Picture a table of manuscripts in Toledo. A translator bends over Arabic commentaries on Aristotle while a Jewish scholar checks a Hebrew gloss and a Latin cleric copies the result onto fresh vellum. The ink stains more than fingers. It stains the way “God” will be argued about for centuries.
Medieval philosophy of God did not begin with a blank slate or a single voice. It grew in three overlapping houses—Latin Christian, Islamic, and Jewish—each furnished with scripture, inherited Greek philosophy, and the habits of its schools. The same words moved between them, but in different rhythms. “Cause,” “substance,” “intellect,” “will.” And above all: “one.”
Frameworks and Sources: How Medieval Thinkers Approach “God”
Start with the sources. The Bible, the Qur’an, and the Hebrew Bible do not present “God” as a theorem; they speak in stories, laws, prayers. Philosophers turned these living words over and over, weighing them with Aristotle’s categories and Neoplatonic metaphors. Augustine mined Scripture to frame God as creator and measure of all being, while borrowing Plato’s ladder of ascent. Avicenna read Aristotle so carefully that he carved out a new distinction—essence and existence—that would become the backbone of later Latin arguments about the divine. Maimonides sifted the biblical text with clinical caution, stripping away any hint of bodily language about God and insisting that most of our predicates mislead.
The library that fed them was not simple. If you open a twelfth-century Latin shelf, you find “Aristotle” on the soul and the heavens; a text called the Book of Causes attributed to Aristotle (but actually drawn from Proclus); and the writings of Pseudo-Dionysius, a late antique monk writing under an apostolic pseudonym. Authority could wear a mask. That mattered. When “Aristotle” seemed to teach emanation, not creation, philosophers had to reconcile this pressure with a scriptural picture of a free creator. Some bent, some resisted, most negotiated.
Institutions shaped the style of thought. Monasteries copied and prayed; cathedral schools trained clerics; universities set schedules, syllabi, and forms of argument. In Baghdad, the House of Wisdom gathered and translated, drawing Greek science into Arabic and then re-exporting it west. Madrasas taught kalām—dialectical theology that argued in quick, precise moves. Yeshivot rehearsed Talmudic methods and sharpened attention to language. Ideas did not float; they were drilled, recited, disputed, and examined. You can almost hear the room: voices trading objections, a teacher chalking a schema, the scrape of a quill in the margins.
The dominant genre was the commentary. Al-Fārābī and Averroes read Aristotle line by line, stitching clarifications into the text until a hybrid garment emerged: Aristotle, patched with Arabic thread. In the Latin world, the commentary grew into the quaestio and the disputation, formal exercises that staged conflicts and forced a verdict. A question stood on the page like a scaffold: objections are raised; an authoritative counter-text is quoted; a solution is hammered out and then each objection is answered in turn. The method looks dry. In practice it cut to the bone.
Beneath these practices lay a map of reason and revelation. Few of the major figures thought the two were enemies; they disagreed on the borders. Aquinas placed them as lights of different intensity—reason can prove that God exists and is one, simple, and the source of being; revelation speaks of mysteries (like the Trinity) that reason cannot reach unaided. Al-Ghazālī distrusted blanket claims about necessary causation and warned that the philosophers had shrunk God’s freedom. Yet he argued with a philosopher’s knife, not a preacher’s club. Maimonides drew a tight circle around what can be proved and then advised silence where talk becomes idolatry in prose form. The common conviction: God is not the conclusion of a hasty syllogism. (And even when arguments worked, they were never the whole.)
The conceptual toolkit was shared and continually sharpened. Aristotle’s act and potency gave thinkers a way to describe change and rest; applied to God, they yielded a being “pure act,” lacking the unsettledness of potency. Avicenna’s necessary versus possible distinction reframed the question of existence itself: everything in the world might exist or not, but the Necessary Existent has no such fragility. From late Platonism came participation and emanation—the picture of creatures drawing their limited being from an overflowing source, like light spilling from a lamp. Dionysian hierarchies placed angels, souls, and bodies in ordered ranks, all turning toward the One. Each piece of the kit came with tensions. Push emanation too hard and creation looks automatic. Push divine will too hard and rational structures look arbitrary.
