The purpose of a definition is to pick out only those instances of a set you're attempting to refer to. The set of objects subject to causal influence by member

The purpose of a definition is to pick out only those instances of a set you're attempting to refer to. The set of objects subject to causal influence by members of the set is well-defined and unique. Your example with black doesn't work because there are multiple non-intersecting sets that satisfy the critera, so we need some further conceptual machinery to distinguish them. >You seem to be approaching a causal closure of non-physical existence, though one I am not sure is right. I'm not sure I follow. To be clear, the "causal closure" was referring to the fact that the physical is subject to causation, rather than a generic term describing a set of self-similar items.