 Dispositions are, at first pass, those properties picked out by predicates like ‘is fragile’ or ‘is soluble’, or alternatively by sentences of the form ‘x is disposed to break when struck’ or ‘x is disposed to dissolve when placed in water.’ Dispositions so understood have figured centrally in the metaphysics and philosophy of science of the last century (Carnap 1936 &amp; 1937, Goodman 1954), and also in influential accounts of the mind (Ryle 1949). They are like abilities in many significant respects, in particular in the fact that they are properties of things that can exist even when not manifested: as a glass may be fragile even when it is not broken, so may a person have the ability to raise her arm even when she is not raising her arm.