Humean metaphysics versus a metaphysics of powers

The paper considers the opposition between Humean metaphysics and the metaphysics of powers, focusing on laws, probabilities and causation. It argues that within Humean metaphysics, everything is a matter of contingency. Consequently, there is no deep metaphysical difference between a deterministic world and a world in which only probabilistic laws hold. This position is contrasted with the foundations of probabilities according to the metaphysics of powers, in particular the view that traces probabilities back to propensities. The paper then goes into arguments for these positions, recalling first the central argument against Humean metaphysics, and then claiming that, contrary to a widespread belief, the metaphysics of powers is compatible with physics and is able to provide for an ontology that does justice to both physics and the special sciences. 7.1 Humean metaphysics Whereas the philosophy of science was dominated in the second half of the twentieth century by epistemological issues raised in the context of logical empiricism and its critics, the project of a metaphysics of nature (metaphysics of science) has been rehabilitated recently. One can broadly distinguish three positions within that project: a Humean metaphysics that is close to empiricism (e.g. David Lewis, Barry Loewer and Helen Beebee), a metaphysics of universals (e.g. David Armstrong) and a metaphysics of powers (e.g. Sydney Shoemaker, Alexander Bird, Stephen Mumford as well as Charles Martin and John Heil). This paper is about the opposition between the first and the third of these positions. I shall first outline the Humean view on properties, laws, causation, and probabilities and point out how on the one hand this view is parsimonious, whereas on the other hand it provokes the objection that it is deficient (this section). I shall explain how the metaphysics of powers seeks to remedy these deficiencies and consider its view of probabilities (section 2). The paper then recalls the standard argument against the conception of properties in Humean metaphysics, goes into arguments from physics and finally maintains that the metaphysics of powers, in contrast to Humean metaphysics, is able to do justice to both the ontological commitments of physics and of the special sciences (section 3). Humean metaphysics gets its name from the denial of the view that there are necessary connections between distinct entities in the world. Its most prominent formulation in contemporary philosophy is David Lewis’ thesis of Humean supervenience: Humean metaphysics vs. a metaphysics of powers 2 It is the doctrine that all there is to the world is a vast mosaic of local matters of particular fact, just one little thing and then another. (...) We have geometry: a system of external relations of spatio-temporal distance between points. Maybe points of spacetime itself, maybe point-sized bits of matter or aether or fields, maybe both. And at those points we 120 have local qualities: perfectly natural intrinsic properties which need nothing bigger than a point at which to be instantiated. For short: we have an arrangement of qualities. And that is all. There is no difference without difference in the arrangement of qualities. All else supervenes on that. (Lewis