theory change, structural realism, and the relativised a priori

7/28/2019 Theory Change, Structural Realism, and the Relativised a Priori

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International Studies in the Philosophy of Science

Vol. 22, No. 1, March 2008, pp. 520

Theory Change, Structural Realism,and the RelativisedA Priori

Dan McArthurTaylorandFrancisCISP_A_328253.sgm10.1080/02698590802280860InternationalStudiesin thePhilosophyof Science0269-8595 (print)/1469-9281 (online)OriginalArticle2008OpenSocietyFoundation221000000March2008Prof.DanM [email protected] ;daniel.mcarth [email protected]

In this paper I claim that Quinean naturalist accounts of science, that deny that there are

anya priori statements in scientific frameworks, cannot account for the foundational role

of certain classes of statements in scientific practice. In this I follow Michael Friedman who

claims that certain a priori statements must be presupposed in order to formulate empirical

hypotheses. I also show that Friedmans account, in spite of his claims to the contrary, is

compatible with a type of non-Quinean naturalism that I sketch. Finally I also show that

Friedmans account needs amending because it cannot provide a rational account of theory

change. I accomplish this by arguing for a structural realist view of theory change. I show

how this view fits well with an account like Friedmans and helps it deal with the problem

of theory change and in retaining its superiority over Quinean naturalism.

1. Introduction

In this paper I argue for the superiority of Friedmans account of the role of the a priori

in science over so-called naturalist views, specifically those holistic naturalist views

that take all the statements of science to be empirical. However, I also contend that

Friedmans view is not trouble free. Specifically, I claim that in spite of its utility in

characterising the role ofa priori statements, it cannot fully address the question of the

rationality of theory change, a problem Friedman shares with Kuhn. I thus amendFriedmans view in order to retain its advantages while avoiding its difficulties with

theory change. This will be done by arguing for the compatibility of Friedmans view

with structural realism which offers a more promising way of looking at theory change.

I will also show, in spite of Friedmans anti-naturalistic leanings, that this amended

version of Friedmans account is compatible with certain non-holistic versions of

naturalism. I outline the form that this argument will take and make it clear exactly

what I mean by holistic and non-holistic naturalism below.

Dan McArthur is at the Department of Philosophy, York University. Correspondence to: Department of Philoso-

phy, York University, 625 Atkinson Building, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada. E-mail:[email protected] and [email protected]


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6 D. McArthur

The term naturalism is used very broadly and has been used to describe any position

that takes philosophy and science to be in some sense continuous. Nevertheless, the

term is usually used in a narrower sense, i.e. to describe those views motivated in large

measure by the linguistic holism of Quine. Such a position informs some characteristic

naturalistic views such as those of Laudan (1990, 1996), Rouse (2002) or Cartwright(1999). All these views deny that certain classes of statements are presupposed or are a

priori in any sense. However, a closer look at scientific practice reveals serious short-

comings in holistic naturalisms ability to account for scientific practice, specifically the

role ofa priori knowledge. Nevertheless, following some recent arguments by Stump

and others I will argue that a form of naturalism, conceived broadly, can accommodate

a robust role for a priori knowledge that is compatible with Friedmans recent work on

the role of the a priori in science.

After sketching the outline of this wider sort of naturalism, I will take on the question

of the rationality of theory change. This question of course has long plagued accountsof comprehensive theory change and any plausible view must be able to account for

such change. I will show that Friedmans proposed solution, that theory change is a

communicatively rational process, cannot adequately avoid charges of irrationalism. In

the last sections of the paper, I will nevertheless argue that this weakness does not

require abandoning a role for the a priori in scientific frameworks in favour of a return

to holistic naturalism. I will defend this claim by showing that a structural realist

attitude to theory change is both compatible with a position like Friedmans and that it

can help us reformulate an account of framework change that can avoid the charges of

irrationalism that plague Friedmans view.

2. The RelativisedA Priori

As I just noted, most recent naturalists find their inspiration in Quines linguistic holism.

For Quine, the rejection of the analytic/synthetic distinction leaves us a picture of science

where all the propositions of science face the tribunal of experience as a corporate body.

That is, no body of statements can be a priori, or can have a purely philosophical justi-

fication. In fact, no qualitative difference exists between any of the statements of science

(in the last analysis) since they are all, at least in principle, refutable by experience. This

includes the propositions of logic and mathematics too, since these can be rejected giveninconsistency with experience. In practice of course some statements are reserved from

refuting evidence, but for Quine and his contemporary followers this is just the result

of psychological commitment, not because of any feature of the statement.

This sort of linguistic holism motivates a robust naturalism. After all, if every state-

ment is, at the end of the day, empirical, then philosophy just becomes a part of science

and the two can be seen as part of the same enterprise. However, appealing as the view

is, recently some commentators such as Friedman (1997, 1999, 2001), Tsou (2003) and

myself (2005) have moved away from this view because of its inability to capture certain

features of scientific theories and the particular roles that certain statements play within

them. The question that motivates critics of holism is not whether or not psychologicalcommitment accounts for the differences between statements in a framework.


