The Structure of Scientific Revolutions
prepared by Professor Frank Pajares
Chapter I - Introduction: A Role for History.Kuhn begins by formulating some assumptions that lay the foundation for subsequent discussion and by briefly outlining the key contentions of the book.
- A scientific community cannot practice its trade without some set of received beliefs (p. 4).
- These beliefs form the foundation of the "educational initiation that prepares and licenses the student for professional practice" (5).
- The nature of the "rigorous and rigid" preparation helps ensure that the received beliefs exert a "deep hold" on the student's mind.
- Normal science "is predicated on the assumption that the scientific community knows what the world is like" (5)scientists take great pains to defend that assumption.
- To this end, "normal science often suppresses fundamental novelties because they are necessarily subversive of its basic commitments" (5).
- Research is "a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education" (5).
- A shift in professional commitments to shared assumptions takes place when an anomaly "subverts the existing tradition of scientific practice" (6). These shifts are what Kuhn describes as scientific revolutions"the tradition-shattering complements to the tradition-bound activity of normal science" (6).
- New assumptions (paradigms/theories) require the reconstruction of prior assumptions and the reevaluation of prior facts. This is difficult and time consuming. It is also strongly resisted by the established community.
- When a shift takes place, "a scientist's world is qualitatively transformed [and] quantitatively enriched by fundamental novelties of either fact or theory" (7).
Chapter II - The Route to Normal Science.In this chapter, Kuhn describes how paradigms are created and what they contribute to scientific (disciplined) inquiry.
- 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" (10).
- These achievements must be
- sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity and
- sufficiently open-ended to leave all sorts of problems for the redefined group of practitioners (and their students) to resolve, i. e., research.
- These achievements can be called paradigms (10).
- "The road to a firm research consensus is extraordinarily arduous" (15).
- "The successive transition from one paradigm to another via revolution is the usual developmental pattern of mature science" (12).
- Students study these paradigms in order to become members of the particular scientific community in which they will later practice.
- Because the student largely learns from and is mentored by researchers "who learned the bases of their field from the same concrete models" (11), there is seldom disagreement over fundamentals.
- Men whose research is based on shared paradigms are committed to the same rules and standards for scientific practice (11).
- A shared commitment to a paradigm ensures that its practitioners engage in the paradigmatic observations that its own paradigm can do most to explain (13), i.e., investigate the kinds of research questions to which their own theories can most easily provide answers.
- "It remains an open question what parts of social science have yet acquired such paradigms" (15). [psychology? education? teacher education? sociology?]
- Paradigms help scientific communities to bound their discipline in that they help the scientist to
- create avenues of inquiry.
- formulate questions.
- select methods with which to examine questions.
- define areas of relevance.
- [establish/create meaning?]
- "In the absence of a paradigm or some candidate for paradigm, all the facts that could possibly pertain to the development of a given science are likely to seem equally relevant" (15).
- A paradigm is essential to scientific inquiry"no natural history can be interpreted in the absence of at least some implicit body of intertwined theoretical and methodological belief that permits selection, evaluation, and criticism" (16-17).
- How are paradigms created, and how do scientific revolutions take place?
- Inquiry begins with a random collection of "mere facts" (although, often, a body of beliefs is already implicit in the collection).
- During these early stages of inquiry, different researchers confronting the same phenomena describe and interpret them in different ways (17).
- In time, these descriptions and interpretations entirely disappear.
- A preparadigmatic school (movement) appears.
- Such a school often emphasizes a special part of the collection of facts.
- Often, these schools vie for preeminence.
- From the competition of preparadigmatic schools, one paradigm emerges"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" (17-18), thus making research possible.
- As a paradigm grows in strength and in the number of advocates, the preparadigmatic schools (or the previous paradigm) fade.
- "When an individual or group first produces a synthesis able to attract most of the next generation's practitioners, the older schools gradually disappear" (18).
- Those with "older views . . . are simply read out of the profession and their work is subsequently ignored. If they do not accommodate their work to the new paradigm, they are doomed to isolation or must attach themselves to some other group" (19), or move to a department of philosophy (or history).
- A paradigm transforms a group into a profession or, at least, a discipline (19). And from this follow the
- formation of specialized journals.
- foundation of professional societies (or specialized groups within societiesSIGs).
- claim to a special place in academe (and academe's curriculum).
- fact that members of the group need no longer build their field anewfirst principles, justification of concepts, questions, and methods. Such endeavors are left to the theorist or to writer of textbooks.
- promulgation of scholarly articles intended for and "addressed only to professional colleagues, [those] whose knowledge of a shared paradigm can be assumed and who prove to be the only ones able to read the papers addressed to them" (20)preaching to the converted.
- (discussion groups on the Internet and a listerserver?)
- A paradigm guides the whole group's research, and it is this criterion that most clearly proclaims a field a science (22).
Chapter III - The Nature of Normal Science.If a paradigm consists of basic and incontrovertible assumptions about the nature of the discipline, what questions are left to ask?
- When they first appear, paradigms are limited in scope and in precision.
- "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" (23).
- But more successful does not mean completely successful with a single problem or notably successful with any large number (23).
- Initially, a paradigm offers the promise of success.
- Normal science consists in the actualization of that promise. This is achieved by
- extending the knowledge of those facts that the paradigm displays as particularly revealing,
- increasing the extent of the match between those facts and the paradigm's predictions,
- and further articulation of the paradigm itself.
- In other words, there is a good deal of mopping-up to be done.
- Mop-up operations are what engage most scientists throughout their careers.
- Mopping-up is what normal science is all about!
- This paradigm-based research (25) is "an attempt to force nature into the preformed and relatively inflexible box that the paradigm supplies" (24).
- no effort made to call forth new sorts of phenomena.
- no effort to discover anomalies.
- when anomalies pop up, they are usually discarded or ignored.
- anomalies usually not even noticed (tunnel vision/one track mind).
- no effort to invent new theory (and no tolerance for those who try).
- "Normal-scientific research is directed to the articulation of those phenomena and theories that the paradigm already supplies" (24).
- "Perhaps these are defects . . . "
- ". . . but those restrictions, born from confidence in a paradigm, turn out to be essential to the development of science. By focusing attention on a small range of relatively esoteric problems, the paradigm forces scientists to investigate some part of nature in a detail and depth that would otherwise be unimaginable" (24).
- . . . and, when the paradigm ceases to function properly, scientists begin to behave differently and the nature of their research problems changes.
- Mopping-up can prove fascinating work (24). [You do it. We all do it. And we love to do it. In fact, we'd do it for free.]
- The principal problems of normal science.
- Determination of significant fact.
- A paradigm guides and informs the fact-gathering (experiments and observations described in journals) decisions of researchers?
- Researchers focus on, and attempt to increase the accuracy and scope of, facts (constructs/concepts) that the paradigm has shown to be particularly revealing of the nature of things (25).
- Matching of facts with theory.
- Researchers focus on facts that can be compared directly with predictions from the paradigmatic theory (26)
- Great effort and ingenuity are required to bring theory and nature into closer and closer agreement.
- A paradigm sets the problems to be solved (27).
- Articulation of theory.
- Researchers undertake empirical work to articulate the paradigm theory itself (27)resolve residual ambiguities, refine, permit solution of problems to which the theory had previously only drawn attention. This articulation includes
- determination of universal constants.
- development of quantitative laws.
- selection of ways to apply the paradigm to a related area of interest.
- This is, in part, a problem of application (but only in part).
- Paradigms must undergo reformulation so that their tenets closely correspond to the natural object of their inquiry (clarification by reformulation).
- "The problems of paradigm articulation are simultaneously theoretical and experimental" (33).
- Such work should produce new information and a more precise paradigm.
- This is the primary work of many sciences.
- To desert the paradigm is to cease practicing the science it defines (34).
Chapter IV - Normal Science as Puzzle-solving.Doing research is essentially like solving a puzzle. Puzzles have rules. Puzzles generally have predetermined solutions.
- A striking feature of doing research is that the aim is to discover what is known in advance.
- This in spite of the fact that the range of anticipated results is small compared to the possible results.
- When the outcome of a research project does not fall into this anticipated result range, it is generally considered a failure, i.e., when "significance" is not obtained.
- Studies that fail to find the expected are usually not published.
- The proliferation of studies that find the expected helps ensure that the paradigm/theory will flourish.
- Even a project that aims at paradigm articulation does not aim at unexpected novelty.
- "One of the things a scientific 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" (37).
- The intrinsic value of a research question is not a criterion for selecting it.
- The assurance that the question has an answer is the criterion (37).
- "The man who is striving to solve a problem defined by existing knowledge and technique is not just looking around. He knows what he wants to achieve, and he designs his instruments and directs his thoughts accordingly" (96).
- So why do research?
- Results add to the scope and precision with which a paradigm/theory can be applied.
- The way to obtain the results usually remains very much in doubtthis is the challenge of the puzzle.
- Solving the puzzle can be fun, and expert puzzle-solvers make a very nice living.
- To classify as a puzzle (as a genuine research question), a problem must be characterized by more than the assured solution.
- There exists a strong network of commitmentsconceptual, theoretical, instrumental, and methodological.
- There are "rules" that limit
- the nature of acceptable solutionsthere are "restrictions that bound the admissible solutions to theoretical problems" (39).
