Causation, influence, and effluence
1. Influence Lewis proposes that C causes E iff C stands in the ancestral of counterfactual influence1 to E. C stands in the ancestral of counterfactual influence to E iff there is a chain of events D1, D2, ... , Dn (for n 2 0) such that C influences D1, D1 influences D2, ... , Dn influences E.