The Structure of the World by Steven French

 

Context

Positivism is a philosophical school that holds that all genuine knowledge is either true by definition, or positive, referring to a posteriori facts derived by reason and logic from sensory experience. Other ways of knowing, such as intuition, introspection, or religious faith, are rejected or considered meaningless.

Positivism was replaced by Antirealism, a philosophy that denies the existence of an objective reality independent of our perceptions, beliefs, or theories. Antirealism argues that scientific language should not be taken literally.

Realism in the philosophy of science opposes Antirealism and asserts that the world exists independently of our thoughts and that our perceptions can provide us with knowledge about that world.

The recent structuralist realism approaches to the philosophy of science are based on John Worrall's paper, Structural Realism: The Best of Both Worlds? (1989). His presentation of structural realism reads:

"On the structural realist view what Newton really discovered are the relationships between phenomena expressed in the mathematical equations of his theory."

The author proposes that there is a retention of structure, despite theory change. This concept of the philosophy of science is related to that of epistemic structural realism, a position originally and independently held by Henri Poincaré, Bertrand Russell and Rudolf Carnap. They claimed that only the structure of reality is knowable, not reality itself.

When the target of explanation becomes science itself and its history of empirical success as a whole, we arrive at the no-miracles argument famously presented in 1975 by Hilary Putnam as follows:

"The positive argument for realism is that it is the only philosophy that doesn’t make the success of science a miracle."

In the same year as Worrall, Howard Stein signalled a more radical departure from realist physics:

"[O]ur science comes closest to comprehending “the real”, not in its account of “substances” and their kinds, but in its account of the “Forms” which phenomena “imitate”." 

“Forms” here refers to theoretical structures and “imitate” to representations.

In 1999 Michael Redhead stated:

“the best candidate for what is ‘true’ about a physical theory is the abstract structural aspect”. 

Ontic structural realism goes beyond epistemic structural realism to claim that there is only structure. This implies that reality does not possess a 'nature' below its observable structure. Reality is structural.

Worrall questions standard scientific realism which, he asserts, states that the nature of the unobservable objects that cause the phenomena we observe is correctly described by our best theories. For example, the reason the same side of the Moon always faces the Earth was explained by Newton in the third book of Principia in terms of a gravitational tidal lock, and this explanation and related counterfactuals and predictions are retained in current physics even though Newtonian gravitation has been superseded by General Relativity. Against this approach Worrell proposes that we should adopt structural realism and commit ourselves to the mathematical or structural content of our theories. He asserts that there is retention of structure across theory change. Structural realism avoids us accepting beliefs about the theory’s description of the furniture of the world and also averts committing us to the claim that the theory’s structure, apart from its empirical content, describes the world.

The cosmologist Max Tegmark takes this concept even further in his mathematical universe hypothesis, which is a speculative 'theory of everything'. The hypothesis is that the universe is a mathematical object in itself. Tegmark hypothesises that all mathematical objects exist, which he describes as a form of Platonism. He concludes that if our universe is only a particular structure, then it is no more real than any other structure.

Commentary

The Structure of the World: Metaphysics and Representation by Steven French was published in 2014.

Preface

The author characterises as 'bottom-up' metaphysics the idea that reality is made up of objects with properties which are connected in ways that scientific laws describe. It is based on intuition, but fails when applied to physics and biology.

The author suggests an alternative approach, which he defines as top-down. It requires that we create our metaphysical concepts from the best theories. He defends a form of structural realism that asserts that the fundamental being of the world is one of structures and that objects, as we normally conceive them, are derivative and even eliminable.

In Chapter 1 he addresses Pessimistic Meta-Induction. This is the argument that if past successful and accepted scientific theories were found to be false, we have no reason to believe the scientific realist's claim that our currently successful theories are approximately true. 

In his notion of epistemic structural realism, Worrall offered the hope that this could include quantum theory. However, as Décio Krause and French argue, you can articulate, formally and metaphysically, a notion of non-individual objects within quantum physics and you can show that quantum mechanics is compatible with the notion of an individual object.