- Solutions should be consistent with paradigmatic assumptions.
- There are quasi-metaphysical commitments to consider.
- There may also be historical ties to consider.
- the steps by which they are to be obtained (methodology).
- commitments to preferred types of instrumentations.
- the ways in which accepted instruments may legitimately be employed.
- Despite the fact that novelty is not sought and that accepted belief is generally not challenged, the scientific enterprise can and does bring about such unexpected results.
Chapter V - The Priority of Paradigms.How can it be that "rules derive from paradigms, but paradigms can guide research even in the absence of rules" (42).
- The paradigms of a mature scientific community can be determined with relative ease (43).
- The "rules" used by scientists who share a paradigm are not easily determined. Some reasons for this are that
- scientists can disagree on the interpretation of a paradigm.
- the existence of a paradigm need not imply that any full set of rules exist.
- scientists are often guided by tacit knowledgeknowledge acquired through practice and that cannot be articulated explicitly (Polanyi, 1958).
- the attributes shared by a paradigm are not always readily apparent.
- "paradigms may be prior to, more binding, and more complete than any set of rules for research that could be unequivocally abstracted from them" (46).
- Paradigms can determine normal science without the intervention of discoverable rules or shared assumptions (46). In part, this is because
- it is very difficult to discover the rules that guide particular normal-science traditions.
- scientists never learn concepts, laws, and theories in the abstract and by themselves.
- They generally learn these with and through their applications.
- New theory is taught in tandem with its application to a concrete range of phenomena.
- "The process of learning a theory depends on the study of applications" (47).
- The problems that students encounter from freshman year through doctoral program, as well as those they will tackle during their careers, are always closely modeled on previous achievements.
- Scientists who share a paradigm generally accept without question the particular problem-solutions already achieved (47).
- Although a single paradigm may serve many scientific groups, it is not the same paradigm for them all.
- Subspecialties are differently educated and focus on different applications for their research findings.
- A paradigm can determine several traditions of normal science that overlap without being coextensive.
- Consequently, changes in a paradigm affect different subspecialties differently"A revolution produced within one of these traditions will not necessarily extend to the others as well" (50).
- When scientists disagree about whether the fundamental problems of their field have been solved, the search for rules gains a function that it does not ordinarily possess (48).
Chapter VI - Anomaly and the Emergence of Scientific Discoveries.If normal science is so rigid and if scientific communities are so close-knit, how can a paradigm change take place? This chapter traces paradigm changes that result from discovery brought about by encounters with anomaly.
- Normal science does not aim at novelties of fact or theory and, when successful, finds none.
- Nonetheless, new and unsuspected phenomena are repeatedly uncovered by scientific research, and radical new theories have again and again been invented by scientists (52).
- Fundamental novelties of fact and theory bring about paradigm change.
- So how does paradigm change come about?
- Discoverynovelty of fact.
- Discovery begins with the awareness of anomaly.
- The recognition that nature has violated the paradigm-induced expectations that govern normal science.
- A phenomenon for which a paradigm has not readied the investigator.
- Perceiving an anomaly is essential for perceiving novelty (although the first does not always lead to the second, i.e., anomalies can be ignored, denied, or unacknowledged).
- The area of the anomaly is then explored.
- The paradigm change is complete when the paradigm/theory has been adjusted so that the anomalous become the expected.
- The result is that the scientist is able "to see nature in a different way" (53).
- But careful: Discovery involves an extended process of conceptual assimilation, but assimilating new information does not always lead to paradigm change.
- Inventionnovelty of theory.
- Not all theories are paradigm theories.
- Unanticipated outcomes derived from theoretical studies can lead to the perception of an anomaly and the awareness of novelty.
- How paradigms change as a result of invention is discussed in greater detail in the following chapter.
- The process of paradigm change is closely tied to the nature of perceptual (conceptual) change in an individualNovelty emerges only with difficulty, manifested by resistance, against a background provided by expectation (64).
- Although normal science is a pursuit not directed to novelties and tending at first to suppress them, it is nonetheless very effective in causing them to arise. Why?
- An initial paradigm accounts quite successfully for most of the observations and experiments readily accessible to that science's practitioners.
- Research results in
- the construction of elaborate equipment,
- development of an esoteric and shared vocabulary,
- refinement of concepts that increasingly lessens their resemblance to their usual common-sense prototypes.
- This professionalization leads to
- immense restriction of the scientist's vision, rigid science, and resistance to paradigm change.
- a detail of information and precision of the observation-theory match that can be achieved in no other way.
- New and refined methods and instruments result in greater precision and understanding of the paradigm/theory.
- Only when researchers know with precision what to expect from an experiment can they recognize that something has gone wrong.
- Consequently, anomaly appears only against the background provided by the paradigm (65).
- The more precise and far-reaching the paradigm, the more sensitive it is to detecting an anomaly and inducing change.
- By resisting change, a paradigm guarantees that anomalies that lead to paradigm change will penetrate existing knowledge to the core.
Chapter VII - Crisis and the Emergence of Scientific Theories.This chapter traces paradigm changes that result from the invention of new theories brought about by the failure of existing theory to solve the problems defined by that theory. This failure is acknowledged as a crisis by the scientific community.
- As is the case with discovery, a change in an existing theory that results in the invention of a new theory is also brought about by the awareness of anomaly.
- The emergence of a new theory is generated by the persistent failure of the puzzles of normal science to be solved as they should. Failure of existing rules is the prelude to a search for new ones (68). These failures can be brought about by
- observed discrepancies between theory and factthis is the "core of the crisis" (69).
- changes in social/cultural climates (knowledge/beliefs are socially constructed?).
- There are strong historical precedents for this: Copernicus, Freud, behaviorism? constructivism?
- Science is often "ridden by dogma" (75)what may be the effect on science (or art) by an atmosphere of political correctness?
- scholarly criticism of existing theory.
- Such failures are generally long recognized, which is why crises are seldom surprising.
- Neither problems nor puzzles yield often to the first attack (75).
- Recall that paradigm and theory resist change and are extremely resilient.
- Philosophers of science have repeatedly demonstrated that more than one theoretical construction can always be placed upon a given collection of data (76).
- In early stages of a paradigm, such theoretical alternatives are easily invented.
- Once a paradigm is entrenched (and the tools of the paradigm prove useful to solve the problems the paradigm defines), theoretical alternatives are strongly resisted.
- As in manufacture so in scienceretooling is an extravagance to be reserved for the occasion that demands it (76).
- Crises provide the opportunity to retool.
Chapter VIII - The Response to Crisis. The awareness and acknowledgment that a crisis exists loosens theoretical stereotypes and provides the incremental data necessary for a fundamental paradigm shift. In this critical chapter, Kuhn discusses how scientists respond to the anomaly in fit between theory and nature so that a transition to crisis and to extraordinary science begins, and he foreshadows how the process of paradigm change takes place.
- Normal science does and must continually strive to bring theory and fact into closer agreement.
- The recognition and acknowledgment of anomalies result in crises that are a necessary precondition for the emergence of novel theories and for paradigm change.
- Crisis is the essential tension implicit in scientific research (79).
- There is no such thing as research without counterinstances, i.e., anomaly.
- These counterinstances create tension and crisis.
- Crisis is always implicit in research because every problem that normal science sees as a puzzle can be seen, from another viewpoint, as a counterinstance and thus as a source of crisis (79).
- In responding to these crises, scientists generally do not renounce the paradigm that has led them into crisis.
- They may lose faith and consider alternatives, but
- they generally do not treat anomalies as counterinstances of expected outcomes.
- They devise numerous articulations and ad hoc modifications of their theory in order to eliminate any apparent conflict.
- Some, unable to tolerate the crisis (and thus unable to live in a world out of joint), leave the profession.
- As a rule, persistent and recognized anomaly does not induce crisis (81).
- Failure to achieve the expected solution to a puzzle discredits only the scientist and not the theory ("it is a poor carpenter who blames his tools").
- Science is taught to ensure confirmation-theory.
- Science students accept theories on the authority of teacher and textwhat alternative do they have, or what competence?
- To evoke a crisis, an anomaly must usually be more than just an anomaly.
- After all, there are always anomalies (counterinstances).
- Scientists who paused and examined every anomaly would not get much accomplished.
- An anomaly can call into question fundamental generalizations of the paradigm.
- An anomaly without apparent fundamental import may also evoke crisis if the applications that it inhibits have a particular practical importance.
- An anomaly must come to be seen as more than just another puzzle of normal science.
- In the face of efforts outlined in C above, the anomaly must continue to resist.
- All crises begin with the blurring of a paradigm and the consequent loosening of the rules for normal research. As this process develops,
- the anomaly comes to be more generally recognized as such.
- more attention is devoted to it by more of the field's eminent authorities.
- the field begins to look quite different.
- scientists express explicit discontent.
- competing articulations of the paradigm proliferate.
- scholars view a resolution as the subject matter of their discipline. To this end, they
- first isolate the anomaly more precisely and give it structure.
- push the rules of normal science harder than ever to see, in the area of difficulty, just where and how far they can be made to work.
- seek for ways of magnifying the breakdown.
- generate speculative theories.
- If successful, one theory may disclose the road to a new paradigm.
