Opening

Of every creature one can ask: "What is it made of?" Of God, the Catholic tradition holds, this question has no purchase. God is not made of anything. God is not assembled. God is not God by participating in some prior reality called divinity; God is divinity. The doctrine that God is metaphysically simple — without parts, without composition of any kind — is one of the oldest convictions of philosophical theology, and it is the conciliar teaching of the Catholic Church 800.

This article reports what divine simplicity means, why the tradition holds it, where it is defined, and what it excludes. LV reports; it does not teach.

1. What is meant by "simplicity"

In Aristotelian-Thomistic metaphysics, a thing is composed if it has distinguishable parts. The kinds of composition are several:

  • Quantitative parts — a body is made of arms, legs, organs. Spatial extension is a composition of parts outside of parts.
  • Matter and form — a statue is composed of bronze (matter) and shape (form).
  • Essence and existence — what a thing is (its essence: "horse," "human") differs from that it is (its existence: this horse, this human, exists).
  • Substance and accident — Socrates is a substance; his being seated, standing, walking are accidents that come and go without changing what he is.
  • Genus and species — "animal" plus "rational" makes "human."

Aquinas argues, in Summa Theologiae I q.3, that none of these compositions is in God I q.3 a.1 I q.3 a.2 I q.3 a.3 I q.3 a.4 I q.3 a.7. God is not a body. God is not matter and form. In God, essence and existence are not distinct: God's essence is to exist; God's what and that are one. God has no accidents — God's mercy is not something added to God, as if God could lose mercy and remain God. God has no genus.

The Catechism summarises: "He is the fullness of Being and of every perfection, without origin and without end. All creatures receive all that they are and have from him; but he alone is his very being, and he is of himself everything that he is" §213.

2. Where the doctrine is defined

Lateran IV (1215) is the conciliar definition: "one only true God, eternal and immeasurable, almighty, unchangeable, incomprehensible, and ineffable, Father, Son, and Holy Spirit: three persons indeed, but one essence, substance, or nature absolutely simple" 800. The phrase substantia absolute simplex is the conciliar formula.

Vatican I (1870) reaffirms it in Dei Filius: "the holy, catholic, apostolic, Roman Church believes and confesses that there is one true and living God, creator and lord of heaven and earth… simple altogether and unchangeable [omnino simplex et incommutabilis]" 3001.

The doctrine is therefore not a Thomist preference; it is conciliar dogma.

3. Why the tradition holds it

The argument runs in stages.

(a) From the First Cause. Whatever is composed has parts; parts are prior to the whole; whatever has parts is therefore caused — by the parts that compose it, or by an agent that composes them. But God, as First Cause, is uncaused. Therefore God has no parts. The argument is in Aquinas I q.3 a.7 and earlier in Augustine Augustine, CityOfGod 11.10.

(b) From Pure Act. Whatever has potency to be otherwise is composed of act and potency. But the First Mover (the conclusion of the First Way) is pure act, with no unactualised potential I q.2 a.3 — for if it had unactualised potential, something else would have to actualise it, and it would not be First. Therefore God is not composed of act and potency.

(c) From Aseity. Aseity is the property of having one's being from oneself — a se, "from oneself." Creatures receive their existence from another; God does not. But if God's essence and existence were really distinct, God's existence would be something received by his essence — i.e., God would receive his existence from another. Therefore God's essence is his existence I q.3 a.4.

The classical conclusion is summarised by Aquinas: in God, Deus est ipsum suum esse — "God is His own act of being" I q.3 a.4.

4. The Fathers' witness

Divine simplicity is not a medieval invention. Augustine teaches it explicitly: God is "what he has" — God is good, is wise, is just; he does not have goodness, wisdom, justice as accidents Augustine, On The Trinity 5.10 Augustine, On The Trinity 6.7. Athanasius defends it against the Arians: the Son cannot be of a different substance from the Father, for there are no parts in the Father to be of Athanasius, Against The Arians 3.4. John of Damascus systematises the patristic consensus in De Fide Orthodoxa: God is "without parts, simple, uncompounded, incorporeal" John of Damascus, Exposition of the Orthodox Faith 1.9.

Pseudo-Dionysius — received by both East and West — develops the apophatic form of the doctrine: God is named "by negations," because every affirmative name we possess is borrowed from creatures, and creatures are composed in ways God is not Pseudo-Dionysius, Mystical Theology 1.

5. What simplicity does not claim

Three common misunderstandings.

Simplicity does not mean lack of complexity in our description. God's being is unitary; our knowledge of God is necessarily multi-aspectual because we are finite. We name God's wisdom, justice, mercy with different words; in God these are one and the same divine essence under different aspects of our knowing. The Catechism notes: "God's various attributes do not arise from any composition in him" §202.

Simplicity does not deny the real distinction of the Trinitarian Persons. Lateran IV holds simplicity and the three Persons in the same paragraph 800. The distinction in God is not a distinction of parts but of relations of origin: the Father is unbegotten, the Son is begotten of the Father, the Spirit proceeds from the Father (and the Son, in the Latin tradition). The Persons are not three pieces of God; each Person fully possesses the one divine essence.

Simplicity does not flatten the Incarnation. The Son's assuming a human nature does not introduce composition into the divine essence. The hypostatic union joins the two natures in the one Person of the Word, without composition of natures, without conversion of one into the other 302 (Chalcedon). The divine essence remains absolutely simple; the Son who is God becomes also man without God ceasing to be simple.

6. Why this matters pastorally

If God is not simple, then God is not first. If God is composed, the parts are prior, and there is something behind God that explains him — and that something would be the real God. The doctrine of simplicity is the metaphysical face of the Shemaʿ: "The Lord our God, the Lord is one" Deut 6:4. Christian prayer is addressed to the One who is not assembled, the One whom no system contains, the One who is not a member of any genus.

The doctrine also frames the language of the Christian life. When the believer says God is love 1 John 4:8, the is is not predication of an accidental quality. God's love is identical with God's being. To love is to participate in the very life of God. The simplicity of God is the hidden architecture of every act of charity.

7. What this article does not claim

It does not enter the contemporary analytic-theology debates over simplicity (Plantinga, Wolterstorff vs. Stump, Pruss, Feser). It does not decide the disputed questions about how to articulate the Trinity in simplicity (the psychological and social analogies remain analogies). It does not address the Eastern essence-energies distinction (which holds simplicity differently and would require its own article).

Closing

Divine simplicity is the doctrine that God is not made of anything — that God's nature, attributes, and existence are one. It is the conciliar teaching of Lateran IV and Vatican I. It is the consensus of the Fathers and the Doctors. It is what Christian prayer presupposes when it addresses the one God who is not constructed, not parts-composed, not less than what God is.

— The Editors, LumenVeritatis