Focus of lecture: Kuhn views the development of scientific knowledge and scientific disciplines as analogous to biological evolution.



I. Sample talk delivered at a physics conference

II. The sociology of scientific communities

III. Biological evolution as an analog for the evolution of scientific knowledge and disciplines

IV. Kuhn's view of scientific progress and his influence

Freshman Studies Lecture on The Structure of Scientific Revolutions, by Thomas Kuhn.

Matthew R. Stoneking, 4 February 2002

I. Sample talk delivered at a physics conference

Title: Coherent oscillations observed in a toroidal pure electron plasma; diocotron mode or magnetron mode?

1. title slide: I am reporting today on work done in a toroidal pure electron plasma at Lawrence University in Appleton, Wisconsin.

2. Here are the parameters for our system... major radius is 43 cm, minor radius is 4.5 cm, density is in the range ..., and the magnetic field is about 200 G. The density is therefore quite low compared to the Brillouin limit, but sufficiently dense that the Debye length is smaller than the minor radius. Collective effects are therefore expected to be important. Note also, the electrons are well-magnetized as evidenced by the range of Larmor radius values

3. We have measured the confinement time for this plasma, by the same method used in Malmberg-Penning traps. The collector signal, shown here, has a prominent feature around 90 - 100 microseconds.

4. Plasma modes are observed with a wall probe diagnostic.  In this trace, the coherent oscillation is observed prior to the trapping phase of the experiment.  The power spectrum for that signal shows a distinct feature at around 100 thousand REVOLUTIONS per second, with a couple of harmonics also evident.

5. The oscillation frequency is inversely proportional to the strength of the magnetic field, an observation that first led us to interpret this oscillation as a diocotron mode. However, the frequency does not depend on plasma density, but does show substantial dependence on the vacuum electric field… a result that seems more consistent with the magnetron mode.




II. The sociology of scientific communities

scientific jargon

Whew ... not too many people walked out. I expect that none of you understood what I have been talking about for the last few minutes. Just now, you were the recipients of information "formatted," so to speak, for a different audience... an audience of plasma physicists. Last summer, I attended a workshop where I presented something similar to what you just heard.  I expect (and hope) that everyone in that room did understand everything I said.

Well... had I actually used this figure in that presentation, somebody would have stopped me. That is because this graph does not display data from a "collecter," and does not represent a measurement of the "confinement time" for the plasma. Rather this graph should be labeled like this... This is a graph of the number times the word 'paradigm' (or variations like 'paradigmatic') appears on each page of Thomas Kuhn's The Structure of Scientific Revolution
(third edition). Yes, 'paradigm' shows up 13 times on page 94 alone! Check for yourself.  The word 'paradigm' certainly must be connected to Thomas Kuhn's main points in a fundamental way.  In fact, Kuhn coined a new use for this word in the very essay you are reading, which was published in 1962.  You have probably read it or heard people use it in ways that are descended from Kuhn’s work.  I know I used the word in a distinctly Kuhnian sense long before I picked up the book at a bookstore in Madison more than five years ago.  A search of newspapers on the web last week yielded number of instances of ‘paradigm’ used in this way.  From a New York Times article on President Bush’s State of the Union address on the 30th of January… a foreign policy specialist at the Brookings Institution is quoted as saying,


“The hard-liners have been arguing that after September 11 it is intolerable to live in a world in which Iraq, Iran, and North Korea have weapons of mass destruction.  Bush has now fully embraced this paradigm.” (article by Michael R. Gordon, 30 Jan. 2002, New York Times)


In the Los Angeles Times, from a theater review of a new musical based on the legend of John Henry,


“…Whether founded in fact or wholly fictitious, John Henry has obvious historical significance, both as a post-slavery paradigm of black proficiency and as a proletarian prototype in an era before the rise of American labor unions.” (article by F. Kathleen Foley, 31 Jan. 2002, Los Angeles Times)


In Madison, where I lived for quite a few years, a popular bumper sticker read ... "subvert the dominant paradigm." I doubt that Mr. Kuhn intended his pet word to become a tool for political revolutionaries... or wannabe revolutionaries at least.  Sometimes the uses of ‘paradigm’, or ‘paradigm shift’ in popular culture strike closer to Kuhn’s original sense, but one has the suspicion this might be purely coincidence given the extent to which the term has permeated our culture.  On the 29th of January a Washington Post columnist wrote about the timely way that a new cancer drug has found its way into the scripts of TV’s “The West Wing” and “Law and Order.” In that article she quoted a drug development expert at the National Cancer Institute,


“The development of Gleevec can be used as a paradigm for the development of other agents.” (column by Abigail Trafford, 29 Jan. 2002, Washington Post)


If you have not noticed phrases like these, you will in the future, now that you have read (or are reading) the book that launched ‘paradigm’ into the popular usage it now enjoys.  Most of the popular uses of the word go far beyond the intentions of Mr. Kuhn, but they are testimony to the influence his essay has had in our larger culture.


My goals in this lecture are first to provide you with some background information on how scientific communities function and second to more discuss a metaphor that Kuhn introduces near the end of the essay, a metaphor that illustrates the most controversial element of his thesis.   Both of these objectives are intended to aid you in your struggle to subdue this work.  After all, you probably already have the feeling that this book was not written with college freshmen in mind. My guess is that you reacted to your first contact with this book like you did to my physics talk.  In both cases, the author and the intended audience share much more common background information than either of us do with the people in this room.  The Structure of Scientific Revolutions is an academic essay written for philosophers and historians of science.   My presentation was a non-neutral plasma physics presentation, meant for an audience of fellow plasma physicists.


