incommensurabilities in the work of thomas kuhn

Available online at www.sciencedirect.comStudies in History

www.elsevier.com/locate/shpsa

Stud. Hist. Phil. Sci. 39 (2008) 133–142

and Philosophyof Science

Incommensurabilities in the work of Thomas Kuhn

Ipek Demir

Department of Sociology, University of Leicester, University Road, Leicester LE1 7RH, UK

Received 5 May 2006; received in revised form 21 May 2007

Abstract

I distinguish between two ways in which Kuhn employs the concept of incommensurability based on for whom it presents a problem.First, I argue that Kuhn’s early work focuses on the comparison and underdetermination problems scientists encounter during revolu-tionary periods (actors’ incommensurability) whilst his later work focuses on the translation and interpretation problems analysts facewhen they engage in the representation of science from earlier periods (analysts’ incommensurability). Secondly, I offer a new interpre-tation of actors’ incommensurability. I challenge Kuhn’s account of incommensurability which is based on the compartmentalisation ofthe problems of both underdetermination and non-additivity to revolutionary periods. Through employing a finitist perspective, I dem-onstrate that in principle these are also problems scientists face during normal science. I argue that the reason why in certain circum-stances scientists have little difficulty in concurring over their judgements of scientific findings and claims while in others theydisagree needs to be explained sociologically rather than by reference to underdetermination or non-additivity. Thirdly, I claim that dis-agreements between scientists should not be couched in terms of translation or linguistic problems (aspects of analysts’ incommensura-bility), but should be understood as arising out of scientists’ differing judgments about how to take scientific inquiry further.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Thomas Kuhn; Incommensurability; Normal science; Revolutionary science; SSK; Finitism

When citing this paper, please use the full journal title Studies in History and Philosophy of Science

1. Introduction

This paper aims to provide a novel way of looking atincommensurability as described and defended in Kuhn’swork. It does this by distinguishing between two ways inwhich Kuhn employs this concept. One way Kuhn uses thisterm can be found in his earlier work, more specifically inThe structure of scientific revolutions (SSR). There, Kuhnemploys the term incommensurability in order to point

0039-3681/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.shpsa.2007.11.011

E-mail address: [email protected] As the quotation below will show, Kuhn mostly uses the category ‘historian

distinction between the two groups.

out the problems of comparison and communicationthat actors (that is, scientists) face. He discusses how,during revolutionary periods, scientists talk at cross pur-poses as a result of their disagreements over theory choice.For the remainder of this paper I will dub this form ofincommensurability ‘actors’ incommensurability’. The sec-ond use of incommensurability can be found in Kuhn’slater work where incommensurability is employed in orderto underline the various differences the analyst1 perceives

’, not ‘analyst’. I prefer to use ‘actor’ and ‘analyst’ as they better reflect the

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134 I. Demir / Stud. Hist. Phil. Sci. 39 (2008) 133–142

between scientific traditions from different periods. In par-ticular, it points to a problem that the analyst faces: theimpossibility of full translation. I will call this ‘analysts’incommensurability’.2

In the course of this article, I will bring to the fore thesetwo uses of incommensurability in Kuhn’s work. It will beseen that the incommensurability that actors and analystsface are not of the same kind, at least within the frameworkof Kuhn’s conceptualisation of them. Actors’ incommensu-rability refers to problems scientists encounter when theyare doing science and hence as they move forward intothe future; analysts’ incommensurability refers to problemsanalysts face as they interpret and translate the science ofearlier periods and hence as they move backwards intothe past. Besides enabling us to understand and unpackone of the central concepts of the Kuhnian endeavour,identifying and drawing attention to this implicit distinc-tion that exists in Kuhn’s work will also enable me to con-sider the relationship between the actors’ and analysts’incommensurability.

The distinction between actors’ and analysts’ incom-mensurability follows a historical line. Actors’ incommen-surability is discussed mainly in Kuhn’s SSR (1996[1962]) and in his two articles in Criticisms and the growth

of knowledge (1970a,b). Analysts’ incommensurability isdiscussed in Kuhn’s later work, some of which have beencompiled in The road since Structure (2000). The aim of thispresent article, however, is not just to document howKuhn’s concept of incommensurability has changed overthe years. The studies of Hoyningen-Huene and HowardSankey, for example, have traced the revisions and modifi-cations in Kuhn’s idea of incommensurability effectivelyand in detail (Hoyningen-Huene, 1990, 1993; Hoyningen-Huene & Sankey, 2001; Sankey, 1993). This present paperinstead aims to unearth the different uses of the concept ofincommensurability in Kuhn’s work based on for whom itconstitutes a problem. Rather than arguing that Kuhn’sviews about incommensurability have moderated over theyears, it will be seen that the incommensurability Kuhndefends has changed its focus. Analysts’ incommensurabil-ity, not actors’, is the focal point of Kuhn’s later work.3

The focus of this paper, however, is actors’ incommen-surability. My aim is to return to Kuhn’s original concerns,namely problems confronting working scientists. In hislater work, Kuhn offers a solution to analysts’ incommen-surability. My paper will not only highlight the solution heprovided, an aspect of his work which has received littleattention, but more importantly will demonstrate that thefocus of Kuhn’s later work, namely analysts’ incommensu-

2 Just as it turned out to be the case that for Kuhn ‘paradigm’ has twincommensurability, another important concept his work, is employed in two

3 This distinction I draw between Kuhn’s focus on actor’s incommensurabilimirrors the distinction Bird draws between Kuhn’s focus on exemplars in his e2002). The early versus later Kuhn categorisation could be further extended: Kversus his focus on theory in his later work, or his focus on history in his ear

4 All references are from Kuhn unless otherwise indicated.

rability and its resolution, are inadequate to the task ofunderstanding and explaining the disagreements and con-troversies scientists face.

