1. Matter underlies and persists through substantial changes. A substance is generated (destroyed) by having matter take on (lose) form.
1. A house is created when bricks, boards, etc., are put together according to a certain plan and arranged in a certain form. It is destroyed when the bricks, boards, etc., lose that form.
2. An animal is generated when matter (contributed by the mother) combines with form (contributed by the father).
2. This suggests that the primary substances of the Categories, the individual plants and animals, are, when analyzed, actually compounds of form and matter. And in the Metaphysics, Aristotle suggests that a compound cannot be a substance (Z3, 1029a30).
3. This may seem a strange move for Aristotle to be making. But the idea may be this: a compound cannot be a basic ontological ingredient. Cf. these compounds:
a brown horse
Each of these is a compound of substance + attribute:
a brown horse = a horse + brownness
a scholar = a human + education
In these cases, the compound is a compound of entities that are more basic.
("A scholar is not an ontologically basic item in the world - a scholar is just a human with a liberal education.")
4. If then primary substance (in the Metaphysics conception of primary substance) cannot be a form-matter compound, what is primary substance? The possibilities seem to be: matter and form. (Aristotle actually discusses more possibilities - this is a simplification.)
5. In Z3, Aristotle considers the claim of matter to be substance, and rejects it. Substance must be separable and a this something (usually translated, perhaps misleadingly, as "an individual").
1. Separable: to be separable is to be nonparasitic. Qualities, and other non-substances of the Categories, are not separable. They only exist...