Minimal Divine Simplicity and the Trinity

Just a note: I will probably be laying kind of low for a while, since I am now moved in at my new school and taking summer courses. I will be kind of busy for the next two months, so please do not be offended if I don't reply to comments quickly on this blog. I will get back to you eventually. Anyway, enjoy the post!

For Catholics, belief in the doctrine of God's simplicity is dogmatically defined to be held by all the faithful just as much as the doctrine of the Trinity (see the Fourth Lateran Council as well as Vatican I). Does the official dogma of divine simplicity contradict the revealed truth about the Holy Trinity? Not necessarily, at least on a certain construal of divine simplicity. Call this the "minimal doctrine of divine simplicity":

(MDS) God has no proper parts, either metaphysical or physical.

This means that God possesses of course no physical parts, but also no properties, ontological constituents, tropes, accidents, immanent universals, distinct intellectual parts (e.g. distinct will and intellect), etc.

Is this what the Church intends to define when it says God is simple? Arguably so. The definition of simplicity must be strong enough to rule out theistic personalist views of God, for this is not found in the teaching of the Fathers and is arguably inconsistent with the other divine attributes which are mentioned in connection with simplicity in these Councils (e.g. God's being immutable, incomprehensible, infinite in will). Hence, it must mean more than that God is simply non-physical; God isn't just simple in the sense that an angel is. On the other hand it must be weaker than simply identifying God's essence with his existence. For if the Church meant to endorse dogmatically the Thomistic teaching on simplicity, this would make anyone who did not hold to this view in substance to be heretical; hence, the teachings of the Cappadocian Fathers as well as St. Maximus the Confessor, and likely even Bl. Duns Scotus, would be heresy. This is why MDS seems to be a likely candidate for the minimal required belief in divine simplicity for orthodoxy.

But given MDS, this is a truth about the Trinity:

(TR) It is not the case that the persons of the Trinity are proper parts, either metaphysical or physical.

For the persons of the Trinity all share fully in the divine essence; the Father is fully God, just as the Son is fully God, just as the Holy Spirit is fully God. To suppose the persons are proper parts of God would mean there is something G which is fully God, and that each person of the Trinity does not fully share in the essence of G (since, after all, G essentially has as proper parts each of the persons of the Trinity, whereas the same does not hold for each of the individual persons). Hence, the persons of the Trinity cannot be understood to be proper parts of God in any sense; hence, the doctrine of the Holy Trinity cannot contradict the minimal doctrine of divine simplicity.

This seems to show that the Church's teaching here is consistent; it is a separate matter whether Aquinas's teaching which includes the doctrine that God's essence = his existence, as well as that God is pure actuality, can be made consistent with the Trinity.