2. Actors’ incommensurability

Kuhn’s use of incommensurability in his early workrefers to periods where scientists are faced with more thanone paradigm. These are the times when normal scientificactivity is interrupted. The dominant paradigm encountersanomalies which cannot be ignored and put aside. As moreand more scientists start seeing the resolution of the anom-alies as crucial for the future of their field, they devoteattention to overcoming them. During this time, the onto-logical, methodological and other commitments of the par-adigm are questioned. New and different perspectives beginto appear. Over time, one of those new perspectives gainsincreasing attention and numbers of supporters. Scientistsin the field find themselves faced with a choice: either tostay with the old paradigm and its defenders or to switchallegiance to the newly emerging paradigm. The choice isnot straightforward. There are no general, impartial, uni-versal criteria which scientists can use to resolve their differ-ences concerning the superiority of one paradigm over theother. The practitioners of the two rival paradigms disagreeabout their ‘problem fields’ and what counts as a permissi-ble solution to them. They also attribute different meaningsto some of the terms they both use. Moreover, new exem-plars (model problems and their solutions) emerge, olderones are applied in totally new and unexpected ways, sim-ilarity and dissimilarity relations are altered. The newlyemerging paradigm not only describes nature differentlybut also establishes new relationships between existingterms (1996 [1962]).4

It is for this reason that Kuhn describes the two para-digms as incommensurable: there is no common measureto which the proponents of two rival paradigms can appealin order to resolve their differences. As a consequence, theproponents of the two paradigms face communication,comparison and adjudication problems. When discussingthe superiority of their claims they ‘fail to make completecontact with each other’s viewpoints’ (ibid., p. 148). Theuse of different sets of criteria prevents comparative judg-ment and evaluation being carried out in a way that wouldcompel the scientists to change to this or that paradigm. InKuhn’s words:

the choice between competing paradigms regularlyraises questions that cannot be resolved by the criteria

o meanings (disciplinary matrix and exemplars), it will be seen thatdistinct ways.

ty in his early work and on analyst’s incommensurability in his later workarly work and his focus on philosophy of language in his later work (Bird,

uhn’s focus on the practices and activities of scientists in his early workly work versus his focus on philosophy in his later work.

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I. Demir / Stud. Hist. Phil. Sci. 39 (2008) 133–142 135

of normal science. To the extent, as significant as it isincomplete, that two scientific schools disagree aboutwhat is a problem and what a solution, they will inevita-bly talk through each other when debating the relativemerits of their respective paradigms. In the partially cir-cular arguments that regularly result, each paradigm willbe shown to satisfy more or less the criteria that it dic-tates for itself and to fall short of a few of those dictatedby its opponent. (Ibid., pp. 109–110)

Hence, according to Kuhn, incommensurability arises asa problem for scientists during revolutionary periods whenthere are two rival paradigms with no common criteria towhich to appeal. Incommensurability, however, does notimply that there is a total breakdown in communication(1970b, p. 232). Nor does it mean that there are no goodreasons for choosing a particular paradigm (ibid., p. 234).Incommensurability only implies that there are partialcommunication failures, partial comparison problems andno single good reason or set of good reasons which canunequivocally tell scientists which of the paradigms is supe-rior. For example, when considering the role cognitive val-ues such as accuracy or fruitfulness can play, Kuhn statesthat ‘they can thus be differently applied, individually andcollectively, by men who concur in honoring them’ (1996[1962], p. 199). In the case of different paradigms involvingthe same terms, Kuhn claims that the proponents ‘must beattaching some of those terms to nature differently’ (ibid.,p. 198). In the case of relative problem-solving ability, heargues that ‘paradigm debates are not really about relativeproblem-solving ability, though for good reasons they areusually couched in those terms’ (ibid., p. 157). And in thecase of being persuaded by the potential problem-solvingability of a paradigm, Kuhn tells us that a ‘decision of thatkind can only be made on faith’ (ibid., p. 158). In the caseof methodological rules and standards constraining thechoice of paradigms, Kuhn argues that disagreementscannot be terminated by invoking rules and standards.

3. Analysts’ incommensurability

The initial concept of incommensurability—the conceptpivotal in SSR—attracted a lot of criticism (see, for exam-

In SSR, Kuhn also discusses incommensurability to underline the diffommensurability to challenge the then dominant cumulative, linear and telllenge our view of the history of science and its development. Henceommensurability constitutes the main focal point of his defence of incommIrzik & Grunberg (1998) have called this ‘Kuhn’s linguistic turn’ and have tras on language and perception. Bird (2002) criticises the emphasis Kuhn, in hpractical and epistemological role exemplars play in scientific activity.While Quine argues that there is always an infinite number of ways in whicheterminacy of translation), Kuhn argues that no single full translation is poitions. It must be noted that in the ‘1969 Postscript’, Kuhn had seen translblems and theory choice: ‘Briefly put, what the participants in a communicatmunities and then become translators . . . Since translation, if pursued,

ariously something of the merits and defects of each other’s view, it is a potenseen below, he not only negates the possibility of full translation in his late

ple, Laudan, 1984; Popper, 1970; Shapere, 1971,1989; Shef-fler, 1967). In response to these criticisms, Kuhn began toelaborate and present his notion of incommensurabilityin a new way. As a consequence, Kuhn’s discussion ofincommensurability in his later work changed its focus:the untranslatability and unmappability of scientific termsacross traditions from different periods became a dominanttheme. Analysts and how they encounter translation prob-lems as they move into the past were now central to Kuhn’sanalysis of incommensurability.

