  It should be clear from   principle AF  that all atomic facts hold; that is, all of them reflect  actual exemplification relations. Obviously, however, possibility  encompasses more than what is actual, that is, there are  possible facts as well as actual facts; the world's  universals might have been exemplified by its objects very  differently. If they had — if the world's objects and  universals had combined in a very different way — there would  have been a very different set of atomic facts and, hence, a very  different world. 