 Since the counterpart relation is determined by similarity, everything is its own counterpart. Other than that, Lewis imposes few general restrictions on the counterpart relation. In Lewis (1968), he suggests that nothing can be a counterpart of a different object in the same world, but this assumption is later dropped (Lewis 1986e, 232, fn.22). Unlike strict trans-world identity, counterparthood is not assumed to be transitive, symmetric, or functional. An object can have multiple counterparts at a world, and different objects can have a common counterpart.