Kuhn’s later work, then, shift his justification for incom-mensurability from a discussion of the communication andcomparison problems scientists face as a result of thememploying different standards and practices to a discussionof the untranslatability analysts face when engaged in therepresentation of science from earlier times.5 Emphasison philosophy of language and translation becomes a dom-inant theme in his later work.6 Kuhn argues:

The claim that two theories are incommensurable is thenthe claim that there is no language, neutral or otherwise,into which both theories, conceived as sets of sentences,can be translated without residue or loss. (2000, p. 36)

Applied to a pair of theories in the same historical line,the term [incommensurability] meant that there was nocommon language into which both could be fully trans-lated. Some statements constitutive of the older theorycould not be stated in any language adequate to expressits successor, and vice versa. Incommensurability thusequals untranslatability . . . (Ibid., p. 60)

My claim has been that key statements of an olderscience, including some that would ordinarily be consid-ered merely descriptive, cannot be rendered in thelanguage of a later science and vice versa. (Ibid., p. 55)

As these passages show, Kuhn’s arguments aboutincommensurability in his later work are centred on thenotion of untranslatability.7 More specifically, they relyon the idea that each scientific tradition uses a specific lan-guage and that translation from one to another is riddledwith problems. According to Kuhn, problems of untrans-latability occur because each scientific paradigm incorpo-rates a specific lexical structure. The meanings of the set

erences he, as a historian, sees between successive traditions. He useseological view of the development of science. In other words, he wants toanalysts’ incommensurability is also present in SSR. However, actors’ensurability in SSR.ied to explain it by making connections between Kuhn’s views and Whorf’sis later work, placed on philosophical and linguistic arguments rather than

an utterance can be translated, (never any single one and hence his idea ofssible (2000, p. 61). Hacking (1982) underlines this difference between theiration as a means through which scientists could overcome communicationion breakdown do is recognise each other as members of different languageallows the participants in a communication breakdown to experience

t tool for both persuasion and for conversion’ (1996 [1962], p. 202). As willr work, but, more importantly, ceases to consider it for actors.


of terms employed within a paradigm are interrelated. InNewtonian mechanics, for example, the terms ‘force’ and‘mass’ are interconnected. One cannot learn, explain orrepresent these terms independently of each other. Besidesthis interrelatedness of scientific terms within a given tradi-tion, Kuhn underlines a further difficulty. He suggests thatdifferent traditions sometimes attribute different meaningsto the same scientific term, thereby contributing to transla-tion problems for analysts.8 In addition, Kuhn drawsattention to the fact that different scientific paradigms havedistinct taxonomical structures. By this Kuhn means thatobjects in each paradigm are classified in a particularway. Kuhn argues that there is no overlap between classi-fication systems in different paradigms which makes fulland accurate translation and mapping impossible (ibid.,p. 92).9 According to Kuhn, not only word for word trans-lation, but any translation which aims to render ideas andstatements from an earlier science in the language of thelater science is problematic due to the holistic nature of sci-entific languages. Similarly, enriching one scientific para-digm with terms translated and borrowed from anotherparadigm is plagued by problems in that ‘the enriched lan-guage would project two incompatible images of the sameareas of the same world’ (Kuhn, 1999, p. 35).

An example Kuhn gives which illustrates all threeaspects of analysts’ incommensurability is the differencebetween the Ptolemaic system and the Copernican system.In the Ptolemaic system the term ‘planet’ refers to both theSun and the Moon. In the Copernican system the term ‘pla-net’ acquires a new meaning. The Sun becomes a star, theEarth becomes a planet like Mars and Jupiter and theMoon becomes a new sort of a body, a satellite (2000, p.15). The lexical structure and classification in both systems,as well as the meaning attributed to ‘planet’ are all differentin these two traditions. These types of fundamental differ-ences between two traditions, according to Kuhn, generateproblems when analysts attempt translation:

the content of the Copernican statement ‘planets travelaround the sun,’ cannot be expressed in a statement thatinvokes the celestial taxonomy of the Ptolemaic state-ment ‘planets travel around the earth’. The differencebetween the two statements is not simply one of fact.The term ‘planet’ appears as a kind term in both, andthe two kinds overlap in membership without either’scontaining all the celestial bodies contained in the other.

8 This is something which Kuhn argued in his earlier work and continued to de9 Kuhn draws similarities between translating scientific texts and translating liter

scientific text, whether into a foreign tongue or into a later version of the languagethan has generally been supposed. In both cases the translator repeatedly encountwhich captures them completely’ (ibid., p. 62). In this way Kuhn aims to underproblematic as in other areas where this problem is taken for granted.10 Obviously there some passages where Kuhn does talk about scientists in his late

actors’ incommensurability. Nor does he provide examples from the history of sciecommunication difficulties for scientists. His examples are based on how he, as auntranslatable, or how he, as an analyst, found it difficult to recover meanings in hfor me emerged from attempts to understand apparently nonsensical passages en

All of which is to say that there are episodes in scientificdevelopment which involve fundamental change in sometaxonomic categories and which therefore confront laterobservers [i.e. analysts] with problems like those the eth-nologist encounters when trying to break into anotherculture. (Ibid., p. 94)

Kuhn’s later work relies also on other examples ofuntranslatability. These, like the previous example, aremost often based on the analyst’s experience of movinginto the past. One of these is an old favourite of Kuhn’s,namely ‘phlogiston’. In his exchanges with Kitcher, Kuhngives the example of phlogiston to show that a replacementfor it cannot be found in modern chemistry: ‘a small groupof terms remains for which the modern chemical vocabu-lary offers no equivalent. Some have vanished from the lan-guage of chemistry entirely, ‘phlogiston’ being the presentlymost obvious example’ (ibid., p. 42). However, the problemis not only that the term ‘phlogiston’ is not ‘in use’ in mod-ern chemistry, but, more importantly, that phlogiston ispart and parcel of an altogether different scientific para-digm which imposes a different structure to the worldand produces problems of translation and representationfor analysts. This is why Kuhn argues as follows:

What I am presupposing will be suggested by the follow-ing claim: to understand some body of past scientificbelief, the historian must acquire a lexicon that hereand there differs systematically from the one current inhis own day. Only by using that older lexicon can heor she accurately render certain of the statements thatare basic to the science under scrutiny. Those statementsare not accessible by means of translation that uses thecurrent lexicon, not even if the list of words it containsis expanded by the addition of selected terms from itspredecessor. (Ibid., pp. 58–59)

