 The split property (Valente 2010, p. 1035) is a strengthening of the condition of microcausality (observables on space-like separated regions commute). Summers (2009) argues that it is meaningful to speak of independent subsystems in relativistic quantum theory if they can be localized in spacetime regions \(A, B\) whose algebras \(R_{A}, R_{B}\) posses the split property; and that most, if not all, physically relevant models of quantum field theories have this property (for sufficiently space-like separated regions \(A, B)\).