 Although a final cause is in a certain way more eminent than all others and even prior [to them], its nature of causing is, nevertheless, more obscure and for that reason was almost entirely unknown to the ancient philosophers… For this reason … in order to explain this more thoroughly and to resolve the difficulties, it should first be inquired as to whether an end is a cause, then in what manner and what it causes, and also how many kinds of ends there are and what the nature of causing is for each one of them (DM XXIII 1.1)