Abstract
This essay is about how the notion of “structure” in ontic structuralism might be made precise. More specifically, my aim is to make precise the idea that the structure of the world is (somehow) given by the relations inhering in the world, in such a way that the relations are ontologically prior to their relata. The central claim is the following: one can do so by giving due attention to the relationships that hold between those relations, by making use of certain notions from algebraic logic.
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Notes
There are other motivations, of course, such as metaphysical underdetermination (Ladyman 1998; French 2006, 2011), or certain features of particle physics (Roberts 2011; McKenzie 2014a, b). I only outline two here, because they are the two which connect most directly with what I want to say; for a comprehensive overview of structuralism and the motivations for it, see Frigg and Votsis (2011).
Worrall (1989).
Worrall (1989, p. 157).
This is an instance of the general argument discussed by Roberts (2008).
Here, I’m employing Melia (1999)’s definition of haecceitism as “the view that there are distinct possibilities that differ only over which objects play which roles.”
Esfeld and Lam (2010).
cf. Kaplan (1975).
I read Weatherall (2016) as advocating that haecceitism should be modelled in this latter fashion.
French and Ladyman (2010, p. 33).
Wolff (2012, p. 607).
Chakravartty (1998, p. 399).
The structure of what? For the purposes of this discussion, either the world, or some model-theoretic representation thereof.
Thus, this proposal—especially if taken in an eliminativist vein—may naturally be viewed as a form of the bundle theory.
Isomorphic, in this context, meaning that there is a bijection f between the two algebras which preserves the algebraic operations (so \(f(a \cdot b) = f(a) \cdot f(b)\), \(f(- a) = - f(a)\), etc.).
This corresponds to the well-known observation that the bundle theory is (at least prima facie) committed to the identity of indiscernibles.
I stress that the language is without identity in order to stress that the elementary equivalence here is with respect to that language: i.e., that \({\mathcal {M}}^+\) and \({\mathcal {N}}^+\) will not (in general) satisfy the same identity-sentences.
As this suggests, one can think of cylindric algebras as polyadic algebras enriched with an operation of identity: more precisely, one can show that the “locally finite” polyadic algebras with identity are equivalent to the “locally finite” cylindric algebras (see Galler (1957) or (Plotkin 2000, §1.2)).
cf. Leitgeb and Ladyman (2008).
Thus, the elements of the algebra are sets of infinite sequences, not—as one might have thought—sets of n-tuples. This just avoids certain technical wrinkles that we would have to deal with if working with sequences of different lengths: see the discussion in Németi (1991, §4).
The cylindric set algebras of the form \(C({\mathcal {M}})\), for some model \({\mathcal {M}}\) of predicate logic, are exactly the \(\omega \)-dimensional cylindric set algebras which are “regular” and “locally finite”: see (Monk 2000, §11).
Strictly speaking, the representable cylindric algebras are those which are isomorphic to some subdirect product of cylindric set algebras. But one can show that any such algebra is directly representable as a cylindric set algebra (see (Németi 1991, p. 503)).
See Henkin et al. (1986) for a survey.
(Dasgupta 2009, pp. 52–53).
Dasgupta (2009, p. 66).
Here’s a possible answer: elsewhere, Dasgupta writes that “it is arguably analytic of the existential quantifier that existentially quantified facts are grounded in their instances.” (Dasgupta 2011, p. 131) The problem is that what makes this an analytic feature of the existential quantifier is surely the form of the semantics for it—as Dasgupta then goes on to say, “this understanding of the quantifier is arguably implicit in the standard Tarskian semantics for PL.” (Dasgupta 2011, pp. 131–132). If so, then it will equally well be analytic of the operator \(\mathbf{c}\) that facts of the form \((\mathbf{c}\mathbf {\Phi }^1)^0 \, \mathbf {obtains}\) are grounded in instantiations of \(\varvec{\Phi }^1\).
The hermeneutic/revolutionary distinction is borrowed from Burgess (1983).
My thanks to an anonymous referee for raising this concern.
Indeed, in modern differential geometry one standardly defines a vector field as a derivation on the smooth algebra (e.g. (Baez and Muniain 1994, chap. 3)).
For further discussion of Einstein algebras, see Rosenstock et al. (2015).
See Ruetsche (2011) for more on this question.
See (Landsman 2017, chap. 7).
Although, as discussed above, the application to scientific theories requires more detailed work.
Lam and Wüthrich (2015, p. 624).
Psillos (2001, p. S22).
Not to be confused with the distinction between radical and moderate ontic structuralism! After all, as I argue here, algebraic structuralism is a radical form of ontic structuralism, but a moderate form of anti-individualism.
Sider (2017, p. 93).
It remains an open question, to my mind, whether there is or could be such an apparatus: the best hope is likely something category-theoretic, but the details remain to be made out.
This is, essentially, the point that Rynasiewicz (1992) makes in the context of spacetime algebras.
One might have thought that characterising the structure of a theory would just be a matter of characterising the structure of each of its models. However, that risks neglecting those aspects of a theory’s structure concerning the relationships between models, which may be important for determining the theory’s content (see Halvorson (2012, §7) for an elaboration of this claim).
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Dewar, N. Algebraic structuralism. Philos Stud 176, 1831–1854 (2019). https://doi.org/10.1007/s11098-018-1098-3
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DOI: https://doi.org/10.1007/s11098-018-1098-3