ISBN 0-7923-6989-0
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ISBN 0-7923-6989-0
Published by Kluwer Academic Publishers, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. Sold and distributed in North, Central and South America by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers, P.O. Box 322, 3300 AH Dordrecht, The Netherlands.
Printed on acid-free paper
All Rights Reserved © 2001 Kluwer Academic Publishers No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. Printed in the Netherlands.
HOWARD SANKEY /PAULHOYNINGEN-HUENE
INTRODUCTION
1. THE INCOMMENSURABILITY THESIS The aim of this book is to assess the merits and current fortunes of one of the most controversial theses to emerge in the philosophy of science during the latter half of the twentieth century. This is the thesis ofthe incommensurability ofscientific theories. The controversy about incommensurability dates to the year 1962, the year in which the thesis of incommensurability was first explicitly proposed by its two chief advocates, Paul Feyerabend and Thomas Kuhn. It is convenient to treat the year 1962 as the year in which the incommensurability thesis first emerged because that is when the thesis was first asserted in print by Feyerabend and Kuhn. Feyerabend originally claimed that some successive theories may be incommensurable in his paper "Explanation, Reduction and Empiricism" (1962).1 The claim was made in the course of his critique of the reductionist account of the relations between scientific theories proposed by logical empiricism. Kuhn ascribed a central role to incommensurability in his theory of the development of science as a sequence ofrevolutionary transitions between scientific paradigms, which he presented in his classic work The Structure ofScientific Revolutions (1962). 2 It is, however, something of an oversimplification to take 1962 as the year in which the incommensurability thesis first emerged. For, in proposing the idea ofincommensurability, Kuhn and Feyerabend were drawing on earlier developments in the philosophy and history of science, as well as in philosophy at large. In n1any respects, the incommensurability thesis is a product of the philosophical climate of the late 1950's and early 1960's. This was a tin1e that saw the rise of the professional discipline of the history of science, the influence of Gestalt psychology on the philosophy ofperception, the decline of the logical positivism of the Vienna Circle, the widespread influence of the later Wittgenstein and Quine's attack on the analytic/synthetic distinction. Apart from being a product of its time, the incommensurability thesis is also one of the characteristic claims of a new moven1ent in the philosophy of science that began to emerge in the late 1950's and early 1960's. Together with the thesis of the theorydependence of observation, the rejection of a fixed scientific method, and insistence on the importance ofthe history of science to the philosophy of science, the incommensurability thesis is one of the leading claims of what came to be known as the postpositivist or historical philosophy ofscience. In addition to Kuhn and Feyerabend, other initial participants in this movement also included such figures as Norwood Russell Hanson, Michael Polanyi and Stephen Toulmin. 3 vii P. Hoyningen-Huene and H. Sankey (eds.). Incommensurability and Related Matters, vii-xxxiv. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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HOWARD SANKEY / PAUL HOYNINGEN-HUENE
2. WHAT IS INCOMMENSURABILITY? Before turning to the thesis of incommensurability, a word of caution is in order with regard to the concept of incommensurability itself. Productive discussion of the incommensurability thesis may at times be impeded by lack of consistent use or clear meaning ofthe term 'incommensurability'. The term has a standard use in mathematics, where it implies the absence of a common unit of measurement. To say that two n1agnitudes are incommensurable is to say that there is no common unit of measurement, whole units of which may be used to measure both magnitudes. But application ofthe n1athematical concept to the case of alternative scientific theories is an extension of the concept that leaves considerable scope for alternative interpretations. Discussion of the incommensurability of scientific theories rarely proceeds in accordance with the mathematical concept of incommensurability. Instead, discussion of incommensurability tends to be framed in terms of a range of concepts and considerations of a broadly semantic and episten1010gical nature. The discussion is frequently couched, for example, in terms of such factors as the incomparability of the content of scientific theories, variation in the meaning of scientific terms, translation failure between the vocabulary of theories, or absence of common standards of theory appraisal. This raises the question of the relationship between the concept of incommensurability in the strict sense of lack of a common Ineasure, and the various other claims which have framed the discussion ofthe incommensurability thesis. Is the incommensurability of scientific theories some single, unified relation between theories, ofwhich the various associated factors constitute mere aspects or component parts? Or is it instead the case that there are a number of different things, such as the incolnparability of the content of theories, or lack of shared evaluative standards, which are each a source of incommensurability in their own right? To answer this question one way or the other is already to take a side in the dispute. The question of how to apply the concept of incommensurability in the present context is itself one of the questions at stake. Some parties to the dispute take incommensurability to be a relation that may obtain in its own right between theories, of which such things as meaning variance and lack of shared evaluative standards are mere aspects or constitutive parts. In contrast, other parties to the dispute treat the claim of incommensurability as consisting entirely in one or another of the various claims associated with talk of incommensurability, such as the claim that the content of alternative theories is unable to be compared due to meaning variance ofthe terms employed by the theories. Given such potential variation in use, it is important to bear in mind that not all parties to the dispute may understand the concept of incomn1ensurability in the same way. 4 3. ARE THERE DIFFERENT FORMS OF INCOMMENSURABILITY? Let us now turn to the thesis of incommensurability. If one takes an overview of the critical literature concenled with the incommensurability thesis, it can hardly escape notice that this literature contains a variety of separate discussions that are conducted in quite different terms. Some authors write about the topic of meaning variance and
