 James takes as the point of departure of his analysis of change the view commonly attributed to Aristotle by the medievals according to which substantial change involves a natural agent educing a form from the potency of matter. His contention is that for the form to be educed from prime matter it has to preexist in prime matter in an “incipient or inchoate” state. Otherwise the forms would have to be put into matter by an external cause. That cause could only be a natural agent or a supernatural one. It cannot be the latter, for then change would no longer be natural; but nor can it be the former because James holds that forms do not “migrate” from one substance to another. Hence the forms must preexist in matter. 