a c t u a l a n d t h e o r e t i c a l n o v e l t y a r e i n t e r t w i n e d i n scientific discovery examine a particularly famous example, the discovery of oxygen. (p. 65)

Clearly we need a new vocabulary and concepts for analyzing events like the discovery of oxygen. Though undoubtedly correct, the sentence, “Oxygen was discovered,” misleads by suggesting that discovering something is a single simple act assimilable to our usual (and also questionable) concept of seeing. That is why we so readily assume that discovering, like seeing or touching, should be unequivocally attributable to an individual and to a moment in time. (p. 67)

any attempt to date the discovery must inevitably be arbitrary because discovering a new sort of phenomenon is necessarily a complex event, one which involves recognizing both that something is and what it is. (p. 67)

That theory was the keystone for a reformulation of chemistry so vast that it is usually called the chemical revolution. (p. 68)

Notice, however, since it will be important later, that the discovery of oxygen was not by itself the cause of the change in chemical theory. Long before he played any part in the discovery of the new gas, Lavoisier was convinced both that something was wrong with the phlogiston theory and that burning bodies absorbed some part of the atmosphere. (p. 68)

Neither ox ygen nor X-rays emerged without a further process of experimentation and assimilation. At what point in Roentgen’s investigation, for example, ought we say that X-rays had actually been discovered? No (p. 69)

Nor, it is almost as clear, can the moment of discovery be pushed forward to a point during the last week of investigation, by which time Roentgen was exploring the properties of the new radiation he had already discovered. We can only say that X-rays emerged in Würzburg between November 8 and December 28, 1895. (p. 70)

In short, consciously or not, the decision to employ a particular piece of apparatus and to use it in a particular way carries an assumption that only certain sorts of circumstances will arise. There are instrumental as well as theoretical expectations, and they have often played a decisive role in scientific development. (p. 71)

Paradigm procedures and applications are as necessary to science as paradigm laws and theories, and they have the same effects. Inevitably they restrict the phenom- enological field accessible for scientific investigation (p. 72)

Recognizing that much, we may simultaneously see an essential sense in which a discovery like X-rays necessitates paradigm change—and therefore change in both procedures and expectations—for a special segment of the scientific community. As a result, we may also understand how the discovery of X-rays could seem to open a strange new world to many scientists and could thus participate so effectively in the crisis that led to twentieth-century physics. (p. 73)

Our final example of scientific discovery, that of the Leyden jar, belongs to a class that may be described as theory-induced (p. 73)

But not all theories are paradigm theories. (p. 73)

Those characteristics include: the previous awareness of anomaly, the gradual and simultaneous emergence of both observational and conceptual recognition, and the consequent change of paradigm categories and procedures often accompanied by resistance. (p. 74)

Either as a metaphor or because it reflects the nature of the mind, that psychological experiment provides a wonderfully simple and cogent schema for the process of scientific discovery. In science, as in the playing card experiment, novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation. Initially, only the anticipated and usual are experienced even under circumstances where anomaly is later to be observed. Further acquaintance, however, does result in awareness of something wrong or does relate the effect to something that has gone wrong before. That awareness of anomaly opens a period in which conceptual categories are adjusted until the initially anomalous has become the anticipated. At this point the discovery has been completed. I have already urged that that process or one very much like it is involved in the emergence of all fundamental scientific novelties. (p. 76)

In the development of any science, the first received paradigm is usually felt to account quite successfully for most of the observations and experiments easily accessible to that science’s practitioners. Further development, therefore, ordinarily calls for the construction of elaborate equipment, the development of an esoteric vocabulary and skills, and a refinement of concepts that increasingly lessens their resemblance to their usual common-sense prototypes. That professionalization leads, on the one hand, to an immense restriction of the scientist’s vision and to a considerable resistance to paradigm change. The science has become increasingly rigid. On the other hand, within those areas to which the paradigm directs the attention of the (p. 76)

group, normal science leads to a detail of information and to a precision of the observation-theory match that could be achieved in no other way. (p. 77)

novelty or dinarily 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. The more precise and far- reaching that paradigm is, the more sensitive an indicator it provides of anomaly and hence of an occasion for paradigm change. (p. 77)

By ensuring that the paradigm will not be too easily surrendered, resistance guarantees that scientists will not be lightly distracted and that the anomalies that lead to paradigm change will penetrate existing knowledge to the core. The very fact that a significant scientific novelty so often emerges simultaneously from several laboratories is an index both to the strongly traditional nature of normal science and to the completeness with which that traditional pursuit prepares the way for its own change. (p. 77)