Steve Stanley’s Reviews > 40 Questions About the Trinity > Status Update

First, the divine will is not a ‘part’ of God but just is his essence, as is the case with his other attributes. Second, for each divine person to possess their own will would imply that they possess an attribute distinct from one another, which would then mean they do not share in the same essence. This is trithesim.

[W]e need to be crystal clear on the fact that the missions are not three separate activities undertaken by three distinct agents, but instead the revelation of the one triune God through his acts of creation and redemption, acts that are singular in their willing because there is one and only one God. This is the clarification provided by the doctrine of inseparable operations.

In his [Aquinas's] scholastic treatment of the doctrine, there is one essence (the shared divine nature), two processions (eternal generation and eternal spiration), three persons (Father, Son, and Spirit), four relations (paternity, filiation, joint spiriation, and procession), and five notions (innascibility, paternity, filiation, joint spiriation, and procession).

[According to Aquinas, there are] five notions: innascibility and paternity (by which we know the Father), filiation (by which we know the Son), spiration (by which we know the Father and Son jointly), and procession (by which we know the Holy Spirit).

At the risk of being cheeky, we can summarize Thomas's Trinitarian contribution by counting to five: one essence, two processions, three persons, four relations, five notions.

The scriptural names for the persons faithfully communicate who they are. The Son is from the Father. The Spirit comes forth from the Father. These relations of origin secure at once the substantial equality and the personal distinctions of the three persons.

The three [persons] are distinguished not by substance, by will, or by role. They are distinguished only by relation. The Son is begotten from and the Holy Spirit proceeds from the unbegotten Father.