Paradigms Gone Wild

The​ tragedy of Thomas Kuhn’s life was to have written a great book. The Structure of Scientific Revolutions was published in 1962, when he was forty, and he spent the rest of his life distressed by its success. It has sold 1.7 million copies, and has been translated into 42 languages. Very few academic books sell in those numbers and scarcely any are still seen as state of the art sixty years after publication. Structure crosses disciplines. It is read by historians, sociologists and philosophers whose business is thinking about what science is and how it changes, and also by scientists with a reflective turn of mind. It is read by theologians pondering the differences and similarities between science and religion, and by anthropologists considering the characteristics of ‘Western’ and ‘non-Western’ thought. The book has insinuated itself into everyday language. Kuhn plucked the word ‘paradigm’ from linguistics – where it referred to the permutation of forms having a common root, like the conjugation of verbs or the declension of nouns – and repurposed it as the term for a key regulative resource in scientific inquiry, a concrete model of ‘the right way to go on’. Eventually, lots of things meant to be thought of as ‘innovative’ and ‘good’ were branded as ‘paradigm shifts’: new ways of producing factory-farmed chicken, the latest solution to the difficulties posed by Brexit for trade arrangements in Northern Ireland, the emergence of celebrity chef culture. A New Yorker cartoon shows tramps leaning against a wall: ‘Good news – I hear the paradigm is shifting.’ Another has two men, their clothes billowing out in the wind, speculating that there must have been a ‘paradigm shift’. You can buy a bumper-sticker: ‘Shift Happens: Buddy Can You Paradigm?’

The ‘last writings’ collected here include the texts of several lectures Kuhn gave in the 1980s, which circulated as samizdat texts among academics close to him, but the main interest of the book is in the edited drafts of about two-thirds of the ‘magnum opus’ on which Kuhn had been working for more than ten years when he died in 1996, given the provisional title ‘The Plurality of Worlds: An Evolutionary Theory of Scientific Development’. Last Writings will be assessed and picked over by philosophers in the Kuhn commentariat. I won’t do that here. Instead, I describe the significance of the path that Kuhn took from his study of physics as an undergraduate at Harvard in the 1940s, to the writing of Structure, and then on to his lifelong effort to manage the outbursts of both enthusiasm and criticism the book unleashed.

A theory of scientific change isn’t an obvious subject for an American bestseller. But in the culture at the time Structure was published, thinking about the nature of science was highly charged. In the Second World War, radar and the atomic bomb had established that science could deliver military might, and the US government began to pour unprecedentedly large sums of money into academic research. The continuing mobilisation of science in the Cold War arms race secured the place of physics and several other disciplines in the state’s favour, but the closeness to government, the military and big industry made some sectors of the intelligentsia uneasy. Were the virtues of science the same as those of liberal democracy – open-minded, universal, set against authority – or could science flourish in secret spaces, its agenda controlled by external forces, its beliefs distorted by dogma? The American scientific community was much engaged by questions of this sort, the tone set by the physicists who had built the Bomb. In 1961, Eisenhower’s farewell address warned of the political dangers posed by the ‘military-industrial complex’ and of the potential for the corruption of science when it was done at state command. In the first part of the 20th century in capitalist countries, science was considered to be a fragile plant, thriving only in the soil of open societies; by the early 1960s, anxieties were emerging about the role of science in buttressing political authority and even setting authoritarian agendas.

Criticism was one response to these new conditions but another, more novel, possibility was to write about science as a normal cultural and social phenomenon, not something set apart from civil concerns but integral to them, and not to be celebrated or condemned but disinterestedly described and interpreted. So, at this time, there was fertile ground for an engagingly written general theory of science. The Structure of Scientific Revolutions was just 172 pages of lightly footnoted text, mostly accessible to general readers, liberally salted with stick-in-the-mind aphorisms: a remarkable merger of intellectual and literary virtue, small but perfectly formed. Kuhn regarded it as little more than a ‘highly schematic sketch’ of a much longer and more professional monograph that he had in mind for the future. It wasn’t originally intended as a free-standing book at all, having been commissioned as an extended entry in the International Encyclopedia of Unified Science, edited by émigré Vienna Circle philosophers. Even so, Kuhn anticipated an exclusively academic audience, mainly historians and philosophers of science. He was unprepared for popular success: he couldn’t deal with it, and he didn’t like it.

