Weatherson on Influence

At the AOC conference Brian Weatherson gave a paper on causation defending a disjunctive account. The paper begins by considering various causative statements, e.g. 'John opened the window'. It then argues that the obtaining of the special causal relation that obtains when a causative statement is true is sufficient (but not necessary) for causation.

The other disjunct (or sufficient condition) is influence. Influence differs from causal dependence. An event E causally depends on a prior event C iff if C hadn't occurred, then E wouldn't have occurred. Causal dependence is sometimes taken to be a necessary constraint on influence. However, for C to influence E, it must also be the case that if C had occurred at a different time, then E would have occurred at a different time, and if C had occurred differently, then E would have occurred differently. Weatherson argues that causal dependence is not a necessary constraint on influence.

However, I think this latter assumption is problematic. Here is a potential counterexample. Suppose there is an evacuation "test" event during which a number of American residents are evacuated out of America (Brian is one of them), and suppose Brian moves to Rutgers right after the evacuation event (a bit later than he otherwise would have).

The evacuation event is not the cause of Brian moving to Rutgers. Yet if the evacuation event had occurred at a different time, then we can imagine that Brian's move would have occurred at a different time as well (we can set up the case that way). Moreover, if the evacuation event had occurred differently (suppose e.g. that Brian was not one of the chosen ones), then his move to Rutgers might have occurred differently as well (e.g., it wouldn't involve a trip from overseas).

The right kind of response to this example, I think, is to take causal dependence to be a necessary constraint on influence. Brian would still have moved to Rutgers even if the evacuation event hadn't occurred.

Of course, if we *do* take causal dependence to be a necessary constraint on influence, then we need to find a way to avoid counting the following sort of causal claim as true:

(1) 2 + 2 = 4 and the evacuation event (as described above) are the joint cause of Brian's move to Rutgers.

On the standard Lewisian account of counterpossibles, 'if 2 + 2 weren't 4, then Brian wouldn't have moved to Rutgers' is vacuously true. So, if causal dependence is a necessary constraint on influence, and influence is sufficient for causation (Brian agrees to the latter), then (1) is true. So we want to rule out that counterpossibles are vacuously true across the board (but, as Joe and I argued at the conference, there are ways to do that).