- If unsuccessful, the theories can be surrendered with relative ease.
- may turn to philosophical analysis and debate over fundamentals as a device for unlocking the riddles of their field.
- crisis often proliferates new discoveries.
- All crises close in one of three ways.
- Normal science proves able to handle the crisis-provoking problem and all returns to "normal."
- The problem resists and is labeled, but it is perceived as resulting from the field's failure to possess the necessary tools with which to solve it, and so scientists set it aside for a future generation with more developed tools.
- A new candidate for paradigm emerges, and a battle over its acceptance ensues (84)these are the paradigm wars.
- Once it has achieved the status of paradigm, a paradigm is declared invalid only if an alternate candidate is available to take its place (77).
- Because there is no such thing as research in the absence of a paradigm, to reject one paradigm without simultaneously substituting another is to reject science itself.
- To declare a paradigm invalid will require more than the falsification of the paradigm by direct comparison with nature.
- The judgment leading to this decision involves the comparison of the existing paradigm with nature and with the alternate candidate.
- Transition from a paradigm in crisis to a new one from which a new tradition of normal science can emerge is not a cumulative process. It is a reconstruction of the field from new fundamentals (85). This reconstruction
- changes some of the field's foundational theoretical generalizations.
- changes methods and applications.
- alters the rules.
- How do new paradigms finally emerge?
- Some emerge all at once, sometimes in the middle of the night, in the mind of a man deeply immersed in crisis.
- Those who achieve fundamental inventions of a new paradigm have generally been either very young or very new to the field whose paradigm they changed.
- Much of this process is inscrutable and may be permanently so.
- When a transition from former to alternate paradigm is complete, the profession changes its view of the field, its methods, and its goals.
- This reorientation has been described as "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" or "picking up the other end of the stick" (85).
- Some describe the reorientation as a gestalt shift.
- Kuhn argues that the gestalt metaphor is misleading: "Scientists do not see something as something else; instead, they simply see it" (85).
- The emergence of a new paradigm/theory breaks with one tradition of scientific practice that is perceived to have gone badly astray and introduces a new one conducted under different rules and within a different universe of discourse.
- The transition to a new paradigm is scientific revolutionand this is the transition from normal to extraordinary research.
Chapter IX - The Nature and Necessity of Scientific Revolutions. Why should a paradigm change be called a revolution? What are the functions of scientific revolutions in the development of science?
- A scientific revolution is a noncumulative developmental episode in which an older paradigm is replaced in whole or in part by an incompatible new one (92).
- A scientific revolution that results in paradigm change is analogous to a political revolution. [Note the striking similarity between the characteristics outlined below regarding the process of political revolution and those earlier outlined regarding the process of scientific revolution]
- Political revolutions begin with a growing sense by members of the community that existing institutions have ceased adequately to meet the problems posed by an environment that they have in part createdanomaly and crisis.
- The dissatisfaction with existing institutions is generally restricted to a segment of the political community.
- Political revolutions aim to change political institutions in ways that those institutions themselves prohibit.
- During a revolution's interim, society is not fully governed by institutions at all.
- In increasing numbers, individuals become increasingly estranged from political life and behave more and more eccentrically within it.
- As crisis deepens, individuals commit themselves to some concrete proposal for the reconstruction of society in a new institutional framework.
- Competing camps and parties form.
- One camp seeks to defend the old institutional constellation.
- One (or more) camps seek to institute a new political order.
- As polarization occurs, political recourse fails.
- Parties to a revolutionary conflict finally resort to the techniques of mass persuasion.
- Like the choice between competing political institutions, that between competing paradigms proves to be a choice between fundamentally incompatible modes of community life. Paradigmatic differences cannot be reconciled.
- The evaluative procedures characteristic of normal science do not work, for these depend on a particular paradigm for their existence.
- When paradigms enter into a debate about fundamental questions and paradigm choice, each group uses its own paradigm to argue in that paradigm's defensethe result is a circularity and inability to share a universe of discourse.
- Fundamental paradigmatic assumptions are philosophically incompatible.
- Ultimately, scientific revolutions are affected by
- the impact of nature and of logic.
- techniques of persuasive argumentation (a struggle between stories?).
- A successful new paradigm/theory permits predictions that are different from those derived from its predecessor (98).
- That difference could not occur if the two were logically compatible.
- In the process of being assimilated, the second must displace the first.
- Consequently, the assimilation of either a new sort of phenomenon or a new scientific theory must demand the rejection of an older paradigm (95).
- If this were not so, scientific development would be genuinely cumulative (the view of science-as-cumulation or logical inclusivenesssee Chapter X).
- Recall that cumulative acquisition of unanticipated novelties proves to be an almost nonexistent exception to the rule of scientific developmentcumulative acquisition of novelty is not only rare in fact but improbable in principle (96).
- Normal research is cumulative, but not scientific revolution.
- New paradigms arise with destructive changes in beliefs about nature (98).
- Kuhn observes that his view is not the prevalent view. The prevalent view maintains that a new paradigm derives from, or is a cumulative addition to, the supplanted paradigm. [Note: This was the case in the late 1950s and early 1960s, when the book was published, but it is not the case today. As Kuhn points out, logical positivists were carrying the day then, but Structure proved revolutionary itself, and Kuhn's view is reasonably influential these days. Many would argue that Kuhn's view is now the prevalent view.] Objections to Kuhn's view include that
- only the extravagant claims of the old paradigm are contested.
- purged of these merely human extravagances, many old paradigms have never been and can never be challenged (e.g., Newtonian physics, behaviorism? psychoanalytic theory? logical positivism?).
- a scientist can reasonably work within the framework of more than one paradigm (and so eclecticism and, to some extent, relativism rear their heads).
- Kuhn refutes this logical positivist view, arguing that
- the logical positivist view makes any theory ever used by a significant group of competent scientists immune to attack.
- to save paradigms/theories in this way, their range of application must be restricted to those phenomena and to that precision of observation with which the experimental evidence in hand already deals.
- the rejection of a paradigm requires the rejection of its fundamental assumptions and of its rules for doing sciencethey are incompatible with those of the new paradigm.
- if the fundamental assumptions of old and new paradigm were not incompatible, novelty could always be explained within the framework of the old paradigm and crisis can always be avoided.
- revolution is not cumulation; revolution is transformation.
- the price of significant scientific advance is a commitment that runs the risk of being wrong.
- without commitment to a paradigm there can be no normal science.
- the need to change the meaning of established and familiar concepts is central to the revolutionary impact of a new paradigm.
- the differences between successive paradigms are both necessary and irreconcilable. Why?
- because successive paradigms tell us different things about the population of the universe and about that population's behavior.
- because paradigms are the source of the methods, problem-field, and standards of solution accepted by any mature scientific community at any given time.
- the reception of a new paradigm often necessitates a redefinition of the corresponding science (103).
- Old problems are relegated to other sciences or declared unscientific.
- Problems previously nonexistent or trivial may, with a new paradigm, become the very archetypes of significant scientific achievement.
- Consequently, "the normal-scientific tradition that emerges from a scientific revolution is not only incompatible but often actually incommensurable with that which has gone before" (103).
- The case for cumulative development of science's problems and standards is even harder to make than the case for the cumulative development of paradigms/theories.
- Standards are neither raised nor do they decline; standards simply change as a result of the adoption of the new paradigm.
- Paradigms act as maps that chart the direction of problems and methods through which problems may be solved.
- Because nature is too complex and varied to be explored at random, the map is an essential guide to the process of normal science.
- In learning a paradigm, the scientist acquires theory, methods, and standards together, usually in an inextricable mixture.
- Therefore, when paradigms change, there are usually significant shifts in the criteria determining the legitimacy both of problems and of proposed solutions (109).
- To the extent that two scientific schools disagree about what is a problem and what a solution, they will inevitably talk through each other when debating the relative merits of their respective paradigms (109).
- In the circular argument that results from this conversation, each paradigm will
- satisfy more or less the criteria that it dictates for itself, and
- fall short of a few of those dictated by its opponent.
- 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?
- In the final analysis, this involves a question of values that lie outside of normal science altogetherit is this recourse to external criteria that most obviously makes paradigm debates revolutionary (see B-8/9 above).
Chapter X - Revolutions as Changes of World View. When paradigms change, the world itself changes with them. How do the beliefs and conceptions of scientists change as the result of a paradigm shift? Are theories simply man-made interpretations of given data?
- During scientific revolutions, scientists see new and different things when looking with familiar instruments in places they have looked before.
- Familiar objects are seen in a different light and joined by unfamiliar ones as well.
- Scientists see the world of their research-engagement differently.
- Scientists see new things when looking at old objects.
- In a sense, after a revolution, scientists are responding to a different world.
- This difference in view resembles a gestalt shift, a perceptual transformation"what were ducks in the scientist's world before the revolution are rabbits afterward." But cautionthere are important differences.
- Something like a paradigm is a prerequisite to perception itself (recall G. H. Mead's concept of a predisposition, or the dictum it takes a meaning to catch a meaning).
- What people see depends both on what they look at and on what their previous visual-conceptual experience has taught them to see.
- Individuals know when a gestalt shift has taken place because they are aware of the shiftthey can even manipulate it mentally.
