Epistles 6 to 8 are from the first division of the Episltes, on the propaedeutical and mathematical sciences. Epistle 6 develops ideas concerning natural numbers and their arithmetic, geometric, and harmonic proportions, marked by the influence of Nicomachus of Gerasa and of Euclid. The Brethren here emphasize practical applications of proportionality in music, medecine, 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; the epistle presents a remarkable classfication 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 underpinned by the Brethren's perennial tropes of the microcosm-macrocosm analogy and the emanative hierarchy of existents.
de Callatay, G. (2018). On Composition and the Arts. An Arabic Critical Edition and English Translation of Epistles 6-8. Oxford University Press in association with The Institute of Islamili Studies. https://hdl.handle.net/2078.5/22906