 Whether or not David and Lump share all the same parts, it is clear that they share many of the same properties. Both have the same weight, the same size, and the same shape. Indeed, the two seem to be perfect duplicates, right down to their sub-atomic structure. But this raises a puzzle: how could duplicates of this kind differ in their temporal properties, persistence conditions, and the like? We will refer to this as the grounding objection since it appeals to the common idea that such properties must be grounded in more basic features of an object. (For different statements of this worry, see Simons 1987, pp. 225–6, Heller 1990, pp. 30–2, Burke 1992, Zimmerman 1995, pp. 87–8, and Olson 2001. The objection is sometimes put in terms of  supervenience,  but, as Bennett 2004 points out, supervenience is importantly different from  grounding.)