 As for intermedial-motion, that is, the motion that exists extra-mentally, here is where Avicenna’s novel analysis of motion at an instant comes to play. He first notes that the perfection in question in Aristotle’s definition could not refer either to the starting point or to the ending point of the motion, since in the first case the motion has not yet begun and in the second case the motion is already completed. Thus the perfection must refer to some perfection of the moving object while it is in an intermediate state between these two extremes. So, for example, an object moving between x and z is not in motion at either x or z, but only while it is in the space between x and z. That intermediate state, in turn, could refer either to the whole continuous medium between the two extremes or to a point. So, again, the intermediary state might refer to the whole of the motion along the entire continuous distance between x and z or to the moving object’s being at one or another single point along the distance, as for example, y. Avicenna next observed that at every instant during a moving object’s continuous motion it is moving, and yet there is no instant at which the whole of the motion exists as some extended magnitude. Thus the perfection in the definition of motion must refer to the perfection of the moving thing at one or another point between the starting and ending points, albeit, as the moving thing is at that point for only an instant. It is the very fact that the moving object is only at the intermediate point for precisely an instant that guarantees that the object is undergoing motion; for should it remain at some point for more than an instant, and so for a period of time, the object would in fact be at rest at that point.