In his studies of nature, Aristotle pursues a series of connected inquiries. He elicits a series of sets of elements; none of the steps is abandoned in favor of later ones. Each set of elements discovers primary constituents of an appropriate sort. Substratum, form, and privation are the most fundamental for the study of generable objects.
DuBose, L. Shannon, "Aristotle's Doctrine of Elements" (1974). The Society for Ancient Greek Philosophy Newsletter. 78.