An Argument for Theoretical Primary Substances

Is there a way to determine whether, in the Categories, Aristotle by 'primary substance' means what I called a 'commonsensical' or a 'theoretical' substance? It would be desirable to establish the latter, I think, since this then brings the Categories into greater harmony with the Metaphysics. In the former work, too, Aristotle would be concerned with 'the substance of a thing', and he would be conceiving of it as that which places that thing in a system of genus-species classification.

It proves difficult to find arguments based on language alone. One consideration is that proper names do not figure in Cat 5, whereas they are used freely in the postpraedicamenta when they are needed to make a point-- which gives some support to the suggestion that primary substances are not what are indicated by proper names.

Here is an argument based on the reduplicative idiom qua.

"Socrates qua quality" asks us to consider some quality of Socrates, say, that he is pale, and thus we may say "Socrates qua quality is pale." In such a sentence, the word 'pale' predicates paleness of Socrates, and in the context the expression "Socrates qua quality" picks out, not Socrates, but this quality which Socrates has.

Similarly, if we say, "Socrates qua quantity is five feet tall", then "five feet tall" predicates five feet of Socrates and "Socrates qua quantity" picks out, not Socrates, but this quantity that Socrates has.

By parity, then, if we say "Socrates qua substance is a man", then "a man" predicates humanity of Socrates, and "Socrates qua substance" picks out, not Socrates, but this substance that Socrates has.

This substance that Socrates has would not be a secondary substance (note that we do not wish to say that "Socrates is man", but rather "a man", indicating an 'atom' or instance of humanity).

The point is that the reduplicative idiom has a use as regards the category of substance, just as it does for the other categories, and then what it picks out is not the individual, Socrates, nor the species or genus, but rather some instance of a nature. The claim would be what this picks out would go undesignated, and something else would be given two designations, unless 'primary substance' indicated this.