 Is the argument successful? As Sider and McDaniel are well aware, the term ‘distinct from’ needs to mean something other than ‘not identical to’, if the recombination principle, Premise 4, is to get off the ground. After all, the state of affairs of o's being 2 kg in mass and the state of affairs of o's being 3 kg in mass are both contingent, and they are not identical to each other, but presumably it is not possible that they both obtain. (Presumably it's not possible that something is both 2 kg and 3 kg in mass.)