The connection between haecceitism and physicalism is controversial. If we understand physicalism as the unqualified thesis that physical properties like mass and charge exhaustively fix all other properties, haecceitistic differences present a prima facie challenge. For, if some worlds differ haecceitistically but are alike with respect to the distribution of physical properties, then, contrary to physicalism, possible worlds or maximal possibilities can be physically indiscernible yet fail to be indiscernible simpliciter. Moreover, some follow Hofweber (2005) in taking the irreducibility of haecceities and other non-qualitative properties to physical properties to constitute a challenge to more sophisticated conceptions of physicalism. (See Daly and Liggins (2012) and Almotahari and Rochford (2012) on Hofweber’s argument. See Ninan (2009: 433) on haecceitism and its relation to physicalism.)