Incommensurability in science – the last writings of Thomas S. Kuhn

Varvara Stepanova, Meeting, 1919


Excerpt from the “Introduction” by the organizer of the recently published posthumous book by the author of “The Structure of Scientific Revolutions”

More than twenty years have passed since the untimely death of Thomas S. Kuhn. The book that made him famous, The Structure of Scientific Revolutions, has achieved classic status: it is indispensable reading for any enlightened person. It is increasingly recognized that Thomas S. Kuhn was not only one of the most important philosophers of science, but also one of the most relevant thinkers of the 20th century, whose influence extended to diverse academic fields and, in some cases, transformed them. completely.

To tell the truth, some of Thomas S. Kuhn's views are still as controversial as they were in 1962, when The structure burst upon an audience still immersed in logical empiricism, but today its philosophy is better understood than before and its complexity, as well as its nuances, much more appreciated.

This is due, in large measure, to Thomas S. Kuhn's sustained efforts to explain and defend the central theses of The structure. Over time, however, Kuhn became convinced that further clarifications – even careful ones – would not be enough; He began to think that his philosophy of science needed to be revised to some extent, and that it also needed to be situated within a broader philosophical framework and reworked. Kuhn published a series of articles in which he presented an overview of the new direction his philosophy had taken. This work should culminate in a new magnum opus, a book that was his main project for over a decade; unfortunately, Thomas S. Kuhn did not live to complete it.

This volume finally brings to the public eye all the draft chapters of this eagerly awaited book, which had the working title of The Plurality of Worlds: An Evolutionary Theory of Scientific Development. This manuscript is preceded by two interrelated texts, never previously published in English: Thomas S. Kuhn's article “Scientific knowledge as a historical product” and its Shearman Memorial Lectures, “The presence of past science”. The volume also includes two summaries, one for the Shearman Lectures and the other for The plurality. Although they are editorial creations, the summaries use Kuhn's own formulations whenever possible. They show, at a glance, the areas of thematic overlap between the two works. Additionally, the summary for The plurality outlines the main topics with which the unwritten parts of the book should be concerned, as far as these topics can be reconstructed responsibly.

This Introduction to the volume consists of three parts. Part I presents the history of the three manuscripts, their relationship to each other and their current status. Part II, intended primarily for readers not completely familiar with Kuhn's philosophical interests and development after The Structure, provides this information and context, as well as sketching the contours that the book The Plurality was intended to have. This part is, as it were, a road map through primary material that is complex, often repetitive, and fundamentally unfinished.

Part III of the Introduction offers concluding observations about the nature and contents of this volume.


In working on this volume, I drew on several sources. Although I do not discuss here all of Thomas S. Kuhn's previously published texts, or the rich secondary literature about him, these works provided the necessary background for my editorial work. Some of the articles that Kuhn published in the late 1980s and 1990s were especially useful, as this is when Kuhn's philosophical project The plurality of worlds starts to take shape.

Even more important were the indications, in the draft chapters of the manuscript, of what should come later in the book. In addition, Thomas S. Kuhn left a rich archive of unpublished texts of various types, most of which are held by the Institute's Archives and Special Collections at Massachusetts Institute of Technology. The most important among them, to reconstruct Thomas S. Kuhn's unfinished book, are the Thalheimer Lectures, Kuhn's lecture notes and handouts for his graduate seminars at MIT, in which he frequently discussed his book in progress, as well as his correspondence with colleagues, especially his exchange of letters with Quentin Skinner in the wake of Shearman Lectures.

However, an important source, which I drew on when reconstructing A plurality, is not publicly available: these are the unrevised notes that Thomas S. Kuhn left for each projected chapter of the book. These notes, for the most part, are brief and suggestive rather than detailed and explicit; Despite this, I found them very useful when producing the summary for The plurality. Jehane Kuhn, Kuhn's widow and literary executor, gave me a copy of the transcribed conversations between Thomas S. Kuhn, James Conant, and John Haugeland, in which she occasionally participated.

The conversations took place at Kuhn's house, between June 7 and 9, 1996, in five work sessions, totaling around seven hours. Kuhn wanted the tapes of the conversations destroyed and never implied that the transcripts should be publicly available. Out of respect for Kuhn's wishes, I have not used these transcriptions as a source of information about his philosophical views, but only to reconstruct the history of his work in the manuscripts published in this volume.

None of these sources offers anything even approaching a first version of the unwritten parts of The plurality. Instead, they give us a sense of Thomas S. Kuhn's general philosophical direction, with very clearly stated reasons, here and there, against a particular misunderstanding of his views, or against a rival philosophical position that could be confused with the from Kuhn himself. Thus, the available sources only shed partial, diffuse light on the project. The plurality, which Kuhn was still pondering in June 1996. No one can know now what the final, detailed version of his conception would have been if he had taken the time to fully articulate it, however, the overall contours of his position can be sketched and, at least some of its details, filled in.