- In a gestalt switch, alternate perceptions are equally "true" (valid, reasonable, real).
- Because there are external standards with respect to which switch of vision can be demonstrated, conclusions about alternate perceptual possibilities can be drawn.
- But scientists have no such external standards
- Scientists have no recourse to a higher authority that determines when a switch in vision has taken place.
- As a consequence, in the sciences, if perceptual switches accompany paradigm changes, scientists cannot attest to these changes directly.
- A gestalt switch: "I used to see a planet, but now I see a satellite." (This leaves open the possibility that the earlier perception was once and may still be correct).
- A paradigm shift: " I used to see a planet, but I was wrong."
- It is true, however, that anomalies and crises "are terminated by a relatively sudden and unstructured event like the gestalt switch" (122).
- Why does a shift in view occur?
- Genius? Flashes of intuition? Sure.
- Paradigm-induced gestalt shifts? Perhaps, but see limitations above.
- Because different scientists interpret their observations differently? No.
- Observations (data) are themselves nearly always different.
- Because observations are conducted (data collected) within a paradigmatic framework, the interpretive enterprise can only articulate a paradigm, not correct it.
- Because of factors embedded in the nature of human perception and retinal impression? No doubt, but our knowledge is simply not yet advanced enough on this matter.
- Changes in definitional conventions? No.
- Because the existing paradigm fails to fit. Always.
- Because of a change in the relation between the scientist's manipulations and the paradigm or between the manipulations and their concrete results? You bet.
- It is hard to make nature fit a paradigm.
Chapter XI - The Invisibility of Revolutions. Because paradigm shifts are generally viewed not as revolutions but as additions to scientific knowledge, and because the history of the field is represented in the new textbooks that accompany a new paradigm, a scientific revolution seems invisible.
- An increasing reliance on textbooks is an invariable concomitant of the emergence of a first paradigm in any field of science (136).
- The image of creative scientific activity is largely created by a field's textbooks.
- Textbooks are the pedagogic vehicles for the perpetuation of normal science.
- These texts become the authoritative source of the history of science.
- Both the layman's and the practitioner's knowledge of science is based on textbooks.
- A field's texts must be rewritten in the aftermath of a scientific revolution.
- Once rewritten, they inevitably disguise no only the role but the existence and significance of the revolutions that produced them.
- The resulting textbooks truncate the scientist's sense of his discipline's history and supply a substitute for what they eliminate.
- More often than not, they contain very little history at all (Whitehead: "A science that hesitates to forget its founders is lost.")
- In the rewrite, earlier scientists are represented as having worked on the same set of fixed problems and in accordance with the same set of fixed canons that the most recent revolution and method has made seem scientific.
- Why dignify what science's best and most persistent efforts have made it possible to discard?
- The historical reconstruction of previous paradigms and theorists in scientific textbooks make the history of science look linear or cumulative, a tendency that even affects scientists looking back at their own research (139).
- These misconstructions render revolutions invisible.
- They also work to deny revolutions as a function.
- Science textbooks present the inaccurate view that science has reached its present state by a series of individual discoveries and inventions that, when gathered together, constitute the modern body of technical knowledgethe addition of bricks to a building.
- This piecemeal-discovered facts approach of a textbook presentation illustrates the pattern of historical mistakes that misleads both students and laymen about the nature of the scientific enterprise.
- More than any other single aspect of science, that pedagogic form [the textbook] has determined our image of the nature of science and of the role of discovery and invention in its advance.
Chapter XII - The Resolution of Revolutions. How do the proponents of a competing paradigm convert the entire profession or the relevant subgroup to their way of seeing science and the world? What causes a group to abandon one tradition of normal research in favor of another? What is the process by which a new candidate for paradigm replaces its predecessor?
- Scientific revolutions come about when one paradigm displaces another after a period of paradigm-testing that occurs
- only after persistent failure to solve a noteworthy puzzle has given rise to crisis.
- as part of the competition between two rival paradigms for the allegiance of the scientific community.
- The process of paradigm-testing parallels two popular philosophical theories about the verification of scientific theories.
- Theory-testing through probabilistic verification.
- Comparison of the ability of different theories to explain the evidence at hand.
- This process is analogous to natural selection: one theory becomes the most viable among the actual alternatives in a particular historical situation.
- Theory-testing through falsification (Karl Popper).
- A theory must be rejected when outcomes predicted by the theory are negative.
- The role attributed to falsification is similar to the one that Kuhn assigns to anomalous experiences.
- Kuhn doubts that falsifying experiences exist.
- No theory ever solves all the puzzles with which it is confronted at a given time.
- It is the incompleteness and imperfection of the existing data-theory fit that define the puzzles that characterize normal science.
- If any and every failure to fit were ground for theory rejection, all theories ought to be rejected at all times.
- If only severe failure to fit justifies theory rejection, then theory-testing through falsification would require some criterion of improbability or of degree of falsificationthereby requiring recourse to 1 above.
- It makes little sense to suggest that verification is establishing the agreement of fact with theory.
- All historically significant theories have agreed with the facts, but only more or less.
- It makes better sense to ask which of two competing theories fits the facts better.
- Recall that scientists in paradigmatic disputes tend to talk through each other.
- Competition between paradigms is not the sort of battle that can be resolved by proofs.
- Since new paradigms are born from old ones, they incorporate much of the vocabulary and apparatus that the traditional paradigm had previously employed, though these elements are employed in different ways.
- Moreover, proponents of competing paradigms practice their trade in different worldsthe two groups see different things (i.e., the facts are differently viewed).
- Like a gestalt switch, verification occurs all at once or not at all (150).
- Although a generation is sometimes required to effect a paradigm change, scientific communities have again and again been converted to new paradigms.
- 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 grow up that is familiar with it.
- But Kuhn argues that Planck's famous remark overstates the case.
- Neither proof nor error is at issue.
- The transfer of allegiance from paradigm to paradigm is a conversion experience that cannot be forced.
- Proponents of a paradigm devote their lives and careers to the paradigm.
- Lifelong resistance is not a violation of scientific standards but an index to the nature of scientific research itself.
- The source of the resistance is the assurance that
- the older paradigm will ultimately solve all its problems.
- nature can be shoved into the box the paradigm provides.
- Actually, that same assurance is what makes normal science possible.
- Some scientists, particularly the older and more experienced ones, may resist indefinitely, but most can be reached in one way or another.
- Conversions occur not despite the fact that scientists are human but because they are.
- How are scientists converted? How is conversion induced and how resisted?
- Individual scientists embrace a new paradigm for all sorts of reasons and usually for several at once.
- idiosyncracy of autobiography and personality?
- nationality or prior reputation of innovator and his teachers?
- The focus of these questions should not be on the individual scientist but with the sort of community that always sooner or later re-forms as a single group (this will be dealt with in Chapter XIII).
- The community recognizes that a new paradigm displays a quantitative precision strikingly better than its older competitor.
- A claim that a paradigm solves the crisis-provoking problem is rarely sufficient by itself.
- Persuasive arguments can be developed if the new paradigm permits the prediction of phenomena that had been entirely unsuspected while the old paradigm prevailed.
- Rather than a single group conversion, what occurs is an increasing shift in the distribution of professional allegiances (158).
- But paradigm debates are not about relative problem-solving ability. Rather the issue is which paradigm should in the future guide research on problems many of which neither competitor can yet claim to resolve completely (157).
- A decision between alternate ways of practicing science is called for.
- A decision is based on future promise rather than on past achievement.
- A scientist must have faith that the new paradigm will succeed with the many large problems that confront it.
- There must be a basis for this faith in the candidate chosen.
- Sometimes this faith is based on personal and inarticulate aesthetic considerations.
- This is not to suggest that new paradigms triumph ultimately through some mystical aesthetic.
- The new paradigm appeals to the individual's sense of the appropriate or the aestheticthe new paradigm is said to be neater, more suitable, simpler, or more elegant (155).
- What is the process by which a new candidate for paradigm replaces its predecessor?
- At the start, a new candidate for paradigm may have few supporters (and the motives of the supporters may be suspect).
- If the supporters are competent, they will
- improve the paradigm,
- explore its possibilities,
- and show what it would be like to belong to the community guided by it.
- For the paradigm destined to win, the number and strength of the persuasive arguments in its favor will increase.
- As more and more scientists are converted, exploration increases.
- The number of experiments, instruments, articles, and books based on the paradigm will multiply.
- More scientists, convinced of the new view's fruitfulness, will adopt the new mode of practicing normal science (until only a few elderly hold-outs will remain).
- And we cannot say that they are (were) wrong.
- Perhaps the scientist who continues to resist after the whole profession has been converted has ipso facto ceased to be a scientist.
Chapter XIII - Progress Through Revolutions. In the face of the arguments previously made, why does science progress, how does it progress, and what is the nature of its progress?
- Perhaps progress is inherent in the definition of science.
- To a very great extent, the term science is reserved for fields that do progress in obvious ways.
- This issue is of particular import to the social sciences.
- Is a social science a science because it defines itself as a science in terms of possessing certain characteristics and aims to make progress?
- Questions about whether a field or discipline is a science will cease to be a source of concern not when a definition is found, but when the groups that now doubt their own status achieve consensus about their past and present accomplishments (161).
