Active Mind and Material Causality

According to Aristotle, in On the Soul, III, 5, Active Mind is "a cause which is productive in the sense that it makes" all the particulars in a class.  However, there is no obvious way that this productive process exemplifies one of his four Causes.  Nevertheless, since 1. the production of particulars is the inverse of their unification; 2. unification is effected by Formal Causality; and 3. the multiplicity corresponding to a Form is its Matter, this productive cause should be characterized as Material Causality.  In other words, Material Causality, properly considered, is defined as the production of multiplicity, rather the mere presence of inert stuff, which is how it is conceived in the Physics.  Thus, Matter is the product of Material Causality, not merely a given inert existent.  The implications of this gap-filling revision at the heart of the origin of Intellectual History are far-reaching.