Fictions, Conditionals, and Stellar Astrophysics

Abstract

This article argues in favour of an inferential role for fictions in scientific modelling. The argument proceeds by means of a detailed case study, namely models of the internal structure of stars in stellar astrophysics. The main assumptions in such models are described, and it is argued that they are best understood as useful fictions. The role that conditionals play in these models is explained, and it is argued that fictional assumptions play an important role as either background or antecedent conditions. I then expand on the argument for the compatibility of fictions and scientific realism. I argue that realism and antirealism plausibly offer correspondingly different accounts of the semantics of these fictional conditionals.

Acknowledgements

I thank audiences at Paris, Vancouver (APA Pacific conference), LSE, and Montreal (PSA conference), and Alisa Bokulich, Steve Downes, Catherine Elgin, Arnon Levy, James McAllister, Henrik Zinkernagel, and an anonymous referee of this journal for helpful and detailed comments and reactions. Thanks also to the Harvard Philosophy Department and the London Institute of Philosophy for sponsorship during research visits there. Financial help is acknowledged from the Spanish Government, research project grant FFI2011-29834-C03-01.

Notes

The claim that idealisations split into these two forms, at least, is by now entrenched in the literature. Morrison (2005, actually written and circulated about a decade earlier), Suárez (1999), and Batterman (2009) share a very similar understanding of the distinction, and put it to similar epistemic uses.

The term ‘instrumental reliability’ was introduced and applied to idealisations in this way in Suárez (1999). Winsberg (2010, ch. 7) applies the same concept to simulations.

The HR law was independently discovered by the Danish astronomer Ejnar Hertzsprung (1873–1967) and the American Henry Norris Russell (1877–1957). A typical diagram displaying the law is reproduced as Figure 2.

It is worth remarking that these fundamental empirical properties are not observable in van Fraassen's (1981) sense of the term. Hence even if these properties lie at the end of some of the inferential chains that start off with fictional assumptions, the sort of antirealist position that would ensue from restricting commitment to such properties is not constructive empiricism. (Other differences with constructive empiricism are emphasised later in the text in discussing the nature of fictional conditionals.) The fact that constructive empiricism may be understood as a kind of fictionalism (e.g. Rosen 1994) does not imply that fictionalism, in general, requires constructive empiricism, or that it is committed to it.

For the distinction between wide and narrow fictions, or fictionalism more generally, see Suárez (2009). In this article, I am developing the fine-grained distinction between fiction and idealisation, so I correspondingly adopt a narrow sense of scientific fiction.

On the inferential conception of representation that I have defended (Suárez 2004), the aims of ‘faithfully representing’ and ‘reliably inferring’ are not only unopposed, but may be said to ride upon each other. These two activities are in fact closely linked conceptually—since reliable inference turns out to be a necessary (albeit neither sufficient nor constitutive) condition on representation. The views that I defend in this paper regarding fictional assumptions in models are a corollary of my more general views regarding representation, but they may also be adopted independently of any views regarding scientific representation in general.

The distinction between fictions and hypotheses was often emphasised by Vaihinger (1924) and informs the standard line on fictions that was rehearsed in section 1 above.