In the philosophy of science, structuralism (also known as scientific structuralismAlisa Bokulich, Peter Bokulich (eds.), Scientific Structuralism, Springer, 2011, p. xi. or as the structuralistic theory-concept)Wolfgang Balzer, C. Ulises Moulines (ed.), Structuralist Theory of Science: Focal Issues, New Results, Walter de Gruyter, 1996, p. 226. asserts that all aspects of reality are best understood in terms of empirical scientific constructs of entities and their relations, rather than in terms of concrete entities in themselves.

Overview

Structuralism is an active research program in the philosophy of science, which was first developed in the late 1960s and throughout the 1970s by several analytic philosophers.

As an instance of structuralism, the concept of matter should be interpreted not as an absolute property of nature in itself, but instead of how scientifically grounded mathematical relations describe how the concept of matter interacts with other properties, whether that be in a broad sense such as the gravitational fields that mass-produces or more empirically as how matter interacts with sense systems of the body to produce sensations such as weight.

Structuralism's aim is to comprise all important aspects of an empirical theory in one formal framework. The proponents of this meta-theoretic theory are Frederick Suppe, Patrick Suppes, Ronald Giere,Alisa Bokulich, Peter Bokulich (eds.), Scientific Structuralism, Springer, p. 140 n. 52. Joseph D. Sneed, Wolfgang Stegmüller, , Wolfgang Balzer, John Worrall, Elie Georges Zahar, Pablo Lorenzano, Otávio Bueno, Anjan Chakravartty, Tian Yu Cao, Steven French, and Michael Redhead.

The term "structural realism" for the variation of scientific realism motivated by structuralist arguments, was coined by American philosopher in 1968.Maxwell, G. (1968), "Scientific Methodology and the Causal Theory of Perception", in: Imre Lakatos and Alan Musgrave (eds.), Problems in the Philosophy of Science, Amsterdam: North-Holland Publishing Company. In 1998, the British structural realist philosopher James Ladyman distinguished epistemic and ontic forms of structural realism.Ladyman, J., 1998. "What is structural realism?" Studies in History and Philosophy of Science, 29: 409–424.

Variations Epistemic structural realism The philosophical concept of (scientific) structuralism is related to that of epistemic structural realism (ESR). ESR, a position originally and independently held by Henri Poincaré (1902),Henri Poincaré, Science and Hypothesis. New York: Dover, 1952 .Poincaré's structuralism was combined with neo-Kantian views about the nature of arithmetic. Bertrand Russell (1927),Bertrand Russell (1927). The Analysis of Matter, London: George Allen & Unwin. and Rudolf Carnap (1928),Rudolf Carnap (1928). The Logical Structure of the World, Berkeley: University of California Press. was resurrected by John Worrall (1989), who proposes that there is retention of structure across theory change. Worrall, for example, argued that Fresnel's equations imply that light has a structure and that Maxwell's equations, which replaced Fresnel's, do also; both characterize light as vibrations. Fresnel postulated that the vibrations were in a mechanical medium called "ether"; Maxwell postulated that the vibrations were of electric and magnetic fields. The structure in both cases is the vibrations and it was retained when Maxwell's theories replaced Fresnel's.J. Worrall (1989). "Structural realism: The best of both worlds?" Dialectica, 43: p. 119; available online. Because structure is retained, structural realism both (a) avoids pessimistic meta-induction and (b) does not make the success of science seem miraculous, i.e., it puts forward a no-miracles argument.The term is due to Hilary Putnam (see Putnam, H., 1975. Mathematics, Matter and Method, Cambridge: Cambridge University Press, p. 73).

Newman problem The so-called Newman problem (also Newman's problem, Newman objection, Newman's objection) refers to the critical notice of Russell's The Analysis of Matter (1927) published by Max Newman in 1928.M. H. A. Newman, 1928. "Mr. Russell's causal theory of perception," Mind, 37: 137–148. Newman argued that the ESR claim that one can know only the abstract structure of the external world trivializes scientific knowledge. The basis of his argument is the realization that "[a]ny collection of things can be organized so as to have structure W, provided there are the right number of them", where W is an arbitrary structure.Roman Frigg and Ioannis Votsis (2011), "Everything you always wanted to know about structural realism but were afraid to ask," European Journal for Philosophy of Science 1(2):227–276, esp. p. 250.

