  Hand in glove with the irreducible nature of modality is the nature  of intensional entities. Concretists define intensional entities in  terms of worlds, as described in   §2.1.3.  Abstractionists, by contrast, define worlds in terms of intensional  entities. This divergence in their choice of ontological primitives  reflects, not only their differing stances toward modality, but also  an important methodological difference with regard to metaphysical  inquiry. The concretist is far more pragmatic; notions of  property, relation, proposition, and the  like play certain roles in our theorizing and are subject to a  “jumble of conflicting desiderata” (Lewis 1986,  54). Within a given theory, any entities that can play those roles  fruitfully for the purposes at hand are justifiably identified with  those notions — regardless of how well they comport with  pre-theoretic intuitions. Thus, Lewis finds it to be a strength of  his position that he is able to adopt the set theoretic definitions  in §2.1.3. By contrast, at least some abstractionists —  Plantinga (1987) perhaps most notably — believe that we have  intuitive, pre-theoretic knowledge of intensional entities that  precludes their being identified with set theoretic constructions of  any   sort.[31]  (See Stalnaker 1976 for a particularly illuminating discussion of the contrast between concretism and abstractionism with respect to the  treatment intensional entities.) 