Dispositional essentialists claim that dispositional properties are essentially dispositional: a property would not be the property it is unless it carried with it certain dispositional powers. Categoricalists about dispositional properties deny this, asserting that the same properties might have had different dispositional powers had the contingent laws of nature been otherwise.
As I have described it, that debate concerns properties that can be characterized as dispositional. We could expand that debate to include another one. How many different metaphysical kinds of property are there? Just one, or two or more? The monist thinks that there is just one kind of property. The categoricalist described above is likely to be a monist, asserting that all properties are categorical in nature. On this view, all properties are alike in essence; they confer, of themselves alone, no potentialities, no causal powers. A (categorical) property can confer such powers, but only because there is a law relating that property to some other property. Armstrong is a categorical monist (Armstrong et al. 1996:15-18; Armstrong 1997:69, 80-3). Another kind of monist thinks that the distinction between different kinds of property is misconceived, and that dispositionality and categoricity are different aspects of one kind of property. Martin and Mumford have expressed this sort of view (Armstrong et al. 1996:71-5; Mumford 1998:64-7). A dualist may think that the distinction is well conceived and that some properties are categorical (i.e. are just as the categorical monist thinks all properties are), whereas some others are essentially dispositional. One could, perhaps, be a more liberal pluralist, thinking that substance and kind properties (being gold, being a tiger) and mathematical properties (being odd, being well founded) are yet different kinds of property, being neither dispositional nor categorical. Dualists and other pluralists may be egalitarian - none of the different kinds of property has any special priority relative to the others. Or they may be hierarchical, holding that one kind of property (the categorical, for example) explains or is the basis for the other kind(s).
In this chapter I wish to examine the prospects for dispositional monism. This view is monistic in that it holds that there is only one kind of property,