 One way to argue in favour of transworld identity (distinct from the defensive strategies discussed in Sections 4 and 5 above) is what we might call ‘the argument from logical simplicity’ (Linsky and Zalta 1994, 1996; Williamson 1998, 2000). The argument begins by noting that Quantified Modal Logic—which combines individual quantifiers and modal operators—is greatly simplified when one accepts the validity of the Barcan scheme, ∀x□A → □∀xA (Marcus 1946). The resulting logic is sound and complete with respect to constant domain semantics, in which each possible world has precisely the same set of individuals in its domain. The simplest philosophical interpretation of this semantics is that one and the same individual exists at every possible world.