Kuhn wasn’t trained in philosophy, and Structure referred to the work of only a few 20th-century philosophers (Wittgenstein, Quine, Popper, Nelson Goodman, Norwood Russell Hanson), but philosophers recognised it as an exercise belonging to their discipline. Science was seen as the instantiation of rationality, objectivity, open-mindedness and progressiveness. Science methodically compared theoretical expectations against observational and experimental evidence; it purged itself of bias and prior expectations; its knowledge was cumulative; the quality of that knowledge was guaranteed by explicit methodological standards shared throughout the scientific community; the various bits of science were part of a fundamental unity, whether of concepts, facts, or methods; it arrived at, or at least approached, truth. The Structure of Scientific Revolutions denied all this. Observations could not be checked against a specific theory but only against an extended network of theories, making the notions of confirmation and disconfirmation problematic. Scientists were not notably open-minded. Their training encouraged the embrace of what Kuhn frankly called ‘dogma’: theirs was ‘a narrow and rigid education, probably more so than any other except perhaps in orthodox religion’. If the account in Structure were accepted, Kuhn wrote, the notions of ‘“scientific progress” and even “scientific objectivity” may come to seem in part redundant.’ We may ‘have to relinquish the notion’ that scientific change brings scientists ‘closer and closer to the truth’. Scientific knowledge did not accumulate: it moved from moments of puzzle-solving ‘normal science’ governed by one paradigm, through ‘crisis’ and ‘revolution’, to subsequent moments of ‘normal science’ governed by another paradigm. And the paradigms (Aristotelian and classical mechanics, say, or Earth-centred and Sun-centred astronomies) were ‘incommensurable’: there was no independent way of adjudicating between them; the embrace of a new paradigm ‘can only be made on faith’.

Kuhn’s book fell in with revisionist tendencies then emerging among historians of science. The new thinking was that you couldn’t intelligibly describe past science as failed present science; you couldn’t bring ‘an older science to the bar of judgment of a later one’. In crucial instances of scientific judgment, ‘there is no standard higher than the assent of the relevant community.’ Kuhn’s paradigms – embedded in the everyday practice of everyday science – supplied what formal method and reason could not: they ‘may be prior to, more binding, and more complete than any set of rules for research that could be unequivocally abstracted from them’. In fact, Structure implicitly challenged the notion that there was such a thing as a unified scientific community; rather, there were many communities, each of them organised through its commitment to specific achievements, specific methods and specific standards of fit between expectation and evidence. The much treasured idea of ‘scientific unity’ was also sacrificed: science was a ‘ramshackle structure with little coherence among its various parts’. Philosophers of science had long accepted their role in justifying science, making the case that scientific knowledge is – take your pick – true, objective, rational, reliable, progressive, powerful. Kuhn seemed to be arguing that philosophers had been aiming their inquiries at the wrong targets.

Structure made Kuhn an intellectual rock star. So many readers, so many – as Kuhn reckoned – misreaders. From the time the book was published until his death, Kuhn couldn’t shake them free. Everyone wanted to know what he really thought; whether he approved their readings of his book; whether he accepted their criticisms; and, especially, what would come next. Some readers Kuhn ignored; some he sneered at; and some he spent the rest of his career trying desperately to satisfy. By and large, the philosophers were critical, some violently so. They took the book to be a virulent instance of the despised ‘relativism’, ‘constructivism’ or ‘subjectivism’. Kuhn recalled being told that, soon after publication, groups of philosophers had ‘gathered and said that the book should be burned’. Historians were intrigued, but few of them saw theorising about ‘the nature of science’ as their business. Sociologists were eventually among the book’s enthusiasts, but mostly a small number of sociologists of knowledge in Britain; the far larger body of American sociologists took longer to appreciate what was going on. The human sciences were notably absent from the book – almost all the historical examples were drawn from physics, astronomy and chemistry. In his preface, Kuhn suggested that the inspiration for the paradigm/normal science idea had come to him during a year spent at the Stanford Centre for Advanced Study in the Behavioural Sciences, where he was amazed to see that human scientists argued about the fundamentals of their disciplines, while in the physical sciences in which he’d been trained there appeared to be a great consensus.

