 Reply: Young Oscar and Old Oscar are the same dog, but it makes no sense to ask: “What is the mass of that one dog.” Given the possibility of change, identical objects may differ in mass. On the relative identity account, that means that distinct logical objects that are the same \(F\) may differ in mass — and may differ with respect to a host of other properties as well. Oscar and Oscar− are distinct physical objects, and therefore distinct logical objects. Distinct physical objects may differ in mass.