According to ersatzist views, which identify possible worlds with abstract entities like sentence-types, properties, propositions, or sets, the truth of World Indiscernibility will turn, not on whether there are distinctively haecceitistic possibilities, but on whether such entities are qualitatively indiscernible from one another. (Qualitatively indiscernible entities share all their qualitative properties, while qualitative duplicates share only their intrinsic qualitative properties.) So, if one holds that sets or propositions have no qualitative features, then World Indiscernibility is true, regardless of one’s views about what is and what is not possible. So, for many ersatzists, the status of World Indiscernibility does not depend upon any distinctive modal commitments, but is settled by apparently orthogonal questions regarding the nature of the entities with which possible worlds are identified. (The inadequacy of World Indiscernibility as a formulation of haecceitism within the Lewisian modal realist framework is explained below. Crucially, Lewis (1986) takes the issue of haecceitism to turn, not on issues regarding qualitatively indiscernibility, but on how possible worlds represent de re possibilities.)