The point of the partial physics conference presentation with which I began, was to begin to give you some understanding of aspects of the operation of scientific communities.  The first aspect of scientific communities I wish to discuss is the specialized language that members of the community employ to communicate with other members of the same community.

language barrier between the scientist and non-scientist

Why was my physics presentation so opaque to you? And why would I be reasonable in supposing that my colleagues in the COMMUNITY of plasma physicists would find it transparent? The public at large often views scientists as speaking another language. At times that view takes on the form of admiration. Some segment of the public associates the fact that they cannot understand the scientist’s language with the superior intelligence of the scientist. The real reason scientists understand each other is because they have been trained (some might say indoctrinated) to speak the language of their discipline. At other times, the 'language barrier' between scientists and non-scientists is a source of suspicion.  Perhaps scientists use complicated jargon to hide what they are doing with taxpayer dollars.

Why do scientists speak in 'jargon'? Must there be a 'language barrier' between non-scientist and scientists? The specialized use of words (many of which are used in common speech with different meanings) represents a shorthand for concepts, phenomena and practices that the scientists have incorporated into their view of their work (and perhaps of the world). The scientists who heard my talk in San Diego last summer and I share a common set of views about plasma physics, views we share because we have had very similar training, we read the same scientific journals, and attend the same scientific conferences. In Kuhn's terminology, we share a common 'paradigm' or 'set of paradigms' or as he calls them in the post-script of Structure
, a common 'disciplinary matrix.' All the people in the audience of last summer's workshop were familiar with what I meant when I said 'diocotron mode' or 'confinement time' or 'power spectrum.’  I did not need to start from scratch and explain these ideas to them. I could start with those concepts, principles, and techniques and build on them. You can imagine how much longer my talk would have been if I had had to teach them (as I would have to teach all of you if I wanted you to understand the results of my experiments) all the fundamental ideas on which my work is built. Given all the background knowledge we shared, I could proceed very quickly to a presentation of extremely esoteric aspects of my work and be reasonably certain that I would be understood.  The scientific enterprise functions efficiently because the participants in scientific dialogue share a common paradigm.

As he all but admits in the post-script to Structure
, Professor Kuhn was not completely certain what he meant by his new use of the word ‘paradigm” when he wrote the original essay.  There, he enumerates more carefully the kinds of things he meant.  He identifies new terms like 'symbolic generalizations,' 'models,' 'values,' and 'exemplars' as being varieties of ‘paradigm.’  For philosophers and historians of science such distinctions are important.  I recommend, however, that you keep the following, somewhat plastic definition of ‘paradigm’ in your mind while you read the essay: let the word ‘paradigm’ represent all the things that a scientist can assume that his or her colleagues will understand about their common subject of study without explicitly explaining them ... all the major prior results in the field... all the important experimental techniques ... all the important theoretical ideas or concepts that guide their research… all the basic examples or categories of examples that the members of a scientific community learned as a part of their training, i.e. the end-of-chapter problems in the textbooks that Kuhn writes about.

So please excuse scientists for speaking in jargon... at least when we are speaking amongst ourselves.  We save a lot of time by referring to all the above elements of our paradigm in the shorthand of our discipline-specific jargon.  If we did not use jargon, the scientific enterprise would not function as efficiently as it does. 


language barrier between scientists of difference disciplines

I was careful to identify the intended audience for my earlier presentation as an audience of plasma physicists. I did not say an audience of scientists. I did not even say, an audience of physicists.  I said an audience of plasma physicists, and perhaps I should have further specified the audience as a collection of plasma physicists who study non-neutral plasmas.  The distinction is significant, because much of the jargon I used would only be completely understood by men and women who study non-neutral plasmas. If I were to show up at a conference on protein chemistry or sedimentary geology or aquatic ecology or even a physics conference on string theory and give the talk I gave in San Diego, my audience would be nearly as much in the dark as you were. And, likewise, if I were to stay and listen to some of the presentations at any of those conferences, I would not come away knowing any more than when I entered ... other than something about my ignorance of those fields. The language barrier that exists between the scientist and the non-scientist also exists between members of different scientific DISCIPLINES. There are as many scientific dialects as there are scientific disciplines or sub-disciplines.   To be sure, I will probably get a little more out of a talk given by a physicist, than I will from a talk given by a chemist.  My paradigm, or disciplinary matrix has a greater overlap with those of other physicists in other sub-disciplines, than it does with the chemist’s.

The language barrier exists even between members of closely allied disciplines.  Jonathan Weiner’s excellent book titled The Beak of the Finch
is about recent research in the field of evolutionary biology.  The book was on the term II Freshman Studies reading list the two years prior to this one.  Weiner quotes one of the evolutionary biologists commenting on the field of molecular biology,


" 'It really is a foreign language, ' ... 'I suppose ours is too, but I do have the impression that theirs is harder.'" -Beak of the Finch, p. 215

This quotation reveals not only the perception of a language barrier that exists between members of two sub-disciplines of biology, but also a hint of a sense of inferiority of one sub-discipline with respect to another.  Scientific communities are communities of humans and as such their members display all the typical aspects of human nature that are so readily observed in other human communities… prejudice, intolerance, etc.