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International Studies in the Philosophy of Science 7

Very briefly, according to Friedman, certain statements within scientific frameworks

in fact enjoy something other than strong psychological commitment. These particular

statements must be assumed in order to interpret the other statements in the frame-

work. Such statements operate in an a priori fashion since they need to be presupposed

in order to formulate empirical hypotheses in the first place. Moreover they need to beassumed so that an interpretation can be made of observations so that their consistency

with hypotheses can be determined. For Friedman such a priori statements can be

identified in contemporary physical theory. When sciences like mathematical physics

are considered, this a priori component is easy to identify. As Friedman observes, The

mathematical background of Einsteins theory functions as a necessary presupposition

of that theory, as a means of representation or a language without which the theory

could not even be constituted or envisioned in the first place (Friedman 1997, 12).

This a priori mathematical background forms a basis of a framework that coordi-

nates empirical laws with observations and tests. This mathematical background doesnot face the tribunal of experience on the same footing as empirical generalisations or

observation statements. In fact, this background is a necessarya priori presupposition

needed to formulate the empirical generalisations in the first place. Nevertheless,

Friedman is not returning to a position exactly like Carnaps even though the kinship

between the two is obvious. Friedman argues for a relativised conception of the a priori

that does not require an analytic/synthetic distinction that is defined outside of the

framework in the way that Carnaps notion does. For Carnap a priori statements are

only revised in a new formal language. Friedman does not attempt to formally define a

universal scientific meta-language. This is so because Friedman holds that the

constitutive principles are not unrevisable, they represent a relativised a priori thatdiffers between theoretical frameworks and examples abound in the history of physics

(cf. Friedman 2001, 3539).

According to Friedman, for example, Euclidean geometry functions as the basis of a

mathematical framework that permits empirical generalisations such as the law of

universal gravitation. Euclidean geometry coordinates the mathematical structure of

Newtonian physics with experience. It is true of course that classical absolute space, and

eventually even Euclidean geometry was replaced by the new mathematical basis of

relativistic physics. Thus, the a priori framework for classical physics was eventually

revised. But rejecting the basic assumptions of classical physics meant adopting acompletely new framework, special relativity, with its wholly new and different

relativised constitutive a priori principles. In the framework of special relativity, for

example, empirical theories such as Maxwells equations presuppose Euclidean spatial

geometry, Lorentzian mechanics and Minkowski space-time, which together play the a

priori constitutive role. We witness a similar framework change again in the shift to

general relativity. In general relativity the constitutive role is played by the manifold

conception of the structure of space-time that admits a Reimannian metrical structure,

which the theory identifies from the distribution of energy and mass (cf. Friedman

2001, 7980).

This view can be extended to contemporary fundamental physical theories as well.For example, in standard model particle physics all possible decays and interactions


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8 D. McArthur

are governed by a small set of conservation laws. Empirical hypotheses about the

results of a decay or a collision presuppose these laws. In these cases, what makes

conservation laws take on their a priori role is not the degree of psychological commit-

ment that they enjoy but their particular role in the scientific framework. They must be

presupposed in order for the rest of the framework to be deployed empirically. If sucha picture is at all accurate, then there is more to say about the nature and structure of

scientific frameworks that Quinean naturalism can accommodate.

If Friedmans view is correct, then it represents a serious problem for Quinean

holism. The central feature of the position is its rejection of the Quinean claim that the

parts of a scientific framework cannot be differentiated. Specifically, and most impor-

tantly it represents a rejection of the claim that, within a framework, every statement is

empirical, including those of mathematics or logic. The specific feature of the view that

makes it different from holism is that, within a framework, certain statements can be

identified as having a functionallya priori role. This need not imply, as Kants viewdoes for example, that there exist classes of statements that are immune from revision,

or that basic framework assumptions such as those of logic and mathematics are never

in any sense revisable on the basis of experience. The view also need not imply a

complete rejection of philosophical naturalism, just the particular variety associated

with Quinean holism.

Naturalism, recall, in the broadest sense is simply the view that science and philoso-

phy are continuous and that science need not be held accountable to extra scientific

restrictions imposed by philosophical fiat. If one agrees that within science one finds a

robust role for constitutive a priori principles, relativised to their frameworks though

they might be, one can agree that some statements can have a priori basis and still be anaturalist. Although Friedman does not consider himself to be a naturalist, Stump

(2003) has recently argued for such a position.

For Stump, a position that is naturalist, fallibilist and empiricist can in fact recognise

a role for a functionally a priori component in science. This is so because many of

Quines main arguments against traditional accounts of the a priori do not hold against

a fully relativised and functional account of the a priori such as Friedmans. This is so

because for any scientific framework in question, scientific theory determines what

statements are to be taken as a priori. The designation is not made by some theory of

language or meaning that applies to all frameworks. Moreover, the functional a prioridoes not require that some aspects of knowledge remain permanently untestable, only

that some aspects of a scientific theory be accepted conditionally (Stump 2003, 1157).

