Tobias Hansson Wahlberg argues in a recent article (2009) that the truth of “Hesperus is Phosphorus” depends on the assumption that the endurance theory of persistence is true. The statement is not true (or at least can reasonably be doubted), he argues, if one assumes (a) the theory of persistence according to which objects are four-dimensional entities, persisting through perdurance, i.e. by having temporal parts that are numerically distinct, and (b) the thesis of unrestricted mereological composition (UMC), that is, that (...) any two things, however scattered in space or time, compose a sum. (shrink)