- Do economists worry less than educators about whether their field is a science because economists know what a science is? Or is it economics about which they agree?
- Why do not natural scientists or artists worry about the definition of the term?
- We tend to see as a science any field in which progress is marked (162).
- Does a field make progress because it is a science, or is it a science because it makes progress?
- Normal science progresses because the enterprise shares certain salient characteristics,
- Members of a mature scientific community work from a single paradigm or from a closely related set.
- Very rarely do different scientific communities investigate the same problems.
- The result of successful creative work is progress (162).
- No creative school recognizes a category of work that is, on the one hand, a creative success, but is not, on the other, an addition to the collective achievement of the group.
- Even if we argue that a field does not make progress, that does not mean that an individual school/discipline within that field does not.
- The man who argues that philosophy has made no progress emphasizes that there are still Aristotelians, not that Aristotelianism has failed to progress.
- It is only during periods of normal science that progress seems both obvious and assured.
- In part, this progress is in the eye of the beholder.
- The absence of competing paradigms that question each other's aims and standards makes the progress of a normal-scientific community far easier to see.
- The acceptance of a paradigm frees the community from the need to constantly re-examine its first principles and foundational assumptions.
- Members of the community can concentrate on the subtlest and most esoteric of the phenomena that concern it.
- There are no other professional communities in which individual creative work is so exclusively addressed to and evaluated by other members of the profession.
- Other professions are more concerned with lay approbation than are scientists.
- Because scientists work only for an audience of colleagues, an audience that shares values and beliefs, a single set of standards can be taken for granted.
- This insulation of the scientist from society permits the individual scientist to concentrate attention on problems that she has a good reason to believe she will be able to solve.
- Unlike in other disciplines, the scientist need not select problems because they urgently need solution and without regard for the tools available to solve them [note the important contrast here between natural scientists and social scientists].
- The social scientists tend to defend their choice of a research problem chiefly in terms of the social importance of achieving a solution.
- Which group would one then expect to solve problems at a more rapid rate?
- The effects of insulation are intensified by the nature of the scientific community's educational initiation.
- The education of a social scientist consists in large part of
- reading original sources.
- being made aware of the variety of problems that the members of his future group have, in the course of time, attempted to solve, and the paradigms that have resulted from these attempts.
- facing competing and incommensurable solutions to these problems.
- evaluating the solutions to the problems presented.
- selecting among competing existing paradigms.
- In the education of a natural scientist
- textbooks (as described earlier) are used until graduate school.
- textbooks are systematically substituted for the creative scientific literature that made them possible.
- classics are seldom read, and they are viewed as antiquated oddities.
- The educational initiation of scientists is immensely effective.
- The education of scientists prepares them for the generation through normal science of significant crises (167).
- In its normal state, a scientific community is an immensely efficient instrument for solving the problems or puzzles that its paradigms defineprogress is the result of solving these problems.
- Progress is also a salient feature of extraordinary scienceof science during a revolution.
- Revolutions close with total victory for one of the two opposing camps.
- When it repudiates a paradigm, a scientific community simultaneously renounces most of the books and articles in which that paradigm had been embodied.
- The community acknowledges this as progress.
- In a sense, it may appear that the member of a mature scientific community is the victim of a history rewritten by the powers that be (167).
- But recall that the power to select between paradigms resides in the members of the community.
- The process of scientific revolution is in large part a democratic process.
- And what are the characteristics of these scientific communities?
- The scientist must be concerned to solve problems about the behavior of nature.
- Although the concerns may be global, the problems must be problems of detail
- The solutions to problems that satisfy a scientist must satisfy the community.
- No appeals to heads of state or to the populace at large in matters scientific.
- Members of the community are recognized and are the exclusive arbiters of professional achievement.
- Because of their shared training and experience, members of the community are seen as the sole possessors of the rules of the game.
- To doubt that they share some basis for evaluation would be to admit the existence of incompatible standards of scientific achievement.
- The community must see paradigm change as progressas we have seen, this perception is, in important respects, self-fulfilling (169).
- Discomfort with a paradigm takes place only when nature itself first undermines professional security by making prior achievements seem problematic.
- The community embraces a new paradigm when
- the new candidate is seen to resolve some outstanding and generally recognized problem that can be met in no other way.
- the new paradigm promises to preserve a relatively large part of the concrete problem-solving ability that has accrued to science through its predecessors.
- Though science surely grows in depth, it may not grow in breadth as well. When it does,
- this is manifest through the proliferation of specialties,
- not in the scope of any single specialty alone.
- We may have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth (171).
- The developmental process described by Kuhn is a process of evolution from primitive beginningsa process whose successive stages are characterized by an increasingly detailed and refined understanding of nature.
- This is not a process of evolution toward anything.
- Important questions arise.
- Must there be a goal set by nature in advance?
- Does it really help to imagine that there is some one full, objective, true account of nature?
- Is the proper measure of scientific achievement the extent to which it brings us closer to an ultimate goal?
- The analogy that relates the evolution of organisms to the evolution of scientific ideas "is nearly perfect" (172).
- The resolution of revolutions is the selection by conflict within the scientific community of the fittest way to practice future science.
- The net result of a sequence of such revolutionary selections, separated by period of normal research, is the wonderfully adapted set of instruments we call modern scientific knowledge.
- Successive stages in that developmental process are marked by an increase in articulation and specialization.
- The process occurs without benefit of a set goal and without benefit of any permanent fixed scientific truth.
- What must the world be like in order that man may know it?
Thomas Kuhn (1962)
The Structure of Scientific Revolutions
Source: The Structure of Scientific Revolutions (1962) publ. University of Chicago Press, 1962. One chapter plus one postscript reproduced here;
Transcribed: by Andy Blunden in 1998; proofed and corrected March 2005.
IX. The Nature and Necessity of Scientific Revolutions
These remarks permit us at last to consider the problems that provide this essay with its title. What are scientific revolutions, and what is their function in scientific development? Much of the answer to these questions has been anticipated in earlier sections. In particular, the preceding discussion has indicated that scientific revolutions are here taken to be those non-cumulative developmental episodes in which an older paradigm is replaced in whole or in part by an incompatible new one. There is more to be said, however, and an essential part of it can be introduced by asking one further question. Why should a change of paradigm be called a revolution? In the face of the vast and essential differences between political and scientific development, what parallelism can justify the metaphor that finds revolutions in both?
One aspect of the parallelism must already be apparent. Political revolutions are inaugurated by a growing sense, often restricted to a segment of the political community, that existing institutions have ceased adequately to meet the problems posed by an environment that they have in part created. In much the same way, scientific revolutions are inaugurated by a growing sense, again often restricted to a narrow subdivision of the scientific community, that an existing paradigm has ceased to function adequately in the exploration of an aspect of nature to which that paradigm itself had previously led the way. In both political and scientific development the sense of malfunction that can lead to crisis is prerequisite to revolution. Furthermore, though it admittedly strains the metaphor, that parallelism holds not only for the major paradigm changes, like those attributable to Copernicus and Lavoisier, but also for the far smaller ones associated with the assimilation of a new sort of phenomenon, like oxygen or X-rays. Scientific revolutions, as we noted at the end of Section V, need seem revolutionary only to those whose paradigms are affected by them. To outsiders they may, like the Balkan revolutions of the early twentieth century, seem normal parts of the developmental process. Astronomers, for example, could accept X-rays as a mere addition to knowledge, for their paradigms were unaffected by the existence of the new radiation. But for men like Kelvin, Crookes, and Roentgen, whose research dealt with radiation theory or with cathode ray tubes, the emergence of X-rays necessarily violated one paradigm as it created another. That is why these rays could be discovered only through something’s first going wrong with normal research.
This genetic aspect of the parallel between political and scientific development should no longer be open to doubt. The parallel has, however, a second and more profound aspect upon which the significance of the first depends. Political revolutions aim to change political institutions in ways that those institutions themselves prohibit. Their success therefore necessitates the partial relinquishment of one set of institutions in favour of another, and in the interim, society is not fully governed by institutions at all. Initially it is crisis alone that attenuates the role of political institutions as we have already seen it attenuate the role of paradigms. In increasing numbers individuals become increasingly estranged from political life and behave more and more eccentrically within it. Then, as the crisis deepens, many of these individuals commit themselves to some concrete proposal for the reconstruction of society in a new institutional framework. At that point the society is divided into competing camps or parties, one seeking to defend the old institutional constellation, the others seeking to institute some new one. And, once that polarisation has occurred, political recourse fails. Because they differ about the institutional matrix within which political change is to be achieved and evaluated, because they acknowledge no supra-institutional framework for the adjudication of revolutionary difference, the parties to a revolutionary conflict must finally resort to the techniques of mass persuasion, often including force. Though revolutions have had a vital role in the evolution of political institutions, that role depends upon their being partially extrapolitical or extrainstitutional events. The remainder of this essay aims to demonstrate that the historical study of paradigm change reveals very similar characteristics in the evolution of the sciences. 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 these 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 defence.
