Now, when the potentiality of Motion consists in an ability to walk, it may be imagined as thrusting a man forward and causing him to be continually adopting a different position; when it lies in the capacity to heat, it heats; when the potentiality takes hold of Matter and builds up the organism, we have growth; and when another potentiality demolishes the structure, the result is decay, that which has the potentiality of demolition experiencing the decay. Where the birth-giving principle is active, we find birth; where it is impotent and the power to destroy prevails, destruction takes place — not the destruction of what already exists, but that which intervenes upon the road to existence.
Health comes about in the same way — when the power which produces health is active and predominant; sickness is the result of the opposite power working in the opposite direction.
Thus, Motion is conditioned, not only by the objects in which it occurs, but also by its origins and its course, and it is a distinctive mark of Motion to be always qualified and to take its quality from the moved.