 For a proponent of particulars, universals, and states of affairs, this problem takes the form of the following questions: what is the ontological ground of the difference between the sum a+F and the unified state of affairs Fa? It could be the case that both a and F exist at a world, and thus that the sum a+F exists at such a world, without it being the case that Fa obtains (but, say, a being G and b being F obtain). What then is the ground of such a difference? Similarly, what provides an ontological ground of the difference between the sum a+R+b and the unified state of affairs aRb? It might be the case that all three a, R, and b exist at a world, and hence that their sum is given, without it being the case that aRb obtains (instead, say, aRc and bRd obtain). The same sort of question can be posed, of course, for other ontologies. For instance, for a bundle trope theorist the question will be: what is the ontological ground of the difference between the sum F1+G1+H1 of property tropes and a unified trope bundle constituted out of them? (See Armstrong 1989, 1997; Vallicella 2000, 2002; Maurin 2010; and Meinertsen 2008, amongst others for such a formulation of the problem.)