David Lewis's awkward cases of redundant causation
The main line of Lewis's account of causation is in terms of chains of counterfactual dependence. According to his original account (1973), a causal chain is a sequence of two or more events, with counterfactual dependence at each step; and one event is a cause of another if there is a causal chain from one to the other. But some awkward cases involving redundant causation lead him to introduce the notion of quasi-dependence (1986: 205-7). Laurie Paul (1998) has suggested a way of dealing with one important class of these cases in terms of dependence proper. I shall suggest a different (and, I argue, preferable) way of dealing with this class of cases; I shall also suggest that it is possible to deal with other awkward cases too in terms of dependence proper.