 In “Causation” (1973b), Lewis put forward an analysis of  causation in terms of counterfactual dependence.  The idea was that event B was counterfactually dependent on event A if and only if the counterfactual Had A not occurred, B would not have occurred was true. Then event C causes event E if and only if there is a chain C, D1, …, Dn, E such that each member in the chain (except C) is counterfactually dependent on the event before it. In summary, causation is the ancestral of counterfactual dependence.