Is divine simplicity in Aquinas and Ibn Sīnā logically coherent, or does it collapse under the criticism of van Inwagen and Plantinga?

Divine simplicity — one of the most complex concepts in classical divine philosophy — constitutes a sharp point of tension between classical philosophical theology (Thomas Aquinas, Ibn Sīnā, Moses Maimonides) and contemporary analytic philosophy (Peter van Inwagen, Alvin Plantinga, Richard Swinburne). The debate over its logical coherence reveals a deep disagreement about the nature of metaphysics itself and the limits of language in describing the divine.

Inadequate Responses to Avoid

From some defenders of divine simplicity:

"Critics of simplicity don't understand the classical tradition." This is unproductive character assassination. Van Inwagen and Plantinga are rigorous philosophers who have studied classical texts carefully. Their critique is technical, not superficial.

"Divine simplicity is above human logic." This is an escape from philosophical debate. Even Aquinas and Ibn Sīnā provided logical arguments for simplicity; they only resorted to "mystery" after exhausting analysis.

"Rejecting simplicity leads to anthropomorphizing God." This begs the question. The issue is: Is absolute simplicity logically coherent? One cannot respond by assuming its correctness.

From some critics of simplicity:

"Divine simplicity is an obvious contradiction." This is reductive oversimplification. Simplicity is a complex concept with multiple formulations, and judging it requires careful analysis.

"Analytic philosophy has surpassed classical metaphysics." This is historical hastiness. There is a strong contemporary revival of classical metaphysics (Edward Feser, David Bentley Hart, Eleonore Stump).

The Classical Concept of Divine Simplicity

Divine simplicity in Aquinas (Summa Theologiae I.3) and Ibn Sīnā (al-Ishārāt wa-l-tanbīhāt, Fourth Method) means:

First: Negation of absolute composition. God is not composed of parts (no material parts, no matter and form, no substance and accidents, no separate essence and existence).

Second: Identity between attributes and essence. God's attributes (knowledge, power, will) are not "additions" to His essence, but are His essence considered from different aspects. God's knowledge = God's power = God's will = God's essence.

Third: Identity between essence and existence. In creatures, essence (what the thing is) differs from existence (that the thing is). In God, His essence is His existence. He is "pure being" (ipsum esse subsistens in Aquinas, wājib al-wujūd in Ibn Sīnā).

Fourth: Absolute necessity. God cannot be other than what He is. All His attributes are necessary, not accidental.

Classical Arguments for Simplicity

Argument from perfection: Composition entails imperfection (parts limit each other). God is absolutely perfect, so there is no composition in Him.

Argument from priority: The composite needs a composer or cause for its composition. God is absolutely first, so there is no composition in Him.

Argument from necessity: The composite is contingent (its parts can be separated). God is absolutely necessary, so there is no composition in Him.

Van Inwagen's Critique

Peter van Inwagen in "Three Persons in One Being" (2003) and "Divine Simplicity" (2009) presented a rigorous analytical critique:

First Critique: The Problem of Identity of Attributes.

If God's knowledge = His power, this means that "God knows that 2+2=4" is identical to "God has the power that 2+2=4." But this is unintelligible. Knowledge and power are different concepts and cannot be made identical even in God.

The classical response (Brian Davies, Edward Feser): The identity is not at the level of our concepts, but at the level of divine reality. We understand God through multiple concepts (knowledge, power), but these concepts refer to one simple reality.

Van Inwagen's counter-response: Even if we accept the distinction between concept and reality, saying that one reality fulfills all different attributes remains obscure. How can one simple thing be simultaneously knowledge, power, and will?

Second Critique: The Problem of Divine Freedom.

If all God's attributes are necessary (by virtue of simplicity), then His will is necessary. But God created the world freely (He could have refrained from creating). This is a contradiction: a will that is both free and necessary.

The classical response: Distinguish between God's will in itself (necessary) and the object of will (creation, accidental). God wills Himself by necessity and wills others freely.

Van Inwagen's response: This distinction reintroduces composition. If God's will for creation differs from His will for Himself, there is multiplicity in will, and this contradicts simplicity.

