Hillel Steiner argues that a necessary and sufficient condition for the compossibility of a set of rights is that those rights be extensionally differentiable. However, given that two or more actions can extensionally overlap without thereby being mutually unperformable, if such actions are specified in the relevant rights, then those rights will not be incompossible, notwithstanding their extensional overlap. The set of compossible sets of rights then is greater than the subset of extensionally differentiable rights, and extensional differentiability is a (...) sufficient but unnecessary condition of compossibility. (shrink)