Augustine says (De Trin. vi, 7): "When we say the person of the Father we mean nothing else but the substance of the Father."
Yet Thomas Aquinas also says: "Concerning this, the abbot Joachim erred in asserting that as we can say "God begot God," so we can say "Essence begot essence": considering that, by reason of the divine simplicity God is nothing else but the divine essence." In this he was wrong, because if we wish to express ourselves correctly, we must take into account not only the thing which is signified, but also the mode of its signification as above stated (q. 39, a. 4).
Summa theologiae III Question 39.
The persons in relation to the essence
- Is the essence in God the same as the person?
- Should we say that the three persons are of one essence?
- Should essential names be predicated of the persons in the plural, or in the singular?
- Can notional adjectives, or verbs, or participles, be predicated of the essential names taken in a concrete sense?
- Can the same be predicated of essential names taken in the abstract?
- Can the names of the persons be predicated of concrete essential names?
- Can essential attributes be appropriated to the persons?
- Which attributes should be appropriated to each person?