Thomas Kuhn has this to say (on p. 21) about the language barrier that exists between scientists in different disciplines,

"Although it is customary, and is surely proper to deplore the widening gulf that separates the professional scientist from his colleagues in other fields, too little attention is paid to the essential relationship between that gulf and the mechanisms intrinsic to scientific advance." -SSR p. 21

He is referring to his contention that the specialized language of a scientific community is central to its efficient operation, not only because it is a powerful shorthand or abbreviation for an enormous amount of collectively agreed upon background material for other member of one's own community... but also because it prevents the polluting influence of others who might distract the work of the community with too many questions about fundamental and already resolved issues. Since the 'others' do not speak the language, they are effectively prevented from communicating with 'us' about our work.


professional societies, scientific conferences and workshops

Scientists can be "labeled" as members of a particular discipline or community in a number of interrelated ways. If you observe a large group of scientists speaking their special language, chances are you are in the middle of a scientific conference, where members of a scientific community gather to present and discuss their work face-to-face. Scientific conferences are usually organized by professional societies or associations. All the right people end up coming to a particular scientific conference because they are all members of the professional society that is sponsoring the conference. They are all on the society's mailing list and receive its newsletters, etc. For example, most physicists in this country belong to the American Physical Society (or APS). Most chemists belong to the American Chemical Society (or ACS), etc.  Scientific societies have a long history.  Galileo was inducted into one of the first such societies, the Lyncean or “Lynx” Academy of Rome, immediately following the sensational response to the publication of his astronomical observations, Sidereus Nuncius, the work you have just finished reading (from Galileo’s Daughter, pp. 42-3).  Isaac Newton was the president of the Royal Society in England for the last twenty-five years of his life. 


Today, most scientific societies are subdivided into smaller units or divisions. So for example the American Physical Society has a Division of Nuclear Physics, a Division of Particle Physics, a Division of Plasma Physics, and others. Each of these divisions may organize their own specialized conferences attended by specialists working in for example, plasma physics. The subdivision of the discipline reaches even further down with topical workshops organized by members of a division who are working on a very specific problem or small set of problems. The workshop I attended last summer was such a topical workshop.

scientific journals

Besides organizing conferences, another primary function of professional societies like the APS is to edit and publish scientific journals, conference proceedings and research monographs.  The Lyncean Academy was one of Galileo’s principle publishers.  The Proceedings of the Royal Society in England continues to be an important scientific publication.


Presentations at scientific conferences and publications in scientific journals are the two principal ways that scientists communicate their results to the rest of the community. And, just as there is a hierarchy of specialization within the membership of the society (nuclear physicists, particle physicists, plasma physicists, etc.) and in the organization of conferences, there is also a hierarchy of specialization within the set of journals read by members of the society. For example, the American Association for the Advancement of Science (AAAS), a society that includes all of the natural sciences, publishes a journal called Science. Science contains articles from a wide range of scientific disciplines, and is therefore read by scientists from a wide range of disciplines. The American Physical Society publishes a journal titled Physical Review Letters, a journal that is widely read by physicists in many subspecialties. The APS also publishes a series of journals titled Physical Review A, Physical Review B, Physical Review C, Physical Review D, and, most creative of all, Physical Review E. Phys. Rev. A contains only articles on atomic, molecular and optical physics and is read almost exclusively by physicists working in the area of atomic, molecular and optical physics. Phys. Rev. B contains articles pertaining to condensed matter and materials physics and is read by researchers working in those areas. You get the point. For each level in the hierarchy of scientific disciplines there are professional societies that 1) organize conferences and 2) edit and publish journals or conference proceedings. They do other things like communicate scientific results to the public, advise governmental organizations on science policy, etc... but their primary function is to facilitate communication between their members.

the family tree of natural science

I have attempted to draw an oral sketch of the way scientists identify themselves in relation to other scientists, how that association is facilitated by professional societies, and how scientists communicate their work to each other. The image I would like you to hold in your mind is, like most organizational diagrams, something like a tree. At the top we have all natural sciences, a representative society being the AAAS with its journal Science. One level down are the major disciplines of the natural sciences.. with abbreviations given for a few representative societies and journals. I then break down the discipline of physics into some of its sub-disciplines and the sub-discipline of plasma physics into some its primary research areas. You can imagine how the chart would be completed by breaking down each of the major disciplines into its sub-disciplines and further into major areas of research.  The most frequent and the most complete communication occurs between members at the finest subdivision of the sciences... between scientists who are working on very similar types of problems. For example, I will very rarely read more than the title of a physics article in the area of particle physics or condensed matter physics. I will read abstracts of articles in most areas of plasma physics, but will read entire articles in only two or three narrowly defined research areas.  Likewise my attendance at conferences will be most frequent in areas close to my research work.  The proximity of members of one research group to another in this organizational tree reflects the closeness of their scientific jargon and therefore the extent of the overlap of their set of paradigms.  You should therefore add to your evolving definition of paradigm, the notion that there is a hierarchy of paradigms that reflects the general structure of this tree.  There are some paradigms that all natural scientists share, others that only chemists share, others that only organic chemists share, etc.

