Super-Humeanism and Mental Causation
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Super-Humeanism and mental causation Michael Esfeld University of Lausanne, Department of Philosophy CH-1015 Lausanne, Switzerland [email protected], www.michaelesfeld.com (for Anna Marmodoro, Christopher Austin and Andrea Roselli (eds.): Time, laws and free will, Dordrecht: Springer, Synthese Library) (final version 8 August 2021) Abstract The stance that has become known as Super-Humeanism is a minimal ontology of the natural world in the spirit of scientific realism. The paper enquires to what extent this ontology, due to its parsimony, can be employed to remove commitments from the scientific image that are the source of the clash with the view of ourselves as persons (the manifest image). The paper argues that Super-Humeanism provides the conceptual space to accommodate persons as irreducible to matter in motion, attribute to them free will (even in the libertarian sense) and recognize their volitions as causing some of their behaviour without coming into conflict with science. Keywords: free will, Humeanism, libertarianism, manifest image, mental causation, persons, scientific image, Super-Humeanism 1. (Super-)Humeanism, laws and free will At the core of how we conceive of ourselves as persons, there is free will and mental causation in the sense that a good deal of our behaviour is caused by free decisions. We could have done otherwise and are therefore responsible for what we actually do. This conception of ourselves is part and parcel of what is called – following Sellars (1962) – the manifest image. This paper seeks to make a new contribution to bring this conception of ourselves together with the scientific image. The idea is that an ontology that is minimally sufficient to accommodate what natural science (notably physics) tells us about the world leaves enough conceptual space open to include the central features of the view of ourselves as persons. What is known as Super-Humeanism is a minimal ontology in this sense. On the basis of what Super-Humeanism says about physical magnitudes, laws and causation, this paper points out the conceptual space left open for free will (this section) and then explores the account of persons and mental causation that can be built on this basis. Humeanism about laws of nature and causation in the natural world is, roughly speaking, the view that first comes the configuration of matter of the universe and its evolution, then come the laws and with them causal relationships between events as supervening on the evolution of the configuration of matter. Hence, it is not the laws or causation that fix, determine or produce that evolution. Quite the contrary, the evolution that actually happens fixes or determines the laws and with them causal relationships. Causal relationships between earlier and later stages of that evolution obtain, but they depend on the evolution that actually occurs instead of predetermining it. There are laws because this evolution exhibits some stable, but contingent regularities. Given such regularities, what is known as the best system Super-Humeanism and mental causation 2 is the system that achieves the optimal combination of simplicity and informational content in representing the evolution of the configuration of matter of the universe. Laws are theorems of the best system. The laws then specify which causal relationships obtain. The best system – and thus the laws – can be deterministic in the sense that given the propositions stating the laws and the specification of initial conditions about the configuration of matter at any given time, the propositions about the entire past and future evolution of the configuration of matter are entailed by these propositions. But there is no predetermination of anything. The supervenience basis for the laws is, strictly speaking, the entire evolution of the configuration of matter of the universe. Hence, if one formulates laws on the basis of the configuration of matter and its evolution that is accessible to us at the present day, one may be justified in taking these laws to be the laws of the universe (or approximations of them). But even if this is so, there is nothing in the present configuration of matter and the laws, thus conceived, that governs, predetermines or even produces the future evolution of the configuration of matter. That notwithstanding, the laws still are explanatory, namely in the sense of unification: they bring out the salient patterns in the evolution of the configuration of matter. Explanations in science end once such patterns are identified. For instance, suppose that a law of gravitation is part of the best system. Science cannot explain why there is gravitation, that is, why bodies attract each other. Science can only trace the particular phenomena of attractive motion back to the general pattern of gravitation. The same holds in case the best system contains no deterministic, but only probabilistic laws. Again, the laws and with them the objective probabilities for certain events to occur supervene, strictly speaking, on the entire evolution of the universe. This comes out in a clear manner in what is known as the Mentaculus account presented in Loewer (2012). Our assumptions about the objective probabilities for future events formulated on the basis of the configuration of matter and the evolution that is accessible to us at the present day can be correct. Yet, there is nothing in the present configuration of matter and the laws, thus conceived, that instantiates a tendency in nature for a particular future evolution to occur. In other words, there are no fundamental propensities, dispositions or power in nature that ground the objective probabilities. Against this background, it has been established in the literature that Humeanism offers a distinct stance to make laws of nature – be they deterministic or probabilistic – compatible with human free will. Jenann Ismael, in her recent book How physics makes us free, writes: When we adopt a globalist perspective, our activities become part of the pattern of events that make up history. Since our activities partly determine the pattern, and the pattern determines the laws, our activities partly determine the laws.1 Hence, free will is compatible with the laws of nature because the physical events that are expressions of the free will of humans are part and parcel of the supervenience basis of the laws. By way of consequence, if persons had chosen to do otherwise, the laws of nature would have been slightly different. However, one can object that this stance gives us too much: our bodily movements are not that important in the universe that they have an influence on what the laws of nature are.2 1 Ismael (2016, p. 111; see also pp. 225-226). See also Beebee and Mele (2002), Swartz (2003, ch. 11, in particular p. 127) and Perry (2004, pp. 237-239). 2 See the objection of Hüttemann and Loew (2019) and Hüttemann (this volume, ch. 1). Super-Humeanism and mental causation 3 Whatever humans choose to do, the laws will be the same. Quite the contrary, laws of nature are useful for our actions, because they set the frame for what we can do and what we cannot do. In other words, we need laws of nature and must keep them fixed to delimit the range within which we can freely choose our actions. For instance, a person can choose to walk slowly or quickly, but she cannot jump up to the roof of her house – gravitation prevents her from doing so. How fast and in which direction her body moves is an issue of the initial conditions and not of the laws. It is here that the position that has become known as Super-Humeanism in recent years makes a contribution to the free will debate.3 It thereby joins several proposals that have been set out recently and that all seek to vindicate free will not by taking human decisions to contribute to determining what the laws are, but to contribute to determining what exactly the initial or boundary conditions of the universe are.4 Super-Humeanism is in the first place a proposal for an even more parsimonious ontology of the natural world than standard Humean metaphysics as exemplified by David Lewis’s thesis of Humean supervenience, formulated in Lewis (1986, introduction). It deletes the commitment to natural intrinsic properties instantiated at space-time points and keeps only the commitment to one type of natural relation, namely distance relations individuating point particles. The ontology of the physical world is given by these two axioms conceived in Esfeld and Deckert (2017, p. 21): (1) There are distance relations that individuate simple objects – namely, matter points. (2) The matter points are permanent, with the distances between them changing. Everything else supervenes on the Humean mosaic thus defined. Consequently, not only the laws, but also all the physical magnitudes apart from position supervene on the relative positions of the point particles and their evolution throughout the history of the universe. The reason is that in physical theories, only position has to be admitted as primitive and all the other magnitudes can be introduced in terms of their functional role for the evolution of the particle positions and thus be located in that evolution.5 That is to say: the values of such diverse magnitudes as mass, charge, constants of nature, the wave function of the universe, etc. are not instantiated in the initial configuration of matter of the universe, but are fixed only in the course of the evolution of that configuration. Super-Humeanism hence is a parsimonious ontology – arguably the most parsimonious one – that endorses scientific realism: it frees us not only from the heavy metaphysical baggage that comes with countenancing primitive modality (fundamental dispositions, powers, laws as primtives, etc.), but also from the problems that arise from subscribing to natural intrinsic properties: if they are not dispositions or powers, implementing a primitive modality, they are categorical properties with the ensuing commitments to quidditism and humility, as acknowledged by Lewis (2009).