 On this new theory, causation is a degree concept, rather than an ‘all-or-nothing’ concept, since counterfactual dependence comes in degrees. Sometimes Lewis says we properly ignore small amounts of causation. For instance, the location of nearby parked cars influences the smashing of a window by a rock in virtue of small gravitational effects of the cars on the flight of the rock. But it’s very little influence, and we properly ignore it most of the time.