Brief Account

Three major kinds of structural realism can be identified, each with its own satellite variants:

(1) Epistemic Structural Realism, or ESR for short, holds that our epistemic access is restricted to structural features of the world.

The position can be traced back at least to the beginning of the 20th century, namely to the independent work of Henri Poincaré and Bertrand Russell. The latter's structuralist inclinations can be seen as early as The Problems of Philosophy (1912). A fully-fledged account only emerged in The Analysis of Matter (1927). There he argued that there are external causes to our perception, admitting that we should “not expect to find a demonstration that perceptions have external causes” (1927, 198). The twentieth chapter of this book is devoted to a causal theory of perception, rejecting “the view that perception gives direct knowledge of external objects” (1927, 197). We only have direct epistemic access to percepts, i.e. the items of our perception. The only way to attain knowledge of the external world is to draw inferences from our perceptions. To underwrite such inferences Russell employed a number of principles. The most important of these are:

Helmholtz-Weyl Principle (H-W): Different effects (i.e. percepts) imply different causes (i.e. stimuli/physical objects)) (1927, 255).*

Mirroring Relations Principle (MR): Relations between percepts mirror (i.e. have the same logico-mathematical properties as) relations between their non-perceptual causes (1927, 252).

Armed with these assumptions Russell argues that from the structure of our perceptions we can “infer a great deal as to the structure of the physical world, but not as to its intrinsic character” (1927, 400). More precisely, he argues that there is at most an isomorphic relation between the structure of our perceptions and the structure of the physical world.

The recent interest in structural realism was instigated by the publication of John Worrall’s ‘Structural Realism: The Best of Both Worlds?’ in 1989. The article is inspired by Poincaré's brand of ESR which is more sensitive to the history of science. Worrall associates the search for a lasting solution to the scientific realism debate with the need to take into consideration two warring arguments: the no-miracles argument (NMA) and the pessimistic meta-induction argument (PMI). In short, PMI holds that since predictively successful scientific theories have eventually been discarded, we have inductive evidence that even our current theories, despite being even more successful, will also be discarded one day. NMA holds that realism is the only view that does not make the predictive success of science a miracle. Worrall offers ESR as a weaker (in terms of epistemic commitments) but more justifiable realist position that underwrites both of these arguments, and situates itself midway between constructive empiricism and traditional scientific realism. It underwrites the NMA because it argues that the success of science reflects the fact that we have got the structure of the world right. It underwrites the PMI because it concedes that although there is radical discontinuity in theory change, viz. where non-structural descriptions of the nature of entities are involved, there is also considerable continuity at the structural level.

Stathis Psillos calls the Russellian approach the ‘upward path’ to structural realism, in contrast to the Poincaréan/Worrallian approach or ‘downward path’ to structural realism. One important difference lies in the way the two views are motivated. The Poincaréan approach takes the preservation of structure through theory change as indicative of its truth/approximate truth. The Russellian approach looks not in history but in perception to provide a reconstruction of our non-perceptual knowledge about the world. Another related difference concerns the way in which structure gets demarcated. Worrall and Elie Zahar (2001) favour the Ramsey sentence approach, while Ioannis Votsis (2003, 2005) rejects it in favour of the notion of abstract structure as it is explicated in Michael Redhead (2001). Of course the disagreement is not merely a question of which formal tools are best equipped for the job of representing the structure of the world but also a question of how to draw the line between the structural and the non-structural.

(2) Ontic Structural Realism, or OSR for short, holds that our ontology is in some sense primarily structural in nature.