Response to the Newman problem John Worrall (2000) advocates a version of ESR augmented by the Ramsey sentence reconstruction of physical theoriesWorrall, J. (2000), "Miracles and Models: Saving Structural Realism?", paper given to the Annual Meeting of the British Society for the Philosophy of Science, Sheffield, 2000. (a Ramsey sentence aims at rendering propositions containing non-observable theoretical terms clear by substituting them with observable terms). John Worrall and Elie Georges Zahar (2001) claim that Newman's objection applies only if a distinction between observational and theoretical terms is not made.Worrall, J. and Zahar, E. (2001), "Ramseyfication and Structural Realism", Appendix IV in E. Zahar, Poincare's Philosophy: From Conventionalism to Phenomenology, Chicago and La Salle (IL): Open Court.

Ramsey-style epistemic structural realism is distinct from and incompatible with the original Russellian epistemic structural realismVotsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, p. 122. (the difference between the two being that Ramsey-style ESR makes an epistemic commitment to Ramsey sentences, while Russellian ESR makes an epistemic commitment to abstract structures, that is, to (second-order) isomorphism classes of the observational structure of the world and not the (first-order) physical structure itself).Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, pp. 43 and 122. Ioannis Votsis (2004) claims that Russellian ESR is also impervious to the Newman objection: Newman falsely attributed the trivial claim "there exists a relation with a particular abstract structure" to ESR, while ESR makes the non-trivial claim that there is a unique physical relation that is causally linked with a unique observational relation and the two are isomorphic.Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, p. 129.

Further criticism The traditional scientific realist and notable critic of structural realism Stathis Psillos (1999) remarks that "structural realism is best understood as issuing an epistemic constraint on what can be known and on what scientific theories can reveal."Stathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. 142. He thinks that ESR faces a number of insurmountable objections.Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, pp. 68–9. These include among others that ESR's only epistemic commitment is uninterpreted equations which are not by themselves enough to produce predictionsStathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. 141. and that the "structure versus nature" distinction that ESR appeals to cannot be sustained.Stathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. 148.

Votsis (2004) replies that the structural realist "does subscribe to interpreted equations, but attempts to distinguish between interpretations that link the terms to observations from those that do not"Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, pp. 73–4. and he can appeal to the Russellian view that "nature" just means the non-isomorphically specifiable part of entities.Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, p. 104.

Psillos also defends David Lewis's descriptive-causal theory of referenceStathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. 279. (according to which the abandoned theoretical terms after a theory change are regarded as successfully referring "after all") and claims that it can adequately deal with referential continuity in conceptual transitions, during which theoretical terms are abandoned,Stathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. 271. thus rendering ESR redundant.

Votsis (2004) replies that a scientific realist needs not tie the approximate truth of a theory to referential success.Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, p. 148. Notably, structural realism initially did not dictate any particular theory of reference;Votsis, I. (2004), The Epistemological Status of Scientific Theories: An Investigation of the Structural Realist Account, University of London, London School of Economics, PhD Thesis, p. 219. however Votsis (2012) proposed a structuralist theory of reference according to which "scientific terms are able to refer to individual objects, i.e. in a term-by-term fashion, but that to fix this reference requires taking into account the relations these objects instantiate" (in this view, structural descriptions serve as reference determiners).Ioannis Votsis, "A Structuralist Theory of Reference", Invited talk presented at the Reference and Scientific Realism Symposium, Wuhan University, August 17, 2012.

Ontic structural realism While ESR claims that only the structure of reality is knowable, ontic structural realism (OSR) goes further to claim that structure is all there is. In this view, reality has no "nature" underlying its observed structure. Rather, reality is fundamentally structural, though variants of OSR disagree on precisely which aspects of structure are primitive. OSR is strongly motivated by modern physics, particularly quantum field theory, which undermines intuitive notions of identifiable objects with intrinsic properties. Some early quantum physicists held this view, including Hermann Weyl (1931),Hermann Weyl, 1950 . The Theory of Groups and Quantum Mechanics (translated by H. P. Robertson). New York: Dover. Ernst Cassirer (1936),Ernst Cassirer, 1956 . Determinism and Indeterminism in Modern Physics, New Haven: Yale University Press. and Arthur Eddington (1939).Arthur Eddington (1939), The Philosophy of Physical Science, Cambridge University Press. Recently, OSR has been called "the most fashionable ontological framework for modern physics".Kuhlmann, Meinard, "Quantum Field Theory", The Stanford Encyclopedia of Philosophy (Summer 2015 Edition), Edward N. Zalta (ed.).

Max Tegmark takes this concept even further with the mathematical universe hypothesis, which proposes that, if our universe is only a particular structure, then it is no more real than any other structure.Berthold, Oswald. "Computational Universes." Berlin: Humboldt Universitat zu Berlin, Institut fur Informatik (2009), p. 15.

Definition of structure