Third Critique: The Problem of Divine Knowledge of Possibles.

God knows all possibles. But possibles are infinite and different. How can one simple knowledge encompass an infinity of different pieces of information?

Plantinga's Critique

Alvin Plantinga in "Does God Have a Nature?" (1980) presented a critique from a different angle:

The Problem of Necessary Properties:

Plantinga accepts that God has necessary properties (being omniscient, omnipotent). But he sees these properties as abstracts separate from God's essence. God "exemplifies" these properties, rather than "being" them.

This contradicts absolute simplicity: God and the properties He exemplifies are separate entities.

The classical response: Abstract properties are not entities separate from God, but ways we conceive of God. Realism about universals (Platonism) is not necessary.

The Problem of Divine Sovereignty:

If necessary properties (such as "lying being evil") are independent of God, then God is "subject" to them. This contradicts His absolute sovereignty.

Divine simplicity solves this by making all necessities part of God's nature. But Plantinga sees this solution as far too costly.

Contemporary Defenses of Simplicity

Eleonore Stump (The God of the Bible and the God of the Philosophers, 2016):
Develops "analytical Thomistic" reading — attempts to reconcile analytical precision with classical depth. Distinguishes between ontological simplicity and conceptual complexity.

Edward Feser (Five Proofs, 2017):
Defends simplicity from the perspective of Aristotelian-Thomistic metaphysics. Sees analytic philosophers' criticism as starting from different metaphysical assumptions (conceiving existence as a property, realism about possibles).

David Bentley Hart (The Experience of God, 2013):
Proposes that divine simplicity is not a theory about God so much as a negation of any similarity between God and beings. God is "beyond being and non-being" in the classical sense.

Jeffrey Brower (Simplicity and Aseity, 2008):
Develops a contemporary formulation of simplicity that avoids some problems. Distinguishes between "strong simplicity" (all attributes identical) and "moderate simplicity" (no composition, but formal distinction between attributes).

Philosophical Assessment

Divine simplicity faces serious challenges:

Regarding logical coherence: Difficulty in explaining how conceptually different attributes can be really identical.

Regarding divine freedom: Difficulty in reconciling absolute necessity with free acts.

Regarding religious language: Difficulty in understanding religious texts that attribute distinct attributes to God.

But it achieves philosophical gains:

Solving the composition problem: Explaining why God needs no cause.

Guaranteeing divine transcendence: Radical distinction between Creator and creature.

Unifying divine attributes: Explaining why God's attributes do not conflict.

Contemporary Debate

Philosophers divide into three currents:

Defenders of absolute simplicity: Feser, Hart, Davies, Stump. They see analytical criticism as starting from questionable metaphysical assumptions.

Rejecters of simplicity: Plantinga, van Inwagen, Swinburne, Hasker. They see it as incoherent and unnecessary for preserving divine perfection.

Middle positions: Brower, Kretzmann, Leftow. They accept modified simplicity that preserves basic intuitions without problematic commitments.

From the Perspective of Rational Preference (rajḥān ʿaqlī)

Divine simplicity is a concept with explanatory power but faces difficulties. The balance points to—

Where We Stand in This Debate Today

The debate over divine simplicity witnessed notable acceleration between 2020 and 2026. On the defenders' side, "Analytical Thomism" approaches developed in more technical ways: James Dolezal in his revised edition (A Study of God's Simplicity, 2021) reformulated simplicity using tools of contemporary logic, and Timothy O'Connor and others developed models combining simplicity with ground-theoretic foundations as alternatives to the language of properties and universals. On the critics' side, Ryan Mullins (2022) and Jordan Wesserman (2023) presented formal formulations of problems regarding divine freedom and knowledge of particulars, raising the level of precision required from both sides. The striking trend is the decline of sharp polarization: an increasing number of philosophers — such as William Vallicella and Alexander Pruss — are exploring middle formulations that preserve the essence of simplicity (negation of real composition) without committing to strict identity between all attributes. The debate remains unsettled, but has become more mature and less reductive than it was in the 1980s when Plantinga launched his initial critique.