Chapter 2 deals with underdetermination and the ways in which it might be avoided or broken. The underdetermination thesis asserts that all evidence necessarily underdetermines any scientific theory. Underdetermination exists when available evidence is insufficient to identify which belief one should hold about that evidence.

French analyses underdetermination to find ways to eliminate objects from metaphysical examination, aiming for a more minimal position than the standard one. However, he is careful to retain a balance so that his metaphysical position does not collapse.

To achieve this metaphysical equilibrium whilst minimising object recognition French deals with Chakravartty’s Challenge, which emphasises that realist philosophy needs to provide a clear understanding while remaining metaphysically informed.

Chakravartty's Challenge primarily addresses the nature of scientific theories and the status of scientific realism versus antirealism. He argues that scientific theories should be understood in terms of their empirical adequacy rather than their truth. This challenge raises questions about how we can know what exists in the world based on scientific theories and whether these theories can truly represent reality or if they are merely useful tools for predicting observations.

The challenge often involves discussions about the interpretation of scientific theories, the role of models in science, and the implications of scientific practice for our understanding of reality. It invites further exploration into how scientific knowledge is constructed and the philosophical implications of that construction.

Chapter 3 explains that in order to achieve the necessary equilibrium French adopts the ‘Viking Approach’ to metaphysics. This means plundering metaphysics for appropriate resources that he can then use to articulate a structuralist ontology. Kerry McKenzie has suggested alternative imagery in which metaphysics is regarded as a toolbox, from which we can take various implements to use in order to fashion an appropriate notion of structure.

Chapter 4 is a historical review of structuralist ideas. It covers Poincaré, Wigner, Weyl, and the Application of Group Theory, Quantum Statistics, Eddington’s Subjective Structuralism, Braithwaite, Cassirer’s Kantianism, Space-time, Structures, and Group Theory, Quantum Mechanics, Causality, and Objects.

In Chapter 5, French sets out his answer to the question: ‘what is structure?’. He affirms that the structure of the world is presented to us by means of the relevant laws and symmetries. Philosophers of science then represent that structure by means of various meta-level resources, such as the Semantic Approach. The author opts for the interpretation of Melia and Saatsi and their emphasis on the intentional character of laws. They encourage a careful analysis of the language and concepts used in science, which can lead to a deeper understanding of the nature of scientific knowledge, but not of the nature of reality itself.

The semantic approach is often situated within the broader debate between scientific realism (the view that scientific theories accurately describe the world) and antirealism (the view that theories are merely useful instruments for predicting observations).

The Melia and Saatsi semantic approach refers to a framework for understanding and analysing the semantics of scientific theories, particularly in the context of scientific realism and antirealism debates. This approach emphasises the importance of the meanings of terms and concepts used in scientific theories and how they relate to the entities and phenomena they describe.

One aspect of this approach focuses on the semantic content of scientific theories, which includes the meanings of the terms and the relationships between them. This is important for understanding how theories represent the world.

In theory-entity relations the authors explore how scientific theories relate to the entities they hypothesise. This involves examining how theoretical terms refer to real or abstract entities and the implications for scientific realism.

Melia and Saatsi also discuss the role of models in scientific practice, emphasising how models can serve as intermediaries between theories and the world, and how their semantic content can influence our understanding of scientific claims.

In Chapter 6 the author tackles the issue of how we are to understand the presentation of the structure of the world in terms of the laws and symmetries of the relevant theories, in particular, the role of the mathematics of group theory in informing this picture, and of the specific nature of certain symmetries that feature in current physics.

Chapter 7 adopts the Viking Approach in order to indicate how an eliminativist stance towards objects does not need to have the devastating implications that some take it to have. In particular, he argues that we can still tell truths about physical objects, while eliminating them from our fundamental ontology in favour of structure. 

