Reply Obj. 1: Person and property are really the same, but differ in concept. Consequently, it does not follow that if one is multiplied, the other must also be multiplied. We must, however, consider that in God, by reason of the divine simplicity, a twofold real identity exists as regards what in creatures are distinct. For, since the divine simplicity excludes the composition of matter and form, it follows that in God the abstract is the same as the concrete, as "Godhead" and "God." And as the divine simplicity excludes the composition of subject and accident, it follows that whatever is attributed to God, is His essence Itself; and so, wisdom and power are the same in God, because they are both in the divine essence. According to this twofold identity, property in God is the same as person. For personal properties are the same as the persons because the abstract and the concrete are the same in God; since they are the subsisting persons themselves, as paternity is the Father Himself, and filiation is the Son, and procession is the Holy Ghost. But the non-personal properties are the same as the persons according to the other reason of identity, whereby whatever is attributed to God is His own essence. Thus, common spiration is the same as the person of the Father, and the person of the Son; not that it is one self-subsisting person; but that as there is one essence in the two persons, so also there is one property in the two persons, as above explained (Q. 30, A. 2).
Reply Obj. 2: The properties are said to be in the essence, only by mode of identity; but in the persons they exist by mode of identity, not merely in reality, but also in the mode of signification; as the form exists in its subject. Thus the properties determine and distinguish the persons, but not the essence.
Reply Obj. 3: Notional participles and verbs signify the notional acts: and acts belong to a suppositum. Now, properties are not designated as supposita, but as forms of supposita. And so their mode of signification is against notional participles and verbs being predicated of the properties. _______________________
SECOND ARTICLE [I, Q. 40, Art. 2]
Whether the Persons Are Distinguished by the Relations?
Objection 1: It would seem that the persons are not distinguished by the relations. For simple things are distinct by themselves. But the persons are supremely simple. Therefore they are distinguished by themselves, and not by the relation.
Obj. 2: Further, a form is distinguished only in relation to its genus. For white is distinguished from black only by quality. But "hypostasis" signifies an individual in the genus of substance. Therefore the hypostases cannot be distinguished by relations.
Obj. 3: Further, what is absolute comes before what is relative. But the distinction of the divine persons is the primary distinction. Therefore the divine persons are not distinguished by the relations.
Obj. 4: Further, whatever presupposes distinction cannot be the first principle of distinction. But relation presupposes distinction, which comes into its definition; for a relation is essentially what is towards another. Therefore the first distinctive principle in God cannot be relation.
On the contrary, Boethius says (De Trin.): "Relation alone multiplies the Trinity of the divine persons."