Nothing is part of Everything

Extensional mereology, that is, a mereology without intensional operators (such as modal or temporal functions), mirrors, in many respects, set theory. What is missing in this reconstruction is the mereological analog of the empty set, which might be called “null object". Mereology, in its traditional formulation, avoids all reference to null objects and the reasons are, basically, ontological. Even if the admission of a null object seems ontologically suspicious, it would have the advantage of allowing mereology to develop the analogy with set theory to its fullest extent. Since the null object, if given, is a particular instance of "atom", I want to consider what sort of relation holds between atoms and the null object and I propose an interpretation that seems to make sense of the very idea of a ”null object”. But the ontological perplexities about the interpretation of such notion may be still there. And, actually, it is the ontological point of view that has prompted us to test whether mereology could be a good replacement of set theory.