A characterization of haecceitism

Anti-haecceitism is the thesis that things cannot differ from actuality in a purely non-qualitative fashion. Anti-haecceitism being a modal notion, we would expect it to be explicable in terms of possible worlds. Bradford Skow denied that, arguing that alternative conceptions of possible worlds prompt non-equivalent characterizations of anti-haecceitism. Therefore, the haecceitism debate should take place in the modal language, rather than in the language of possible worlds. The aim of this paper is to provide a metaphysically neutral possible-world characterization of anti-haecceitism, i.e. one compatible with alternative understandings of the nature of possible worlds.