The image is very rough and can be misleading, for there are twigs of this tree that one could easily identify with two or more of its major branches. For example, on which branch of this tree should I place biochemistry or geophysics. These are examples of interdisciplinary fields.  Their existence reminds us of the limitations of using any organizational structure to simplify a complex network.  Despite the limitations of this way of viewing the way scientists are related through their professional associations and personal identifications, I think it captures some aspects of the relationships between members of different scientific disciplines and the hierarchy of underlying paradigms that members of different disciplines possess.  One can also view this chart as a crude representation of the historical origins of the various sub-disciplines of chemistry, physics, etc. , as a family tree for scientific disciplines. In the late nineteenth century, there were few or no sub-fields of physics. Although physicists were working on a wide range of problems, many of which were the seeds for future sub-disciplines, the community of physicists was both smaller and more unified. Over the course of the last century, the sub-disciplines of atomic physics, nuclear physics, particle physics split off. Going further back into the nineteenth century the distinction between physicist and chemist was nonexistent.  So I think you can view this tree (again with some caution) as a depiction of the historical relations of these sub-fields to each other.

distinguishing scientific from non-scientific academic communities

Much of what I have said about the sociology of science applies also to nonscientific disciplines ... to the community of scholars of English poetry... to the community of economists ... to the community of scholars of American history ... etc. What is it that makes scientific communities different from other academic communities?  In Kuhn's view, what makes a community scientific is its almost universal agreement about the set of paradigms that they share... an agreed upon world view (at least in so far as the subject of their communal professional interests go). In most social sciences (at least at the time Kuhn was writing) and especially in the creative arts and humanities, disciplines are characterized by competing schools of thought. The observation that social scientific communities were characterized by severe disagreements over very fundamental issues that went to the heart of the communities subject of study, whereas scientific communities almost never engaged in this kind of debate, was critical to Kuhn's initial conception of a 'paradigm.' In the preface to Structure he writes,

" the Center for Advanced Studies in the Behavioral Sciences ... I was struck by the number and the extent of the overt disagreements between social scientists about the nature of legitimate scientific problems and methods ... Attempting to discover the source of [the] difference [between the natural and social sciences] led me to recognize the role in scientific research of what I have since called 'paradigms.' " -SSR
, preface p.x


The existence of a universally accepted 'paradigm' within a given academic discipline is for Kuhn the criterion by which we should determine whether the discipline is scientific or not. Several key sentences from section II of Kuhn's essay illustrate the point:

"Men whose research is based on shared paradigms are committed to the same rules and standards for scientific practice. That commitment and the apparent consensus it produces are prerequisites for normal science... Acquisition of a paradigm and of the more esoteric type of research it permits is a sign of maturity in the development of any given scientific field." -SSR p. 11

"... and it remains an open question what parts of social science have yet acquired such paradigms at all." -SSR p. 15

"What is surprising, and perhaps also unique in its degree to the fields we call science, is that such initial divergences [competing schools] should ever largely disappear. For they do disappear to a very considerable extent and then apparently once and for all." -SSR p. 17

"Except with the advantage of hindsight, it is hard to find another criterion [other than the acquisition of a paradigm] that so clearly proclaims a field a science." -SSR p. 22

Scientific communities are unusually united in their view of their own discipline. They agree on what types of questions are worth asking and what constitutes an acceptable answer to a question.  They share a common paradigm (or set of paradigms or disciplinary matrix). In disciplines of the social sciences, humanities and arts, there are frequently competing schools of thought ... adherents to competing paradigms. Exceptions to the rule that scientific communities are unified in the way described are scientific communities in crisis or dealing with anomalies ... communities ripe for revolution.

In light of Kuhn's view of science as inherently a social enterprise, you might want to think about how Kuhn would view Victor Frankenstein's status as scientist at various stages of Frankenstein's career. Can one be a scientist in Kuhn's view if you are working alone and not communicating your results to anyone else? I can imagine such a question would make a fine midterm exam question.

III. Biological evolution as a metaphor for the evolution of scientific knowledge and disciplines

How does my overview of the sociology of science help you to understand Thomas Kuhn's The Structure of Scientific Revolutions? Let's look at the very last section of Structure... not the post-script, but Section XIII: Progress Through Revolutions, and read some of Kuhn's parting words from 1962. Probably none of you have yet read to the end of this book. I hope you are not offended by my giving away the ending, but after all you are not reading an Agatha Christie mystery, but rather an academic essay. On page 170, Kuhn writes,

"The developmental process described in this essay has been a process of evolution
[my emphasis] from [Kuhn's emphasis] primitive beginnings - a process whose successive stages are characterized by an increasingly detailed and refined understanding of nature." -SSR p. 170.

Kuhn asks us to view the development of science as analogous to the development of biological organisms.  Darwin's evolution is to be a metaphor for how the scientific enterprise “evolves.”  Kuhn introduces this analogy in the very last section of the essay, in a section that he probably viewed as the most speculative and preliminary. It is also the section that contains the most serious implications for the philosophy of science and made this essay as influential and controversial as it has been for forty years. The reason for introducing the analogy is to reinforce his argument about what kind of scientific "progress" can occur over the course of a scientific revolution... do we step closer to ultimate Truth? I will return to this import issue briefly at the end of my lecture, but for the moment I would like to take Kuhn's evolution metaphor and see how it plays out for the less controversial elements of his thesis. As Kuhn himself warns not two pages after he first introduces it that...

"The analogy that relates the evolution of organisms to the evolution of scientific ideas can easily be pushed too far." -SSR
p. 172.

