The Epistles of the Brethren of Purity

An encyclopedia of fifty-two epistles composed by an anonymous circle of scholars, probably in tenth-century Basra, who called themselves the Brethren of Purity. Its aim is to purify the soul through knowledge and so prepare it for the next life. The epistles fall into four sections: the mathematical sciences, including number, geometry, astronomy and music; the natural sciences, from matter and motion to minerals, plants, animals and the human body; the psychological and intellectual sciences, which set out a Neoplatonic order of being descending from the Creator through Intellect and Soul; and theological and legal matters, including religious practice and the brotherhood's own way of life. Pythagorean number symbolism runs throughout. The best-known epistle is The Case of the Animals versus Man before the King of the Jinn, a fable in which animals put humanity on trial for its claim to rule over them. The authors' identity and their links with Ismailism are still debated.

It offers a whole medieval worldview in one place, joining science, philosophy and religion, and its animal fable is one of the most readable early debates about how humans treat other creatures.