 First we can look at the starting point. There was a great deal of argument, in the thirteenth and fourteenth century, about the precise interpretation of  Aristotle’s theory of change: this theory talks about the bringing about of change, by an agent, in a patient, and, furthermore,  it talks about the change happening because of the transmission of a form  from the agent to the patient.  The key text for this is  Aristotle, Physics III, cc2–3 (202a9–20), and it is very obscure.  Because of this obscurity, there is room for a good deal of disagreement about the details: see (Löwe 2017) for a particularly baroque example.  