In an effort to widen the discussions about internal resistance in 14th century theories of motion, this article examines the evolution of the concept in the work of the Parisian scholar Nicole Oresme. In his Physics, he presents a position that is not fully developed; as well, he raises some questions regarding the motive qualities of the elements constituting mobile objects. This ambiguity becomes even more evident when his position changes later in his discussions in the treatise On the Heavens. (...) Oresme is then even less inclined to accept the idea of internal resistance in motion. (shrink)