You have opened up fundamental questions.
Aristotle’s “primary substance”, the “this something”, the “tode ti” (e.g., the red apple over there on the table) is fraught with particularity.
But the “particularity” of “primary substance” is not the “particularity” of “person”. Robert Spaemann sums this up neatly when he points out that “person” is deeper than “substance”.
I agree that " substance " and " person " are different. I don’t know if I would call " person " deeper than " substance. "
Aristotle and Thomas distinguish between First and Second Substance and First and Second Act. First Substance would be what you see, feel, sense, etc. Second Substance would be the composite of matter and form activated by the act of existence. First Act would be the activation of this composit.
But as yet there is nothing to " see. " At this point the substance can take on any set of " accidents " imaginable - in theory. In fact though, the form and the matter and the act of existence are determined to a specific set of accidents. When they appear we have second act and First Substance - Second Substance with all the accidents we experience, by which we identify a person.
And " person " is the result of the formation of both Second and First Substance ( which includes all the " accidents " by which we identify a " person. "). But the " person " cannot be separated from the Second Substance and the First Act from which it flows as from its origin.
So, I would say that " person " is not deeper than " substance. " Rather it is a defined way or a specific way in which we view the " substance " we call a human being. It is a " looking " at the substance we call man in a human way, a " personal " way. A person is someone we know and can relate to, we can hardly relate to a substance or a being. So a person is merely a living, human metaphore for a human being, as opposed to his metaphysical composition.
You will note that your reference is to a post by Imelahn on another thread which I quoted.
I think you need to reread the quote again. Imelahn draws a distinction on how person and relationships are understood in God. In God, Persons are distinct, yet they are the same substance and not accidents. In God’s creatures substance has accidents and relationships are one of these accidents. I haven’t read Spaemann so I can’t comment on his thought.
I would expand your comment. “Person”, whether human or divine, transcends Aristotelian categories. “Person”, in particular (no pun intended), is not reducible to the Aristotelian “accidental” category of “relation”. Nor can “person” be explained in terms of species/genus - there is no “form”, no “eidos”, for a “person”.
I’m not sure I agree because I can’t recall Aristotle’s understanding of " person, " and of course he never considered " person " as Thomas did of the Divine Nature. One cannot criticize Aristotle for that. I would agree that " person " transcends Aristotle’s categories. And Imelahn did not equate " person " with " relation, " he said that the understanding of the Divine Persons was that each Person flowed from its origin, the substance of God the Father and was expressed and understood as a relationship. But this relationship in God is not an accident as it would be in men, for in God there are no accidents.
We have to be careful about one thing. We try to express the Divine Nature and the Divine Persons with limited human knowledge and understanding. We always reach for something which cannot actually be reached. So our attempts to experss these things will always be at fault to some extent. Perhaps it is that we cannot express or explain more that we have. One thing is certain, the Divine Persons are real and distinct but it is a distinction of relationships, yet each is the same substance and nature. This seems contradictory and it would be for man, but not in God. So, it is something our minds can’t actually understand, define, or explain. We know it is true, we just don’t have the intellect to understand and explain it. Only the Divine Intellect can. So we need not be frustrated and we should not criticize any thinker or philosopher for failing to explain adequately what cannot be adequately explained, and which will never be adequately explained.
All this has led to a rethinking of metaphysics in the 20th century (e.g., Heidegger , Levinas, Marion ).
Aristotle and Thomas are more than enough for me.
Pax
Linus2nd