 After “Causation” the focus, at least of those interested in reductive theories, moved to counterfactual theories. And it became clear that Lewis had a bit of work left to do. He needed to say more about the details of the notion of counterfactual dependence. He did this in “Counterfactual Dependence and Time’s Arrow” (1979c), as discussed in section 2. He needed to say more about the nature of events. In “Events” (1986g) he said that they were natural properties of regions of space-time. (At this stage he assumed that events were the relata of the causal relation. This assumption is criticised by L. A. Paul (2000), and in (2004d) Lewis drops it.) And prodded by Jaegwon Kim (1973), he needed to add that A and B had to be wholly distinct events for B to counterfactually depend on A. The alternative would be to say that an event’s happening is caused by any essential part of the event, which is absurd.