Ned Hall

What is the compositional structure of reality? That question divides naturally into these two: What is the compositional structure of the particulars that populate reality? And what is the structure of the properties and relations that fix what these entities are like? David Lewis‘s work in ontology and mereology provides the materials for an extraordinarily clean answer to the first question. First, among the particulars1 that populate reality are mereological simples: entities that have no proper parts. Second, every collection of such entities has a unique mereological fusion. And third, every particular is either a simple, or a fusion of simples.2 That‘s it. I propose to take this answer on board.3 What, then, about our second question? Here it looks as though we can draw on an additional Lewisian thesis: Joints: There is a distinction — at the level of metaphysics — between more and less natural properties. Some properties are perfectly natural; others are less-but-still-quite natural; still others are not very natural at all. This distinction earns its philosophical keep because of the number and centrality of the philosophical projects that must presuppose it. And to say that this distinction resides at the level of metaphysics is, at least in part, to say that it is not grounded in facts about human psychology.

This chapter investigates the prospects for an important position that falls under the "mere patterns" approach: what, for reasons that will emerge, the author calls"Humean reductionism" about laws of nature, a view championed perhaps most prominently by David Lewis. He reviews some of the most interesting arguments against this position from the literature, and adds some of his own that, he thinks, are more effective. The chapter considers how the best system account (BSA) would apply to the Newtonian particle world. The BSA has been challenged in a wide variety of ways: it violates certain intuitions; It makes a hash out of the connection between laws on the one hand, and counterfactuals, explanation, and induction on the other. The author thinks that the problem he has raised‐challenging though he hopes it is, is really an occasion for the Humean reductionist to sharpen his position still further.

Causation is a deeply intuitive and familiar relation, gripped powerfully by common sense. Or so it seems. As is typical in philosophy, however, that deep intuitive familiarity has not led to any philosophical account of causation that is at once clean, precise, and widely agreed upon. Not for lack of trying: the last thirty years or so have seen dozens of attempts to provide such an account, and the pace of development is, if anything, accelerating. (See Collins et al. [2003a] for a comprehensive sampling of the latest work.)

In the metaphysics of laws of nature, one fundamental philosophical question is whether we should give a metaphysical or rather an epistemic account of what they are; that is the core issue that divides ‘Humeans’ from ‘anti-Humeans’. In much the same way, a key question we face with essences is whether to give a metaphysical or rather an epistemic account of what they are. (So note well: in choosing to deploy the term ‘essence’ this chapter is not taking sides on the ‘Go metaphysical, or go epistemic?’ question. Just as we can be anti-metaphysical and still freely use the expression ‘law of nature’, so too we can be anti-metaphysical and freely use ‘essence’.) And the advantage of connecting these two topics is that we have made enough progress on the former for the lessons learned to provide valuable guidance for investigating the latter. Despite the author’s agnosticism about which approach is correct, the chapter mostly investigates the prospects for the ‘go epistemic’ option—what it calls ‘Humean reductionism about essence’.