What is important for my overall argument is that byfocusing on untranslatability, Kuhn moves away from hisearlier concern with communication and interactionbetween scientists (actors’ incommensurability) and insteadends up focusing on the interpretation, translation andmapping problems analysts face (analysts’ incommensura-bility). In other words, his later work change for whom

incommensurability presents a problem. The historian,not the scientist, becomes Kuhn’s ‘subject-matter’.10

Since this is central to the argument I am defending, I will

fend in his later work.ary texts: ‘I am suggesting, in short, that the problems of translating ain which it was written are far more like those of translating literatureers sentences that can be rendered in several alternative ways, none ofline the fact that translations in science are as difficult and hence as

r work, but he does not return to his original conceptualisation, namelynce where, during revolutions, translation failures cause comparison orn analyst, sees theories from different periods of science as mutuallyistorical texts. As he emphasises: ‘Incommensurability is a notion that

countered in old scientific texts’ (ibid., p. 91).


provide a few more quotes from Kuhn’s later work tounderline this:

My claim, then, has been that circumstances of this sort[incommensurability] are regularly encountered, if notalways recognized, by historians of science attemptingto understand out-of-date scientific texts. (Ibid., p. 40)

One cannot get from the old to the new simply by anaddition to what was already known. Nor can one quitedescribe the new in the vocabulary of the old or viceversa. (Ibid., p. 15)

Some statements previously descriptive of possibleworlds prove untranslatable in the terminology devel-oped for the subsequent science. These are the state-ments the historian first encounters as anomalousword strings; one cannot imagine what those whouttered or wrote them were trying to say. (Ibid., p. 76)

It is lexical change of this sort that results in the appar-ent textual anomalies with which this paper began.Encountered by a historian in a text of the past, theystrenuously resist elimination by any translation orparaphrase that uses the historian’s own lexicon, theone he or she initially brought to the text. (Ibid., p. 85)

Having underlined two aspects of Kuhn’s later concep-tualisation of incommensurability, namely his dual focuson untranslatability and analysts, I will now discuss a thirdimportant characteristic of it which is the solution Kuhnpresents to the problem of the incommensurability facedby analysts.

Kuhn’s notion of incommensurability in his later workdepends crucially on the distinction he makes betweentranslation and interpretation. As the quotes above haveshown, Kuhn argues that different scientific traditions areincommensurable in that they cannot be translated intoone another. He rejects the idea that the vocabulary andstatements of an old science can be easily represented in,or and mapped onto, the language of a new paradigm.However, although Kuhn claims that translation problems(and hence incommensurability) exist for the analysts, healso presents a solution to this problem: interpretation,rather than translation, is the method employed by analystswhen they attempt to make intelligible the science of earlierperiods. Analysts can come to learn the language of the sci-entific tradition they are studying. They can break into its

11 The use of metaphors and expressions from anthropology in his later workperception and recognition (e.g. Bruner and Postman’s card experiment) and mmove away from psychological explanations. For example, Kuhn abandons ttones and its insufficiency to represent adequately how a community (as oppofrom individuals to groups is, however, clearly metaphorical, and in this casecommunities as though they were individuals-writ-large misrepresents the procgestalt switches’ (2000, p. 88). Elsewhere, in his Foreword to Hoyningen-HuStructure the gestalt switch is repeatedly used also as a model for what happensalso noted that the use of the gestalt switch metaphor by Kuhn ‘was a categoryonly to an individual’ (Nersessian, 2003, p. 185). However, it should also be nodescribe how actors’ (scientists’) perceptions change during revolutions, expredescribing how Kuhn, or other analysts, move into the conceptual scheme of

conceptual circle. They can discover what a particular termmeans, learn its relationship to other ones as well as discernthe taxonomical categories employed in that tradition.Kuhn often refers to this process as ‘second language learn-ing’ (and at times as ‘bilingualism’) and compares it to theencounters ethnologists face ‘when trying to break intoanother culture’ (ibid., p. 94).11

Kuhn’s own account of how he came to understandAristotelian physics is a good example:

I was sitting at my desk with the text of Aristotle’s Phys-

ics open in front of me and with a four-colored pencil inmy hand. Looking up, I gazed abstractedly out the win-dow of my room—the visual image is one I still retain.Suddenly the fragments in my head sorted themselvesout in a new way, and fell into place together. My jawdropped, for all at once Aristotle seemed a very goodphysicist indeed, but of a sort I’d never dreamed possi-ble. Now I could understand why he had said whathe’d said, and what his authority had been. Statementsthat had previously seemed egregious mistakes, nowseemed at worst near misses within a powerful and gen-erally successful tradition. (Ibid., pp. 16–17)

Having grasped Aristotelian physics, Kuhn goes on todescribe it. He presents an explanation of the categoriesand terms Aristotle used. This is a perfect example ofKuhn, the analyst, extending his categories in order tounderstand the science of an earlier epoch. Rather thanattributing error and confusion to the scientists of earliertimes, he aims to understand older texts in their own terms:

A historian reading an out-of-date scientific text charac-teristically encounters passages that make no sense. Thatis an experience I have had repeatedly whether my sub-ject was an Aristotle, a Newton, a Volta, a Bohr, or aPlanck. It has been standard to ignore such passagesor to dismiss them as the products of error, ignorance,or superstition, and that response is occasionally appro-priate. More often, however, sympathetic contemplationof the troublesome passages suggests a different diagno-sis. The apparent textual anomalies are artifacts, prod-ucts of misreading. (Ibid., p. 59)