Chapter 8 understands structure to be physical, but distinguishing the physical from the non-physical, and from the mathematical, is problematic. A number of comparisons have been drawn between structural realism and structuralism in mathematics, mostly to the detriment of the former, and he thinks these comparisons have come from an inappropriate basis. 

One significant difference between the mathematical and physical realms concerns the supposed role of causality and he considers how this might be integrated within ontic structural realism. He suggests that we should focus on the relevant dependencies underpinning the causal claims. 

Chapter 9 analyses the two main rivals to the causal claims: Humean structuralism, which assumes the structure to be categorical, and dispositional structuralism, represented by Chakravartty’s semi-realism. This holds that the structure flows from or is grounded in an understanding of the relevant properties. 

French argues that both views are problematic. Humean structuralism faces problems when it comes to its view of laws. Property dispositionalism also faces problems, especially when understanding fundamental properties in the context of modern physics.

However, the author esteems that dispositionalism can be effectively reverse engineered to offer a kind of structuralism which is modally informed. Once one has moved beyond the Humean stance and accepted that there is modality ‘in’ the world, the issue is where to place it. Here the difference between the object-oriented and the structural realist comes into play: the former reads ontology from theories at some remove, by taking the laws and symmetries that the theories present to be underpinned by property-possessing objects. The latter reads ontology directly from these theories, by taking the very same laws and symmetries as features of the structure of the world. Now, whereas the dispositionalist takes the laws to arise from or be dependent in some way upon the properties of those objects, he suggests that we should invert that order, taking the properties to be dependent upon the laws and symmetries. With this inversion, the associated modality is shifted. Thus, instead of expanding our fundamental ontology with dispositions, thereby inflating our metaphysical commitments, he stays with the structure that we read off our theories and invests that with the required modality.

His answer to the question ‘what is structure?’  is the laws and symmetries of our theories of contemporary physics, appropriately metaphysically understood via notions of dependence and taken as modally informed. 

Chapter 10 explores the nature of these dependencies and sets out a view of structure as primitively modal, which in the philosophy of science refers to the foundational concepts of possibility and necessity that underpin scientific theories, explanations, and reasoning. It is a critical area of inquiry for understanding how we interpret and engage with scientific knowledge since it deals with the fundamental ways in which we understand and categorise different kinds of possibilities and necessities within scientific theories and explanations.

French applies modal informing by spelling out the sense in which laws and symmetries encode the relevant possibilities via the relevant models. He then considers three issues: representation, fundamentality, and counterfactuals.

Regarding representation, he suggests that the vehicle of representation should be considered as extending beyond the immediate model used to describe a system and to involve modal features. With regard to fundamentality, he draws on recent work in metaphysics to suggest that laws, as determinables, are acceptable as elements of our ‘fundamental base’. 

Considering relationships between laws and counterfactuals, he argues that standard accounts of this relationship, and of the supposed necessity of laws, rely on an object-oriented image that the structuralist should reject. It is the primitive modality that gives laws their modal stability, as compared to accidents, and which explains those counterfactuals that are not rejected as inappropriate.

In Chapter 11 he examines the issue of unitarily inequivalent representations in quantum field theory, which is a theoretical framework that combines field theory and the principle of relativity with ideas behind quantum mechanics. Quantum field theory is used in particle physics to construct physical models of subatomic particles and in condensed matter physics to construct models of quasiparticles. It is the current standard model of particle physics.

The author then deals with the question of an appropriate ontology of quantum field theory. He presents the problem of how unitarily equivalent representations, different representations of the same physical system, can lead to different descriptions of the state space. For example, the position and momentum representations of quantum states are unitarily inequivalent. They can be deflated in various ways, and in particular by adopting the view of modality outlined in the previous chapter.

In Chapter 12, he draws on the work of Mitchell and others to explore the extent to which some kind of structuralist ontology can be articulated. Of course, the motivations are different, as it is not clear that the Pessimistic Meta-Induction represents the same threat as it does for physics-based realism, nor is there anything like the kind of metaphysical underdetermination regarding individuality as outlined in Chapter 3.