Thus, the sort of functional account of the a priori such as the sort advocated by Stump

or Friedman can even admit the proposition that mathematics and logic are in some

sense empirical. But, this is only so in the extremely tenuous sense that the general

theory that classified them as a priori is itself an empirical theory (Stump 2003, 1158).

3. Communicative Rationality, Relativism and Theory Change

If we regard the a priori concepts found in science as a relativised a priori as Stump andFriedman suggest, a fairly congenial compromise position emerges. Although Friedman


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(unlike Stump) does not see his view as any sort of compromise with naturalism, by

adopting his view of the a priori we need not wholly abandon all aspects of philosophical

naturalism, just the strong account of holism that we find in Quine and his followers.

Nevertheless, Friedman and Stumps view of the a priori has its difficulties. One

consequence of adopting such a position is accepting the clear kinship it has withKuhns account of theory change. Both views accept that scientific concepts are inter-

preted relative to basic framework assumptions, the relativised a priori in Friedmans

case. Likewise, it immediately demands of its adherents an answer to a classic objection

to Kuhns view, specifically, how can theory change be considered to be rational? This

is a pressing difficulty for Kuhn given his well-known claim that rationality is internal

to the paradigm, or framework, and his claim that paradigms are incommensurable.

Thus, in spite of his many attempts to distance himself from the sort of conceptual

relativism latent in his internalist view, Kuhn never provides a clear answer to the

charge that theory change is, on his account, irrational. Thus, in what remains of thispaper, I will address Friedmans attempt at providing a non-irrationalist account of

framework change.

Stump and Freidman of course are not univocal in their views about the relativised

a priori. Stump for example has very little to say about the rationality of theory

change. His general view in fact seems to be that framework rejection is in the last

analysis empirical. For him frameworks are replaced along with their relativised a

priori assumptions when the framework in general becomes empirically unsuccessful.

Friedman on the other hand sees the picture as quite a bit more complicated and in

some sense is somewhat more consistent with the role pictured for the a priori. A

priori propositions structure the interpretation of empirical observations. Thus theireventual rejection cannot be an entirely empirical affair. It is, as we shall see below, his

appeal to a third philosophical level of discourse and to Habermass concept of

collective rationality that prevents framework change from being irrational. We will

consider Friedmans notion of a philosophical discourse level first.

While Stump is silent on the question of framework change and its rationality,

Friedman asserts that a more detailed look at the relation between the various types of

sentences in a framework can defuse the relativistic implications of a thesis like

Kuhns. For Friedman a framework can be seen in terms of three levels. Empirical

statements comprise the first, the second level is comprised by the relativised a prioristatements that coordinate our understanding of the empirical statements. However

there is a third level, this the level of philosophical debate. For Friedman the adoption

of a framework and its background a priori assumptions takes place against a

background of philosophical debate that can last for centuries and sets the general

background of inquiry. This level of discourse forms a common background against

which frameworks are adopted.

An illustrative example is the long philosophical debate over whether space is an

absolute empty background in which events take place or whether space itself is

defined relative to the events that take place within it. This debate has its origins in the

debate over absolute space between Newton and Leibniz but continued all through theperiod of classical physics through the work of Mach and others. Seen this way


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10 D. McArthur

Einsteins rejection of Newtonian absolute space was not the presentation of a new and

incommensurable concept with (from the classical point of view) no rational basis.

Rather it can be seen as a reasonable and well-precedented Machian/Leibnizian move

in the long-standing debate between relative and absolute space. Thus while this shared

set of philosophical concerns may not have rationally mandated the move to theEinsteinian conception of relative space, it nevertheless rendered his move as a

comprehensible and reasonable option well worth considering on it empirical merits

(Friedman 2001, 106). Thus not only does the appreciation of the various levels of

discourse, empirical, a priori and philosophical establish the roles various sorts of state-

ments have in scientific enquiry, it also helps to eliminate the threat of Kuhnian

incommensurability. It also establishes the possibility, as we shall see below, of regard-

ing framework change as a communicatively rational process between scientists who

may differ in many foundational and even a priori assumptions.

Friedmans recourse to the postulated third level of philosophical discourse isintended to explain how Habermass notion of communicative rationality can function

in the context of theory change. Science, he claims, cannot really be characterised as

instrumentally rational because different practitioners might not share the same goals

such as prediction vs. causal explanation. It is nevertheless a communicatively rational

enterprise. Parties working within a framework or paradigm share common assump-

tions and tools and can, through a process of negotiations, arrive at shared conclusions.

The shared recourse to a stable level of philosophical discourse is especially important

for Friedman in facilitating collective rationality. Different parties converge on new

frameworks after a process of discussion and compromise. The solution arrived at is

viewed as at least reasonable to all since everyone at least began the process from thesame shared set of assumptions, even if the new framework brings in a set of new

assumptions. And everyone has recourse to the philosophical level of discourse in any

event.

