abstract: This paper intervenes in a contemporary debate on the animal ethics of the Brethren of Purity's (Iḫwān al-Ṣafāʾ) epistle on animals. I argue that they present a case for justice for animals by rejecting the fallacious link between ontological superiority and moral superiority. Since human beings are vice-regents of God and since the rational soul is the vice-regent, the Brethren's account of human beings as superior in virtue of their rationality establishes a moral obligation toward animals. The Brethren develop this account partially under the influence of the Muʿtazilī theological tradition, and as a result, their position falls in line with other positions on justice for animals found during their time. Even on the issue of animal use, the Brethren maintain that the human need for animal labor emphasizes the obligation to treat animals justly. In the end, the greater rational capacity of human beings entails greater moral responsibility toward animals, not moral impunity.