What, then, remains of analysts’ incommensurabilityonce we have second language learning and interpretationin place? It might be useful to ask whether one needs to

signals another shift in Kuhn’s thinking. Whilst psychological accounts ofetaphors (e.g. gestalt switch) play a significant role in SSR, his later work

he gestalt switch metaphor in his later work because of its individualisticsed to an individual) changes: ‘The transfer of terms like ‘‘gestalt switch”

the metaphor proves damaging . . . More important, treating groups oress of conceptual change. Communities do not have experiences, much lessene’s Reconstructing scientific revolutions (Kuhn, 1993), he states: ‘But into a group, and that use now seems to me mistaken’ (p. xiii). Nersessian hasmistake since he had applied to a community a notion that rightly appliedted that whilst the gestalt switch metaphor was used by Kuhn in order tossions and metaphors from anthropology in his later work are aimed atanother period.


retain the concept of analysts’ incommensurability at all.One could say that Kuhn should have stopped seeing inter-pretation as a ‘solution’ to the incommensurability problemanalysts face, and should instead have used second languagelearning as the way in which analysts enter into previousepochs without invoking the category of translation at all.Hence it might be said that his account of analysts’ incom-mensurability is redundant as it is not a problem: analystscan, like Kuhn, become second language learners.

However, I argue that second language learning doesnot fully remove analysts’ incommensurability. The analystcan understand both of the language schemes, but may faceproblems when it comes to representing one scheme in thelanguage of the other. This is because it may not be possi-ble to express concepts from one language in another con-ceptual scheme. In Kuhn’s words: ‘language learning, aprocess that need not, and ordinarily does not, make fulltranslation possible’ (ibid., p. 238).

This is why Kuhn deems it important to retain analysts’incommensurability:

There are things that can be said in one language thatcannot be articulated in another . . . It is not the case thata proposition true in one language (or within one para-digm) can be false in another. It is rather that someproposition which may be true (or false) in one languagecannot even be formulated in another. It is not truthvalue but effability that varies with language. (1999,p. 35)12

There are many other questions to which Kuhn’s discus-sion of analysts’ incommensurability gives rise. Most basi-cally, it might be worth examining whether Kuhn’s claimsabout the problems historians face when dealing with oldtexts are justified. Or it might be valuable to investigatethe extent to which second language learning is employedby historians. Alternatively, it might be worth researchingthe other tools historians use when faced with untranslat-able (hence incommensurable) texts. However, subjectingKuhn’s account of analysts’ incommensurability to sus-tained scrutiny is beyond the aims of this paper. Instead,I will take for granted Kuhn’s account of analysts’ incom-mensurability and explore how actors’ incommensurabilityrelates to the later Kuhn’s characterisation and resolutionof analysts’ incommensurability. Before providing thisanalysis, however, I will examine and rethink Kuhn’s char-acterisation of actors’ incommensurability.

4. Analysis of actors’ incommensurability

As I summarised earlier on, for Kuhn actors (scientists)face incommensurability during revolutionary times whenthere are rival paradigms and no universal criteria to which

12 It might be useful to think of an extreme example to understand the argumelanguage of dancers and a language of chess players. One can learn both, but wother. It is not the intelligibility of science from an earlier period that Kuhn is pof the analyst that he is underlining.

the communities can appeal in order to resolve their dis-agreement. The scientists cannot unequivocally decidewhich paradigm they should follow. The choice betweenthe two paradigms is underdetermined. The members ofthe two rival paradigms talk past one another since theyprioritise different problems and perceive different answersas acceptable solutions.

I argue that in order to analyse this form of incommen-surability we need to go back to Kuhn’s construction ofnormal science, more specifically to the demarcation crite-ria Kuhn uses in order to distinguish between normal sci-ence and revolutionary science. A better understanding ofhow evaluation and interaction during normal science arecarried out, how agreement is reached during ‘peaceful’times can enable us to rethink Kuhn’s characterisation ofcrisis periods and hence incommensurability. In order todo so, we need to challenge some aspects of Kuhn’s analy-sis of normal science. Interestingly, the source of this chal-lenge can be found not amongst the work of those who areKuhn’s familiar critics, but from the Sociology of ScientificKnowledge (SSK), a tradition which sometimes sees itselfas an heir to the Kuhnian project.

According to Kuhn, normal science is the period inwhich scientists engage in the collection of data and thearticulation of theories. During this period what is knownis extended and the paradigm is refined and expanded.Observation and measurement techniques are developedand elaborated in great detail. The construction of newproblems and their solutions within a community are car-ried out by drawing analogies with existing exemplars(i.e. problems and solutions that are available to a commu-nity). Kuhn sees such analogies, and hence the establish-ment of new similarity and dissimilarity relations, asmore or less unproblematic during normal science. Heargues that scientific work during normal science has thecharacter of puzzle-solving. The use of the term ‘puzzle’underlines not only the assured existence of a solutionbut also the relatively unproblematic nature of evaluation,assessment and validation during normal science. It is thispuzzle-solving activity which is interrupted during revolu-tions. For Kuhn, during normal science scientists areengaged mainly in ‘mopping up operations’ (1996 [1962],p. 24), focusing on the articulation of theories that the par-adigm supplies. Moreover, normal science is cumulative(ibid., p. 96; 1970b, p. 250). Research is efficient and effec-tive as disputes over how to take the next step or about fun-damental assumptions do not arise. Scientists have a firmunderstanding of which scientific results are to be devel-oped and which ones are to be abandoned and they canundertake more detailed, precise types of work.

SSK in general, and Barry Barnes’s book on Kuhn inparticular, have taken Kuhn’s identification of exemplars

nt Kuhn is putting forward. Let us assume that there are two languages, aill still face problems describing the activity of one in the language of the

roblematising; rather, it is the inability to represent it fully in the language


and his recognition of the importance of drawing similarityrelations in science as his main contributions (Barnes,1982a). However, rather than accepting the unproblematicnature of normal science, Barnes has argued that the con-struction of new puzzles and new puzzle-solutions bydrawing analogies with existing exemplars is not straight-forward even during normal science.13 The next stage inresearch, that is, how to take the inquiry further, whatkind of similarity relations to project from exemplars andhow to interpret and apply existing terms and theories tonew situations is itself an open and inventive process.Applying exemplars is much more than a ‘mopping upoperation’.

