Abstract

In this paper I present a new definition of endurance. I argue that the three-dimensionalist ought to adopt a different understanding from the four-dimensionalist, of what it is to have a part simpliciter. With this new understanding it becomes possible to define endurance in a manner that both preserves the central endurantist intuitions, whilst avoiding commitment to any controversial metaphysical theses. Furthermore, since this endurantist definition is a mereological one, there is an elegant symmetry between the definitions of endurance and perdurance in that the theories of three- and four-dimensionalism are both expressed in the language of mereology. Nevertheless, though both definitions are expressed within the same broad language, some of the terms of that language have subtly different meanings within the context of each theory. It is in understanding on the one hand that each theory is essentially a mereological theory and that therefore each shares some underlying theoretical similarities, and yet also that there are some subtle differences in the way each theory understands some of the terms of mereology, that allows us to see clearly what lies at the heart of the debate between these two accounts of persistence.