Haecceity Mereology

Abstract Haecceities are non-qualitative properties for individuation but the current theories about haecceities are still to be much more explored. This paper aims to develop a “haecceity mereology” – that is, an ontological system that understands substances as mereological combinations of haecceities and qualitative properties. In this way, the view developed is an alternative to Paul’s (2002. “Logical Parts.” Noûs 36 (4): 578–96; 2006. “Coincidence as Overlap.” Noûs 40 (4): 623–59) mereological approach. Three rules are proposed: (1) If S is a substance, then there is one and only one haecceity which is S’s qualitative part; (2) For all the fusions with the same haecceity, at most only one of those fusions is a substance; (3) When all the relevant elements are abundant, every element must overlap at least one substance. This is the first ontology of haecceities in the recent literature and would be a model for systematic metaphysics.