Primary texts

“Scientific knowledge as a historical product” and the Shearman Memorial Lectures, “The Presence of Past Science,” by Thomas S. Kuhn are both philosophically important in their own right and relevant as milestones in the development of the central ideas of Kuhn's unfinished book. Arranged chronologically, the three texts reveal the philosophical trajectory of Thomas S. Kuhn from the 1980s until his death in 1996.

“Scientific Knowledge as a Historical Product” was written and revised multiple times between 1981 and 1988. Various versions of this text were made for conferences to which Kuhn was called as a guest speaker. In the first of Shearman Lectures, Kuhn observes that “Scientific knowledge as a historical product” should “appear in Synthesis” (meaning the Revue de Synthèse, a French journal on the history and philosophy of science), but the text was not published there. The latest version, included in this volume, was made for a conference in Tokyo in 1986 and subsequently published in Green– in Japanese translation.

It offers the best available account of Kuhn's analysis of the origins and commitments of the traditional epistemology of science, the problems that plagued it, and the ways in which Kuhn's evolutionary understanding of science avoids these problems. Although there is no significant textual overlap between this article and the opening chapter of The plurality of worlds, the two texts share the same title and fulfill the same function of justifying Thomas S. Kuhn's philosophy of science, which is evolutionary, sensitive to historical context, and practice-oriented. I tend to think of this article, then, as a protochapter 1 of The plurality.

“The Presence of Past Science” is a series of three Shearman Memorial Lectures that Thomas S. Kuhn spoke in University College London in November 1987. The lectures explore Kuhn's historical-evolutionary approach to science and begin to articulate the philosophical consequences of adherence to such an approach. Two other series of conferences preceded them: the Notre Dame Lectures, “The Nature of Conceptual Change”, delivered at the University of Notre Dame in November 1980, which appears to be lost; and the Thalheimer Lectures, “Scientific development and lexical change”, presented at Johns Hopkins University in November 1984.

As Shearman Lectures They constitute the last complete version of Thomas S. Kuhn's mature philosophy and the best available—if imperfect—guide to what his book aimed to accomplish: they sketch the entire philosophical landscape that the planned book was to cover. The last conference is particularly important for giving us an idea of ​​what the content of Part III and the Epilogue of The plurality if Kuhn had lived to write these parts of the book.

Thomas S. Kuhn did not publish the Shearman Lectures, nor any other lectures he gave in the late 1980s and early 1990s. He treated them as drafts, more or less successful, of his book. However, he revised and refined the manuscript of the Shearman Lectures and shared it with many of his colleagues, friends and students; This manuscript still circulates semi-clandestinely in some philosophical circles. Thus, the Shearman Lectures they have become an unpublished source of the greatest importance for the appreciation of Kuhn's late philosophy.

Two splendid articles – the first by Ian Hacking and the second by Jed Buchwald and George Smith – analyze and discuss the Shearman Lectures in philosophically stimulating ways, rich in nuance and detail; a full understanding of these articles, as well as Kuhn's published response to Hacking, requires familiarity with Kuhn's original text. Thus, since the Shearman Lectures are now widely discussed but not generally accessible, and since the book that was to replace them was not completed, Kuhn's literary executors and the University of Chicago Press decided that this important text should be included in this volume, despite Thomas S. Kuhn's original intention not to publish it.

The centerpiece of this volume is, of course, Thomas S. Kuhn's unfinished book, published here under the working title it had at the time of his death: The plurality of worlds: an evolutionary theory of scientific development. If Kuhn had lived to complete the book, it is likely that he would have given it a different title. The original working title appears to have been Words and worlds: an evolutionary conception of scientific development. This is the title that Thomas S. Kuhn proposed in his successful application for a fellowship at the National Science Foundation in history and philosophy of science in 1989. It is not clear why Kuhn abandoned this title, which adequately announces the intended content, nor why he did not return to it when he became concerned that The plurality of worlds could be confused with On the Plurality of Worlds by David Lewis and that it was wrongly assumed that it was, like Lewis's book, about modal logic.

Thomas S. Kuhn expressed this concern to Jehane Kuhn, who told me about it in a private communication in 2017. Kuhn's desire to find a new title for his book is also documented in his transcribed conversations with James Conant, John Haugeland, and in this segment of the conversation, with Jehane Kuhn. When referring to the title, Kuhn said that it should include worlds or plurality, but decided to delegate the final decision to Jehane, who decided not to modify it.

Thomas S. Kuhn's plan for the book was ambitious and the work consumed considerable time. The book should begin with acknowledgments and a preface, followed by three substantive parts, each consisting of three chapters: Part I, “The problem”; Part II, “A world of species” and Part III, “Reconstructing the world”. An epilogue should be added and an appendix should conclude the book. Unfortunately, only complete outlines exist for Part I (chapters 1-3) and chapters 4 and 5 of Part II; the draft for Chapter 6 is unfinished. Kuhn left scattered notes for Part III and the Epilogue, but no actual text; the Preface and Appendix are also missing.

