Full Idea
Supervenience is essentially a one-way relation of dependence or determination, …which holds, in the first instance, between properties.
Gist of Idea
Supervenience is a one-way relation of dependence or determination between properties
Source
Mark Rowlands (Externalism [2003], Ch.2)
Book Reference
Rowlands,Mark: 'Externalism' [Acumen 2003], p.15
A Reaction
This definition immediately shows why supervenient properties are in danger of being epiphenomenal (i.e. causally irrelevant). Carefully thought about the notion of a 'one-way' relation will, I think, make it more obscure rather than clearer.