I will take my license to push this one a little further from Kuhn himself, who extended the evolution analogy in some of the ways I will lay out now. He did so in a lecture titled The Road Since Structure delivered in 1990.

scientific disciplines as species

If the scientific enterprise develops in a manner analogous to biological evolution, then what is it that corresponds to the concept of a species? After all the concept of species is central to biology and evolutionary theory purports to describe how species emerge and evolve. So let's step back and ask 'what are biological species?' A species is a geographically and/or reproductively isolated population of organisms. A species maintains its identity due to its isolation. If members of a population frequently bred with members of another group ... the first population would soon lose its separate identity; it would be swallowed up or incorporated into the larger population with which it is mixing. My discussion of the sociology of scientific communities led to an image of a "family tree" for scientific disciplines. My intent was to prepare you for the suggestion that scientific disciplines (or communities) are the entities that correspond to species in the Darwinian metaphor for scientific development. How are scientific disciplines "isolated" in a manner analogous to the reproductive or geographic isolation of a biological species? In The Road Since Structure, Kuhn says,

"... the unit [i.e. species] is a community of intercommunicating specialists, a unit whose members share a lexicon [i.e. jargon] that provides the basis for both the conduct and the evaluation of their research and which simultaneously, by barring full communication with those outside the group, maintains their isolation from practitioners of other specialties." --Road Since Structure
, p. 98

Members of a scientific discipline are isolated by their specialized language ... their jargon. They are isolated by the inability to easily communicate with members of other disciplines on matters that relate to their scientific work. Let me say it another way... a scientist can only engage in "intercourse" (in the sense of communication) easily with another member of his own discipline, just as an animal can only engage in "intercourse" (of the other kind) easily with another member of its own species.  So it is the language barrier that I spoke of earlier… the barrier between scientists of different disciplines that isolates them in a manner analogous to the reproductive (or geographic) isolation of biological species.

interdisciplinary fields as hybrids

Is it really impossible for scientists in different disciplines to communicate about their science?  No, but there are significant obstacles, the language barrier is the surface manifestation of a more profound barrier … the paradigm barrier.  Scientists in different disciplines have acquired, in Kuhn’s view, a different way of “perceiving” the world, or at least that part of the world that they study most intensely.  Occasionally, however, the paradigm barrier is broken and scientists from different disciplines collaborate and achieve something that neither of them could have achieved separately.  I am speaking of interdisciplinary research. In fact, many of the most interesting and promising avenues for scientific research these days lie at the boundaries between traditional disciplines... in such areas as environmental science, materials science, biophysics, neuroscience, etc.  The existence and success of interdisciplinary efforts within the world of scientific research does not make Kuhn's Darwinian metaphor less illuminating.  Biological species are also not completely isolated either geographically or reproductively.  And, just as the boundaries of scientific disciplines are fuzzy, frequently the boundaries between closely related species are also permeable.  Hybridization among members of different animal species is not the rule, but neither is it extremely uncommon.  Usually the products of such hybrid matings are not likely to gain an advantage over members of the existing species. However such hybridization does occur and occasionally provides a fortuitous combination of traits that imparts an advantage to the products of that union. Interdisciplinary work represents hybridization in the evolution analogy.  If hybridization of scientific disciplines produces a successful offspring, a new discipline can be spawned. The field of biochemistry is such an example.

scientific revolutions as speciation events

Let's continue to extend the analogy. The title of Darwin's greatest work was Origin of Species. If the analogy holds, what, in the course of scientific development corresponds to the origin of species... or the origin of new scientific disciplines. What corresponds to "speciation?' I just mentioned one possible way new disciplines can arise ... through hybridization, or interdisciplinary "unions" between members of separate disciplines. But there is a more natural origin for new disciplines and that is the scientific revolution. In Kuhn's view a scientific revolution rearranges the concepts that form the foundation of the worldview for members of the community experiencing it. After a revolution, they view their discipline in an entirely different way. Kuhn suggests they are practicing a different discipline than they were before the revolution.

In addition, a revolution introduces new concepts, maybe even new elements of reality that are open to future investigation. For example, prior to about 1900 the atom was the fundamental constituent of matter. There were a fairly large number of atomic flavors, roughly 100, corresponding to the different chemical elements. Atoms of each element emitted and absorbed their own characteristic wavelengths of light. The atoms of different elements interacted with each other in different ways; they had different chemical properties. As a part of the revolution that brought quantum physics onto the scene in the early decades of the 20th century, the internal structure of the atom became a subject for investigation. The disciplines of nuclear physics and nuclear chemistry could not even have been imagined 25 years prior. The quantum revolution did indeed spawn new disciplines.


In a similar way, the astronomical observations of Galileo introduced new elements of reality into the worldview of astronomers.  Prior to Galileo’s application of the spyglass to observations of the sky, the sole phenomenon of interest associated with the planets was how they moved against the fixed stars.  After Galileo, other internal properties of the planets became subjects for investigation.  Through the telescope the planets were not just brighter points of light as the stars were in fact.  Jupiter had an entourage of satellites.  Saturn was not quite round.  Venus displayed phases like the Moon.  And the Moon itself revealed a fascinating landscape of “mountains” and “valleys.”  After Galileo, astronomy became a different discipline… one that asked questions about the nature of heavenly objects and not just about their locations.  The larger territory for investigation opened up new research niches and therefore to a proliferation subfields of astronomy.  For the discipline of astronomy, Galileo’s observations were revolutionary and represent the rise of a new paradigm.  If we reduce the magnification of our historical lens, his observations were important in persuading scientists and intellectuals of the superiority of the Copernican paradigm.  Galileo was an early convert to Copernicanism and a principle advocate for it during the time of paradigm choice associated with the resolution of the Coperrnican Revolution.


