 In Latin psychology, the influence of Arabic works is particularly strong and lasted well into the sixteenth century. Avicenna and Averroes, the most influential philosophers, presented the West with a faculty psychology in the tradition of Aristotle and enriched by Graeco-Arabic medical doctrines, such as about the cavities of the brain, the nerves, and the spirits which transport information in the body. From about 1220 onwards, the full range of Avicennian faculties (vegetative, external and internal senses, the motive faculties, practical and theoretical intellect) appears in Latin treatises by masters of arts and theologians. This system of faculties remains, by and large, standard for a long time in philosophical handbooks, from the anonymous Philosophy of the Simple (Philosophia pauperum) and Vincent of Beauvais’ Mirror of Nature (Speculum naturale) in the thirteenth century up to the Philosophic Pearl (Margarita philosophica) of the 1490s. Also influential was Avicenna’s definition of the soul as a separate substance (Hasse 2008) and his thought experiment of the “Flying Man” (Hasse 2000, 80–92).