The SSK tradition’s defence of this position has come tobe known as finitism.14 Finitism argues that every term islearned on the basis of a finite number of examples andthat these examples do not determine how the term is tobe used in the next instance, rendering ‘the problem ofthe move to the next step ineradicable’ (Bloor, 1997, p.11).15 Applied to science, finitism’s proponents argue thatboth in training and in undertaking new research, scientistsmake judgements of similarity and dissimilarity using therepertoire of examples and analogies that exist in theircommunity. However, advocates of finitism stress that suchjudgements are underdetermined: nothing in the cognitiveabilities of scientists, in nature or in the rules, laws andexemplars that the paradigm provides dictates whetherthe judgment the individual scientist makes is the rightone. Rather, the acceptability and correctness of such anal-ogies and judgements are communally sanctioned. AsBarnes puts it: ‘Just as the initial paradigm is accepted as

13 Barnes argues: ‘There is one way in which the analogy [Kuhn makes] with pindependent indication of validity is available. A jigsaw, on insertion of the finathe next day’s newspaper. But a piece of normal science does not generate a canthe problem-solution is obtained is communally acceptable, then that in itself cinvention and of validation’ (Barnes, 1982a, p. 50). I argue that the analogy Kudiffers from the one held by Barnes. (See also notes 14 and 16 below).14 Finitism was inspired by Wittgenstein’s critique of meaning determinism

exposition and defence of finitism. Barnes argues that: ‘It is not clear whether KKuhn’s work, and specifically his discussion of learned similarity relations, lenunderstood in this sociologically interesting way’ (Barnes, 1982a, pp. 34–35). Innormal science is finitist’ (Barnes, 1982a, p. 84). I argue that Kuhn can be readbut not when he discusses research during normal science. Hence whilst I agreethat Kuhn has a finitist view of normal science. Kuhn does not develop a finitismakes a distinction between terms such as ‘democracy’ and ‘justice’, whichinterpretation of them), and scientific ones such as ‘element’ or ‘planet’, which15 Finitism can also be applied to scientific practices. We could say that what c

is acceptable, which phenomena are suitable candidates for observation and claalong finitist lines.16 It must be noted that the SSK tradition has not criticised Kuhn for not ha

Kuhn as a finitist (see note 14 above). Barnes’s criticisms of Kuhn have focuselink between Kuhn’s non-finitist view of normal science and his accountincommensurability is inevitable and causes thorny problems, since, accordingduring normal science.17 Historians have traced how models of ether underwent transformations.

transformed existing ether models by applying mechanical explanations. With tthe literature’ and instead ‘ether theorists tended to concentrate on a single ethnew physicists’ conception of the ether lost the pictural appeal of the early ethewater waves. Instead, in order to account for polarisation, theorists suggesttransverse undulations’ (Cantor & Hodge, 1981, pp. 49–50).

a matter of convention, so is every application of it as nor-mal science proceeds’ (Barnes, 1982a, p. 50).

When we take finitism into account, two important con-clusions which have implications for actors’ incommensu-rability can be reached. The first of these is thatevaluative differences between scientists occur even duringnormal science. The existence of established exemplarswithin a community is not sufficient to bring an end toevaluative differences or to determine the outcome ofassessment processes. In other words, there is nothing‘straightforward’ about normal science. If underdetermina-tion is an aspect of science, it is definitely an aspect of nor-mal science, not only of revolutionary science.16 Secondly,even in normal science, the meanings of terms can changewith every new application. As a term is applied in a newcontext, scientists establish new relationships between thatterm and the other terms which belong to the new context;and the meaning of the term is then modified (even if onlyslightly). Similarly, as an existing exemplar is applied to anew situation, as an observation device is used in a newway, as a model is applied to a new phenomenon, or asan existing experimental technique is used for setting upa new experiment, existing similarity relationships andclassifications are modified or transformed, the conceptualfabric and the very nature of scientific practice are re-ordered.17 This non-additive character of normal scienceneeds to be emphasised. These new puzzles, terms or exper-iments are not a mere ‘add on’. By introducing a newpuzzle (p) to paradigm (P1), for example, scientists arenot merely generating (P1 + p), but are generating newsimilarity relations and hence in effect a new paradigm

uzzles could possibly mislead. Sometimes, when a puzzle is completed, anl piece, signals its own completion; the crossword’s validity is confirmed bydidate problem-solution which is then independently validated. If the wayonstitutes grounds for accepting it. Normal science is at once a process ofhn makes with puzzles demonstrates that Kuhn’s picture of normal science

. See Barnes et al., 1996; Bloor, 1997; Kusch, 2002, 2007 for a detaileduhn himself should be characterised as a finitist. What is important is that

ds support to a finitist position, and helps us to see how knowledge can beother places Barnes is more certain: ‘The substance of Kuhn’s account of

as a finitist when he discusses training in science and revolutionary periods,with Barnes’s finitist interpretation of normal science, I disagree with himt interpretation of normal science in his later work either. For example, he

he regards as differing in their applications (i.e. he provides a finitistdo not (2000, p. 57).

ounts as a permissible solution or an experiment, which observation reportssification, or what is an appropriate classification also need be understood

ving a finitist picture of normal science. Instead its proponents have readd on the necessity of revolutions in Kuhn’s work. Actually there is a closeof revolutions and incommensurability: revolutions are necessary andto Kuhn, non-cumulative change, evaluative differences etc. do not occur

For example, it has been noted that between 1800 and 1840 scientistshe rise of mechanical ethers, ‘the diversity of subtle fluids disappeared fromer, which might perform a number of different functions’. Moreover, ‘Ther theories founded on commonplace analogies such as the flow of water ored that ether was like some strange elastic solid, which could transmit


(P2). They are choosing (P2) over (P1) which is formallyidentical with paradigm choice in revolutionary science.18

Normal science and revolutionary science are thus not onlyequally underdetermined, but both also require scientists toaccept or reject changes and to make choices.

