Proportionality and omissions

In response to the exclusion argument against mental causation, Yablo (1992, 1997) proposes a proportionality constraint on what can count as a cause: where distinct, simultaneous putative causes involve properties that stand in the determinable/determinate relation, only the property that is proportional to the effect counts as the cause. The having of property C is proportional to effect E if and only if (i) for any determinable C* of C, had C* obtained without C, E would not have obtained, and (ii) for any determinate C′ of C, had C obtained without C′, E would still have obtained. In Yablo’s terminology, where (i) holds we say C* does not screen off C from E, and where (ii) holds we say C screens off C′ from E. So C is proportional to E iff none of its determinables screen it off, and it screens off all its determinates (Yablo 1997: 267). Proportionality is itself an exclusion principle: only one in a set of properties related by the determinate/determinable relation can be proportional to a specific effect.