On the Causes of Sensible Substances in Metaphysics Lambda, chs. 4-5
This is simply a preliminary thought as I work through Aristotle's thoughts.
In Metaphysics Lambda, books 4 and 5 Aristotle examines the causes and principles of sensible substances. His discussion is a little bit confusing, but he seems to conclude that, in one sense, all sensible substances have the same principles and elements, and this by analogy, but in in another sense, all sensible substances do not have the same principles and elements.
In the first sense, all sensible substances have the same elements by analogy, in the sense that all sensible substances are composed of (what was then considered to be the elements) water, air, earth and fire. In the same way, all sensible substances have the same principles by analogy, in the sense that all sensible substances are composed of form, privation, matter, a proximate first mover (for example, man gives birth to man) and the first mover which moves all things. Therefore, since both the elements and the principles are causes of the sensible substances, therefore, all sensible substances have, by analogy, the same causes.
In a second sense, however, all sensible substances do not have the same elements, nor the same causes/principles. This is the case because every individual sensible substance is different from every other sensible substance. Therefore, the elements of one sensible substance are not the same elements of another sensible substance even if they are of the same species. Also, the principles or causes of one sensible substance are not the same principles or causes of another sensible substance, as they each are different composites of differentiated form, matter and privation, and the proximate first efficient cause (for example, man gives birth to man, horse to horse, maple tree to maple tree).
Interestingly enough, although Aristotle recognizes distinct first causes, he also seems to say, and repeat a couple of times in these chapters, that even in this strict sense in which all individual separate substances are different they all have the same first efficient mover.