Full Idea
It is only to the extent that we relate disposition to 'categorical basis', and difference of disposition to difference of 'categorical basis', that we can speak of dispositions. We must be Realists, not Phenomenalists, about dispositions.
Clarification
'Categorical' is the opposite of 'hypothetical'
Gist of Idea
To be realists about dispositions, we can only discuss them through their categorical basis
Source
David M. Armstrong (A Materialist Theory of Mind (Rev) [1968], 6.VI)
Book Reference
Armstrong,D.M.: 'A Materialist Theory of Mind' [Routledge 1993], p.88
A Reaction
It is Armstrong's realism which motivates this claim, because he thinks only categorical properties are real. But categorical properties seem to be passive, and the world is active.