Muhammad al-Shahrastani, the famous Muslim theologian of the 12th century and author of the Book of Religious and Philosophical Sects, was greatly influenced by Ismaili teachings. In this work al-Shahrastani refutes the metaphysics of Ibn Sina (Avicenna) from an Ismaili point of view.

The Brethren of Purity, the anonymous adepts of a tenth-century esoteric fraternity, 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 Rasa 'il Ikhwan al-Safa'. Its fifty-two epistles offer 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 43-45 are (...) some of the richest and most diverse in the corpus of the Brethren of Purity. This volume includes anecdotes and visions of paradise, Qur'anic quotations and interfaith references, as well as Platonic motifs. The prevailing theme of the immortality of the soul is considered in detail, along with the necessity of co-operation in this world in order for the soul to be able to break free of it. (shrink)