The resulting circularity does not, of course, make the arguments wrong or even ineffectual. The man who premises a paradigm when arguing in its defence can nonetheless provide a clear exhibit of what scientific practice will be like for those who adopt the new view of nature. That exhibit can be immensely persuasive, often compellingly so. Yet, whatever its force, the status of the circular argument is only that of persuasion. It cannot be made logically or even probabilistically compelling for those who refuse to step into the circle. The premises and values shared by the two parties to a debate over paradigms are not sufficiently extensive for that. As in political revolutions, so in paradigm choice – there is no standard higher than the assent of the relevant community. To discover how scientific revolutions are effected, we shall therefore have to examine not only the impact of nature and of logic, but also the techniques of persuasive argumentation effective within the quite special groups that constitute the community of scientists.
To discover why this issue of paradigm choice can never be unequivocally settled by logic and experiment alone, we must shortly examine the nature of the differences that separate the proponents of a traditional paradigm from their revolutionary successors. That examination is the principal object of this section and the next. We have, however, already noted numerous examples of such differences, and no one will doubt that history can supply many others. What is more likely to be doubted than their existence – and what must therefore be considered first – is that such examples provide essential information about the nature of science. Granting that paradigm rejection has been a historic fact, does it illuminate more than human credulity and confusion? Are there intrinsic reasons why the assimilation of either a new sort of phenomenon or a new scientific theory must demand the rejection of an older paradigm?
First notice that if there are such reasons, they do not derive from the logical structure of scientific knowledge. In principle, a new phenomenon might emerge without reflecting destructively upon any part of past scientific practice. Though discovering life on the moon would today be destructive of existing paradigms (these tell us things about the moon that seem incompatible with life’s existence there), discovering life in some less well-known part of the galaxy would not. By the same token, a new theory does not have to conflict with any of its predecessors. It might deal exclusively with phenomena not previously known, as the quantum theory deals (but, significantly, not exclusively) with subatomic phenomena unknown before the twentieth century. Or again, the new theory might be simply a higher level theory than those known before, one that linked together a whole group of lower level theories without substantially changing any. Today, the theory of energy conservation provides just such links between dynamics, chemistry, electricity, optics, thermal theory, and so on. Still other compatible relationships between old and new theories can be conceived. Any and all of them might be exemplified by the historical process through which science has developed. If they were, scientific development would be genuinely cumulative. New sorts of phenomena would simply disclose order in an aspect of nature where none had been seen before. In the evolution of science new knowledge would replace ignorance rather than replace knowledge of another and incompatible sort.
Of course, science (or some other enterprise, perhaps less effective) might have developed in that fully cumulative manner. Many people have believed that it did so, and most still seem to suppose that cumulation is at least the ideal that historical development would display if only it had not so often been distorted by human idiosyncrasy. There are important reasons for that belief. In Section X we shall discover how closely the view of science-as-cumulation is entangled with a dominant epistemology that takes knowledge to be a construction placed directly upon raw sense data by the mind. And in Section XI we shall examine the strong support provided to the same historiographic schema by the techniques of effective science pedagogy. Nevertheless, despite the immense plausibility of that ideal image, there is increasing reason to wonder whether it can possibly be an image of science. After the pre-paradigm period the assimilation of all new theories and of almost all new sorts of phenomena has in fact demanded the destruction of a prior paradigm and a consequent conflict between competing schools of scientific thought. Cumulative acquisition of unanticipated novelties proves to be an almost non-existent exception to the rule of scientific development. The man who takes historic fact seriously must suspect that science does not tend toward the ideal that our image of its cumulativeness has suggested. Perhaps it is another sort of enterprise.
If, however, resistant facts can carry us that far, then a second look at the ground we have already covered may suggest that cumulative acquisition of novelty is not only rare in fact but improbable in principle. Normal 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. (That is why an excessive concern with useful problems, regardless of their relation to existing knowledge and technique, can so easily inhibit scientific development.) The man who is striving to solve a problem defined by existing knowledge and technique is not, however, just looking around. He knows what he wants to achieve, and he designs his instruments and directs his thoughts accordingly. Unanticipated novelty, the new discovery, can emerge only to the extent that his anticipations about nature and his instruments prove wrong. Often the importance of the resulting discovery will itself be proportional to the extent and stubbornness of the anomaly that foreshadowed it. Obviously, then, there must be a conflict between the paradigm that discloses anomaly and the one that later renders the anomaly law-like. The examples of discovery through paradigm destruction examined in Section VI did not confront us with mere historical accident. There is no other effective way in which discoveries might be generated.
The same argument applies even more clearly to the invention of new theories. There are, in principle, only three types of phenomena about which a new theory might be developed. The first consists of phenomena already well explained by existing paradigms, and these seldom provide either motive or point of departure for theory construction. When they do, as with the three famous anticipations discussed at the end of Section VII, the theories that result are seldom accepted, because nature provides no ground for discrimination. A second class of phenomena consists of those whose nature is indicated by existing paradigms but whose details can be understood only through further theory articulation. These are the phenomena to which scientists direct their research much of the time, but that research aims at the articulation of existing paradigms rather than at the invention of new ones. Only when these attempts at articulation fail do scientists encounter the third type of phenomena, the recognised anomalies whose characteristic feature is their stubborn refusal to be assimilated to existing paradigms. This type alone gives rise to new theories. Paradigms provide all phenomena except anomalies with a theory-determined place in the scientist’s field of vision.
But if new theories are called forth to resolve anomalies in the relation of an existing theory to nature, then the successful new theory must somewhere permit predictions that are different from those derived from its predecessor. That difference could not occur if the two were logically compatible. In the process of being assimilated, the second must displace the first. Even a theory like energy conservation, which today seems a logical superstructure that relates to nature only through independently established theories, did not develop historically without paradigm destruction. Instead, it emerged from a crisis in which an essential ingredient was the incompatibility between Newtonian dynamics and some recently formulated consequences of the caloric theory of heat. Only after the caloric theory had been rejected could energy conservation become part of science. And only after it had been part of science for some time could it come to seem a theory of a logically higher type, one not in conflict with its predecessors. It is hard to see how new theories could arise without these destructive changes in beliefs about nature. Though logical inclusiveness remains a permissible view of the relation between successive scientific theories, it is a historical implausibility.
A century ago it would, I think, have been possible to let the case for the necessity of revolutions rest at this point. But today, unfortunately, that cannot be done because the view of the subject developed above cannot be maintained if the most prevalent contemporary interpretation of the nature and function of scientific theory is accepted. That interpretation, closely associated with early logical positivism and not categorically rejected by its successors, would restrict the range and meaning of an accepted theory so that it could not possibly conflict with any later theory that made predictions about some of the same natural phenomena. The best-known and the strongest case for this restricted conception of a scientific theory emerges in discussions of the relation between contemporary Einsteinian dynamics and the older dynamical equations that descend from Newton’s Principia. From the viewpoint of this essay these two theories are fundamentally incompatible in the sense illustrated by the relation of Copernican to Ptolemaic astronomy: Einstein’s theory can be accepted only with the recognition that Newton’s was wrong. Today this remains a minority view. We must therefore examine the most prevalent objections to it.
The gist of these objections can be developed as follows. Relativistic dynamics cannot have shown Newtonian dynamics to be wrong, for Newtonian dynamics is still used with great success by most engineers and, in selected applications, by many physicists. Furthermore, the propriety of this use of the older theory can be proved from the very theory that has, in other applications, replaced it. Einstein’s theory can be used to show that predictions from Newton’s equations will be as good as our measuring instruments in all applications that satisfy a small number of restrictive conditions. For example, if Newtonian theory is to provide a good approximate solution, the relative velocities of the bodies considered must be small compared with the velocity of light. Subject to this condition and a few others, Newtonian theory seems to be derivable from Einsteinian, of which it is therefore a special case.
But, the objection continues, no theory can possibly conflict with one of its special cases. If Einsteinian science seems to make Newtonian dynamics wrong, that is only because some Newtonians were so incautious as to claim that Newtonian theory yielded entirely precise results or that it was valid at very high relative velocities. Since they could not have had any evidence for such claims, they betrayed the standards of science when they made them. In so far as Newtonian theory was ever a truly scientific theory supported by valid evidence, it still is. Only extravagant claims for the theory – claims that were never properly parts of science can have been shown by Einstein to be wrong. Purged of these merely human extravagances, Newtonian theory has never been challenged and cannot be.
Some variant of this argument is quite sufficient to make any theory ever used by a significant group of competent scientists immune to attack. The much-maligned phlogiston theory, for example, gave order to a large number of physical and chemical phenomena. It explained why bodies burned – they were rich in phlogiston – and why metals had so many more properties in common than did their ores. The metals were all compounded from different elementary earths combined with phlogiston, and the latter, common to all metals, produced common properties. In addition, the phlogiston theory accounted for a number of reactions in which acids were formed by the combustion of substances like carbon and sulphur. Also, it explained the decrease of volume when combustion occurs in a confined volume of air the phlogiston released by combustion “spoils” the elasticity of the air that absorbed it, just as fire “spoils” the elasticity of a steel spring. If these were the only phenomena that the phlogiston theorists had claimed for their theory, that theory could never have been challenged. A similar argument will suffice for any theory that has ever been successfully applied to any range of phenomena at all.
