 An immediate implication of (ID-EX) in conjunction with  (EDR)  is that if x depends for its identity upon y, then x is rigidly existentially dependent upon y (although not necessarily vice versa, of course). These two principles are, it seems, quite plausible. As for (ID-EX): surely, x cannot exist unless everything upon which x’s identity depends also exists. Thus an assassination cannot exist unless the person assassinated exists, and a set cannot exist unless its members exist. Indeed, it would seem that we can derive (ID-EX) with the aid of  (ID).  For suppose that x depends for its identity upon y. Then, by (ID), there is a relation R such that x is related by R to y. Given, however, that the relevant R cannot exist unless y exists—because a relation can obtain only between entities all of which exist—it follows that x likewise cannot exist unless y exists. As for (ID-NEX), this seems to follow from the requirement of non-circularity which is a condition on the adequacy of any criterion of identity. For example, given that unit sets are not to be identified with their members, we cannot say both that the identity of a unit set depends upon the identity of its member and that the identity of that member depends upon the identity of that unit set, for this would engender a vicious circle which would seem to deprive both unit sets and their members of well-defined identity-conditions.