Since haecceitistic differences concern qualitatively indiscernible possibilities, it is tempting to think that, since PII rules out the existence of qualitatively indiscernible objects, it thereby undermines haecceitism. Assessing this line of argument raises issues about the proper formulation of PII as well as radically different views about the nature of possible worlds. To see how these issues hang together, it is useful to first consider how PII might be used to argue against haecceitism within the context of Lewisian Modal Realism. In doing so, two versions of PII need to be distinguished.