But to save theories in this way, their range of application must be restricted to those phenomena and to that precision of observation with which the experimental evidence in hand already deals. Carried just a step further (and the step can scarcely be avoided once the first is taken), such a limitation prohibits the scientist from claiming to speak “scientifically” about any phenomenon not already observed. Even in its present form the restriction forbids the scientist to rely upon a theory in his own research whenever that research enters an area or seeks a degree of precision for which past practice with the theory offers no precedent. These prohibitions are logically unexceptionable. But the result of accepting them would be the end of the research through which science may develop further.
By now that point too is virtually a tautology. Without commitment to a paradigm there could be no normal science. Furthermore, that commitment must extend to areas and to degrees of precision for which there is no full precedent. If it did not, the paradigm could provide no puzzles that had not already been solved. Besides, it is not only normal science that depends upon commitment to a paradigm. If existing theory binds the scientist only with respect to existing applications, then there can be no surprises, anomalies, or crises. But these are just the signposts that point the way to extraordinary science. If positivistic restrictions on the range of a theory’s legitimate applicability are taken literally, the mechanism that tells the scientific community what problems may lead to fundamental change must cease to function. And when that occurs, the community will inevitably return to something much like its pre-paradigm state a condition in which all members practice science but in which their gross product scarcely resembles science at all. Is it really any wonder that the price of significant scientific advance is a commitment that runs the risk of being wrong?
More important, there is a revealing logical lacuna in the positivist’s argument, one that will reintroduce us immediately to the nature of revolutionary change. Can Newtonian dynamics really be derived from relativistic dynamics? What would such a derivation look like? Imagine a set of statements, E1, E2, ... En which together embody the laws of relativity theory. These statements contain variables and parameters representing spatial position, time, rest mass, etc. From them, together with the apparatus of logic and mathematics, is deducible a whole set of further statements including some that can be checked by observation. To prove the adequacy of Newtonian dynamics as a special case, we must add to the Ei’s additional statements, like (v/c)2 << 1, restricting the range of the parameters and variables. This enlarged set of statements is then manipulated to yield a new set, N1, N2, ..., Nm, which is identical in form with Newton’s laws of motion, the law of gravity, and so on. Apparently Newtonian dynamics has been derived from Einsteinian, subject to a few limiting conditions.
Yet the derivation is spurious, at least to this point. Though the Ni’s are a special case of the laws of relativistic mechanics, they are not Newton’s Laws. Or at least they are not unless those laws are reinterpreted in a way that would have been impossible until after Einstein’s work. The variables and parameters that in the Einsteinian Ei’s represented spatial position, time, mass, etc., still occur in the Ni’s; and they there still represent Einsteinian space, time, and mass. But the physical referents of these Einsteinian concepts are by no means identical with those of the Newtonian concepts that bear the same name. (Newtonian mass is conserved; Einsteinian is convertible with energy. Only at low relative velocities may the two be measured in the same way, and even then they must not be conceived to be the same.) Unless we change the definitions of the variables in the Ni’s, the statements we have derived are not Newtonian. If we do change them, we cannot properly be said to have derived Newton’s Laws, at least not in any sense of “derive” now generally recognised. Our argument has, of course, explained why Newton’s Laws ever seemed to work. In doing so it has justified, say, an automobile driver in acting as though he lived in a Newtonian universe. An argument of the same type is used to justify teaching earth-centred astronomy to surveyors. But the argument has still not done what it purported to do. It has not, that is, shown Newton’s Laws to be a limiting case of Einstein’s. For in the passage to the limit it is not only the forms of the laws that have changed. Simultaneously we have had to alter the fundamental structural elements of which the universe to which they apply is composed.
This need to change the meaning of established and familiar concepts is central to the revolutionary impact of Einstein’s theory. Though subtler than the changes from geocentrism to heliocentrism, from phlogiston to oxygen, or from corpuscles to waves, the resulting conceptual transformation is no less decisively destructive of a previously established paradigm. We may even come to see it as a prototype for revolutionary reorientations in the sciences. Just because it did not involve the introduction of additional objects or concepts, the transition from Newtonian to Einsteinian mechanics illustrates with particular clarity the scientific revolution as a displacement of the conceptual network through which scientists view the world.
These remarks should suffice to show what might, in another philosophical climate, have been taken for granted. At least for scientists, most of the apparent differences between a discarded scientific theory and its successor are real. Though an out-of-date theory can always be viewed as a special case of its up-to-date successor, it must be transformed for the purpose. And the transformation is one that can be undertaken only with the advantages of hindsight, the explicit guidance of the more recent theory. Furthermore, even if that transformation were a legitimate device to employ in interpreting the older theory, the result of its application would be a theory so restricted that it could only restate what was already known. Because of its economy, that restatement would have utility, but it could not suffice for the guidance of research.
Let us, therefore, now take it for granted that the differences between successive paradigms are both necessary and irreconcilable. Can we then say more explicitly what sorts of differences these are? The most apparent type has already been illustrated repeatedly. Successive paradigms tell us different things about the population of the universe and about that population’s behaviour. They differ, that is, about such questions as the existence of subatomic particles, the materiality of light, and the conservation of heat or of energy. These are the substantive differences between successive paradigms, and they require no further illustration. But paradigms differ in more than substance, for they are directed not only to nature but also back upon the science that produced them. They are the source of the methods, problem-field, and standards of solution accepted by any mature scientific community at any given time. As a result, the reception of a new paradigm often necessitates a redefinition of the corresponding science. Some old problems may be relegated to another science or declared entirely “unscientific.” Others that were previously non-existent or trivial may, with a new paradigm, become the very archetypes of significant scientific achievement. And as the problems change, so, often, does the standard that distinguishes a real scientific solution from a mere metaphysical speculation, word game, or mathematical play. The normal-scientific tradition that emerges from a scientific revolution is not only incompatible but often actually incommensurable with that which has gone before.
The impact of Newton’s work upon the normal seventeenth century tradition of scientific practice provides a striking example of these subtler effects of paradigm shift. Before Newton was born the “new science” of the century had at last succeeded in rejecting Aristotelian and scholastic explanations expressed in terms of the essences of material bodies. To say that a stone fell because its “nature” drove it toward the center of the universe had been made to look a mere tautological word-play, something it had not previously been. Henceforth the entire flux of sensory appearances, including colour, taste, and even weight, was to be explained in terms of the size, shape, position, and motion of the elementary corpuscles of base matter. The attribution of other qualities to the elementary atoms was a resort to the occult and therefore out of bounds for science. Molière caught the new spirit precisely when he ridiculed the doctor who explained opium’s efficacy as a soporific by attributing to it a dormitive potency. During the last half of the seventeenth century many scientists preferred to say that the round shape of the opium particles enabled them to sooth the nerves about which they moved.
In an earlier period explanations in terms of occult qualities had been an integral part of productive scientific work. Nevertheless, the seventeenth century’s new commitment to mechanico-corpuscular explanation proved immensely fruitful for a number of sciences, ridding them of problems that had defied generally accepted solution and suggesting others to replace them. In dynamics, for example, Newton’s three laws of motion are less a product of novel experiments than of the attempt to reinterpret well-known observations in terms of the motions and interactions of primary neutral corpuscles. Consider just one concrete illustration. Since neutral corpuscles could act on each other only by contact, the mechanico-corpuscular view of nature directed scientific attention to a brand-new subject of study, the alteration of particulate motions by collisions. Descartes announced the problem and provided its first putative solution. Huygens, Wren, and Wallis carried it still further, partly by experimenting with colliding pendulum bobs, but mostly by applying previously well-known characteristics of motion to the new problem. And Newton embedded their results in his laws of motion. The equal “action” and “reaction” of the third law are the changes in quantity of motion experienced by the two parties to a collision. The same change of motion supplies the definition of dynamical force implicit in the second law. In this case, as in many others during the seventeenth century, the corpuscular paradigm bred both a new problem and a large part of that problem’s solution.
Yet, though much of Newton’s work was directed to problems and embodied standards derived from the mechanico-corpuscular world view, the effect of the paradigm that resulted from his work was a further and partially destructive change in the problems and standards legitimate for science. Gravity, interpreted as an innate attraction between every pair of particles of matter, was an occult quality in the same sense as the scholastics’ “tendency to fall” had been. Therefore, while the standards of corpuscularism remained in effect, the search for a mechanical explanation of gravity was one of the most challenging problems for those who accepted the Principia as paradigm. Newton devoted much attention to it and so did many of his eighteenth-century successors. The only apparent option was to reject Newton’s theory for its failure to explain gravity, and that alternative, too, was widely adopted. Yet neither of these views ultimately triumphed. Unable either to practice science without the Principia or to make that work conform to the corpuscular standards of the seventeenth century, scientists gradually accepted the view that gravity was indeed innate. By the mid-eighteenth century that interpretation had been almost universally accepted, and the result was a genuine reversion (which is not the same as a retrogression) to a scholastic standard. Innate attractions and repulsions joined size, shape, position, and motion as physically irreducible primary properties of matter.