Getting back to the development of the evolution metaphor, I suggest that scientific revolutions are represented by "speciation events.”

scientific communities in crisis as extinction events

The fossil record that chronicles the history of life to those with enough skill and training to read it, reveals that that life on earth has sustained a fair number of mass extinctions over the course of its history. As Harvard paleontologist and prodigious author Stephen Jay Gould puts it in his book Wonderful Life,

"The history of life is not a continuum of development, but a record punctuated by brief, sometimes geologically instantaneous, episodes of mass extinction and subsequent diversification." --Wonderful Life p. 54

The most famous mass extinction was about 65 million years ago at the end of the Cretaceous Period when it is likely that a comet impact altered the earth's climate for a period long enough to wipe out many species including the dominant large animals of the day ... the dinosaurs. Notice however in the quotation from Professor Gould's book that episodes of mass extinction are coupled to periods of subsequent diversification, i.e. speciation. I have already identified scientific revolutions as a primary origin for new scientific disciplines. If the analogy holds, there may be a corresponding extinction event prior to a major speciation event.   I suggest that the period prior to a scientific revolution, the period of crisis that Kuhn describes in section VII of Structure
is a time when the "environment" in which a scientific community is "living" begins to change. The old way of doing things does not work for the new problems that are emerging. Those who learn to adopt a new (and successful paradigm) at the time of a revolution survive as members of a new discipline. Those who cannot adapt eventually die out.


The world of science was struck by a 'comet' during the 17th century. The man most responsible for the impact was Isaac Newton. Galileo’s experiments with falling objects, balls rolling down inclines and the pendulum laid important foundations for Newton’s revolution.  It is this work that Kuhn cites extensively in Structure, rather than the astronomical work (although you will find an oblique reference to Galileo’s astronomical observations on page 154).  When the dust settled, the scientists who lived and worked under a paradigm going back to Aristotle, were extinct. There are no Aristotelian physicists around. They are the dinosaurs of the scientific world. And similar to the dinosaurs, they ruled the earth a lot longer than their successors have so far. Your modern physicist bears a much stronger resemblance to his Newtonian ancestor than he does to the Aristotelian. The Newtonian physicist is perhaps the rodent who emerged from obscurity once the behemoths had died out. In another rendition of the metaphor, the Aristotelian is the Neandertal, a vaguely human creature, but from whom we are not directly descended, and the Newtonian physicist is represented by our true ancestor, Homo erectus.

normal science as microevolution / local adaptation

In Kuhn's view of scientific development, all of most scientists' lives are spent doing normal science. The normal scientific period is the period between revolutions, when there is nearly universal agreement within a scientific community about what kinds of problems are worth attacking and what techniques should be used to attack them. In this phase of the scientific enterprise, the paradigm (or disciplinary matrix) provides the big picture. It is important to realize that it does not immediately provide all the answers. There is substantial fine-tuning to be done to make the paradigm work in as many specific cases as it possibly can. There are also specific questions that the paradigm can in principle provide answers to, but that require substantial work to derive them from the paradigm.  I must say, as a practicing scientist, that I find Kuhn’s description of normal science rings especially true. Kuhn’s description of the educational process, the apprenticeship that initiates new members of a discipline, the way that training guides the kinds of research questions that asked and how they come to be answered… al that resonates with my experiences.

The work I presented to you at the beginning of this lecture is surely, as Professor DeStasio suggested an example of normal science. I do not take offense that she did does not see the revolutionary aspects of my work, for in truth I do not think there are any. Answering the question of whether the observed oscillations are magnetron or diocotron in origin will not incite a revolution even among the very small community of nonneutral plasma physicists. In principle the answer to that type of question exists within the mathematical framework of nonneutral plasma physics theory. If I was smart enough, I could just do a calculation to get the answer. But in fact, the system is too complex to work out the answers to all such questions. Even though the fundamental physical principles, the elements of the disciplinary matrix are not expected to fail, there are too many particles involved to calculate exactly what they will do. Approximations must be made and then justified on the basis of correct predictions for the outcome of real experimental measurements. This is classic normal science.

In the Darwinian analogy normal science corresponds to “microevolution.”  I am not certain that is a real term in the field of evolutionary biology, but I am sure the concept exists.  What I mean by microevolution is adaptation of existing species to relatively short term changes in the environment.  The research described in Jonathan Weiner’s The Beak of the Finch
illuminates exactly this kind of process.  Weiner describes the study of a handful of finch species on a small atoll on the Galapogos Islands by a team of Princeton evolutionary biologists over the course of more than a decade.  The biologists did not observe the origin of any new finch species in the Galapogos.  Rather they saw existing species adapting to short term changes in their environment. The mechanism that drove this microevolution was the inherent variation that exists within any single species. If all members of a species were identical in all features, then the species would be extremely vulnerable to even minor changes in the environment. As it is, when the environment changes, there are usually members of the species who are better suited to survive under the new conditions. The offspring of those individuals tend to be more numerous and better able to compete for resources than the offspring of other members of the species. The species survives by moving in the direction of those individuals who are best suited to the new environment.  This gradual adaptation, in Darwin’s original conception led to the origin of species over much longer time periods.  The possibility of rapid speciation following a mass extinction event is a relatively new articulation of Darwin’s paradigm, but the basic mechanism is believed to be the same one… following a mass extinction there are many unoccupied niches in the environment.  There are bound to be some individual members of the surviving species that are more suited to one of the unoccupied niches.  Those individuals are successful in occupying the niche, become isolated, adapt more and more to that environment until they become a distinct species.


During periods of normal science, members of a given discipline adapt the paradigm theory to fit observation in as many specific cases as possible. The outcome of that work is a better-articulated paradigm... one that works better in a wider range phenomena. During periods of normal science, the paradigm evolves in a smooth way, in a way analogous to the minor adaptations of species to short term changes in the environment.