Thus, it is true that the shared assumptions and central features of a new paradigm

might not be compatible with the old, as was the case with the change from Euclidean

Geometry in the shift from classical to relativistic physics. Nevertheless, Friedman

contends that a clear historical continuity can be traced from the point of view of the

new framework. The new framework can outline the historical origins of current

concepts that might seem incompatible or irrational when viewed strictly from theolder perspective. For Friedman, moreover, this can be done in a non-anachronistic,

non-Whiggish manner (Friedman 2001, 60).

There is someprima facie appeal to Friedmans approach. Different frameworks do

emphasise differing goals and different constitutive concepts, and therefore a new

framework might not seem immediately rational from the point of view of the old. If

we are to avoid the irrationalist or relativistic consequences of Kuhns views, then the

rationality of theory change must be conceivable from at least a communicatively

rational perspective. However, difficulties remain with Friedmans proposal and his

appeal to communicative rationality and a shared philosophical level as it stands

leaves his account open to the same sort of relativistic charges that apply to Kuhnsposition.


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The main problem with Friedmans answer to the question of theory change is his

view that the rationality of a new framework is still something that must be

constructed in retrospect. In Friedmans main example, the case of the transition of

Euclidean geometry of classical physics to the infinitesimally Euclidean geometry of

relativistic physics, the historical continuity is evident, rendering a strong Kuhnianincommensurability with its relativist implications unnecessary. However, simply

tracing the historical evolution of a concept does not necessarily mean that the transi-

tion from, say, Euclidean to infinitesimally Euclidean geometry was itself a rational

step seen from anything other than the point of view of the current framework. In fact

it does not even show that there was more in the transition than the sort of psycholog-

ical conversion described by Kuhn. This is an especially pressing point since within a

framework what counts as rational derives from the paradigmatic assumptions that

establish the communicative base. How might a specific new framework be seen as a

rational option from the point of view of those who have not yet adopted it? And as weshall discuss at a later point, this can even be the case where adherents of different

frameworks are familiar with a similar philosophical level of discourse. In other words

how can Friedmans claims of rational continuity between frameworks be shown to be

more than Whiggish or anachronistic?

Let us put the matter in slightly different terms. If the framework establishes the

interpretation of all the constituents of the theory, and it determines what is reasonable

(in the sense Friedman has in mind), then the adherents of a given framework will

always be free to interpret its historical origins as rational. Indeed, such an approach

might provide a decidedly poor and anachronistic reading of previous frameworks. If

this is so, how can an account of framework change rebut charges of Kuhn-styleirrationalism?

At this point a holist might use this difficulty with Friedmans view to argue for the

superiority of their own view. No statement in the holist view is immune to revision

(although some are rarely modified), thus changes to one or several statements do not

really represent the sort of radical conceptual change envisioned by Kuhn or

Friedman. Friedmans difficulty with conceptual change introduces much graver

problems, a holist might argue, than it solves with its account of the a priori. Thus, if

Friedmans view is to sustain its claim to be a better account of science than holistic

naturalism, it must not be open to charges of irrationalism with regards to theorychange since the holist can claim to avoid this problem altogether. However in a later

section of this paper I will answer such criticism by sketching an approach to theory

change that is compatible with Friedmans view that can also provide a rational

account of theory change. But before this takes place it is worthwhile to consider and

address some existing literature that criticises Friedmans view. Doing so will assist

with the presentation of a plausible position that addresses the issue of theory change

while still retaining a role for the a priori.

Marc Lange has contended that Friedman overstates the degree of comprehensive

conceptual change that takes place when new frameworks are adopted. For Lange the

concepts that Friedman conceives as changing with the framework actually evolve overtime and thus the problematic break between frameworks never really occurs. To


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12 D. McArthur

provide an example, Lange notes it may therefore make less sense to speak of Maxwells

theory undergoing meaning change than to speak of the theory as itself highly ambig-

uous capable of being precisified in a variety of different ways (Lange 2004, 705).

Furthermore Lange disputes the sharp distinctions between Friedmans three levels

of discourse, empirical, a priori and philosophical. Philosophical notions such as unityand parsimony are always present when theories are considered, not just in times of

revolutions. As Friedman admits, debates over the nature of space characterise the

whole period of classical physics. Likewise the relation between a priori and empirical

statements evolves over time, and a priori principles need not be presupposed to make

sense of data. Newtons second law was formulated before the calculus even though

Friedman views the latter as conceptually prior (Lange 2004, 706).

However this criticism can be deflected when we consider that frameworks evolve

over time, and that Friedman need not suppose that the opposite is true. Making sense

of the second law, for Friedman, requires the calculus because this permits us to makesense of instantaneously changing magnitudes. But, Lange notes, if the calculus is

required to make sense of the second law, how is it that the second law was presented

and used successfully before calculus was formulated? The question is easy to answer.

