Plotinos: Complete Works, v. 1 In Chronological Order,...

6. Now let us speak of bodies. The mutual transformation of elements demonstrates that they must have a substrate. Their transformation is not a complete destruction; otherwise (a general) "being"287 would perish in nonentity. Whereas, what is begotten would have passed from absolute nonentity to essence; and all change is no more than the passing of one form into another (as thought Aristotle).288 It presupposes the existence of permanent (subject) which would receive the form of begotten things only after having lost the earlier form. This is demonstrated by destruction, which affects only something composite; therefore every dissolved object must have been a composite. Dissolution proves it also. For instance, where a vase is dissolved, the result is gold; on being dissolved, gold leaves water; and so analogy would suggest that the dissolution of water would result in something else, that is analogous to its nature. Finally, elements necessarily are either form, or primary matter, or the composites of form and matter. However, they cannot be form, because, without matter, they could not possess either mass nor magnitude. Nor can they be primary matter, because they are subject to destruction. They must therefore be composites of form and matter; form constituting their shape and quality, and matter a substrate that is indeterminate, because it is not a form.