Language, too, had to be engineered. If we say “good” of God, do we mean the same thing we mean when we call a mother or a harvest good? Aquinas answered with analogy: our words stretch upward without snapping. They do not mean exactly the same in God and creatures, nor do they break into mere equivocation; they are related by proportion and cause. Scotus worried that without at least one univocal concept—“being” as such—we could never even begin to argue about God without shifting terms midstream. Maimonides and Pseudo-Dionysius took a harder line: it is safer to negate than to affirm. Say not “God is wise,” but “God is not ignorant,” or “God is beyond wisdom as we know it.” The via negativa does not crush thought; it cleans the mouth before speaking.
None of this was abstract for abstraction’s sake. The debate over divine simplicity, for example, did hard work. If God is simple, then God is not composed of parts, not even really of distinct attributes: God’s wisdom, power, and goodness are not different pieces bolted onto a core. In the Latin schools, this anchored the claim that God is the cause of all composite being. In Islamic and Jewish discussions, simplicity protected divine unity against any hint of division. Yet once you insist on simplicity, you must explain how the world, full of variety, flows from a source without parts. That is why causality occupied so much paper. What does it mean for God to cause without changing? For secondary causes to be real and not rivals? For human freedom to fit under providence? These questions are not yet answered at this stage, but the gears are on the table.
Even the accidents of textual history mattered. Because the Book of Causes came west under Aristotle’s name, it lent Neoplatonic structure the prestige of the Philosopher. Because the works of Aristotle arrived in waves—first logic, then natural philosophy, then metaphysics—Latin thinkers built their systems in stages, revising as new pieces came in. The Rhetoric and Poetics arrived late; one can guess how that shaped the preference for demonstration over persuasion. Meanwhile, Averroes’ fierce insistence that Aristotle be read as a coherent whole pushed Latin readers to sharpen their exegesis, even when they disagreed with his conclusions.
If there is a single image to keep in view, it is the page itself. In the center, a revered text. Around it, a corona of marginal notes in slanted hands. In the margins, the argument grows, branches, doubles back. The notion of God in medieval philosophy was formed in that white space. It is where Augustine’s sermons meet Avicenna’s demonstrations, where Maimonides’ caution taps the brakes on easy metaphor, where Aquinas’ neat syllogisms coexist with Dionysius’ darkness. The God under discussion is not a vague highest being, floating in a vacuum. He is the creator of Genesis, the Necessary Existent of Avicenna, the One of Proclus recast for monotheists—woven together with care.
By the end of this first act, we do not yet have the full portrait of what God is or how God relates to the world. We have the workshop: texts, methods, and tools. We have the habits of reading and disputing that set the stage. And we have a shared conviction, despite major disagreements, that talk about God must be disciplined—by reason, by tradition, by the limits of language. The next moves will test those disciplines. But without this scaffolding, the later structures would never have stood.
What God Is: Essence, Existence, and Names
To medieval eyes, God was not merely worshiped; he was investigated. The question, “What is God?” did not sit in a shrine. It stood in the classroom, chalked on a board, with objections stacked like stones. Then the hammering began.
Begin with existence. Avicenna offers the most austere line. Look at beings around you—horses, stars, syllogisms. Each might have failed to exist. They are possible, not necessary. Possible things, taken as a whole, cannot explain themselves; they lean. Follow that lean backward and you will not find a chain of only leaners. You arrive at something that does not lean: the Necessary Existent. From there, Avicenna chisels consequences. What is necessary in itself cannot be composite (parts would need a composer), cannot be limited (limits imply a boundary-maker), and cannot be multiplied by type (two Necessaries would differ by something other than necessity and so neither would be necessary). The picture is clean, even spare. Critics admired the workmanship, then poked at the joins: does “possible as a whole” require a cause? Can the chain of borrowed existence be infinite? Avicenna’s confidence held. An infinite chain of contingents, he replied, still hangs; it never turns into a hook.
