 Quidditism is to properties what haecceitism is to individuals. Haecceitism famously implies a theory of primitive identity of individuals across possible worlds. Likewise, quidditism implies a theory of primitive transworld identity of properties which asserts that two properties are identical iff they are quiddistically the same, regardless of their theoretical roles (Black 2000; Whittle 2006; Lewis 2009). This being the case, a property could confer upon its instances completely different causal or nomic powers than it actually does but nonetheless continue to be the same property as it actually is so long as it remains quiddistically the same. The causal or nomic profile of a property is thus a merely contingent matter. (Schaffer (2005) points out that this ‘contingentism’ is not necessarily paired with quidditism: ‘anti-quiddistic contingentism’ is a respectable position.)