James Ladyman

What is a complex system

Complex systems research is becoming ever more important in both the natural and social sciences. It is commonly implied that there is such a thing as a complex system, different examples of which are studied across many disciplines. However, there is no concise definition of a complex system, let alone a definition on which all scientists agree. We review various attempts to characterize a complex system, and consider a core set of features that are widely associated with complex systems in the literature and by those in the field. We argue that some of these features are neither necessary nor sufficient for complexity, and that some of them are too vague or confused to be of any analytical use. In order to bring mathematical rigour to the issue we then review some standard measures of complexity from the scientific literature, and offer a taxonomy for them, before arguing that the one that best captures the qualitative notion of the order produced by complex systems is that of the Statistical Complexity. Finally, we offer our own list of necessary conditions as a characterization of complexity. These conditions are qualitative and may not be jointly sufficient for complexity. We close with some suggestions for future work.

On representing the relationship between the mathematical and the empirical

We examine, from the partial structures perspective, two forms of applicability of mathematics: at the “bottom” level, the applicability of theoretical structures to the “appearances”, and at the “top” level, the applicability of mathematical to physical theories. We argue that, to accommodate these two forms of applicability, the partial structures approach needs to be extended to include a notion of “partial homomorphism”. As a case study, we present London’s analysis of the superfluid behavior of liquid helium in terms of Bose‐Einstein statistics. This involved both the introduction of group theory at the top level, and some modeling at the “phenomenological” level, and thus provides a nice example of the relationships we are interested in. We conclude with a discussion of the “autonomy” of London’s model.

Reinflating the Semantic Approach

Abstract The semantic, or model‐theoretic, approach to theories has recently come under criticism on two fronts: (i) it is claimed that it cannot account for the wide diversity of models employed in scientific practice—a claim which has led some to propose a “deflationary” account of models; (ii) it is further contended that the sense of “model” used by the approach differs from that given in model theory. Our aim in the present work is to articulate a possible response to these claims, drawing on recent developments within the semantic approach itself. Thus, the first is answered by utilizing the notion of a “partial structure”, first introduced in this context by da Costa and French in 1990. The second claim is undermined by consideration of van Fraassens understanding of “model” which corresponds well with that evinced by modem mathematicians. This latter discussion, in particular, has an impact on the continuing debate regarding the relative merits of the semantic and syntactic views and the developm...

What's Really Wrong with Constructive Empiricism? Van Fraassen and the Metaphysics of Modality

Constructive empiricism is supposed to offer a positive alternative to scientific realism that dispenses with the need for metaphysics. I first review the terms of the debate before arguing that the standard objections to constructive empiricism are not decisive. I then explain van Fraassens views on modality and counterfactuals, and argue that, because constructive empiricism recommends on epistemological grounds belief in the empirical adequacy rather than the truth of theories, it requires that there be an objective modal distinction between the observable and the unobservable. This conclusion is incompatible with van Fraassens empiricism. Finally I explain some further problems for constructive empiricism that arise when we consider modal matters.

Structural realism versus standard scientific realism: the case of phlogiston and dephlogisticated air

The aim of this paper is to revisit the phlogiston theory to see what can be learned from it about the relationship between scientific realism, approximate truth and successful reference. It is argued that phlogiston theory did to some extent correctly describe the causal or nomological structure of the world, and that some of its central terms can be regarded as referring. However, it is concluded that the issue of whether or not theoretical terms successfully refer is not the key to formulating the appropriate form of scientific realism in response to arguments from theory change, and that the case of phlogiston theory is shown to be readily accommodated by ontic structural realism.

