french s. the dissolution of objects between platonism and phenomenalism 2003

8/13/2019 French S. the Dissolution of Objects Between Platonism and Phenomenalism 2003

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74 STEVEN FRENCH AND JAMES LADYMAN

sought which ensures the impossibility of such things being indistinguish-able. Leibniz saw this and introduced his infamous Principle of Identityof Indiscernibles as just such a guarantee. As we are sure Cao is aware,

this Principle has had a less than happy time of it in the quantum domain.Furthermore, appealing to Strawsons view of individuality may also notbe the best move to make. There are two aspects of his analysis whichare relevant here: the rst has to do with his interpretation of individualityas impredicability the idea that an individual is simply a logical subjectwhich cannot serve as a predicate an interpretation that Ayer charac-teristically dismissed as not illuminating (Ayer 1954, p. 3). The secondaspect concerns the issue of the identication of particulars and Strawsonargues that the general conditions of such identication require a uniedsystem of spatio-temporal entities, such as is constituted by the materialuniverse. Whether such a system is viable and Strawsons conditions met inthe context of modern physics is contentious, to say the least. In particular,the kind of framework Strawson advocates appears least problematic if some form of substantival understanding of space-time is assumed, sincethe relational view leads to an obvious circularity. Unfortunately, it is pre-cisely a form of the latter that Cao advocates in his other work (see Caoforthcoming).

With regard to QFT, the relationship between the particle and eldrepresentations is not as unproblematic as Cao seems to think (see, forexample, the recent survey in Huggett 2000), nor are we as ignorant of recent developments as he suggests. Indeed, we acknowledged that . . .given the rejection of particles as the basic ontology in QFT, it seems tous that the sort of developments Cao very nicely charts provide powerful

support for the metaphysical SR programme. However, we insist that if elds are more fundamental then the standard realist owes us all an an-swer to Redheads question, what is a eld? And such an answer mustbe given in terms of an appropriate metaphysics. It is here that a form of underdetermination arises again, between elds as substantival and eldsas properties of space-time points. Cao, like Chakravartty, thinks this kindof underdetermination is innocuous but the response we gave to Chakrav-artty in footnote 14 applies here too in the case of unobservable entitieslike elds the content of belief in them is exhausted by their theoreticaldescription and if that underdetermines their metaphysical nature then ourbelief is empty. Again, standard realism is gutted. Best, then, to understandelds structurally.


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76 STEVEN FRENCH AND JAMES LADYMAN

3. WHAT IS CAO S POSITION ?

In our paper we tried to explore Caos own position a little, pointing outthat although he has been taken by some to be of the ontic persuasion, hehimself appears to incline towards the epistemic form. Now Cao tells usthat he is neither, that he sees his position as a third way of some sort. Thecentral claim seems to be that we can . . . know underlying entities throughour structural knowledge without dissolving them into mathematical struc-tures. Now this seems strikingly similar to the core idea of Chakravarttyssemi-realism ( op. cit .), which attempts to unite a form of entity realismwith Worralls (epistemic) structural realism. Indeed Chakravartty arguesthat not only does structural realism imply entity realism a claim withwhich Cao will surely be sympathetic but vice versa. The argumenthinges on a distinction between detection properties and auxiliary prop-

erties. As the name suggests, the former are those properties of an entityby means of which we detect it; that is, they concern the causal powersthat come to be associated with the entity. Auxiliary properties, on theother hand, are those further properties which are introduced as part of our efforts to get a theoretical grip on the entity concerned, but whichmay eventually be abandoned in the process of theory change (and, of course, properties that are initially thought of as detection propertiesmight eventually come to be seen as auxiliary). Entity realism, then,is the view that we should be realists about those entities which possessthe relevant detection properties. According to Chakravartty, it is impliedby structural realism since the kinds of structures identied by the struc-tural realist as being retained through theory change are precisely thosewhich feature these detection properties. Relatedly, entity realism impliesstructural realism because moving in the other direction the detectionproperties picked out by the entity realist will feature in those structuresemphasised by the structural realist. Of absolutely critical importance inthis argument is an assumption, explicitly made by Chakravartty, that rela-tions cannot subsist without relata; it is only by means of this assumptionthat the rst implication can move from detection properties as features of some structure, to detection properties as giving us access to some entityunderlying that structure.

Just like Cao, Chakravartty insists that we know entities by means of our structural knowledge without dissolving them into the structures and,

again just like Cao, Chakravartty can claim that his form of realism mesheswith the attitudes of physicists towards the entities they discover. Thus wepresent semirealism as a possible way of making sense of Caos position.But, of course, apart from the above assumption, there is nothing here that


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