Although form and matter will be "reduced" in a substantial change to the category of substance as principles of substance, they should not be thought of as substances or quasi-substances in their own right.
First, from the formal cause, accident could be the cause of individuation, but from the efficient cause the principles of substance (matter and form) are the efficient causes of the one substance.
In Γ.2, Aristotle adds that for this reason it studies the causes and principles of substances (ousiai).
Still, the soul can be called substance by analogy, insofar as it is the formal principle of a substance.
In that sense it is a principle of a substance, 'principle' being a technical term that refers back to the first entry, arche, in Aristotle's philosophical lexicon in the Metaphysics, as well as Thomas' commentary on it, and Thomas' On the Principles of Nature.
He begins by pointing out that Leibniz says that the action of the primitive power ("the internal principle of a substance that brings about change, or the passage from one perception to another") "can be called appetition" (Monadology §15; also, Principles of Nature and Grace §2).
But even these have collapsed in negotiations, such that the final declaration now reveals only vague principles, denuded of substance by spoiler governments.
Toxicity and/or persistence determine the polluting principle of these substances.
Thus, while the substance of the Categories serves as a principle of individuation, the substance of the Metaphysics is more complicated, serving both to individuate Bucephalus and Seabiscuit and to capture the connection or sameness that holds between them.
