A Mereology for the Change of Parts

A theory of temporal mereology is formulated in which the principles of Existence and of Uniqueness of Composition hold. The theory is consistent both with a three-dimensionalist ontology and with the change of parts, that is, with the view that at least one object has distinct parts at distinct times. Some interesting consequences of the theory joined with the change of parts, taken as an axiom, are proven. It is usually held that certain well known ontological puzzles must be solved either by adopting a four-dimensionalist ontology or by restricting some mereological principles. Here a solution to those puzzles is stated, which allows to keep all mereological principles in their generality, without adopting a four-dimensionalist ontology. The solution is achieved by denying the persistence of some of the entities involved, along the “Chrysippean” lines advocated by M. Burke and M. Rea. Although good reasons for this move are provided, some problems of the solution are also highlighted and tentatively answered.