According to one theory of dispositions, any dispositional property requires a causal basis consisting of one or more categorical properties (e.g., see Prior et al. 1982). However, several metaphysicians and philosophers of science have recently claimed that pure dispositions (or, pure powers) are either actual or at least metaphysically possible. 1 Bird (2007a), Ellis (2001), McKitrick (2003a), Molnar (2003), and Mumford (2006) all accept the following thesis or something akin:

Pure Dispositions Thesis: It is metaphysically possible that there is some type of dispositional property of which any instance, F, does not have a distinct causal basis for its manifestation, where a causal basis consists of some instance of either another dispositional property or property-complex, or a categorical property or property-complex, or combination thereof. 2