In his preface the author notes that given the reactions to the papers on which this chapter is based he emphasises that his intention is not to attempt an imperialistic extension of ontological structural realism, but simply to consider to what extent something like it can be sustained within biology.

Themes

Structure?

What do structural realists mean by 'structure'? Worrall's original paper discussed laws and equations describing certain mathematical relationships as surviving theory change. It is natural to fit this mathematical notion of structure into the theory offered by epistemic structural realists since, although there may be objects, we can't know their intrinsic nature, all we can know is the mathematical relationships they obey. 

However ontic structural realists, like French and his student, Ladybird, ask: how could there be nothing but mathematical relationships? There must be objects that are the subjects of these relationships. French's aim is to use the resources of contemporary metaphysics to make clear what the nature of the world's fundamental structure is and, in particular, how it is not mathematical, in order to answer what he calls "Chakravartty's challenge" to give a metaphysically informed, clear picture of the world.

French wants to distance himself from the structuralism defended by Bertrand Russell in The Analysis of Matter. Here the structure of the world is a system of relations between objects mirroring the relations between our perceptual experiences caused by those objects. French argues that any structuralism based on this picture of Russell's will have trouble accommodating quantum theory, in particular the lessons of quantum statistics. Quantum statistics (Bose-Einstein statistics for bosons, Fermi-Dirac statistics for fermions) differs from classical statistics in that they cannot be distinguished by any of their intrinsic or relational features, so can't be distinguished using a principle of the identity of indiscernibles. As early as 1926, Max Born called quantum particles "non-individuals". It is this quantum theory that leads French away from the more common Russellian structuralist ontology.

French offers compelling reasons to think a metaphysical position informed by physics should be suspicious of objects with either intrinsic or dispositional natures. As for what positively it should include, this is only the beginning of the discussion.

Modality

Modal realism posits that there are many possible worlds that are just as real as the actual world. Primitive modalities in this context involve the basic distinctions between what is possible, necessary, and impossible across these worlds.

In the philosophy of science, primitive modalities can be important for understanding how scientific explanations work. For instance, when scientists formulate theories, they often make claims about what is possible or necessary within a given framework. Understanding these modalities helps clarify the implications of scientific theories.

Primitive modality is linked to the discussion of counterfactuals, which are statements about what could have happened under different circumstances. In scientific reasoning, counterfactuals are crucial for understanding causal relationships and the implications of scientific laws.

The concept of primitive modality is also relevant when discussing the laws of nature. Philosophers debate whether these laws are merely descriptive (what happens) or prescriptive (what must happen), which ties into the necessity and possibility of events in the natural world.

Epistemic modality refers to the ways in which knowledge and belief interact with modality. In science, understanding what is epistemically possible (what we can know or believe) versus what is metaphysically possible (what could exist) is crucial for evaluating scientific claims.

Primitive modalities also play a role in discussions about induction and the justification of scientific generalisations. The ability to infer general laws from specific instances often relies on an understanding of what is possible or necessary in the context of the phenomena being studied.

Modal realism is the view propounded by the philosopher David Lewis that all possible worlds are real in the same way as is the actual world: they are "of a kind with this world of ours." This is based on modal epistemology, the exploration of how we know what is possible or necessary. It examines the ways in which we can justify claims about what could be the case or what must be the case.

Cutting the chain of correlations

In his most recent book, A Phenomenological Approach to Quantum Mechanics: Cutting the Chain of Correlations (2023), Steven French relies on concepts from phenomenology to explore the idea of how scientific theories and models can be understood in terms of their relationships and correlations rather than direct representations of reality.

French argues that the correlations between different scientific entities and phenomena can sometimes lead to a misunderstanding of the underlying nature of those entities. By "cutting the chain of correlations", he suggests that we should critically examine the connections we draw between different scientific theories and the entities they describe, rather than assuming that these correlations reflect a deeper, more fundamental reality.

This approach encourages a more nuanced understanding of scientific theories, emphasising the importance of context, interpretation, and the limitations of our models.