Dispositions and laws of nature
David Lewis's doctrine of Humean supervenience has exercised an extremely powerful hold on the imagination of philosophers – both on its adherents and its opponents. Humean supervenience is the hypothesis that the world consists of instantaneous qualities that are intrinsic to points of space time. So in good Humean fashion, causation is understood not as a fundamental relation between events, but rather as an extrinsic relation: events of this sort tend to be followed in time by events of that sort. If this sort of regularity holds often enough (and is part of our best systematisation of all the contingent facts) then it is a causal connection.
A good deal of my research has examined a competitor to this worldview: dispositionalism (also known as dispositional essentialism, or a “powers” view). Dispositionalists hold that the fundamental properties of the world are relational in some sense: they are always already primed for causal activity, and causal connections are therefore not reducible to regular patterns in spacetime.
Spelling out exactly what this means, without invoking an intolerable quantity of unverifiable metaphysical posits, has proven difficult. One of my main aims has been to develop a variety of dispositionalism that is only minimally more metaphysically loaded than Humean supervenience. In the papers, Humean Dispositionalism, and Dispositions, manifestations, and causal structure, I developed a view whereby dispositional potency is explained in terms of internal relations between properties of things and the structural properties of the causal processes by which dispositions are manifested. So being H2O, for instance, is an essential part of the property being a process of salt dissolving in water. This sort of essential property is relatively uncontroversial, even among Humeans, and goes some way towards explaining why water has the power to dissolve salt.