  Now these are just standard puzzles for four-dimensionalism about  persons (see Olson 1997b, van Inwagen 2002, and the entry on    personal identity).  But there are also puzzles for four-dimensionalism specific to its  treatment of the responsibility case. For instance, if responsibility depends on identity, and identity is a transitive relation, then if  Y is responsible for the actions of X (insofar as  Y is unified with X as part of the same  person-worm), and Z is responsible for the actions of  X (insofar as Z is unified with X as part  of the same person-worm), then wouldn't Y also be  responsible for the actions of Z (and vice versa)? Of  course, unity relations are not identity relations, but it is unclear just why they do not have to be transitive in the way the identity  relation is supposed to be (in Sider 2001a, 203, he simply insists  that they do not have to be, without saying why). Furthermore, the  four-dimensionalist solution is meant to preserve the commonsense  slogan, but it does so in virtue of a solution that seems about as far from commonsense as can be. Indeed, the slogan is about the responsibility of persons, but four-dimensionalism offers  only a solution regarding the responsibility of  person-stages (Ibid.; see also Parfit 1976).