Simplicity vs. Trinity: Theological Responses

Question #15: What Catholic theological responses exist to the objection that divine simplicity is incompatible with the Trinity, and how effectively do they preserve both doctrines as taught in Church tradition (cf. Augustine, De Trinitate)?

Throughout Christian history, theologians have repeatedly addressed the concern that divine simplicity (the doctrine that God has no parts or composition) conflicts with Trinitarian teaching–that there are three distinct, co-equal Persons in the one God. Catholic tradition offers several key responses, many of which draw from St. Augustine’s De Trinitate, to show that both doctrines can–and must–be upheld without contradiction.

1. Augustine’s Relational Distinctions

In his De Trinitate, Augustine emphasizes that the Father, Son, and Holy Spirit share exactly one indivisible divine substance, while also being truly distinct. Augustine explains these distinctions by highlighting relations of origin: the Father begets the Son, and the Holy Spirit proceeds from the Father (and, in Western theology, from the Son as well). These relations do not introduce “parts” into God but characterize how the one divine nature is expressed in three irreducible modes. Because each Person wholly possesses the same essence, there is no composition in God, preserving simplicity.

2. Subsistent Relations vs. Composition

Drawing from Augustine and developed further by later Scholastics (e.g., Aquinas), Catholic teaching explains that the three Persons are “subsistent relations.” Each Person is the one divine essence, but in a distinct relational “stance” (begetting, begotten, or proceeding). As such, God remains one infinite act (no composition), yet the real personal distinctions derive from eternal relations, not from dividing up the essence into parts. This approach directly addresses the objection that Trinitarian plurality implies “components”: the “plurality” is purely relational within the same, undivided essence.

3. Medieval and Modern Appropriations

Medieval scholastics–like Aquinas in his Summa Theologiae–refined Augustine’s insights, insisting that “relation” in God is not an accidental property, as it would be in creatures, but is the divine essence considered according to an origin-distinction. Modern theologians and philosophers, including those who embrace “relational ontologies,” continue to show how these internal relationships do not contravene the Church’s affirmation that “all that is in God is God.” Because the Persons do not “add on” any ingredient besides the divine nature, God’s simplicity stands intact.

4. Efficacy of These Responses

These theological strategies, stemming from Augustine’s foundational contributions, have proven remarkably enduring in the Catholic tradition. They allow the Church to insist on God’s simplicity–no composition, no unrealized potential–while acknowledging three real and eternal distinctions in God. The result is a synthesis that has guided Magisterial statements across centuries (e.g., Fourth Lateran Council, Council of Florence), all of which reiterate that there is but one divine essence, yet three Persons unconfused and co-eternal.

• Scholastic Affirmation: By emphasizing that the one nature is fully actualized in each Person, without dividing it, these theologians effectively demonstrate that a plurality of relations does not introduce a plurality of essences.

• Augustinian Legacy: Augustine’s language of “relations of origin” remains foundational to Catholic theology, showing that even though the Father, Son, and Spirit differ, their difference does not break God’s unity.


In this manner, Catholic responses–rooted especially in Augustine’s De Trinitate–have consistently preserved both the Trinitarian distinctions and the classical doctrine of divine simplicity, addressing the objection that they are incompatible by clarifying the unique, relational mode of divine “plurality.”

(see #11, #12, #13, #14, #27 for more)