  Perhaps the biggest — if not the most philosophically  sophisticated — challenge to Lewis's theory is “the  incredulous stare”, i.e., less colorfully put, the fact that  its ontology is wildly at variance with common sense. Lewis faces  this objection head on: His theory of worlds, he acknowledges,  “does disagree, to an extreme extent, with firm common  sense opinion about what there is” (1986, 133). However, Lewis  argues that no other theory explains so much so economically. With  worlds in one's philosophical toolkit, one is able to provide elegant explanations of a wide variety of metaphysical, semantical, and  intentional phenomena. As high as the intuitive cost is, Lewis (135)  concludes, the existence of worlds “ought to be accepted as  true. The theoretical benefits are worth it.” 