 The grounding objection. The third challenge for the constitution theorist was to identify a ground for the different features of coinciding objects. The same challenge can be put to the friend of temporal parts. In the case of the statue and the clay, for example, we have two objects that are perfect duplicates whenever they both exist—in virtue of what, then, do they differ with respect to their temporal properties, persistence conditions, and so on? The temporal parts theorist could follow the constitution theorist in claiming that the relevant objects differ in kind, for example, in virtue of their historical properties or he could simply insist that the difference in kind is grounded in the fact that the two objects have different temporal parts (Wasserman 2002).