 Philosophers who pose the problem in these terms, will often move on to generate a regress argument for any attempt to explain the difference between a sum/list/set of entities and a unified complex that appeals to relations. The next question becomes: what will account for the difference between a sum/list/set of entities a, F, and a relation R (of instantiation or exemplification) on the one hand, and a unified state of affairs of a being F, on the other? The implication is that any addition of further relations will set off Bradley’s regress of relations, with no explanation in sight (see in particular Vallicella (2000)).