Mumford puts forward a new theory of dispositions, showing how central their role in metaphysics and philosophy of science is. Much of our understanding of the physical and psychological world is expressed in terms of dispositional properties--from the spin of a sub-atomic particle to the solubility of sugar. Mumford discusses what it means to say that something has a property of this kind and how dispositions can possibly be real things in the world.
Informative but hardly philosophical. The “homunculus” explanation according to which one thing has a disposition in virtue of a lower level disposition and so on is arguably not a vicious regress but has little explanatory power. For I could very well imagine that a state obtains without the disposition being activated, unless this activation is necessary, which brings us back to Hume’s riddle. As is often the case with this kind of low level analytic philosophy there is more than a fair share of roundabout reasoning but little to be found that is actually striking.