The resulting change in the standards and problem-field of physical science was once again consequential. By the 1740’s, for example, electricians could speak of the attractive “virtue” of the electric fluid without thereby inviting the ridicule that had greeted Molière’s doctor a century before. As they did so, electrical phenomena increasingly displayed an order different from the one they had shown when viewed as the effects of a mechanical effluvium that could act only by contact. In particular, when electrical action-at-a-distance became a subject for study in its own right, the phenomenon we now call charging by induction could be recognised as one of its effects. Previously, when seen at all, it had been attributed to the direct action of electrical “atmospheres” or to the leakages inevitable in any electrical laboratory. The new view of inductive effects was, in turn, the key to Franklin’s analysis of the Leyden jar and thus to the emergence of a new and Newtonian paradigm for electricity. Nor were dynamics and electricity the only scientific fields affected by the legitimisation of the search for forces innate to matter. The large body of eighteenth-century literature on chemical affinities and replacement series also derives from this supramechanical aspect of Newtonianism. Chemists who believed in these differential attractions between the various chemical species set up previously unimagined experiments and searched for new sorts of reactions. Without the data and the chemical concepts developed in that process, the later work of Lavoisier and, more particularly, of Dalton would be incomprehensible. Changes in the standards governing permissible problems, concepts, and explanations can transform a science. In the next section I shall even suggest a sense in which they transform the world.
Other examples of these non-substantive differences between successive paradigms can be retrieved from the history of any science in almost any period of its development. For the moment let us be content with just two other and far briefer illustrations. Before the chemical revolution, one of the acknowledged tasks of chemistry was to account for the qualities of chemical substances and for the changes these qualities underwent during chemical reactions. With the aid of a small number of elementary “principles” – of which phlogiston was one – the chemist was to explain why some substances are acidic, others metalline, combustible, and so forth. Some success in this direction had been achieved. We have already noted that phlogiston explained why the metals were so much alike, and we could have developed a similar argument for the acids. Lavoisier’s reform, however, ultimately did away with chemical “principles,” and thus ended by depriving chemistry of some actual and much potential explanatory power. To compensate for this loss, a change in standards was required. During much of the nineteenth century failure to explain the qualities of compounds was no indictment of a chemical theory.
Or again, Clerk Maxwell shared with other nineteenth-century proponents of the wave theory of light the conviction that light waves must be propagated through a material ether. Designing a mechanical medium to support such waves was a standard problem for many of his ablest contemporaries. His own theory, however, the electromagnetic theory of light, gave no account at all of a medium able to support light waves, and it clearly made such an account harder to provide than it had seemed before. Initially, Maxwell’s theory was widely rejected for those reasons. But, like Newton’s theory, Maxwell’s proved difficult to dispense with, and as it achieved the status of a paradigm the community’s attitude toward it changed. In the early decades of the twentieth century Maxwell’s insistence upon the existence of a mechanical ether looked more and more like lip service, which it emphatically had not been, and the attempts to design such an ethereal medium were abandoned. Scientists no longer thought it unscientific to speak of an electrical “displacement” without specifying what was being displaced. The result, again, was a new set of problems and standards, one which, in the event, had much to do with the emergence of relativity theory.
These characteristic shifts in the scientific community’s conception of its legitimate problems and standards would have less significance to this essay’s thesis if one could suppose that they always occurred from some methodologically lower to some higher type. In that case their effects, too, would seem cumulative. No wonder that some historians have argued that the history of science records a continuing increase in the maturity and refinement of man’s conception of the nature of science. Yet the case for cumulative development of science’s problems and standards is even harder to make than the case for cumulation of theories. The attempt to explain gravity, though fruitfully abandoned by most eighteenth-century scientists, was not directed to an intrinsically illegitimate problem; the objections to innate forces were neither inherently unscientific nor metaphysical in some pejorative sense. There are no external standards to permit a judgment of that sort. What occurred was neither a decline nor a raising of standards, but simply a change demanded by the adoption of a new paradigm. Furthermore, that change has since been reversed and could be again. In the twentieth century Einstein succeeded in explaining gravitational attractions, and that explanation has returned science to a set of canons and problems that are, in this particular respect, more like those of Newton’s predecessors than of his successors. Or again, the development of quantum mechanics has reversed the methodological prohibition that originated in the chemical revolution. Chemists now attempt, and with great success, to explain the colour, state of aggregation, and other qualities of the substances used and produced in their laboratories. A similar reversal may even be underway in electromagnetic theory. Space, in contemporary physics, is not the inert and homogenous substratum employed in both Newton’s and Maxwell’s theories; some of its new properties are not unlike those once attributed to the ether; we may some day come to know what an electric displacement is.
By shifting emphasis from the cognitive to the normative functions of paradigms, the preceding examples enlarge our understanding of the ways in which paradigms give form to the scientific life. Previously, we had principally examined the paradigm’s role as a vehicle for scientific theory. In that role it functions by telling the scientist about the entities that nature does and does not contain and about the ways in which those entities behave. That information provides a map whose details are elucidated by mature scientific research. And since nature is too complex and varied to be explored at random, that map is as essential as observation and experiment to science’s continuing development. Through the theories they embody, paradigms prove to be constitutive of the research activity. They are also, however, constitutive of science in other respects, and that is now the point. In particular, our most recent examples show that paradigms provide scientists not only with a map but also with some of the directions essential for map-making. In learning a paradigm the scientist acquires theory, methods, and standards together, usually in an inextricable mixture. Therefore, when paradigms change, there are usually significant shifts in the criteria determining the legitimacy both of problems and of proposed solutions.
That observation returns us to the point from which this section began, for it provides our first explicit indication of why the choice between competing paradigms regularly raises questions that cannot be resolved by the criteria of normal science. To the extent, as significant as it is incomplete, that two scientific schools disagree about what is a problem and what a solution, they will inevitably talk through each other when debating the relative merits of their respective paradigms. In the partially circular arguments that regularly result, each paradigm will be shown to satisfy more or less the criteria that it dictates for itself and to fall short of a few of those dictated by its opponent. There are other reasons, too, for the incompleteness of logical contact that consistently characterises paradigm debates. For example, 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. Something even more fundamental than standards and values is, however, also at stake. I have so far argued only that paradigms are constitutive of science. Now I wish to display a sense in which they are constitutive of nature as well.
Postscript: Revolutions and Relativism
One consequence of the position just outlined has particularly bothered a number of my critics. They find my viewpoint relativistic, particularly as it is developed in the last section of this book. My remarks about translation highlight the reasons for the charge. The proponents of different theories are like the members of different language-culture communities. Recognising the parallelism suggests that in some sense both groups may be right. Applied to culture and its development that position is relativistic.
But applied to science it may not be, and it is in any case far from mere relativism in a respect that its critics have failed to see. Taken as a group or in groups, practitioners of the developed sciences are, I have argued, fundamentally puzzle-solvers. Though the values that they deploy at times of theory-choice derive from other aspects of their work as well, the demonstrated ability to set up and to solve puzzles presented by nature is, in case of value conflict, the dominant criterion for most members of a scientific group. Like any other value, puzzle-solving ability proves equivocal in application. Two men who share it may nevertheless differ in the judgments they draw from its use. But the behaviour of a community which makes it pre-eminent will be very different from that of one which does not. In the sciences, I believe, the high value accorded to puzzle-solving ability has the following consequences.
Imagine an evolutionary tree representing the development of the modern scientific specialties from their common origins in, say, primitive natural philosophy and the crafts. A line drawn up that tree, never doubling back, from the trunk to the tip of some branch would trace a succession of theories related by descent. Considering any two such theories, chosen from points not too near their origin, it should be easy to design a list of criteria that would enable an uncommitted observer to distinguish the earlier from the more recent theory time after time. Among the most useful would be: accuracy of prediction, particularly of quantitative prediction; the balance between esoteric and everyday subject matter; and the number of different problems solved. Less useful for this purpose, though also important determinants of scientific life, would be such values as simplicity, scope, and compatibility with other specialties. Those lists are not yet the ones required, but I have no doubt that they can be completed. If they can, then scientific development is, like biological, a unidirectional and irreversible process. Later scientific theories are better than earlier ones for solving puzzles in the often quite different environments to which they are applied. That is not a relativist’s position, and it displays the sense in which I am a convinced believer in scientific progress.
Compared with the notion of progress most prevalent among both philosophers of science and laymen, however, this position lacks an essential element. A scientific theory is usually felt to be better than its predecessors not only in the sense that it is a better instrument for discovering and solving puzzles but also because it is somehow a better representation of what nature is really like. One often hears that successive theories grow ever closer to, or approximate more and more closely to, the truth. Apparently generalisations like that refer not to the puzzle-solutions and the concrete predictions derived from a theory but rather to its ontology, to the match, that is, between the entities with which the theory populates nature and what is “really there.”
Perhaps there is some other way of salvaging the notion of ‘truth’ for application to whole theories, but this one will not do. There is, I think, no theory-independent way to reconstruct phrases like ‘really there’; the notion of a match between the ontology of a theory and its “real” counterpart in nature now seems to me illusive in principle. Besides, as a historian, I am impressed with the implausibility of the view. I do not doubt, for example, that Newton’s mechanics improves on Aristotle’s and that Einstein’s improves on Newton’s as instruments for puzzle-solving. But I can see in their succession no coherent direction of ontological development. On the contrary, in some important respects, though by no means in all, Einstein’s general theory of relativity is closer to Aristotle’s than either of them is to Newton’s. Though the temptation to describe that position as relativistic is understandable, the description seems to me wrong. Conversely, if the position be relativism, I cannot see that the relativist loses anything needed to account for the nature and development of the sciences. ...
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