This paper focuses on Porphyry’s account of the just treatment of non-human animals in his treatise On Abstinence from Killing Animals. In responding to the Stoic argument that justice extends only to rational beings and leaves out non-rational animals, Porphyry introduces a number of considerations to show that animals are not entirely deprived of reason. It is usually assumed that Porphyry thereby commits himself to the view that animals are rational, thus breaking from the tradition of treating rationality as distinctive of humans. This assumption has been recently challenged by G. Fay Edwards, who argues that Porphyry neither believes that animals are rational nor that justice extends only to rational beings, but that he is merely trying to trap the Stoics into admitting that animals are rational and for this reason recipients of justice. I will argue that Porphyry ascribes rationality to animals, although he does not think that this is the reason for treating them justly. Central to my interpretation is Porphyry’s claim that rationality admits of degrees, which allows him to ascribe to animals a certain level of rationality without compromising his Platonic ideals.