The preservation of thickly detectable structure: a case study in gravity

Structural realists claim that structure is preserved across instances of radical theory change, and that this preservation provides an argument in favor of realism about structure. In this paper, I use the shift from Newtonian gravity to Einstein’s general relativity as a case study for structural preservation, and I demonstrate that two prominent views of structural preservation fail to provide a solid basis for realism about structure. The case study demonstrates that (i) structural realists must be epistemically precise about the concrete structure that is being preserved, and (ii) they must provide a metaphysical account of how structure is preserved through re-interpretation in light of a new theory. Regarding (i), I describe a means of epistemic access to the unobservable that I call “thick detection” of structure, which isolates the structure that will be preserved. Regarding (ii), I argue that thickly detectable structure is preserved across theory change through a process of extracting the old structure from the new structure, much like what has been done with geometrized versions of Newtonian gravity. With these two responses in hand, the structural realist can adequately account for the preservation of structure and can provide a strong argument in favor of structural realism.