'Virtus' and 'species' in the Philosophy of Nature of Roger Bacon (c. 1220-1293)

The paper examines Roger Bacon’s use of the concept virtus in Communia naturalium and De multiplication specierum. It focuses on roles which species play as vehicles causality inanimate realm. analyses distinct functions played by motion celestial spheres, power natural place, attraction iron to magnet, universal nature. analysis concludes that is an efficient power, a feature form, capable causing local instigating processes. Species matter’s response stimulation made through every action, exclusion motion, made. non-efficient ‘appetite’ internal matter. expression inherent inclination promote perfect itself, result ‘active potentiality’.