 Kilvington applies his new rule of motion to describe the uniformly difform motion of mixed bodies and the motion of simple bodies both in a medium and in a vacuum. Explaining Kilvington’s theory, we must keep in mind that temporal motion is possible only if there is some resistance playing the role of a virtus impeditiva. The motion of a mixed body in a medium is easiest to explain, since then the acting power has to overcome the external resistance of the medium as well as the internal resistance of that element which is moved away from its natural place. The local motion of a simple body in a medium is not problematic either, since it can be explained by its natural desire to attain the natural place determined by its heaviness or lightness. Nor does Kilvington have a problem with explaining the natural motion of a mixed body in a vacuum. He once again adopts Ockham’s view that if there were a void, it would be a place. Since place in the Aristotelian sense is something natural that has essential qualities, it determines the natural motion of elementary bodies and, moreover, their inclination to remain at rest in their natural places. Accordingly, says Kilvington, one could imagine a void in four natural spheres, which despite being empty preserve the proper qualities characteristic of the natural places of earth, water, air, and fire. Hence, the temporal motion of a mixed body in a void is the result of the natural inclination of heavy or light elements to attain their natural places. The heaviness and lightness play the roles of force and resistance, respectively. Although there would be no external resistance in a vacuum, the motion of a mixed body could occur without any difficulty (see Jung-Palczewska 1997).