In the light of these challenges to Kuhn’s construction ofnormal science, we can now answer the question: Whathappens to Kuhn’s actors’ incommensurability when itmeets finitism? Barnes put it thus: ‘From a finitist perspec-tive . . . incommensurable scientific paradigms constitutebut a special case of a much more far reaching problem.All the problems of translation encountered where two cul-tures, and two languages, are involved have analogues inthe case of the temporal development of a single systemof culture’ (Barnes, 1982a, p. 34). I agree with this position.The judgements called upon during revolutions are similarto those involved during normal science. There is no inde-pendent evaluation or validation process in either case. Justas revolutions involve a re-ordering of perception and prac-tice, the latter are also re-ordered during normal science.Just as the conceptual fabric or taxonomical frameworkundergoes alterations during revolutions, so it does duringnormal science. The same is the case for similarity rela-tions: they are modified during either period.

However, this is not to ignore the point that in practicescientists commonly find themselves in two distinct kindsof situations. In some circumstances scientists are able toagree on the significance of new applications, new puzzle-solving techniques and novel findings. They are able tomake routine, unproblematic and unreflective judgementsabout the adequacy or usefulness of these. In those timesthey encounter little difficulty in deciding whether to acceptor reject a novel puzzle solution in spite of the (in principle)underdetermination of such choices. They are able tochange the meaning of the terms without much controversy.In spite of the potential or existing divergences, scientistsare able to establish a socialisation and coordinationmechanism through which order is maintained, extremeevaluative differences are levelled, changes are sanctioned,and agreements, even if they are ad hoc, are reached. Undercertain circumstances, however, such changes and judge-ments do become problematic and scientists find themselvesembroiled in disagreement and controversy. The key pointwhich arises from the finitist position is that both situations,agreement and disagreement, need to be explained in essen-tially the same kind of terms, namely sociologically.19

Whilst in some cases potential or existing divergencesare resolved with relative ease, in other cases the changes

18 I would like to thank the anonymous referee for pointing this out.19 For Kuhn, on the other hand, only the closure of revolutionary periods n20 When replying to criticisms, Kuhn comes close to this position as well:

revolutionary change and suspects that I am, in any case, no longer concernedscience . . . I see the force of these positions, for my own view of revolutionarFollowing this argument, Kuhn then goes on to defend incommensurability o21 ‘A paradigm is what the members of a scientific community share, and, conv

[1962], p. 176).

and choices become a matter of contention. The sourceof both the resolution and the contention is communitydynamics and judgements rather than logical or linguisticincompatibilities. Neither can we locate the source of thecontention in underdetermination or non-additivity. As Idiscussed above, normal science and revolutionary scienceare both equally underdetermined and demand scientists toaccept or reject changes and to make choices. The finitistaccount, then, enables us to rethink the source of actors’incommensurability. It challenges the in principle distinc-tion between normal and revolutionary periods,20 whilstmaking scientists the authors of the in practice distinctionbetween normal and revolutionary periods and hence thesource of incommensurability. This re-characterisation ofactors’ incommensurability not only shifts the source ofincommensurability from linguistic differences to commu-nity judgements and dynamics, but also fits well withKuhn’s communitarian insights. Just as Kuhn resorts tothe ‘community’ when he discusses paradigms,21 we willneed to resort to the ‘community’ in question, how it per-ceives the change and how it reaches judgements whenwe, as analysts, are identifying and explaining actors’incommensurability.

5. The differences between actors’ incommensurability and

analysts’ incommensurability

I will now examine the pragmatic as well as analyticaldifferences between the two types of incommensurabilityin more detail. Identifying these differences may alert usto the problem of imposing the challenges analysts faceonto the actors. More specifically, Kuhn might inadver-tently make us aware of the fact that analysts and actorsare not only faced with different problems, but also eachtype of incommensurability requires different kinds ofexpertise and skills to resolve them. Analysts’ discoveryof the past is not necessarily the same as actors’ progressinto the future.

The first issue to consider is that whilst the analyst is anoutsider, the scientist is a participant. Problems confront-ing working scientists arise out of the difficulty of decidingwhich way to take the inquiry further rather than being amatter of linguistic representation. The paradigm involvesa great deal of practical and often tacit knowledge thatthe scientist has acquired. It also requires a commitmentto the community which defends the paradigm. These inturn have social dimensions, such as the formation ofgroup loyalties, the creation and safeguarding of bound-

eeded to be understood sociologically.‘Kitcher thinks incommensurability is too common to be a criterion ofto distinguish sharply between normal and revolutionary development iny change has increasingly moderated, as Kitcher supposes’ (2000, p. 56).n the basis of translation problems analysts face.ersely, a scientific community consists of men who share a paradigm’ (1996


aries or the maintenance of shared norms and conventions.None of these apply to the analyst who approaches pastand present scientific cultures as an outsider. For the ana-lyst, as described by Kuhn, the problem is indeed one oftranslation and representation. The analyst is mainlyconcerned with representing the paradigm, rather thanevaluating its puzzle-solving potential. The focus istherefore on the linguistic aspects of that paradigm. Theanalyst needs to communicate unfamiliar paradigms interms that make sense to his or her readers. He or she doesnot have an investment in, or social bonds with, the com-munity and the paradigm in a way that the actor does.Explaining and finding a replacement for ‘phlogiston’ inmodern chemistry (analysts’ incommensurability) is analtogether different problem to the one Priestley and Lavoi-sier faced at the height of their disagreements (actors’incommensurability).22

