  Here is a brief summary of the theory. A moving body possesses, at each moment in time, a particular ‘motion’, which is to be thought of as a momentary, quality-like property of the body. Motions are defined to be the cause of conjunctions or disjunctions. A conjunction with a (stationary) body is brought about by displacement in space. We are thus to think of the motion of a body as being either identical with, or else the cause of, its displacement in space between two moments in time. A motion cannot be caused by another motion (as that would lead to perpetual motion). A body is set in motion by its possession of a quality like ‘weight’ or ‘fluidity’. It persists in motion by having a dispositional property, ‘impetus’ or ‘elasticity’, which is the continuous cause of subsequent motions. It is brought to rest by coming into contact with other objects.