"Hyle" means a type of stuff or matter and "morph" means a form of transformation, so essentially "the changing of matter" or "matters change." Aristotle includes the concept of a hylomorph as a explanation for generation as a possible origin of substance in Metaphysics Zeta.
The Aristotelian hylemorphic doctrine of substance and its properties engenders its own general theory of explanation.
When the topic of the hylomorph comes up in Aristotle's Metaphysics ,
it enters the text fairly later in Book Zeta, chapter 7,8, and 9. The inclusion of these three chapters in the Metaphysics
are actually rather controversial because it is a abrupt beak from the terms of the discussion in terms of 1-6 and 10, which follows this group of chapters. Book Zeta essentially talks about the ontology of being, or more simply "what is substance." So in effect, everything that follows from chapter one onwards, even into Book Eta is examining this question "what is substance," including the concept of a hylomorph.
I did my senior thesis on Metaphysics
Zeta, so I cut out an excerpt that deals with the hylomorph with the citations if you question needs evaluation of the Aristotelian rationalizations.
VideCorSpoon Thesis Pg.42 wrote:
In one sense, a part is a measure of the quantity, but for substantial purposes, this may be disregarded. Aristotle begins to talk of parts in a more restrictive sense than he had in previous chapters. Thus, at this point it can be concluded that a part is substantial and non-substantial. "We need to consider only the parts of which a substance is compounded." (1034 b32) Aristotle is not worried about the non substantial part at this point, only the substantial. "If then, there is both matter, and form, and the compound of these. And if each of them is a substance, then there is one way in which even the matter of a thing could be called a part of it, but in another way only the constituents of the formula of its form are parts of the thing. For instance, flesh is not part of concavity, for it is the matter in which the concavity occurs; but it is a part of snubness. Similarly, the bronze is a part of the statue as a combined whole, but not of the statue spoken of as form." (1035 a1) There are two claims made by Aristotle in the preceding excerpt. For the first claim, matter is a part of a composite, and form is a part of the composite. But there is an alternative (second claim), which is only the parts of the formula of which the form of the composite is part of the compound. Take for example a hylomorph (or more precisely more easily known as a composite). From a hylomorph, there is matter and then there is form. The form of human for example can be broken down into A (rationality) and B (animality). The hylomorph could be decomposable into rationality and animality, which are the parts of the formula of its form. So there is an ambiguity about what constitutes the substance of an object. Here there are two possibilities to decode this ambiguity. One is form and matter, and thus matter is a part of the composite and form is a part of the composite as well. Or, it may just be form. So, snubness is a part of flesh because snubness is a hylomorphic entity (formal and material.)
Aristotle elaborates more on this concept by stating "similarly, the bronze is a part of the statue as a combined whole, but not of the statue spoken of as form." (1035 a6) A statue can be conceived of in two ways. On the one hand, it is bronze and human form. On the other hand, it is just human form. The statue is different from concavity and snubness because it is ambiguous in that you could think of it in two different ways. "Each thing may be said to be the form, or the thing qua having the form; but it cannot be said to be in its own right the material part." (1035 a7) So, going back to the concept of the hylomorph, there is matter and form. One way we cannot take it is by matter itself. "It is for this reason that the formula of a circle does not contain that of its segments, which the formula of the syllable does contain that of its letters." (1035 a9) What is the reason? "For the letters are parts of the formula of the form, and are not the matter of the syllable, whereas the two segments are parts only in the way that the matter on which the form supervenes is a part - though they are closer to the form than is the bronze that has circularity in it. " (1035 a11) Aristotle claims two things. In one instance, taking the example of (A,B), the letters A,B are part of the formula of the form ("BA"). In the second instance, two segments (i.e. semicircles) are parts only in the way the matter on which the form that supervenes is a part. This goes back to the last paragraph (hylomorph is matter and form) which is two ways we can think about substance and its parts. But we cannot think of matter as "the" part, though it should also be noted that segments are material parts, and parts of a syllable are formal.