Where philosophers took issue with Structure, Kuhn generally accepted that they had put their fingers on genuine weakness or ambiguities. Perhaps the nature and scope of ‘revolutions’ hadn’t been sufficiently circumscribed. Perhaps the residual ‘rationality’ of science hadn’t been insisted on. Perhaps – especially – the proper sense of ‘paradigms’ hadn’t been coherently specified. Kuhn defined paradigms as ‘universally recognised scientific achievements that, for a time, provide model problems and solutions for a community of practitioners’, or ‘shared examples of successful practice’ that could achieve the sort of collective assent that formal rules could not. But he realised he had invited the possibility that they would be misconceived as binding perceptual frames. Structure includes prominent treatment of the famous duck-rabbit Gestalt switch in which you can see only one of the animals at a time, implying that each represented a different constellation of beliefs or perceptual frame. Kuhn had allowed a metaphorical aid to be taken literally, and later admitted that it had been a ‘dreadful mistake’. He respected the philosophers and was appalled to find that so many of them accused him of being a relativist, an irrationalist or a truth-denier – he was, he said, ‘much fonder of my critics than my fans’.

In the social sciences, there was a tendency excitably to read Structure as a how-to manual for academic success. ‘Some of them even said “Wow, now all we have to do is figure out what our paradigm is and enforce it,”’ Kuhn told an interviewer, as if paradigms were like theories to be grabbed off the shelf in an intellectual supermarket. Natural scientists were not, for the most part, bothered by the book – they were generally too busy doing science to theorise about it – although a casual reading did offer a useful vocabulary for those wanting to distinguish between ‘mature’ and ‘genuine’ sciences (which did have a paradigm) from pretenders in the softer sciences (which did not). These people were just silly, in Kuhn’s view. But what shocked him most deeply was the embrace of the book by 1960s radicals. Kuhn was teaching at Berkeley when it was published, and nowhere was it more likely to be misread as an anti-scientific tract. Kuhn knew this: he was ‘sure that part of the reason the book attracted the attention that it did, particularly among people who were under thirty in the 1960s’, was that ‘it could be used as a whip with which to beat the sciences.’ He was distressed to find that at San Francisco State University – which rivalled Berkeley for radicalism – the students’ two great intellectual heroes were Herbert Marcuse and himself. The idea of ‘being a guru’, he said, ‘scared the shit out of me’.

Campus radicals seized on Kuhn’s book as a brilliantly subversive exposé. Just as they had suspected, science wasn’t the open-minded objective pursuit of truth, but merely one more mode of authoritarianism. Scientists were just as dogmatic as anyone else, and one way of seeing the world was as good as another. If there were no better criteria for judgment than communal assent, why should anyone bow down to scientists’ pronouncements? Student radicals read Structure as revealing irrationality in science – which, Kuhn said, ‘absolutely blew my mind’. ‘Oh thank you, Mr Kuhn, for telling us about paradigms,’ he remembered the students saying. ‘Now that we know about them, we can get rid of them.’ This sort of (mis)understanding did not escape philosophers’ notice. One of Kuhn’s critics – the Hungarian émigré and one-time Communist apparatchik Imre Lakatos – pointed to the political consequences of construing scientific consensus as nothing but ‘mob rule’: ‘Kuhn’s position would vindicate, no doubt unintentionally, the basic political credo of contemporary religious maniacs (“student revolutionaries”).’ Kuhn stood accused of being yet another philosophical ‘corrupter of youth’. Philosophy of science here bled seamlessly into Cold War politics.

Kuhn was contemptuous of the politically radical ‘Kuhnians’. He couldn’t see that there was anything of ideological interest in Structure: it described revolutions but, properly understood, it was ‘a profoundly conservative book’. Scientists were creatures of tradition: they aimed to conserve and extend tradition, not to overthrow it, and revolutionary change – when it occurred – was precisely the product of conservative impulses running up against obdurate evidence. The ‘anomalies’ that brought about scientific crises arose only when scientific communities striving to preserve existing methods and accomplishments were forced to confront failures. Many in the science-teaching business saw in Structure something that the student radicals missed: the book could be used to support the idea that pedagogy should encourage not open-mindedness but its opposite. And if there was any marxisant sentiment in the book, it was the Marx of The Eighteenth Brumaire of Louis Bonaparte: ‘Men make their own history, but they do not make it as they please.’ They make it ‘under circumstances existing already, given and transmitted from the past’.