At this point let me offer a summary of the Darwinian analogy for Thomas Kuhn's view of scientific development:

Summary of the Darwinian analogy for scientific development:

scientific communities/disciplines <---> species

linguistic isolation <--> reproductive or geographic isolation

interdisciplinary fields <---> hybrids

scientific revolutions <---> speciation events

scientific communities in crisis <---> extinction events

emergence of a dominant paradigm <---> survival of the fittest

normal science <---> adaptation or microevolution

The match that this analogy seems to provide leads me to wonder why Kuhn chose for the title of his essay... The Structure of Scientific Revolutions, when a more appropriate title would seem to be ... The Structure of Scientific (r)Evolution(s).

IV. Kuhn's view of scientific progress and his influence

scientific development is contingent

Where does this metaphor lead? Let's allow it to lead us back to Kuhn's original intention when he introduced the metaphor. Recall the quotation from section XIII:

"The developmental process [of scientific knowledge and disciplines] described in this essay has been a process of evolution [my emphasis] from [Kuhn's emphasis] primitive beginnings - a process whose successive stages are characterized by an increasingly detailed and refined understanding of nature." -SSR p. 170.

The next sentence on page 170 is ...

"...But nothing that has been or will be said makes it a process of evolution [my emphasis] toward anything." -SSR p.170.

This is why Kuhn introduces the analogy, because he sees scientific development as a process with profound historical/social influences. He knows that science is a human social enterprise and being so means it is subject to many of the same kinds of influences that affect the development of other human social enterprises. This is his most controversial point. Also from page 170:

"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." -SSR p.170


In Kuhn's description, the worldview that emerges from a period of crisis in a scientific community ... the result of a revolution ... is strongly influenced by factors other than whether the new paradigm is the truest one in any objective sense. Kuhn sees no reason to believe that the progress of science is one that brings humanity closer to an understanding of an objective Reality. His evidence for this view is built up throughout the essay and includes examples of influences such as aesthetics upon the choice of a new paradigm theory. There is plenty of grist here for the millstone of your discussions in your individual sections.   I warn you though, if you and your classmates set off down the path of pursuing objective truth, it is a long and deep sojourn underground and no one has yet emerged on the other side. Many of us continue to believe that there is a promised land on the other side, a land of eternal truth. Meanwhile we wait for an enlightened philosopher, a Platonic Moses to lead us there.

 I do not have time to fully explore Kuhn’s argument for the importance of nonscientific influences on the outcome of scientific revolutions, but I will pursue how it relates to his introduction of the Darwinian metaphor. Kuhn introduces the Darwinian metaphor to illustrate his view that the process of scientific development is contingent upon non-scientific influences, influences that arise from the social context in which science is practiced.

"All the well-known pre-Darwinian evolutionary theories ... had taken evolution to be a goal-directed process. The 'idea' of man and of the contemporary flora and fauna was thought to have been present from the first creation of life, perhaps in the mind of God... [Darwin's work,] Origin of Species recognized no goal set either by God or nature. Instead, natural selection, operating in the given environment and with the actual organisms presently at hand, was responsible for the gradual but steady emergence of more elaborate, further articulated, and vastly more specialized organisms." -SSR p.171


This last quotation emphasizes a feature of Darwinian evolution that is largely misunderstood by the general public.  The misunderstanding is illustrated by a typical image representing Darwin’s evolution… an image of homo sapiens as the culmination of an evolutionary process that has steadily produced more and more sophisticated creatures.  The mechanism of Darwinian evolution assures no such thing.  Debunking this stereotypical iconography of evolution is one of Stephen Jay Gould’s goals in writing Wonderful Life.  In fact, this image was lifted from that book, although images like it are pervasive in our culture.  In explaining Darwinian evolution in action, Gould emphasizes the profound extent to which the detailed progress of biological evolution is historically contingent, that if we were to rewind the tape and start evolution over again from very nearly the same initial conditions, the likelihood that any creature remotely similar to homo sapiens would emerge is vanishingly small.


The principle of contingency is one historians must run up against daily. Change one small detail of the past and what followed would have been entirely different. The title of Gould's book is at once a reference to the author's state of awe at the natural world and a reference to the famous film, starring Jimmy Stewart. In that film, the main character, George Bailey gets to see how things might have been different in his hometown of Bedford Falls had he never existed. Another, more recent, popular film, Back to the Future also explores the idea of historical contingency. Marty McFly goes back in time to witness events surrounding his parents’ courtship. Of course his presence in the past has the potential to influence his own existence in the future. It makes great entertainment, and I suppose is part of the fascination historians have with their field.

As a physicist I would say that the flow of history is extremely sensitive to initial conditions.  Many physical systems, including some relatively simple ones exhibit this feature.  Start two identical systems out with very nearly the same, but not precisely the same starting conditions, wait long enough and the two systems will evolve to very different later states.  Some of the simplest climate models exhibit this feature.  In that context it is sometimes called the “butterfly effect.” A butterfly flaps its wings in the Amazon rainforest… leading to a snowstorm in Wisconsin three weeks later.  I think we all have a sense that human history exhibits this kind of contingent development… or sensitivity to initial conditions.  What if my mother had turned my dad down when he asked her out?  What if my grandfather had not survived a grazing gunshot wound, but instead had received a mortal wound?  What if the butterfly ballot in West Palm Beach had not been a butterfly?  Now there’s a butterfly effect!


