Full Idea
Armstrong says all properties are categorical, but a dispositional predicate may denote such a property; the dispositional predicate denotes the categorical property in virtue of the dispositional role it happens, contingently, to play in this world.
Gist of Idea
Even if all properties are categorical, they may be denoted by dispositional predicates
Source
report of David M. Armstrong (A Theory of Universals [1978]) by Alexander Bird - Nature's Metaphysics 3.1
Book Reference
Bird,Alexander: 'Nature's Metaphysics' [OUP 2007], p.44
A Reaction
I favour the fundamentality of the dispositional rather than the categorical. The world consists of powers, and we find ourselves amidst their categorical expressions. I could be persuaded otherwise, though!