I’ve been reading Lewis’s late papers on causation, and I can’t figure out how to make consistent some of the things he says in ‘Void and Object’ and some of the things he says in ‘Causation as Influence’. Here is one of the objections to applying the Canberra plan to causation that he offers in ‘Causation as Influence’. (Page numbers are from the versions of the papers in Causation and Counterfactuals.)

bq. The problem of the many diverse actual causal mechanisms, or more generally of many diverse mechanisms coexisting in any one world, is still with us. If causation is, one might be, wildly disjunctive, we need to know what unifies the disjunction. For one thing the thug platitudes tell us is that causation is one thing, common to the many causal mechanisms. (76)

But in Void and Object, Willis says that the Canberra plan approach is a good approach to determining what biff is, and he makes the following speculations about what kind of thing biff will turn out to be.

bq. Myself, I’d like to think that the actual occupant of the biff-role is Humean-supervenient, physical, and at least fairly natural; but nothing else I shall say here is premised on that hope. (284)

Here’s the problem. There are, as Lewis says in Causation as Influence, many actually existing causal mechanisms. They don’t seem to have a lot in common. So biff looks like it should be pretty disjunctive. Yet Lewis says, or at least hopes, but it will turn out to be fairly natural. I don’t see how both those things can be true.