 An argument against the perdurance theory that has been the focus of interest is one presented in various guises by a number of writers, including Wiggins (1980), Thomson (1983) and van Inwagen (1990). Applied to persons (it can equally well be applied to other persisting things), it asserts that persons have different properties, in particular, different modal properties, from the summations of person-stages with which the perdurance theory identifies them. Thus, by Leibniz’s Law, this identification must be mistaken. As David Wiggins states the argument: “Anything that is a part of a Lesniewskian sum [a mereological whole defined by its parts] is necessarily part of it…But no person or normal material object is necessarily in the total state that will correspond to the person- or object-moment postulated by the theory under discussion” (1980: 168).