Metaphysics of Divine Simplicity: The Rational History
The pre-modern world accomplished a major human achievement by establishing, through well-formed argumentation, the rational core of what the West later calls the doctrine of God. Spanning Greek, Islamic, Jewish, and Latin worlds, this accomplishment laid the groundwork for what many now take for granted: a coherent standard for ultimacy in which the first cause is pure act, absolutely simple, and beyond any genus. It is a shared achievement of translation, commentary, and synthesis.
Athens
Aristotle launches the project: from motion to an unmoved mover whose being is actuality through and through, and the denial that “being” is a genus. These moves supply the grammar of act and potency, unity, and priority.
Baghdad
The Graeco-Arabic translation movement relocates Aristotle into an Islamic intellectual world. Philosophers systematize the inheritance, sharpening causal analysis and metaphysical vocabulary. The stage is set for precise accounts of necessity, unity, and simplicity.
Avicenna
Avicenna reframes ultimacy as the Necessary Existent whose “what it is” is nothing other than its being. By denying any quiddity added to existence, he secures simplicity and excludes genus membership at the summit, clarifying why the first cause cannot be composite or a case within a wider kind.
Maimonides
Maimonides protects divine unity by rejecting really distinct essential attributes in God and privileging the via negativa. If attributes were added, plurality would follow, so true predication must avoid importing composition. Unity therefore implies absolute simplicity in both method and metaphysics.
Aquinas
With Greek, Arabic, and Hebrew sources in Latin, Aquinas welds the pieces into a single network. Every composite is posterior and has a cause, so the first cause is utterly simple and not in a genus. This medieval synthesis becomes a durable template that later thinkers can presuppose and extend.
The rational base of this tradition is a complex of roughly 6 principles.
1. The first cause is unmoved and wholly actual (no potency).
Argued by: Aristotle (Physics VIII; Metaphysics XII Λ). Adopted and systematized by Aquinas (ST I q.2–3).
2. Any real whole that is more than a heap is one by a unifying cause.
Argued by: Aristotle (Metaphysics VIII.6). Generalized and applied to God by Aquinas (ST I q.3 a.7).
3. Every composite is posterior to parts and has a cause; the first cause, being uncaused, cannot be composite.
Argued by: Aquinas (ST I q.3 a.7). (Reinforced by the unity principle and pure-act premise.)
4. “Being” is not a genus; therefore the first principle cannot be a species under any genus.
Argued by: Aristotle (Metaphysics III.3); applied explicitly to God by Aquinas (ST I q.3 a.5).
5. In the First, essence and existence are not really distinct; the First has no quiddity other than its existence.
Argued by: Avicenna (Ilāhiyyāt VIII.4–5). Received and recast by Aquinas (De ente et essentia; ST I q.3 a.4).
6. Multiplying really distinct essential attributes would destroy divine unity; speak of God without adding composed “parts.”
Argued by: Maimonides (Guide I.50–51, 58). Completed on the Christian side by Aquinas with analogical predication (ST I q.13), preserving simplicity while allowing true names for God.
These thinkers explicitly formalized the doctrine of God in the act/potency + composition idiom. There is more to the story than this formalized metaphysics of simplicity. Plato and Plotinus support the same destination in a different dialect (Good/One, participation/emanation rather than act/potency and essence/existence). Their contribution illuminates the relation of transcendence and immanence—fodder for another paper.
Text Anchors (For Further reading)
Aristotle, Physics VIII; Metaphysics XII (Λ)
• Physics VIII: https://classics.mit.edu/Aristotle/physics.8.viii.html
• Metaphysics XII (Λ): https://classics.mit.edu/Aristotle/metaphysics.12.xii.html
- Aristotle, Metaphysics VIII.6
https://classics.mit.edu/Aristotle/metaphysics.8.viii.html - Thomas Aquinas, Summa Theologiae I, q.3, a.7
https://www.newadvent.org/summa/1003.htm#article7 - Aristotle, Metaphysics III.3
https://classics.mit.edu/Aristotle/metaphysics.3.iii.html - Avicenna, Ilāhiyyāt VIII.4–5 (Metaphysics of the Healing)
https://archive.org/details/the-metaphysics-of-the-book-of-Healing - Maimonides, Guide for the Perplexed I.50–51, 58
• I.50: https://www.sefaria.org/Guide_for_the_Perplexed,_Part_1.50
• I.51: https://www.sefaria.org/Guide_for_the_Perplexed,_Part_1.51
• I.58: https://www.sefaria.org/Guide_for_the_Perplexed,_Part_1.58