At first Newton presented acceleration using relatively rough and imprecise aggrega-

tional methods. While this permitted some successful use of the second law, the

calculus made this easier, quicker and more precise. Its introduction facilitated more

successful applications of the law and over time it came to be assumed as prior. Thus,

the mature classical physics of Maxwells day was much more highly evolved than in its

original form in Newtons time. While Friedmans view may well be sketchy on how

concepts evolve into their a priori status, it is certainly not inconsistent with the sort ofaccount I have just provided. Nevertheless, I will take up the evolution of the relative

status of scientific statements again at a later point. There it will emerge that structural

realism (a view I later will argue for) can be of assistance in marrying Friedmans

account to a more plausible account of the evolution of statements.

Nevertheless, Langes criticism of Friedmans view of conceptual revolutions can

still be motivated given his assertion that the notion of revolutionary change is over-

stated. Friedmans account of revolutions, and the recourse to a shared philosophical

level of discourse, is meant to counter claims about the irrationality of framework

change and the incommensurability of differing frameworks. As I noted earlier, ifFriedman is correct that framework change is as comprehensive as he claims, his

notion of shared recourse to a philosophical level of discourse is probably not enough

to counter the implications of a view like Kuhns. After all, even if the adherents of

differing frameworks can mutually understand shared philosophical considerations,

from the point of view of different frameworks these considerations apply strictly

speaking to quite different things. Thus, even a shared philosophical background

might not provide the ground for an agreement on when it is reasonable to change

frameworks. One could be tempted at this point to reason along Langes lines and

suppose the apparent threat of the irrationality of framework change arises from

exaggerating the differences between frameworks and the comprehensiveness ofinstances of framework change. However, in the next section I will present a


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perspective, structural realism, that is compatible with Friedmans view but can

answer the difficulties that I have presented.

4. Structural Realism

Structural realism (SR) is quite an old view, dating to Poincar (1905) and before.

However, the position has been revived recently by Worrall (1989) and the view has

been since defended in several forms by a very large number of commentators such as

Chakravartty (1998, 2003), Ladyman (1998; French and Ladyman 2003a, b) and me

(McArthur 2003, 2006). In this discussion I follow Chakravarttys suggestions that

develop from Worralls basic presentation of the position.1 However, I will also draw

from some of my own previous work.

SR is a view of theory change. It asserts that equations, which are retained across

instances of theory change, pick out relations that are at least approximately true. This,supporters claim, forms the explanation for why such equations are in fact retained.

However, while SR commits to knowledge of structure (i.e. the equations that describe

relations) it does not commit to knowledge of any nature of the entities in the retained

equations that goes beyond the relations the entities engage in. Thus, for structural

realists such as Worrall, the view represents a compromise position. It accommodates

major conceptual breaks in our understanding of theoretical constituents at the time of

theory change while avoiding the difficulties of conceptual relativism that attach to the

early views of Kuhn. For the structural realist, the history of science is replete with

instances where, despite the conceptual disruptions introduced by theory change,

equations are retained in new theories. The explanation is that while many of thefeatures of the entities named by equations might undergo revision in a theory or

framework change, the relations picked out by the surviving equations do exist. Thus,

while SR picks out continuity between old and new theories, it also recognises that

much of the constituents named by theories do not survive. Examples of such entities

are plentiful and include things such as the ether, caloric phlogiston, etc.

A useful presentation of SR for my purposes is Chakravarttys (1998). He defines the

properties of a theoretical entity as its dispositions for the law-like interactions that it

engages in. And he contends that what can be known about a theoretical entity are

those properties that are utilised in its detection. That is, science provides knowledgeof those causal regularities (expressed in law-like terms, i.e. as equations) that are

involved in experimental interaction with the entity. Since the constituents of theories

are defined in terms of their interaction properties, i.e. structurally, and since some of

these survive theory change, some continuity exists between old and new theories.

Nevertheless, as I have pointed out elsewhere, SR places no restriction on a new

theory adding new interaction properties or recontextualising old properties along

with sets of new ones (McArthur 2003). So, while supporting a continuity of at least

some law-like statements between different domains, structuralists can accommodate

the sort of comprehensive conceptual changes that take place in instances of

framework change. They can even accept two thus related theories referring to largelydifferent ontologies since the view is only committed to the structural relations, that is,


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14 D. McArthur

stable material interactions, that hold in either theory. In fact as I have argued in earlier

publications, a structural realist can actually take a deflationary stance to the theoretical

entities in current theory, and is in no way committed to a theorys whole ontology

(McArthur 2003, 2006). A structural realist can take a theoretical entity to exist or to

simply be a mathematical stopping point used to generate predictions. The structuralrealist need only be committed to the notion that something, however understood,

stands in the relations picked out by well-confirmed equations that survive theory

change. Thus, a structural realist of this sort has no difficulty accounting for structural

relations being recontextualised in a new theory with very different ontological

features.

