Yes, you’re right; I see I made a few mistakes in what I said. I’m no philosopher, and as we’re celebrating the national holiday in my country today I’m not entirely focused on this discussion. I’ll try to reaffirm my basic position.
If you agree that God’s simple existence is personal, or that it is personhood, then it would have to follow that there could not be a multiplicity in persons
I agree that God is personal, and I agree that Gods Simple Existence
is the Person(s). I don’t agree that there can’t be several Persons because I don’t think a Personhood is its own entity. What I mean by that is that I think the Entity is God, and the Personhood derives its existence from that and it is that Entity. To put it vulgarly, the Personhood is the personification of Gods Essence. If one such Personification can exist, then so can three; provided they are perfectly the same. But if there is three, then they cannot be perfectly equal; since a person always forms relationships to other persons they are in contact with, and so we have three perfectly united Persons of the same Essence differentiated by their relationships to each other.
Now, personhood as defined by the Aristotelian-Thomistic tradition, is a rational nature , specifically, an intellect and a will. What this means is that for there to be a multiplicity in persons entails multiple intellects and wills,
Which comes first, the person or the rational nature? If the Intellect and Will is first and drives us to define their combination as a Person it is perfectly possible to define another Person from the same rational nature. These Persons would initially only be distinguished logically, but once the logical distinction is made by one of the involved Persons a real relationship ensues between them and the distinction is now real.
If the Person is first then it is as you say, a different person would have to define a different Intellect and Will (and thus existence).
If you deny that any of these are causing the other in God, then aren’t you denying the very concept of a definable Personhood in Him? I don’t mean this last one rhetorically, by the way, I am not well read on this subject and I don’t have time right now to think about what a “both, and” position would really entail.