  The definition of motion as the actuality of a potentiality of the entity undergoing motion in so far as it is potential requires that in each case the passive potentiality for the change is present in the changing object.  The presence of the potentiality can, nevertheless, be in accordance with the nature of the object—in which case the change is natural (phusei) or according to nature (kata phusin), or can happen in the face of a contrary disposition on the part of the nature of the entity—in which case the change is forced (biâi) or contrary to nature (para phusin). A major presupposition on Aristotle’s part is that  this division is exhaustive: there are no changes to which the  nature of the entity would be indifferent or  neutral.[39]  The major consideration behind such a presupposition is that natures regulate the behaviour of the entities to which they belong in a comprehensive manner, and not merely partially. Any influence the entity is exposed to interacts with its nature in a substantive manner. The entity does not possess potentialities for change which would not be directly related to the tendencies emerging from its nature. 