One fairly classic example of such a comprehensive framework change that retains

equations in the context of a major shift in theoretical ontology is the shift from

Fresnels theory of light to Maxwells electromagnetic theory. The theories are quite

different ontologically; light is a wave through the elastic ether for Fresnel. ForMaxwell, light is not a wave through the ether at all, but a variation of the charge

strength in the electric/magnetic field. However, lights interaction properties, used in

experiments in both theories, remain the same, i.e. light propagates as a transverse wave

described by the same equations in both theories. When we take this approach to SR

we are in a position to use it to ameliorate Friedmans view in a way that lets it answer

the possible objections to it that I outlined earlier.

Recall that recourse to Freidmans shared philosophical level is not enough to render

theory change rational. As I noted above, between frameworks even the subjects of the

philosophical level of discourse can be viewed as applying to entirely different things.

SR can help deflect this concern. For the structural realist, different frameworks sharemathematical structures, such as Maxwells equations, that also serve to accommodate

the same empirical data. This is especially so if we regard the equations as referring to

empirical dispositions, i.e. interaction properties, as I suggested above. Maxwells

equations serve to recover the same data regardless of the framework. In this sense even

dramatic re-interpretations of an equations terms do not alter the fact that different

frameworks appeal to the same structures to accommodate the same empirical

dispositions. In fact Langes point, quoted above, that it may therefore make less sense

to speak of Maxwells theory undergoing meaning change than to speak of the theory

as itself highly ambiguous capable of being precisified in a variety of different waysis very amenable to a structural realist reading. Nevertheless, SR does recognise, in a

way that Lange does not, that such re-evaluations do occur and can be quite compre-

hensive, as was the case with the shift from classical to relativistic physics. In the next

section I will consider in some detail the ways in which SR can help us better

understand theory change and Friedmans account of the role of the a priori.

5. Structural Realism and the Rationality of Theory Change

Recall that the major difficulty with Friedmans proposal to understand theory change

as a communicatively rational process is the fact that it produces a Whiggish under-standing of theory change. That is, it defines the rationality of theory change solely in


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retrospect and potentially anachronistically. The reason for this, as we saw, is Friedmans

fully internal account of rational framework change (including the philosophical level).

What is necessary to truly avoid the irrationalist implications of Friedman (or Kuhns)

account is to establish criteria for theory change that are genuinely extra-theoretic. That

is to say, if we are to avoid irrationalism then we need to identify features that anyplausible new framework must possess. SR presents a straightforward account of such

features.

In the version of SR that I sketched above, the properties of a theoretical entity are

defined by the dispositions for law-like behaviour that they confer. For a structural real-

ist of this sort, the properties that are preserved across instances of theory or framework

change are those dispositions for law-like behaviour that are utilised in experimental

interactions. These interaction properties are expressed as the mathematical equations

that survive at least as limiting cases in new theories. A structural realist view of theory

change, then, asserts that while much of the theoretical entities of an old theory mightdisappear, interaction properties do survive. That is to say, a significant change can take

place in theoretical ontology. A structural realist, as we have seen, is not committed to

the interpretation of an entity named in an equation that is given by any particular

theory, neither is a structural realist committed to the truth of any particular theoretical

ontology. Thus, a structural realist can be quite sanguine about considering any

proposed new framework to be rational so long as it preserves established interaction

properties at least as limiting cases.

A ready example of just such a change is the case of Keplers equations describing

planetary motion that survive in Newtons much more comprehensive theory of

universal gravitation. These equations express the interaction properties whereby wecan predict planetary motion. Moreover, the change from Keplers theory of planetary

motion to Newtons must count as the sort of comprehensive framework, or paradigm

change that Kuhn or Friedman has in mind since the two theories have quite different

ontologies. Newtons theory incorporates planetary motion as part of a more compre-

hensive theory replete with a universal non-mechanical gravitational force quite absent

in Keplers celestial mechanics. Nevertheless, the essential structure for the calculation

of orbital period is preserved in the new theory. This particular interaction property

then represents stable structure that persists across instances of theory change.

And, as we have already seen, perhaps the most discussed example of such interactionproperties surviving instances of theory change is the change from Fresnels wave

theory of light to Maxwells electromagnetic theory. Here the interaction properties in

question are represented by Fresnels account of light propagating as a transverse wave

through the elastic ether. For Maxwell light does not propagate through the elastic ether

in this way, but nevertheless propagates as a transverse wave. In either case though, the

surviving equations describe properties that confer dispositions for specific laboratory

results. Very famously, for example, these include Poissons use of Fresnels equations

to predict that light diffracting around the edge of a disk ought to constructively inter-

fere to create a bright spot in the centre of the disks shadow (a disposition later

confirmed by Arago). And of course a structural realist can regard the change fromFresnels to Maxwells theory as rational not simply because Fresnels theory led to what


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16 D. McArthur

we currently regard as rational, pace Friedman, but because it preserves the interaction

properties found in Fresnels theory. Moreover, this is also the case with the shift from

Maxwells theory to modern quantum mechanical theories of light, where Fresnels

equations still hold as limiting cases.

