 As stated, (10) doesn’t handle cases of symmetric overdetermination – as when Suzy and Billy both throw their rocks independently, each throw is sufficient for the bottle to break, and both rocks hit the bottle – so neither throw preempts the other, since neither throw is on an active route as defined in (9). To deal with such cases, Hitchcock weakens (10) by replacing the ‘active route’ in (10) with the notion of a weakly active route (2001: 290). The essential idea here that there is a weakly active route between X and Z just when Z counterfactually depends on X under the freezing of some possible, not necessarily actual, values of the variables that are not on the route from X to Z. Intuitively, to recover counterfactual dependence between Suzy’s throw and the shattering we hold fixed BT = 0: had Suzy not thrown in the model where Billy doesn’t throw, the bottle would not have shattered. Similarly for Billy’s throw.