Structural Realism or Modal Empiricism?

Abstract

Structural realism (SR) has been suggested as the best compromise in the debate on scientific realism. It proposes that we should be realist about the relational structure of the world, not its nature. However, it faces an important objection, first raised by Newman against Russell: if relations are not qualified, then the position is either trivial or collapses into empiricism, but if relations are too strongly qualified, then it is no longer SR. A way to overcome this difficulty is to talk about modal, or nomological relations instead of purely extensional relations. I argue that this is insufficient, for then, SR collapses into modal empiricism (ME). I suggest, however, that ME could be the best position in the debate on scientific realism. 1Introduction2Objections to Structural Realism3How to Escape Newman’s Objection4Which Modal Relations Are Retained in Theory Change?5Are Modal Relations Real?6Relativity and Fundamentality7Is Modal Empiricism Really Empiricism?8Could Modal Empiricism Be the Best of Both Worlds?

Operational Theories as Structural Realism

“…Thus this approach allows us to make a metaphysical commitment which goes beyond the empirical without explicitly or implicitly invoking theoretical entities of any kind, thus fulfilling the mandate captured in the slogan 'just constructive empiricism plus modal structure.' We therefore circumvent the common objection that structural realism collapses either into standard scientific realism on the one hand, or into constructive empiricism on the other [61,68,74]: we avoid the collapse into standard scientific realism by insisting on a completely operational construction, and we avoid the collapse into constructive empiricism by insisting that even when we have several structures achieving equal empirical adequacy, there is some objective fact of the matter about which of these structures gets closest to the actual objective structure of reality.…”

“…Note that it is important here that we take a non-selective approach, because it is relatively unlikely that all of the axioms that have been used in various places to derive quantum mechanics will be preserved across theory change, and this threatens to derail a selective approach to realism for axiomatisations. For example, ref [74] objects to modal approaches to structural realism on the grounds that modal structure often fails to be preserved through theory change; but of course this is a pertinent objection to modal structural realism only if it is understood as a form of selective realism where we are supposed to be able to identity in advance which particular modal structures are responsible for the success of our theories. The non-selective modal structural realist has no problem here: they are free to acknowledge that modal structure may appear to be lost during theory changes because we don't necessarily know precisely how the theory is embedded into the objective modal structure of reality, and therefore we may simply be wrong about the modal features we assign to our theories.…”

Semantic realism in the semantic conception of theories

“…For example, an ontic structural realist can claim that the kind of relations she is talking about are modal. However, even if the qualitative term modal were enough to make a relation count as real so as to avoid Newman's objection (but see Ruyant, 2019), the cognitive content of the theory cannot be understood exclusively in realistic terms, because these are modal relations between entities that are epistemically identied. And even someone assuming that models posit real entities, such as molecules or phlogiston, has to assume that the cognitive content of a theory, what makes the theory true, is really about how these real entities relate to the epistemic entities that enter into the mapping.…”