Let us apply the lessons learned from a structural realist reading of theory change toFriedmans discussion of theory change as a communicatively rational process. For

Friedman the rationality of theory change comes from the communicatively rational

process whereby a previous theory change can be seen as rational because it led

ultimately to the adoption of the current framework wherein scientific rationality is

defined (Friedman 2001, 93105). However, as we saw earlier, this answer does not

seem to escape the charge that this amounts to Whiggish historiography, that the

history of theory change is rewritten to show it leading to what now counts as rational.

What an account like Friedmans needs then in order to avoid charges of Whiggishness

or irrationalism is extra framework criteria that can help determine what sort ofalternative framework can count as rational.

A structural realist reading of theory change can serve in this role. If my arguments

here are correct then SR can provide an account, external to a given framework, of

what sort of framework can be rationally considered as an alternative. A structural

realist can view a comprehensive theory change as perfectly rational so long as the new

framework preserves, even just as limiting cases, the well-confirmed interaction

properties of superseded theory. Moreover, a structural realist can even recognise that

new frameworks can come with greatly different relativised constitutive principles.

Consider the shift from classical to relativistic mechanics from a structural realist

perspective. As Friedman argues, Newtons laws of motion among other things serve aconstitutive a priori role in classical mechanics (Friedman 2001, 26). These laws no

longer function in a constitutive role but serve as limiting cases within the much

different framework of special relativity. The case is similar with conservation laws; in

classical mechanics mass is a conserved quantity, and this assumption plays an

important constitutive role. In current relativistic physics, mass is not a conserved

quantity, but interaction properties associated with it, such as the properties of elastic

collisions at low velocity, serve as approximating limits in the application of the more

general principle of the conservation of mass/energy.

Friedmans account of theory change can only show the change from classical torelativistic physics to be rational in retrospect. It cannot account for how relativistic

physics might seem rational from the point of view of classical physics. After all, a

framework that abandons basic a priori principles such as the conservation of mass or

the laws of motion can hardly seem rational from Friedmans account since these

determine what is rational, on his account, for classical physics. However, a structural

realist is not as limited in what counts as rational and can take any stance toward

current theory. Thus, major revisions in foundational, even constitutive, a priori

principles can be seen as rational from a structural realist perspective, so long as the

putative new framework preserves well-confirmed interaction properties. Thus, SR

can provide the extra-framework criteria that provide a forward-looking account ofrationality in theory change. It also imposes limits on what sort of framework can be


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entertained as a candidate in the communicatively rational process that Friedman

describes. Candidate frameworks can vary in theoretical ontology or constitutive a

priori principles, but they must preserve well-confirmed interaction properties at least

as limiting cases. From the structural realist point of view, cases of framework change

such as the shift from classical to relativistic physics, or from Keplers to classicalphysics can be seen as rational, and not just in retrospect. The new frameworks in

these cases preserve important, well-confirmed interaction properties and can, thus,

be seen as rational alternatives even from the point of view of the older framework in

question.

One criticism that might be levelled against my argument is that a defender of Fried-

mans account of the a priori cannot make easy recourse to SR because of the nature of

Friedmans constitutive principles which might be said to be more general than the

specific equations picked out by SR. While Friedmans view certainly identified broad

features (such as Euclidean geometry or the calculus) as forming parts of the constitutiveframework, he nevertheless does pick out specific mathematical formulations such as

the ones identified by SR. A good example is Newtons second law that for Friedman is

an important part of the a priori framework of classical physics. This is retained in

contemporary physics as a special case and this is exactly the sort of mathematical

continuity picked out by SR. It is true of course that the second law no longer forms

part of the constitutive framework since it is derivable from the new framework. But

this does not rob a supporter of my position of recourse to it, since its changing role

does not alter the fact that it is retained and the empirical situations it accommodates

persist in the new framework.

One important feature of SR that can help make theory change rational in a way thatthe communicatively rational features of the philosophical level of discourse do not is

that it fixes the empirical dispositions that are similarly accommodated across frame-

works. These dispositions persist as a common problem set which render frameworks

comparable even if the relative relation of statements to each other alters when a

framework changes. Thus while a supporter of SR has no problem accommodating the

role of some statements as functionallya priori in some frameworks, such as the second

law, she has no problem dealing with the fact of such a statement nothaving such a role

in a new framework. Consider again the second law; in Newtons physics it is assumed

in order to formulate any hypothesis that can be made about accelerating objects. Thisis no longer so in contemporary physics, which recognises situations where this is not

the case. However, a large class of cases (indeed the large majority) do exist where the

law is still empirically satisfactory.

Additionally while a supporter of SR can recognise the utility of Freidmans identi-

fication of a class of statements as functionally a priori, there is no problem for a

supporter of Friedmans adopting a structural realist view of theory change. This is so

for the reason that SR simply focuses on the mathematical continuity across frame-

works (such as the persistence of the second law) but in no way denies that they might

have different relative roles with regards to each other in different frameworks.

