 Natural philosophy is the field with the greatest number of Arabic-Latin translations. In this discipline, Arabic philosophers had been particularly active, and Latin philosophers were particularly interested. Arabic natural philosophy reached the Latin West earlier than the other philosophical disciplines. The medical and astrological translations of the late eleventh and early twelfth century transported much philosophical material of the Graeco-Arabic tradition to the Latin world. Under the influence of these Arabic sources, Latin authors of the twelfth century explained natural phenomena by recourse to the four elements, the four qualities, the four humours, the three spiritus (natural, spiritual, animal) and their organs, the localization of the soul’s faculties in different cavities of the brain, the distinction between the sublunar and the heavenly universe, the circular movement of the heavenly spheres, and by using Aristotelian concepts such as matter and form, action and passion, cause and effect. While many Latin writers of the twelfth century continued to understand nature in terms of the Latin Christian tradition, others, in the context of the so-called “school of Chartres”, such as William of Conches, Adelard of Bath, Hermann of Carinthia and Bernardus Silvestris, drew amply on the new medical and astrological sources, often combining them with the doctrines of Plato’s Timaeus (Burnett 1982, introduction; cf. also Lemay 1962). Sometimes they did this by openly dividing their presentation into a section according to the church fathers and a section according to the philosophers and natural scientists (physici), which integrated material from the Latin and Arabic philosophical traditions (e.g. the treatises Philosophia by William of Conches and De natura corporis et animae by William of St.-Thierry).