The dissolution of objects: Between platonism and phenomenalism

One of the motivations for Ladyman’s ‘ontic’ form of SR is that it offers the realist some hope that she may be able to get away with carrying less metaphysical baggage than the ‘standard’ realist without having to fall into the clutches of the constructive empiricist. This seems to us to be a particularly important consideration when it comes to the foundations of quantum physics, whether QM or QFT. In the context of the former, one of us has long argued for a kind of metaphysical underdetermination between particles-as-individuals and particles-as-non-individuals. Ladyman has further insisted that a realism which refuses to address the issue of which package to adopt is a realism in name only, Ontic SR effectively side-steps the underdetermination and thus allows the realist to drop the metaphysics by focusing on the commonality of structure. Cao’s response is to insist that there is no metaphysics to be dropped since we can understand individuality in terms of distinguishability (à la Strawson), which in turn can be empirically ascertained. But this is problematic. First of all, this metaphysical underdetermination is predicated on a conceptual distinction between individuality and distinguishability (one of us – French – has tried to make this clear in all his published work on this subject). If one wishes to deny this distinction then some argument must be given, otherwise the move smacks of simple question begging. More importantly, however, the kind of understanding of individuality Cao supports is famously problematic. If distinguishability is to ground the individuality of things then some form of metaphysical guarantee must be

In Defence of Ontic Structural Realism

In this paper we clarify how ‘epistemic’ (ESR) and ‘ontic’ structural realism (OSR) should be understood and reply to some important criticisms of the latter. We shall begin with an outline of the historical origins of what might broadly be called the ‘structuralist tendency’ within philosophy of science. This has come to be identified with a form of ‘structural realism’ but it should be noted that it also includes those who adopt an anti-realist or empiricist stance. Because of the width of its embrace and its complex history, defining what is meant by ‘structure’ and characterising the tendency in general, is problematic. However, we begin by pointing out that the structuralist tendency always involves a shift in focus away from objects – however they are metaphysically conceived – to the structures in which they are (supposedly) embedded (where the reason for the qualifier ‘supposedly’ will become clear shortly). This is vague but the tendency, both historically and in its current incarnation, is not monolithic but rather includes various overlapping subgroups of structuralists.

Identity and Discernibility in Philosophy and Logic

Questions about the relation between identity and discernibility are important both in philosophy and in model theory. We show how a philosophical question about identity and discernibility can be ‘factorized’ into a philosophical question about the adequacy of a formal language to the description of the world, and a mathematical question about discernibility in this language. We provide formal definitions of various notions of discernibility and offer a complete classification of their logical relations. Some new and surprising facts are proved; for instance, that weak discernibility corresponds to discernibility in a language with constants for every object, and that weak discernibility is the most discerning non-trivial discernibility relation.

What does it mean to say that a physical system implements a computation

When we are concerned with the logical form of a computation and its formal properties, then it can be theoretically described in terms of mathematical and logical functions and relations between abstract entities. However, actual computation is realised by some physical process, and the latter is of course subject to physical laws and the laws of thermodynamics in particular. An issue that has been the subject of much controversy is that of whether or not there are any systematic connections between the logical properties of computations considered abstractly and the thermodynamical properties of their concrete physical realizations. Landauer [R. Landauer, Irreversibility and heat generation in the computing process, IBM Journal of Research and Development 5 (1961) 183-191. Reprinted in Leff and Rex (1990)] proposed such a general connection, known as Landauers Principle. To resolve this matter an analysis of the notion of the implementation of a computation by a physical system is clearly required. Another issue that calls for an analysis of implementation is that of realism about computation. The account of implementation presented here is based on the notion of an L-machine. This is a hybrid physical-logical entity that combines a physical device, a specification of which physical states of that device correspond to various logical states, and an evolution of that device which corresponds to the logical transformation L. The most general form of Landauers Principle can be precisely stated in terms of L-machines, namely that the logical irreversibility of L implies the thermodynamic irreversibility of every corresponding L-machine.

Structural Realism and the Relationship between the Special Sciences and Physics

The primacy of physics generates a philosophical problem that the naturalist must solve in order to be entitled to an egalitarian acceptance of the ontological commitments he or she inherits from the special sciences and fundamental physics. The problem is the generalized causal exclusion argument. If there is no genuine causation in the domains of the special sciences but only in fundamental physics then there are grounds for doubting the existence of macroscopic objects and properties, or at least the concreteness of them. The aim of this paper is to show that the causal exclusion problem derives its force from a false dichotomy between Humeanism about causation and a notion of productive or generative causation based on a defunct model of the physical world.