 The role of form in this hylomorphic context is the topic of Ζ.7–9. (Although these chapters were almost certainly not originally included in Book Ζ—there is no reference to them, for example, in the summary of Ζ given in Η.1, which skips directly from Ζ.6 to Ζ.10—they provide a link between substance and form and thus fill what would otherwise be a gap in the argument.) Since individual substances are seen as hylomorphic compounds, the role of matter and form in their generation must be accounted for. Whether we are thinking of natural objects, such as plants and animals, or artifacts, such as houses, the requirements for generation are the same. We do not produce the matter (to suppose that we do leads to an infinite regress) nor do we produce the form (what could we make it out of?); rather, we put the form into the matter, and produce the compound (Ζ.8, 1033a30–b9). Both the matter and the form must pre-exist (Ζ.9, 1034b12). But the source of motion in both cases—what Aristotle calls the “moving cause” of the coming to be—is the form.