Like haecceitism, quidditism’s proper formulation is contentious and depends heavily upon background metaphysical assumptions. Some formulations of quidditism invoke either maximal possibilities or possible worlds, while modalist formulations of quidditism do without either resource. Additionally, there is a quidditistic analogue of cheap haecceitism, according to which a given possible world represents various maximal possibilities that differ only quidditistically. (On formulations of quidditism and property counterpart theory, see Hawthorne (2002b) and Heller (2002, 2005).)