Kuhn didn’t suffer fools, and he had an inclusive sense of foolishness. He agonised that he might bear some responsibility for the misreadings: ‘In retrospect, I begin to see why this book fed into that, but boy, was it not meant to, and boy, does it not mean to.’ One philosopher targeted what he called Kuhn’s ‘purple passages’ – for example, where he said that there was no standard for scientific judgment higher than ‘the assent of the relevant community’ – and Kuhn accepted the verdict: ‘To my dismay … my “purple passages” led many readers of Structure to suppose that I was attempting to undermine the cognitive authority of science.’ Kuhn felt wearily obliged to put on the official record that he was ‘pro-science’. He was a passionate man, suspicious and prone to outbursts – by his own description, ‘anxious’ and ‘neurotic’. Interviewers were treated as chronic misunderstanders, required to submit written questions in advance and, more often than not, denied access. Kuhn accepted limited liability for misreadings, but a line had to be drawn. Invited to a seminar by Princeton undergraduates inspired by what they took as the book’s anti-authoritarianism, Kuhn erupted, telling them that they just hadn’t read the thing properly: ‘I kept saying, “But I didn’t say that! But I didn’t say that! But I didn’t say that!”’

As a young man, the documentary filmmaker Errol Morris pressed himself into graduate school at Princeton, hoping to study with Kuhn. The experience wasn’t what he had hoped. Morris wrote a thirty-page, double-spaced paper for Kuhn’s seminar, including passages finding fault with the paradigm notion, and he was invited to the professor’s study for discussion. Kuhn hated the paper; he wrote thirty pages of single-spaced commentary in response; the young Morris argued; the professor argued back; tempers flared. As Morris tells the story, ‘the bile just flowed out of him.’ Kuhn ‘started moaning. He put his head in his hands and was muttering, “He’s trying to kill me. He’s trying to kill me.”’ At the end of his tether, Kuhn threw an ashtray ‘with malice’, maybe at Morris, maybe just in his general direction: ‘It came hurtling across the room, spewing butts and ashes.’ (Kuhn and ashtrays were constant companions; he smoked upwards of six or seven packs of cigarettes a day, and died of throat cancer.) First Kuhn threw the ashtray, then he threw Morris out of graduate school. The experience gnawed away at Morris for fifty years, traumatic enough that in 2018 he wrote a book titled The Ashtray (Or the Man Who Denied Reality), in which Kuhn is portrayed dispensing ‘his own brand of pernicious intellectual Kool-Aid’.

I had a handful of encounters with Kuhn myself over the years. They were generally straightforward, although he eventually sized me up as one of his sadly misguided ‘fans’. His moods, however, could be volatile. Once, as quite a junior scholar, I was on a conference panel for which Kuhn was to act as commentator. The night before, he spied me in the conference lobby and said he’d like a word after he checked in. The word turned out to be that in his comments the following morning he would ‘have to destroy’ me. In the event, the panel actually went pretty well, and Kuhn’s commentary was no more than mildly critical. Afterwards, he said he wanted to apologise for his remarks in the lobby: he had reread my paper and realised that he’d ‘confused’ my argument with someone else’s. (I never worked out what all that was about.)

Kuhn​ was persistently ‘pained’ by the reception of Structure. Published criticisms made him so angry that – ashtray-like – he’d ‘throw them across the room’. That criticism should annoy an author is nothing very unusual. What’s more surprising is that Kuhn was surprised, by either the philosophers’ criticisms or the student radicals’ enthusiasm, since the reaction of both groups should have been entirely predictable. But Kuhn was raised in a series of relatively set-apart and insulated environments – and he might not have securely known what ‘everyone knew’. The child of a well-off non-observant New York Jewish family, Kuhn was sent to one progressive private school after another, and then, in 1940, to Harvard, which his father and other members of his family had also attended. Not knowing exactly what he wanted to do, Kuhn wound up in physics, though he found neither his undergraduate degree nor his postgraduate work very thrilling. He dabbled in English literature and took several courses in history. As a new graduate student in physics, he wanted to take more philosophy seminars, but the people he wished to study with weren’t yet back from the war and he was offended by the idea of having to take introductory courses to make up for what he hadn’t done in the past: ‘I couldn’t go back and sit still for that undergraduate chicken-shit.’ Then, while Kuhn was still a PhD student, Harvard’s president, the chemist James Bryant Conant, asked him to teach a new undergraduate course – science for non-scientists – conceived as a response to the new cultural and political importance of science in the post-Hiroshima world. Conant’s idea was to introduce the future leaders of society – for that, of course, was what Harvard graduates were going to be – to the realities of science as it was actually practised. For Conant, this meant that instead of the traditional, textbook image of science, students would be exposed to historical case-studies of experimental practice. It was Kuhn’s first significant encounter with the history of science, and the case-studies in the course featured prominently in Structure.

