ABSTRACT
The preoccupation of ancient philosophers and naturalists with the question of whether non-human animals possess reason was no matter of idle speculation but had enormous practical implications for the lives of humans, not to mention those of non-human animals. Since antiquity, claims that humans stand alone in possessing reason have been used as the basis for an assertion of human moral superiority and as a justification for excluding other animal species from human moral concern. The underlying assumption of much speculation on animal intellect was that rationality in itself conferred moral considerability upon those who possessed it. The Stoics took up Aristotle’s denial of reason (logos, logismos) to animals and gave his essentially biological view of animal intellect a distinctly moral dimension. This is observable in the Stoic doctrine of oikeio¯sis, “kinship, relationship, belonging,” examined in Part I of this volume. Stoicism, in particular among ancient schools, sought to emphasize the “differentness” of irrational animals vis-à-vis their rational human counterparts, while figures such as Plutarch and Porphyry attempted to demonstrate that rationality in animals was not a matter of “all or nothing,” but rather one of degree. If, as the Stoics argued, animals are utterly unlike human beings, humans can have no obligation to refrain from using them in any manner that benefits humans.
