Reply Obj. 4: Relations which result from the mental operation alone in the objects understood are logical relations only, inasmuch as reason observes them as existing between two objects perceived by the mind. Those relations, however, which follow the operation of the intellect, and which exist between the word intellectually proceeding and the source whence it proceeds, are not logical relations only, but are real relations; inasmuch as the intellect and the reason are real things, and are really related to that which proceeds from them intelligibly; as a corporeal thing is related to that which proceeds from it corporeally. Thus paternity and filiation are real relations in God. _______________________
SECOND ARTICLE [I, Q. 28, Art. 2]
Whether Relation in God Is the Same As His Essence?
Objection 1: It would seem that the divine relation is not the same as the divine essence. For Augustine says (De Trin. v) that "not all that is said of God is said of His substance, for we say some things relatively, as Father in respect of the Son: but such things do not refer to the substance." Therefore the relation is not the divine essence.
Obj. 2: Further, Augustine says (De Trin. vii) that, "every relative expression is something besides the relation expressed, as master is a man, and slave is a man." Therefore, if relations exist in God, there must be something else besides relation in God. This can only be His essence. Therefore essence differs from relation.
Obj. 3: Further, the essence of relation is the being referred to another, as the Philosopher says (Praedic. v). So if relation is the divine essence, it follows that the divine essence is essentially itself a relation to something else; whereas this is repugnant to the perfection of the divine essence, which is supremely absolute and self-subsisting (Q. 3, A. 4). Therefore relation is not the divine essence.
On the contrary, Everything which is not the divine essence is a creature. But relation really belongs to God; and if it is not the divine essence, it is a creature; and it cannot claim the adoration of latria; contrary to what is sung in the Preface: "Let us adore the distinction of the Persons, and the equality of their Majesty."
I answer that, It is reported that Gilbert de la Porree erred on this point, but revoked his error later at the council of Rheims. For he said that the divine relations are assistant, or externally affixed.
To perceive the error here expressed, we must consider that in each of the nine genera of accidents there are two points for remark. One is the nature belonging to each one of them considered as an accident; which commonly applies to each of them as inherent in a subject, for the essence of an accident is to inhere. The other point of remark is the proper nature of each one of these genera. In the genera, apart from that of relation, as in quantity and quality, even the true idea of the genus itself is derived from a respect to the subject; for quantity is called the measure of substance, and quality is the disposition of substance. But the true idea of relation is not taken from its respect to that in which it is, but from its respect to something outside. So if we consider even in creatures, relations formally as such, in that aspect they are said to be "assistant," and not intrinsically affixed, for, in this way, they signify a respect which affects a thing related and tends from that thing to something else; whereas, if relation is considered as an accident, it inheres in a subject, and has an accidental existence in it. Gilbert de la Porree considered relation in the former mode only.
Now whatever has an accidental existence in creatures, when considered as transferred to God, has a substantial existence; for there is no accident in God; since all in Him is His essence. So, in so far as relation has an accidental existence in creatures, relation really existing in God has the existence of the divine essence in no way distinct therefrom. But in so far as relation implies respect to something else, no respect to the essence is signified, but rather to its opposite term.