Consider the following speculative example. In contemporary high energy physics, allcollisions and decays are governed by a set of conservation laws. However, these are not


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18 D. McArthur

simply empirical hypotheses obtained from observing collisions and decays but in fact

they are a consequence of the symmetry group representation of the standard model.

If this were to be altered in some future framework change (that did not for example

use the same symmetry group representations), the new framework still needs to

accommodate the same observation set that was accommodated by the conservationlaws. While these would no longer perhaps form part of the constitutive framework,

they would still persist as a class of empirically adequate hypotheses that apply in

certain cases. Just as a supporter of Friedman has no problem pointing to the new role

of the second law in relativistic physics, she would have no problem with what SR

would say about the survival of the conservation laws in some new framework. SR and

Friedmans view compliment each other well. Together we see not only a rational

account of theory change but also a good account of how formerly a priori concepts

might survive without this status in a new theory. And as we saw earlier in the discus-

sion of Langes criticism concerning the relation of the calculus to the second law,Friedmans position can well benefit from a more nuanced account of the evolution of

concepts. As we have just seen, SR can be of assistance with this.

6. Conclusion

The important feature of SR that addresses the problem of rationality in theory change

is its de-emphasis on theoretical ontology and its focus on interaction properties.

Nevertheless, a structural realist is free to accept, or merely provisionally adopt, the

theoretical ontology and constitutive a priori assumptions of any given framework,

providing it is empirically successful. That is to say, SR can easily accommodate the roleof constitutive a priori principles in scientific frameworks in a much more satisfactory

way than can holistic theses about psychological commitment. A structural realist can

for instance accommodate the fact that certain statements must be assumed in order to

formulate empirical theses in a given framework, such as the a priori use of Euclidean

space-time and Newtons laws of motion in classical physics. Nevertheless, since a

structural realist is notcommitted to the idea that the internal features of a framework

wholly define scientific rationality, she can consider it rational to entertain the

adoption of a rival framework that might make very different assumptions. As we saw

earlier, what makes a theory change rational, for the structural realist, is not theretention ofa priori principles, but the retention of interaction properties at least as

limiting cases.

In conclusion then, while there is much to be said for the proposal that versions of

naturalism based on Quinean holism cannot account for the history of the natural (and

especially the mathematical) sciences, it demands that the question of the rationality of

theory change be addressed. Friedmans proposals about understanding framework

change as a communicatively rational process are also intriguing in that they describe

a consensus-building process which in many ways describes the process whereby a

scientific community comes to accept new foundational assumptions. Nevertheless,

Friedmans proposals by themselves cannot finally answer charges of irrationalism in away that is more satisfactory than Kuhns own attempts to answer such charges, and


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they cannot rebut charges that they lead to a Whiggish view of the history of science.

However, if my arguments in this paper are correct, SR can serve to provide a

sufficiently externalist account of theory change that can rebut charges of Whiggishness

and irrationality while still preserving Friedmans central insights about the role of

constitutive a priori principles in scientific frameworks.

Acknowledgements

I would like to thank Corey Mulvihill, Jon Tsou and Idil Boran for their useful

comments on early drafts. I would also like to thank the philosophy faculty of Carleton

University for their comments and for inviting me to present an early draft as part of

their 2005 colloquia series. I also thank the attendees of the 2005 Canadian Philosophical

Association Congress, where I also presented a draft. I would also like to thank the editor

and two anonymous referees for their very extensive comments on earlier drafts.

Notes

[1] Although a review of the current literature on SR is beyond the scope of this paper, some further

comment is warranted on the version I follow. Worralls (1989) view is that science gives us

knowledge of structure and not nature. This has been subject to much criticism because,

according to Psillos (1995, 2001) and others, it includes a difficult to sustain distinction

between structure and nature. Worralls nature, according to Psillos, becomes undefinable,

and this causes Psillos to doubt the plausibility of SR. Chakravartty (1998) accepts this criticism

and avoids the difficulty by identifying objects and their nature in terms of their properties that

are used in laboratory interactions. Ladyman (1998) on the other hand proposes a muchstronger version of SR and asserts that there are no objects at all, only structure. However, this

view is highly problematic. As Psillos (2001) and I also (McArthur 2006) note, it tries to main-

tain a notion of isomorphism without the idea of paired objects. Cao (2003) has pointed out

that by defining everything in terms of structure it can stifle the quest for deeper structures and

causes. Furthermore, I have argued that since it makes all relations internal, it suffers from

regress problems (McArthur 2006). Given all this, I have chosen a version of SR that seems to

lack the problems of Ladymans view and also avoids the difficulties Psillos has noted with

Worralls position. SR is controversial, of course, as Psilloss writings attest, but it is entertained

in a sufficiently wide way to be a candidate for my purposes, and I think the version I have

chosen to follow avoids most of the criticism current in the SR literature.

References

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_______. 2003b. The dissolution of objects: Between Platonism and phenomenalism. Synthese 136:

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