The Brethren of Purity, the anonymous adepts of a tenth-century esoteric fraternity based in Basra and Baghdad, hold an eminent position in the history of science and philosophy in Islam due to the wide reception and assimilation of their monumental encyclopaedia, the Epistles of the Brethren of Purity. This compendium contains fifty-two epistles offering synoptic accounts of the classical sciences and philosophies of the age; divided into four classificatory parts, it treats themes in mathematics, logic, natural philosophy, psychology, metaphysics, and theology, in addition to didactic fables.
Epistles 6 to 8 are from the first division of the Epistles, on the propaedeutical and mathematical sciences. Epistle 6 develops ideas concerning natural numbers and their arithmetic, geometric, and harmonic ratios, marked by the influence of Nicomachus of Gerasa and of Euclid. The Brethren here emphasize practical applications of proportionality in music, medicine, and alchemy. Epistle 7 addresses theoretical scientific knowledge as directed towards the spiritual realities of souls, the goal of which is to actualize human potential; this epistle also presents a remarkable classification of sciences. Epistle 8 surveys material cultures in the Islamic mediaeval milieu, embellished by a consideration of the effects of the heavenly bodies on the predisposition of individuals to follow specific trades. These three epistles are, of course, underpinned by the Brethren's perennial tropes of the microcosm/macrocosm analogy and the emanative hierarchy of existents.
Nader El-Bizri is Professor of Philosophy and Director of the Civilization Studies Program at the American University of Beirut. He has previously taught at the University of Cambridge, the University of Nottingham, and the University of Lincoln. He is also affiliated with the Institute of Ismaili Studies in London and the Centre National de la Recherche Scientifique in Paris. He has published widely in the field of Arabic sciences and philosophy, and he serves on various prestigious editorial boards of book series and journals, as well as acting as the General Editor of the Epistles of the Brethren of Purity OUP-IIS series.
Godefroid de Callatay is Professor of Arabic and Islamic Studies at the Oriental Institute of the University of Louvain. He specializes in the history of Arabic sciences and philosophy, and the role played by Islam in the transmission of Hellenic knowledge to the Latin West during the Middle Ages. Amongst other subjects, he has published extensively on the Rasa'il Ikhwan al-Safa', and has already contributed to the present series by editing and translating Epistle 36, and, together with Bruno Halflants, the short version of the epistle on magic (52a). Since 2012, he is also the director of Speculum Arabicum, a project on comparative medieval encyclopaedism at the University of Louvain.