INTRODUCTION
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content comparison. Some write about conceptual change and the intelligibility of alternative conceptual schemes. Others write about scientific realism and the continuity of reference of theoretical terms. And still others are concerned with the rationality of scientific theory choice, and the availability ofobjective standards oftheory evaluation. The need to address a variety of issues under the heading of incommensurability owes much to the original discussion by Kuhn and Feyerabend. In his original discussion of the topic in "Explanation, Reductiol). and Empiricism", Feyerabend took incommensurability to consist in absence of logical relations due to selnantic variance of the terms used by theories, resulting in the inability to directly compare the content of theories (1981d, pp. 62-69, 92-93). By contrast, in The Structure of Scientific Revolutions, Kuhn treated incommensurability as a multi-dimensional relationship between paradigms, which involves methodological, semantic and perceptual COlTIponents (Kuhn, 1970a, pp. 148-150). According to Kuhn, paradign1s employ diverse standards of theory appraisal, and address different sets of scientific problems. The vocabulary employed by scientists changes meaning in the transition between paradigms. Scientists in rival paradigms perceive the world differently. Perhaps they even inhabit different worlds. With so many then1es already present in Kuhn's and Feyerabend's original discussion, it is no wonder that a host of issues emerged when other philosophers turned to the topic. To impose order on the discussion, we will introduce a distinction between two versions of the incommensurability thesis. The first version, \vhich we will call the semantic incommensurability thesis, is the thesis that alternative scientific theories may be incornn1ensurable due to semantic variance of the tem1S employed by theories. The second version, which we will call the methodological incommensurability thesis, is the thesis that alternative scientific theories may be incommensurable due to absence of common standards oftheory appraisal. We will now sketch the main developments that have taken place in connection with each of these two versions of the incommensurability thesis. 4. SEMANTIC INCOMMENSURABILITY The thesis of semantic incommensurability derives from the claim of Kuhn and Feyerabend that the meaning of the tenns employed by theories varies with theoretical context. Both authors reject the empiricist idea ofan independently meaningful, theoryneutral observation language. Instead, they claim that the n1eaning of the term.s employed by scientific theories depends on the theoretical context in which the vocabulary is employed. Given the contextual nature of meaning, the meaning of scientific terms is subject to variation with the theory in which they occur. 5 The thesis of meaning variance gives rise to the thesis of semantic incollID1ensurability in the following way. Because the meaning of the terms employed by scientific theories varies with theoretical context, the vocabulary ofsuch theories may fail to share common meaning. But if theories are unable to be expressed by means of a common vocabulary, the content ofsuch theories cannot be directly compared. For in the absence of a shared, semantically neutral vocabulary, it is impossible for statements about the world asserted by one theory to either assert or deny the same thing as any statement made by the other theory.6 Theories which are unable in this way either to agree or
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HOWARD SANKEY / PAUL HOYNINGEN-HUENE
disagree with respect to any claim about the world are incommensurable in the sense that their content is unable to be directly compared due to semantic variance. For simplicity, we have formulated the thesis of semantic incommensurability in terms of radical meaning variance which applies to the entirety of the terms employed by a theory. However, a more limited version of the thesis may also be formulated in tem1S of partial meaning variance restricted to a limited portion of the vocabulary employed by theories. The radical version of the meaning variance thesis tends to be associated with Feyerabend, whereas the partial meaning variance thesis tends to be associated with Kuhn. 7 Response to the sen1antic inconm1ensurability thesis divides into two main lines of criticism. On the one hand, advocates ofwhat vve \vill call the referential response argue that there are relations of co-reference between the terms of n1eaning variant theories which suffice for content comparison. On the other hand, advocates ofwhat we will call the translational response argue that the idea of an untranslatable language, to which the n1eaning variance thesis gives rise, is an idea of which no coherent sense can be made. We will first discuss the referential response to semantic incommensurability. The referential response was presented by Israel Scheffler in his 1967 book, Science and Subjectivity. Employing a Fregean distinction between sense and reference, Scheffler pointed out that, even if the sense of a scientific tem1 varies with theory, it does not follow that the reference of the term also varies with theory. Terms n1ay corefer but differ in sense. Hence terms may retain stable reference despite variation in sense. But if terms employed by theories preserve reference through variation of sense, it remains possibIe to compare the theories with respect to content. For statements which theories make about the world may agree or disagree with respect to common states of affairs, provided only that their constituent terms refer to the same things, despite variation of sense. 8 But Scheffler's point that reference need not co-vary with sense was not enough to settle the issue. On the one hand, there are a nUluber of historical cases in which different theories seem to employ the same terms to refer to different things. On the other hand, the existence ofradical conceptual change in science suggests that there has been widespread discontinuity of reference in the history of science, since radical conceptual change seen1S to imply variation ofreference. Thus, while common reference may well suffice for the comparability ofcontent, it remains to be shown how continuity of reference may be sustained in the transition between meaning variant theories. 9 Rather than settle the issue, therefore, Scheffler's appeal to reference serves merely to shift the focus to the issue of reference. For it raises the question of how terms which occur in different theories may preserve reference through variation in the conceptual content which theories associate with them. More specifically, it raises the question of the determination ofthe reference of the terms that are employed by scientific theories. Where Scheffler formulated the referential response in terms of a Fregean theory of reference, the subsequent emergence of the causal theory of reference seemed to offer a promising resolution ofthe issue. It was suggested by such authors as Saul Kripke and Hilary Putnam that reference is determined in a direct manner by means of causal relations between speaker and object, rather than by the descriptive content which speakers associate with the terms they employ (cf. Kripke, 1980; Putnan1, 1975b;