Part I is refined and is clearly close to the intended final version. It motivates the book project as a whole and outlines the chapters planned ahead. Its emphasis is on the nature and philosophical significance of the historical study of science, vividly introduced through detailed case studies of the works of Aristotle, Volta, and Planck. Thomas S. Kuhn used these three case studies to show how exactly the history of science must confront incommensurability in order to generate understanding and to formulate the important philosophical questions that the last part of the book would be charged with addressing.

Although there is considerable textual overlap between the first Shearman Lecture and Chapter 2 of The plurality, the general differences between the two works, separated by less than a decade, are also considerable and very important for revealing the trajectory of Kuhn's thought and the development of his mature philosophical position. The second of Shearman Lectures, for example, discusses the incommensurability between past and present science, in addition to sketching the outlines of a theory of meaning and a theory of knowledge that would allow us to make sense of historical understanding despite incommensurability. To the extent that this lecture gestures toward an empirically grounded explanation of language learning and concept acquisition, it is the germ from which Part II of the book developed; however, the actual text and philosophical methodology differ considerably.

In fact, Part II—in contrast to Part I—will likely come as a great surprise to readers familiar with the published writings of Thomas S. Kuhn. Here, Kuhn seems to be looking for a naturalistic foundation for his prospective theory of meaning, which should, in turn, ground his revised idea of ​​incommensurability. He aimed to use the results of scientific research in cognitive psychology and developmental psychology as the basis for his theory of meaning and understanding across immeasurably different lexical structures and practices. However, this important project is only proposed, but not completed. I suppose that the final version of Part II would have updated and condensed the relevant results of the scientific research and then highlighted their philosophical significance, thereby setting the stage for the last, philosophically more interesting but unwritten segment of the book.

Part III should interweave the historical conception of conceptual change, presented in Part I, and the scientific expositions of concept acquisition, presented in Part II, in order to explain both incommensurability and our ability to understand and communicate despite it. . The plurality treats incommensurability as ubiquitous across cultures, languages, historical periods, and diverse social groups; scientific communities divided by incommensurability are just a special case, albeit a very special one. Thomas S. Kuhn aimed to explain both the way in which science shares universal patterns of conceptual acquisition and structuring of lexicons, and the way in which lexical change in science differs from lexical change in natural languages.

General philosophical questions about meaning, understanding, belief, justification, truth, knowledge, rationality, and reality were all raised by Kuhn's project, and he intended to address them in Part III. The main aim was to develop theories of meaning and knowledge that would take incommensurability as their starting point and find room for, first, a robust notion of the world that science investigates and, second, for the rationality of changing attitudes. belief and, finally, to the idea that scientific development is progressive.

The Epilogue should return to the question of the proper relationship between history and philosophy of science, which had interested Kuhn since The structure and which attracted the attention of both his critics and his admirers. In his early work, Kuhn argued passionately against presentist (or anachronistic) approaches to the history of science, which he saw as characteristic of both logical empiricism and Popperian falsificationism. He was convinced, in The structure and in his 1977 book of essays, The essential tension, that philosophy of science must reject presentist case studies and rely on responsible and detailed historical work that restores the context, concepts, problems and intentions of past scientific communities. However, in the late 1980s, Kuhn began to think that presentist historiography has its own irreplaceable function, which he should explain and discuss in the Epilogue of The plurality. Fortunately, this central idea for the epilogue is very clearly presented in the last of the Shearman Lectures.

Finally, the Appendix should offer a detailed comparison between the concepts presented in The structure, which remained the source of Kuhn's central philosophical ideas, as well as the main problems that interested him until the end of his life, and The plurality, which should be your final word on these issues. The continuities and differences between the two works should be highlighted and explained. As much as we can accurately reconstruct Kuhn's last book, we can also imagine what the substance of the comparative appendix would have been.

However, reconstructing Thomas S. Kuhn's unfinished book in sufficient detail is no easy task. We are forced to rely on several texts – published and unpublished – in addition to the manuscript itself. They were written over more than a decade and it is not always clear which of the ideas Kuhn explored during this period he intended to articulate and defend and which he rejected in the final version of his book.

As much as Part III could be reconstructed, then, I attempted to do so in the summary I created for The plurality. This still leaves the reader with only a skeletal representation of the centerpiece of Thomas S. Kuhn's book. Thus, it is important to keep in mind that the publication of the manuscript, in itself, does not fully represent Kuhn's ambitious philosophical project. Its proper appreciation requires interpretative and imaginative efforts of a different kind from the efforts that were necessary to understand the unfamiliar landscape of The structure at the time of its publication; but, both now and then, the effort will pay off.

*Bojana Mladenovic is a professor in the Department of Philosophy at Williams College. Author, among other books, of Kuhn's Legacy: Epistemology, Metaphilosophy, and Pragmatism (Columbia University Press).


Thomas S. Kuhn. Incommensurability in Science: The Last Writings of Thomas S. Kuhn. Organized by Bojana Mladenovic. Translation: Alexandre Alves. São Paulo, Unesp, 2024, 384 pages. []

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