True Nominalism: Referring versus Coding

One major motivation for nominalism, at least according to Hartry Field, is the desirability of intrinsic explanations: explanations that don’t invoke objects that are causally irrelevant to the phenomena being explained. There is something right about the search for such explanations. But that search must be carefully implemented. Nothing is gained if, to avoid a certain class of objects, one only introduces other objects and relations that are just as nominalistically questionable. We will argue that this is the case for two alleged nominalist views: Field’s fictionalism ([1980], [1989a]), and Frank Arntzenius and Cian Dorr’s geometricalism (Arntzenius and Dorr [2012]). Central to our competing approach to nominalism is a distinction between terms that refer to objects and ones that instead code empirical phenomena while being referentially empty. We next contrast our approach to nominalism, which uses this term-grained distinction between coding and referring, with approaches (to nominalism) that instead attempt to make a sentence-grained distinction between mathematical and non-mathematical content. We show the latter approach (derived from the work of Kitcher, Maddy, and Sober) fails to be responsive to objections raised by van Fraassen. In the end, only one last approach to nominalism is left standing. 1 Introduction2 Troubles for Mathematical Fictionalism 2.1 A distinction 2.2 Field’s programme 2.3 Parts of nominalistically acceptable entities are nominalistically acceptable 2.4 Structural assumptions: How far can these be pushed? 2.5 Cases of indispensable theories where the mathematical posits are known not to be real 2.6 How does science distinguish between the indispensable structural presuppositions taken to be real and those that aren’t? 2.7 Do physicists distinguish between mathematical posits and non-mathematical posits? 2.8 Mathematical coding versus genuine metaphysics. Case study: Fields 2.9 The upshot3 Troubles for Topologism4 Contrasts: Kitcher, Maddy, Sober, and van Fraassen 4.1 Sober’s approach 4.2 Maddy’s approach 4.3 Kitcher’s approach 4.4 Where do we go from here? 4.5 Van Fraassen’s objection to Maddy’s approach to ontological commitment5 Conclusion