As Lewis uses “haecceitism”, it is the denial of Qualitative Supervenience and therefore the claim that non-qualitative features of worlds at least partially determine what worlds represent de re. (On the relation of supervenience, see the entry by McLaughlin and Bennett.) For modal realists who would reject Qualitative Supervenience, qualitatively indiscernible possible worlds can differ with respect to which de re possibilities they represent. Non-Lewisian modal realists of this sort can therefore hold qualitatively indiscernible possible worlds to represent maximal possibilities that differ haecceitistically. But, since Lewis endorses Qualitative Supervenience, he claims that qualitatively indiscernible worlds represent the very same possibilities. Positing qualitative indiscernible worlds therefore provides Lewis with no additional resource for making sense of haecceitistic differences. (Lewis is officially agnostic about whether there are any qualitatively indiscernible worlds. See Lewis (1986: 224).) As a consequence, Lewis holds that we go wrong in assimilating questions of haecceitism to questions about qualitatively indiscernible. For Lewis, haecceitism is an issue regarding how possible worlds represent de re possibilities. So, even if Lewis were to posit distinct yet qualitatively indiscernible worlds, they would differ non-qualitatively but not haecceitistically in the Lewisian sense. In this way, the Lewis’ concern with haecceitism places question of representation rather than qualitative indiscernibility at the forefront.