The second issue is that the historian’s discovery of revo-lutions may be different to the way in which actors experiencerevolutions. In Kuhn’s writings it is possible to find two char-acterisations of revolutions: at times Kuhn has a process-based, transformation or reorientation-centred descriptionof revolutions (e.g. 1996 [1962], pp. 156–158).23 At othertimes, he shrinks this process and presents revolutions as asudden transformative act (e.g. ibid., pp. 111–112, 150).24 Iwould suggest that the reorientation model represents scien-tists’ experiences, whereas the latter approach is based on theanalysts’ discovery of the past. The two should not be con-flated. Kuhn in his later work recognised this:

In recent years I have increasingly recognised that myconception of the process by which scientists move for-ward has been too closely modeled on my experiencewith the process by which historians move into the past.(2000, p. 87)25

It follows that the historian, at least, does experiencerevolutions . . . Whether scientists, moving through timein a direction opposite to the historian’s, also experiencerevolutions is left open by what I have so far said. If theydo, their shifts in gestalt will ordinarily be smaller thanthe historian’s, for what the latter experiences as a singlerevolutionary change will usually have been spread overa number of such changes during the development of thesciences. (Ibid., pp. 56–57)

Historians, working backward, regularly experience as asingle conceptual shift a transposition for which thedevelopmental process required a series of stages . . .To speak, as I repeatedly have, of a community’s under-going a gestalt switch [which is the metaphor Kuhn usedto describe change during revolutions] is to compress an

22 See McEvoy (1988) for a detailed exposition of this debate which highlights23 Elsewhere, Kuhn puts forward an argument against the unitary, instant-lik24 For a criticism of Kuhn’s block periodisation of scientific traditions, see Ga

that Kuhn focused more on structures and patterns and less on processes. In histhe Chemical Revolution as a radical break with the past and provides an acc25 He then has a footnote which cites his ‘What are scientific revolutions?’ ar

extended process of change into an instant, leaving noroom for the microprocesses by which the change isachieved. (Ibid., p. 88)

In his later work, then, Kuhn recognises the differencesbetween actors’ and analysts’ experiences of revolutions.When considering these differences, we must remember thatrevolutionary periods for scientists are not times when twofully fledged traditions conflict with each other. Most ofthe members of the newly emerging paradigm will have been,until shortly before the conflict emerges, members of the par-adigm they are opposing. The scientists they disagree withare their colleagues, their previous partners in research withwhom they shared similar understandings. Conflict duringrevolutions, is about how to reorient research, not betweenthe members of two alien world-views which have recentlymet. This is why disagreements between scientists shouldnot be couched in terms of translation, representation or lin-guistic problems (which are aspects of analysts’ incommen-surability), but should be understood as arising out of thedifficulty of judging and deciding which way to take scientificinquiry further. Neither should disagreements be formulatedas failures of communication. If communication problemsemerge between scientists, these are more likely to be a con-sequence of the different priorities and opinions scientistshold rather than problems of a linguistic or semantic nature.

The third issue to consider is whether or not second lan-guage learning, a method Kuhn presents for analysts, canbe employed by scientists in order to resolve incommensura-bility during revolutions. Can second language learningovercome the incommensurability scientists face? It shouldbe noted that Kuhn considered second language learning asunsuitable for scientists. When replying to Jed Buchwald’spaper (Buchwald, 1993) which assesses this possibility,Kuhn states that although second language learning is ‘vitalto historians, scientists themselves seldom or never use it’(2000, p. 238). I think Kuhn was wrong to reject second lan-guage learning for scientists tout court. As he himself else-where states: ‘Members of one community can acquire thetaxonomy employed by members of another, as the histori-an does in learning to understand old texts’ (ibid., p. 93).However, Kuhn was right not to propose it as a solutionto actors’ incommensurability. This is because, even thoughscientists can understand each other during revolutionaryperiods, they may disagree with each other’s propositionsabout how to resolve the anomaly or how to take theinquiry further. Although understanding the other is a pre-condition for resolving disagreements between conflictingparties in a cordial manner, it is not a sufficient criterionfor ending them. Hence, however successfully Kuhn’s sec-ond language learning may present a solution to analysts’

areas of both agreement and disagreement between Lavoisier and Priestley.e presentation of scientific discovery (1977, pp. 165–177).lison (1997), pp. 13–17 and p. 790. O’Malley & Boucher (2005) also argueanalysis, McEvoy (1988) challenges Kuhn’s (and others’) interpretation ofount which reveals both continuity and discontinuity.ticle as an example.


incommensurability, it is inadequate to the task of under-standing and explaining controversies scientists face.

6. Conclusion

In this paper, I have distinguished between two types ofincommensurability in Kuhn’s work based on for whom itpresents a problem. I argued that whilst the early Kuhnfocuses on comparison and communication problemsbetween actors during revolutionary times, the later Kuhnemploys incommensurability in order to underline thetranslation and interpretation problems analysts face asthey attempt to represent science from earlier periods.Besides enabling me to decode incommensurability, a cen-tral aspect of the Kuhnian trajectory, underlining thisimplicit difference between actors’ and analysts’ incommen-surability allowed me to go back to Kuhn’s original con-cerns, namely the problems confronting scientists. Ichallenged Kuhn’s account of normal science. Throughadopting a finitist approach, I argued that normal scienceand revolutionary science are both equally underdeter-mined and demand that scientists accept or reject changesand make choices. Instead, I located both the source ofagreement and incommensurability in community judge-ments and dynamics. Finally, I discussed the differencesbetween actors’ and analysts’ incommensurability in detail.I demonstrated that the focus of Kuhn’s later work, namelyanalysts’ incommensurability and its resolution, are inade-quate to the task of understanding and explaining the dis-agreements and controversies scientists face.

Acknowledgements

I would like to thank Martin Kusch for many insightfulcomments and discussions. I am also grateful to JohnHolmwood, Steven Kemp, John McEvoy, MaureenO’Malley, Simon Schaffer, Mark Wilkinson and the twoanonymous referees for their helpful suggestions. Iacknowledge the ESRC Postdoctoral Fellowship schemefor financial support and the Department of History andPhilosophy of Science (HPS), Cambridge for providinginstitutional support during my fellowship.

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