If this sounds sufficiently ambiguous, it is because there are so many different variants of OSR that it is difficult to formulate a commonly shared view. OSR was proposed by James Ladyman (1998). The view was subsequently developed jointly with Steven French. Together they argue that structural realism should be understood not just as an epistemic but also as an ontic position. The motivation for OSR draws on underdetermination in modern, and particularly in quantum, physics. Although originally promoted as the view that only structures exist, i.e. objects can be no more than heuristic vehicles, the position has mutated into a number of different variants. One such variant, which we can call the ‘no individuals view’, denies the existence of individuals but accepts the existence of objects and structures. If you’re wondering what sort of objects these are, they are those for which the law of identity does not hold (see, for example, Steven French and Decio Krause 2006). Another variant, which we can call the ‘no intrinsic natures view’, holds that there exist no intrinsic natures, only haecceity-free individuals and structures (e.g. Ladyman et al. 2007). These two as well as the other main OSR alternatives are wonderfully sketched out in Ladyman’s Structural Realism entry in the Stanford Encyclopaedia of Philosophy (2007).

(3) Methodological Structural Realism, or MSR for short, concentrates on the role shared structure plays in characterising scientific theories, in relating high-level theory to low-level data and in identifying links between predecessor and successor theories (see Katherine Brading and Elaine Landry 2006).

Endnote: * The name 'Helmholtz-Weyl' is given by Stathis Psillos (2001) because, according to him, it was they "who first enunciated it". Though I kept the name, the principle goes at least as far back as Descartes. Hume advertises in the Treatise that “Like causes still produce like effects” (Book II, Part III, §1). This is the H-W principle in contrapositive form. Similarly, Descartes in the sixth Meditation says: "I safely conclude that there are in the bodies from which the diverse perceptions of the senses proceed, certain varieties corresponding to them, although, perhaps, not in reality like them; and since, among these diverse perceptions of the senses, some are agreeable, and others disagreeable, there can be no doubt that my body, or rather my entire self, in as far as I am composed of body and mind, may be variously affected, both beneficially and hurtfully, by surrounding bodies".

References: Brading, K. and E. Landry (2006) ‘Scientific Structuralism: Presentation and Representation’, Philosophy of Science, vol. 73(5):571-581.

French, S. and D. Krause (2006) Identity in Physics: A Historical, Philosophical and Formal Analysis, Oxford: Oxford University Press.

Frigg, R. and I. Votsis (2011) ‘Everything you Always Wanted to Know about Structural Realism but Were Afraid to Ask’, European Journal for Philosophy of Science, 2011, vol. 1(2): 227–276.

Ladyman, J. (1998) ‘What is Structural Realism?’, Studies in History and Philosophy of Science, vol. 29: 409-424.

Ladyman, J. (2007) ‘Structural Realism’, The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.), URL =

Ladyman, J. and D. Ross (with D. Spurrett and J. Collier) (2007) Every Thing Must Go: Metaphysics Naturalised, Oxford: Oxford University Press.

Poincaré, H. ([1905]1952) Science and Hypothesis, New York: Dover.

Psillos, S. (2001) ‘Is Structural Realism Possible?’, Philosophy of Science, vol. 68: S13-24.

Redhead, M.L.G. (2001) ‘The Intelligibility of the Universe’, in A.O'Hear (ed.) Philosophy at the New Millennium, Cambridge: Cambridge University Press.

Russell, B. (1912) The Problems of Philosophy, Oxford: Oxford University Press.

Russell, B. (1927) The Analysis of Matter, London: George Allen & Unwin.

Votsis, I. (2003) ‘Is Structure not Enough?’, Philosophy of Science, vol. 70(5): 879-890.

Votsis, I. (2005) ‘The Upward Path to Structural Realism’, Philosophy of Science, vol. 72(5): 1361-1372.

Worrall, J. (1989) ‘Structural Realism: The Best of Both Worlds?’ in Papineau, D. (ed.) The Philosophy of Science, Oxford: Oxford University Press, 1996.

Worrall, J. and E. Zahar (2001) ‘Ramseyfication and Structural Realism’, Appendix IV in E. Zahar, Poincaré's Philosophy: From Conventionalism to Phenomenology, Chicago and La Salle (IL): Open Court.

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