INTRODUCTION
xi
1975c). On such a view, reference is fixed at the initial introduction of a tern1, and the reference of later use of the tern1 traces back by a historical chain to its original use. Because reference is determined independently of descriptive content, the reference of tern1S employed by scientific theories may be preserved despite variation in the concepts associated with such temlS. But if reference remains stable through variation of conceptual content, no problem of theory comparison arises, since reference is preserved even though terms may be associated with divergent conceptual content in the context of alternative theories. So simple a resolution of the issue was, of course, too good to be true. There are several difficulties facing the causal theory which prevent employing it in unmodified form to sustain the referential response. First, it is implausible to suppose that reference is permanently fixed at the initial introduction ofa term, since this excludes in principle the possibility of change ofreference in the history of science (cf. Fine, 1975). Second, if the reference of natural kind terms is fixed by entirely non-descriptive means - e.g., by ostension of samples of a kind - then it is impossible to secure unambiguous reference to a specific natural kind as opposed to the numerous other kinds instantiated by the sample set. This is the so-called qua problem, since the problem is how to pick out an object qua Inember of a given kind (cf. Papineau, 1979; Devitt and Sterelny, 1999; Sterelny, 1983). Third, if the reference of theoretical terms is determined by specification of a causal relation between observed phenomena and the entities responsible for the phenon1ena, then it would be impossible for theoretical tern1S ever to fail to refer. Yet failure of reference would appear to be a routine occurrence in the history of science (cf. En
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NANCY J. NERSESSIAN
resentation of a concept proposed in cognitive science that accommodated these findings. The n1eaning schema was my attempt to construct a form ofrepresentation that could capture these cognitive-historical findings plus my claim that concepts are embedded in problem situations and connected through reasoning. It is a frame-like structure that captures the salient components of a scientific concept central to its descriptive and explanatory functions within a problem situation. The Ineaning schema encompasses theoretical principles and exhibits the fan1ily resemblances over their various historical instantiations (token). An instantiation of concept at a given time is represented by four components: 'ontological status', 'function', 'mathematical structure', and 'causal power'. The components of successive concepts are connected via "chains of reasoning" along both the vertical and horizontal dimensions ofthe schema. Figure 2 provides an outline of a meaning schema for four historical tokens of the concept 'electromagnetic field'. The causal power feature ofa concept marks out the problem situations in which the referent of a concept comes into use in order to explain the situation (i.e. the situations that the concept is used to explain). Note that this dimension captures the cumulative nature of experimental situations Theodore Arabatzis (Arabatzis, 1999) has argued determines whether there is referential stability or not. The mathematical structure corresponds to the laws associated with a group of similar problem situations. Once Maxwell had constructed the field equations, they remained relatively stable in the, form reformulated by Hertz, but their interpretation changed significantly. The function of a concept marks out a specific part of problem situation in which a concept plays an explanatory role and clarifies that role. Here the function is new for physics - nothing had played the role of transmitting action in space where there is no "ordinary" matter before. The ontological status of a concept represents a belief about what kind of "stuff' is responsible for this particular function. For example, corresponding to the function of transmitting the electric action is a state of a mechanical aether in the Maxwellian representation and a state of space in the Einsteinian. In the Lorentzian and Einsteinian representations, charge corresponds to a particle (electron). However, in the Faradayan and Maxwellian representations charge has the ontological status of a state of stress in the medium. For Faraday, it is a state of stress in the lines of force; for Maxwell, a state of stress in the n1echanical aether. Each con1ponent ofthe meaning schema is connected with subsequent forms through the "chains ofreasoning" (COR connections) (see Shapere, this volume) leading to that change. This provides a dimension beyond that offamily resemblances for determining whether there is continuous but non-cumulative development in a specific case. So, for exan1ple, the preferred ontological status of the electromagnetic field in the Faradayan representation is a substance (force in a region of space). In the Maxwellian representation, forces in regions of space are produced in an underlying mechanical medium, the aether. But Faraday's lines offorce become specific configurations ofMaxwell's mechanical aether, so there is continuity between the concept representations. Lorentz's goal of incorporating charged particles into the laws of the electromagnetic field constrains the aether to be non-mechanical, which in tum requires the introduction of the Lorentz force for field-particle interactions into the Maxwellian mathematical structure. Finally, the ontological change introduced by Einstein stems from reasoning that there is no
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