The Ikhwān al-Ṣafāʾ (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 Rasāʾil Ikhwān al-Ṣafāʾ (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.

The final section of the Rasāʾil, on the theological sciences, begins with a lengthy Epistle on religions, succeeded by Epistle 43, which opens this present volume. Here we find a concise explanation of the need to purify one’s soul by performing virtuous acts, after which one can follow the ‘straight path’ to God. The extremely diverse Epistle 44 adopts a more narrative approach, characterized by delightful anecdotes designed to inform the reader of a deeper truth: that of the hereafter following the soul’s separation from the body at death. Alongside many Qurʾanic references are various indications of a familiarity with other religions such as Christianity, Judaism, and Buddhism. Epistle 45 focuses on companionship, resonating strongly with the word ‘Brethren’ by which the authors distinguish themselves. The volume overall is united in its underlying themes addressing the immortality of the soul and the profound need for mutual co-operation. It is informed by the general Neoplatonism of the entire corpus, as well as by Aristotelian and Platonic motifs.