 The choice between these two different ways of proceeding connects with the broader debate about whether causation should be analysed in terms of counterfactuals or vice versa. Lewis, of course, takes the former approach. One attraction of doing so – at least for him – is that it fits within a broadly Humean agenda: since causation is a modal notion, it threatens the thesis of Humean supervenience (Lewis 1986a, ix) unless it can somehow we cashed out in terms of similarity relations between worlds, where those similarity relations do not appeal in turn to causal (or other Humean supervenience-violating) features of worlds. Lewis’s analysis of counterfactuals, together with his analysis of laws, turns that trick. By contrast, other authors have argued that the trick simply cannot be turned: we cannot analyse counterfactuals without appealing to causation (Edgington 2011).