Kuhn’s relationship with Harvard’s president helped him get elected to the elite Society of Fellows, where he had three responsibility-free years to do whatever he liked and read whatever he wanted. He set out on a self-directed programme of reading in the history of science and related areas of psychology and philosophy. After that he stayed on at Harvard, teaching a range of courses in the history of science, and wrote his first book, The Copernican Revolution (1957). The book made a gesture at generality – because Copernicus’s Sun-centred system was ‘in many respects a typical scientific theory, its history can illustrate some of the processes by which scientific concepts evolve and replace their predecessors’ – but it was not a programmatic work, and it did not address the seeming conflict between revolution and evolution. Kuhn hoped the book would secure his tenure at Harvard – Conant, by that time High Commissioner in Germany, wrote a flattering foreword – but his application was refused. ‘Harvard didn’t want me’ was Kuhn’s verdict, but Harvard’s assessment had apparently been that the book relied too much on secondary sources and too little on original archival research. He would have to seek employment elsewhere. Between 1956 and 1964 Kuhn was at Berkeley, spending a year at the Stanford Centre for Advanced Study along the way, then left California for Princeton’s history of science programme. In 1979 he returned to Cambridge, as a professor of philosophy at MIT. It was a golden career, though not what you’d call a normal one. The fortunate academic was insulated from everyday culture and everyday concerns might not much impinge on him.

Asimilar​ disconnectedness bore on Kuhn’s disciplinary identity. He acknowledged that theoretical physics was ‘the only field in which I can claim to have been properly trained’. Everything that went into his published work came from self-study. The Structure of Scientific Revolutions was the result of Kuhn’s wandering around among the disciplines, something that was very difficult then and is almost impossible today. Kuhn was aware of the gaps in his education, but correctly presumed that had he been more systematically educated he would not have written a book like Structure. He went along with the traditional wisdom that historians aimed at narratives about past particulars, philosophers at general theory – and he didn’t think that both goals could be realised at once. When Berkeley came calling, the university offered him appointments in both the philosophy and history departments, and Kuhn accepted the joint arrangement because, as he said, ‘I wanted to do philosophy.’ He thought of Structure as ‘a book for philosophers’. Yet when he asked Berkeley for tenure he was told that ‘the senior philosophers voted unanimously for your promotion – in history’. The rebuff ate away at him for years.

Academic philosophy has exclusionary tendencies, and philosophers’ criticisms of Structure had something to do with Kuhn’s lack of disciplinary professionalism. When he wrote it, he later admitted, ‘I hadn’t read much philosophy of science, and had no idea how much was going on in that field.’ The book is often read as a rude dismissal of ‘positivist’ and ‘logical empiricist’ views of science, but Kuhn’s hostility wasn’t much informed by a deep familiarity with those traditions. When he airily referred to ‘that sort of everyday image of logical positivism’, what he had in mind were the throat-clearing pronouncements on ‘the nature of science’ often found in the first few pages of science textbooks. Kuhn thought that textbooks grossly misrepresented the realities of scientific research and largely assumed that philosophers’ views of science did too. The philosophers didn’t like it; they thought their nuanced positions on scientific objectivity and scientific change were being caricatured, and there was a residual sense that Kuhn wasn’t a proper philosopher at all.

