 Under Quine’s approach to ontology, an argument for the existence of objects of kind \(K\)—whether mereologically complex objects, or concrete possible worlds, or mathematical objects—takes the form of an argument for the thesis that quantification over such objects is indispensable to our best global theory of the world. One of the most familiar instances of such arguments is the Quine-Putnam argument for the existence of mathematical objects. Since mathematical objects are indispensable for scientific purposes, we should expect the quantifiers of our best global theory of the world to range over them. But once we settle the question of whether the quantifiers of our best global theory of the world range over mathematical objects, we have settled the ontological question of whether such objects exist. The entry on  indispensability arguments in mathematics  includes extensive discussion of this and related indispensability arguments in mathematics. Similar arguments have been deployed outside mathematics to argue for the existence of possible worlds, mereologically complex objects, and the like.