Here then is the reason for the metaphor Kuhn introduces. He suggests that the particular scientific theories that emerge from a revolution are contingent upon many details of the scientific communities experiencing them. At least some of the significant influences are in no way connected to the goal of moving toward an objective truth. Using the Darwinian metaphor, Kuhn says,

"... the resolution of revolutions is the selection by conflict within the scientific community of the fittest way to practice further science... And the entire process may have occurred, as we now suppose biological evolution did, without benefit of a set goal, a permanent fixed scientific truth ..." -SSR p. 172

Unlike the global communist revolution that Marx believed was inevitable, the outcome of scientific revolutions is in Kuhn's view far from predetermined.

This is controversial stuff, especially if you are a scientist who has dedicated her professional life to the pursuit of objective truth. I think it is fair to say that most scientists in almost all disciplines are realists, that is they believe there is an objective reality out there and that their work makes contact with that reality somehow. That view of the cumulative achievements of science permeates much of our larger culture. Here is Jonathan Weiner, on page 286 of The Beak of the Finch,

"Science formalizes our special kind of collective memory, or species memory, in which each generation builds on what has been learned by those that came before, following in each other's footsteps, standing on each other's shoulders." -The Beak of the Finch, p. 286

And here is Columbia string theorist and a Lawrence convocation speaker a year ago, Brian Greene from his book, The Elegant Universe,

" proceeds along a zig-zag path toward what we hope will be ultimate truth, a path that began with humanity's earliest attempts to fathom the cosmos and whose end we cannot predict." -The Elegant Universe, p. 20

And here is Steven Weinberg, a Nobel-prize-winning physicist and sometime spokesman for the discipline of physics itself, from an article that appeared in the New York Review, an article in which he voices his opposition to Kuhn's view of scientific progress,

"...for me as a physicist the laws of nature are real in the same sense (whatever that is) as the rocks on the ground... I know that it is terribly hard to say precisely what we mean by 'real' and 'true.' That is why... I added in parentheses 'whatever that is.' I respect the efforts of philosophers to clarify these concepts..." -Steven Weinberg, The NY Review, Oct. 8, 1998.

Although he realizes he is out of his depth when entering the philosophical arena, Weinberg makes his personal views known, views that I daresay resonate with many scientists,

"Kuhn's view of scientific progress would leave us with a mystery: Why does anyone bother? If one scientific theory is only better than another in its ability to solve the problems that happen to be on our minds today, then why not save ourselves a lot trouble by putting these problems out of our minds? ... What drives us onward in the work of science is precisely the sense that there are truths out there to be discovered, truths that once discovered will form a permanent part of human knowledge." --Steven Weinberg, The NY Review, Oct. 9, 1998.

At the same time, some of these same scientists readily admit that there are non-scientific influences, particularly aesthetic ones, on the choice of scientific theories.  Here is Brian Greene again,

"It is certainly the case that some decisions made by theoretical physicists are founded upon an aesthetic sense -- a sense of which theories have an elegance and beauty of structure on a par with the world we experience. Of course, nothing ensures that this strategy leads to truth." --The Elegant Universe p.167

And here is Steven Weinberg again, from the same New York Review article,

"Any set of data can be fit by many different theories. In deciding among these theories we have to judge which ones have the kind of elegance and consistency that make them worth taking seriously." -Steven Weinberg, The NY Review Oct. 8, 1998.

So Kuhn's point is that the scientists present at the time when a new paradigm is being chosen do not necessarily have as their one and only guide ... some objective, ultimate truth. The paradigm that emerges is one with strong historical influences in the same way that the species that emerge as successful from a period of rapid speciation (perhaps following a mass extinction) have their origins in species that existed formerly. Nature does not have access to all possible biological design plans at the time of speciation. Nature had to work with what she had on hand. In the same way, a scientific community in a time of crisis does not have access to all possible theories from which to choose. Inevitably, as many of the old concepts will be preserved as is possible. Others will be modified as little as need be to solve the crisis problems. Does this get us closer to ultimate truth?  I have a few thoughts along these lines, but this lecture is about Thomas Kuhn’s ideas and no so much my own.  In any case, my qualifications to expound upon the philosophy of science are nonexistent.  Instead, if I believed in such things, I would have us hold a seance in which we would summon the spirit of Plato and ask his guidance in this matter. I don't know if any one else can help us here.  Of course, I would run the risk he might turn to me and say… “Mister… can you paradigm?”


Post-script (not included in lecture)

how the analogy is circular

It is important to keep Kuhn's warning in mind... that the analogy (probably any analogy) can easily be pushed too far. Maybe I have already done so. There are a couple of curious ways in which this metaphor is circular: First, Darwin's theory of evolution is a scientific paradigm of the kind Kuhn's framework seeks to explain. In Kuhn's view of scientific development, it is perhaps only a matter of time before Darwin's theory is replaced through a revolutionary event. Darwinian evolution then becomes an "extinct" scientific theory that presumably still functions as a good metaphor for continued scientific development.


On the other hand, assuming Kuhn’s framework of paradigm’s governing the work of a community can be extended to nonscientific disciplines, perhaps including the disciplines of philosophy and history of science, then Kuhn’s ideas about how science develops represents a paradigm within those fields… a paradigm that will also, ultimately be replaced.  Perhaps it already has?



Gould, Stephen Jay, Wonderful Life, Norton (1990).

Greene, Brian, The Elegant Universe, Vintage Books (2000).

Kuhn, Thomas S., The Structure of Scientific Revolutions, 3rd edition, University of Chicago Press (1962).

Kuhn, Thomas S. ed. by J. Haugeland and J. Conant, The Road Since Structure, University of Chicago Press (2000).

Weinberg, Steven, The Revolution That Didn't Happen, The New York Review (8 October 1998).

Weiner, Jonathan, The Beak of the Finch, Vintage Books (1994).