The Structure of Scientific Revolutions had made Kuhn famous. It had brought him an audience he had neither wanted nor expected and whose attentions he found stressful. What to do next? One firm decision was never to write that sort of book again, never to write anything accessible to the general reader, never to strew intellectual pearls before swine. In this, Kuhn entirely succeeded. He was always a slow and nervous producer in any case. It was in 1953 that he was first approached to write the encyclopedia essay that eventually became Structure, but he claimed that the basic conception for the book came to him as an epiphany in 1947 – so that, in the end, the book was a fifteen-year slog. In 1951, he was asked to give a set of general-interest lectures in Boston, which contained a number of ideas central to Structure. He had ‘a dreadful time’ preparing them, he said, and ‘nearly cracked up’. After Structure, it took another sixteen years for Kuhn’s next book to appear. This was Black-Body Theory and the Quantum Discontinuity, 1894-1912 (1978), the only monograph that Kuhn published after Structure, a detailed and demanding account of Max Planck’s role in the development of quantum mechanics. Black-Body Theory was welcomed by historians of modern physics and by some philosophers of science, but it attracted few other readers. Then there was the big book left unfinished at his death, much of which has been edited for inclusion in Last Writings. The book had been promised, and gossiped about, for many years. Kuhn expected it to be definitive, and to resolve many of the questions that Structure had left hanging. Yet, although millions now know the name Thomas Kuhn and know something of his second book, few will be able to name anything else that he wrote, and fewer still will want to, or be able to, work through the drafts contained in Last Writings.

A restricted readership was just what Kuhn intended. In that respect his career tracked the trajectory of academic professionalisation in general. Structure was, as it’s now said, ‘interdisciplinary’ – a word that was just coming into vogue when the book appeared. It was interdisciplinary not because Kuhn intended it as such but because of the problem he was addressing and the institutional environment he was working in, which allowed him to wander freely between the established disciplines. And as those disciplines grew in power over the decades since, so the environment from which Kuhn emerged became an endangered habitat. Kuhn intermittently said that he was a historian, but as time went on he addressed himself more and more to the concerns of Anglo-American philosophy. Black-Body Theory was his last extended work of history. And, the enthusiasm of ‘Kuhnian’ historians notwithstanding, Kuhn despaired at the state of history of science. No one, he felt, including almost all of his students (who were few in number), was doing the close-textured ‘history of analytic ideas’ that he approved; the growing fashion for work on ‘science and society’ irritated him immensely. For many years, he said, he had ‘read practically nothing in the history of science’.

The road from The Structure of Scientific Revolutions to the drafts in Last Writings was, to a large extent, a long walk back – Kuhn’s attempt to clarify, revise, secure and modify the ‘purple passages’, to dissociate himself and his book from the vulgar and the relativists. In one matter, however, he stuck firmly to a sentiment in the book that had given aid and comfort to the supposed ‘enemies of science’. You should not, Kuhn had written, think that scientific change brought practitioners ‘closer and closer to the truth’. In the closing pages, he had sought to retrieve an idea of progress from the account of discontinuous revolutionary change. Here, the language of evolution was used to solve problems precipitated by the idea of revolution. Darwinian evolution described organic change without reference to final purpose – without the idea that change was going towards the perfection of the human species – so why should the notion of scientific change necessarily entail going towards or getting closer to ‘one full, objective, true account of nature’? The outcome of change, in Kuhnian terms, was ‘the selection by conflict within the scientific community of the fittest way to practise future science’. We should substitute ‘evolution-from-what-we-do-know’ for ‘evolution-towards-what-we-wish-to-know’. The Darwinian account of evolution had historically been crafted to dissolve the authority of catastrophic and discontinuous accounts of organic change. Kuhn invoked evolutionary change to solve some of the philosophical problems posed by his own notion of discontinuous scientific revolutions.

In other respects, the walk back from or substantial revision of Structure was more substantial and unfolded over time, from his first responses to critics in the late 1960s through to the drafts contained in Last Writings. The tasks taken up in what the editor of Last Writings admiringly calls ‘the late Kuhn’ or ‘Kuhn’s mature philosophy’ were threefold: repairing and rebranding his original conception of the ‘paradigm’; restricting the scope of ‘incommensurability’ and the problems it posed for scientific objectivity; showing how progress might occur across paradigms and why the involvement of subjectivity in science could be considered innocuous.

