Haecceitism is a modal thesis. Like other modal theses, there are competing metaphysical frameworks in which it might be expressed. Some of these frameworks involve a commitment to possible worlds or maximal possibilities, while other frameworks aim to do without these commitments. To further complicate matters, some frameworks distinguish possible worlds from the maximal possibilities they represent, while other frameworks collapse this putative distinction by identifying maximal possibilities with possible worlds. This section surveys some of the options for formulating and interpreting haecceitism, but, as Skow (2008, 2011) argues, any formulation of haecceitism that employs the framework of possible worlds will tendentiously presuppose something about the nature of possibilities or possible worlds. For this reason, the proper formulation of haecceitism is itself a matter of controversy.