In Arbiter (Arbitrator or Umpire), written about the same time as the Council of Constantinople and surviving only in Syriac translation, Philoponus takes the view that the locution ‘discernible in two natures’ ought to be abandoned. His main strategy is to argue that in this context the meaning of the terms ‘nature’ and ‘hypóstasis’ are essentially identical, so that if Christ is (according to (3)) one hypóstasis he cannot also (as in (4)) be discernible in two natures. The argument goes roughl