For Kuhn, the problems with unrestricted readership were exposed most clearly when it came to the notions of the paradigm and the paradigm shift. The philosophers’ criticisms he considered legitimate: he responded to them immediately, and continued to develop his ideas about regulative structures in science for the rest of his life. But paradigms-gone-wild in the culture also bothered him; he complained that he had ‘totally lost control’ of the term’s proper usage, and vowed that in future he would ‘seldom’ use it. Black-Body Theory contained just one glancing mention of a paradigm and made no reference at all to Structure. All along, Kuhn sought to retain the idea of paradigms as concrete, non-rule-like regulative structures while rebranding them as something less catchy, more recognisable to philosophers, less likely to circulate in the wider culture. One early possibility was the ‘disciplinary matrix’, though as Kuhn glossed the term it looked very like the paradigm-as-exemplar. In Structure, the ‘paradigm’ figured in an account of the way scientific practice was organised on a day to day basis; in drafts of his last work, the word ‘paradigm’ appears almost solely in references to Structure. To pick out what it was that groups held in common and used to coordinate their activities, Kuhn came to prefer the terms ‘structured lexicon’ and ‘structured kind set’, so signalling an affiliation with general theories of language, meaning and concept application.

Perhaps the purplest of Structure’s passages were the ones containing the related claims that paradigms were ‘incommensurable’ and that either side of a paradigm shift scientists live and work ‘in a different world’. There were no bodies of facts, methods for establishing facts, or theories for interpreting the facts, that were paradigm-independent; there was no ‘neutral algorithm’ for judgment. This was the Kuhn who was taken to be a reality and reason-denying relativist. How could you talk of either objectivity or progress given ‘different world’ incommensurability? Realising that the language of Structure had ‘misled’ readers, Kuhn came to distinguish between the problem of understanding for historians and the problem of understanding that confronted the scientists historians wrote about. No matter what issues were disputed among scientific groups in the past, they actually shared a lot – enough that they could, as a matter of course, understand much about opponents’ methods, concepts and factual knowledge. For them, changes would appear piecemeal and incommensurability would only be local. Historians, though, look at the past from a cultural distance. To do their work, they have to learn a whole new language, and for them incommensurability seems total. This was a distinction that bounded the problem of incommensurability and prevented it from spoiling a picture of scientific rationality.

Kuhn also began to identify resources shared among scientists which allowed them rationally to assess the quality of alternative theories – to rely on something other than, and much better than, ‘mob psychology’. These were what Kuhn called the maxims, norms or (his preference) values of science, though he felt no need to offer systematic evidence that these values were generally agreed and invoked. A theory should be accurate and consistent; it should have broad scope; it should simplify accounts of phenomena; and it should be fruitful in disclosing new phenomena or revealing new connections between them. There were, Kuhn acknowledged, substantial problems in applying these values. For example, in assessing a theory, how important was one value compared to another? How unambiguous was a theory’s simplicity or fruitfulness? How pertinent was a specific value to the case in hand? The values were said to be invariant over time and between scientific settings – ‘fixed once and for all’ – and, as a set, they were particular to science, but their application was admittedly a matter of judgment, allowing a limited subjectivity that compromised neither scientific rationality nor scientific progress. ‘Later scientific theories,’ Kuhn insisted, ‘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.’ And those readers of Structure who had assumed otherwise were now instructed in the error of their ways.

The Structure of Scientific Revolutions was the work of an amateur. It had many of the flaws, oversights and overstatements to which amateurs are prone. Its concreteness, its aphoristic moments, and the indeterminacy of its disciplinary identity made it accessible to many. In Kuhn’s account, science remained a towering human achievement, even while he discredited the stories traditionally told about how science worked. Structure did not succeed in providing a completely convincing alternative story, but in its destruction of myth it was a triumph. Kuhn’s writings in his last years are the work of a professional. They are well referenced, well guarded against possible misunderstandings, tightly focused on a particular philosophical audience, purged of the rhetorical purple, styled to ensure their inaccessibility to the intellectually uncouth. Philosophers will eventually give their verdicts. Some will applaud Kuhn’s attempt to ground his account of science in a general theory of meaning and concept application; few, if any, will point out that this is just what was being done years ago by the sociologists of science he so despised. Others will withhold judgment on an unfinished project and take these drafts mainly as source-materials for intellectual biography. But the path from Structure to Last Writings has its own stories to tell. One is about the ambition and edginess of an individual author – brilliant, original, prickly, passionate. Another would be about the power of the disciplines as they came increasingly to control academic life and to disengage from the public sphere.