The Latin schools preferred several roads, each starting on familiar ground. Aquinas sketches five “ways,” less a shopping list than a series of tightly coiled moves. From motion to an unmoved mover; from ordered causes to a first cause; from contingent beings to a necessary being; from degrees of goodness or truth to a maximal source; from the directedness of natural things to an ordering intelligence. The routes differ, but the destination looks much like Avicenna’s: a simple, necessary source. The kalām theologians, for their part, sharpened a temporal argument. The world is made up of things that begin; time itself runs on a string of successive “nows.” What begins requires a beginner. Therefore the world has a first moment and a creator. Al-Ghazālī pressed the point with drama: if past time were infinite, you could not “cross” it to arrive at today. Averroes replied that time does not need crossing; it flows. The dispute did not end in a handshake.
And then there is Anselm, who writes a prayer that turns into an argument that refuses to be shelved. “That than which no greater can be conceived” cannot exist only in the mind; if it did, a greater could be conceived—one that exists in reality. So it exists. Gaunilo, a monk with good sense, answers with a parody about a perfect island. Anselm insists that islands are not the sort of thing the argument targets; only a being whose nonexistence is unthinkable qualifies. Later scholastics sifted the logic and disagreed about the yield. The exchange is instructive even where it fails to convince. It shows how, in this period, prayer, definition, and proof could share a desk.
Not everyone thought such routes were safe. Al-Ghazālī cut the cord of “necessary connection” between created causes and effects, arguing that what we see as law is God’s habit, freely chosen and interruptible. Do not back God into a corner by making fire necessitate burning, he warned, or you will have made an idol of natures. Ockham, centuries later, trimmed with his razor. Many of the grand divine attributes cannot be demonstrated, he argued; revelation and faith, not syllogisms, give them to us. Even where he accepted that God exists, he distrusted thick metaphysical scaffolding. You can feel the air thin.
Suppose, all the same, that we stand at the threshold of “that which is God.” What is there? The first claim, shared widely, is simplicity. God is not made of parts—no matter parts, no form joined to matter, not even distinct features stacked like blocks. Simplicity does a great deal of work. If God were composite, something would compose God; a composed being is posterior to its principles. The simplest statement in Latin scholasticism captures the ambition: God is ipsum esse subsistens—subsistent act of being itself. (Pause here and notice the move: the deepest answer to “what is God?” is not a genus and a differentia, but a way of being without measure.) From simplicity, a cluster of attributes follow: aseity (God depends on nothing outside himself), eternity (not endless time, but the standing present of a life without before or after), immutability (no change, because change implies potency realized), impassibility (no being acted upon). Each term protects divine priority; each threatens, in the wrong hands, to push God out of the drama of history. The medievals knew the cost and argued over the bill.
Power, intellect, and will form the next triad. Aquinas places intellect at the center: God’s knowing is first; will follows intellect’s sight of the good. The universe is rationally ordered because its source thinks and, in thinking, gives being. Scotus tilts the balance toward will. God could have created different orders of law; some moral truths are necessary (do not love hatred), others rest on divine ordination (keep this Sabbath, not another). Ockham pushes freedom harder, wary of binding God to any rational structure we can map. The effect of these differences is visible in the weather of the late medieval world: a breeze toward contingency and divine freedom that will freshen into the early modern period.
Divine knowledge posed a special puzzle: does an unchanging God know changing particulars? Avicenna says yes, but not as we do. God knows particulars “in a universal way”—by grasping their causes and the order in which they flow. To many readers, that sounded like a retreat from real, this-leaf-here knowledge. Al-Ghazālī accused the philosophers of stripping God of attention to the small. Averroes tried to repair the bridge: God knows particulars by knowing himself as their cause; nothing escapes an all-causing intellect. Aquinas picks up the thread and tightens it. Because God causes the being of every creature, he knows each creature not by looking outward and collecting data but by knowing his own creative act; he knows future contingents as present to him, not as we know them through time. Maimonides, more severe, warns that our models of knowing are too coarse. God’s knowledge is neither universal nor particular in our sense. We should say only that God knows—and add, quickly, that how he knows is beyond us. The discussion is not a piece of semantic fussiness. On it hangs providence, prayer, and whether a sparrow’s fall can be said to lie under a divine gaze.
Language is the final instrument, and it must be tuned. When we say “wise” of God, do we speak univocally (the same meaning in God and us), equivocally (completely different), or analogically (related meanings)? Scotus defends a careful univocity for at least one key term—being—so that arguments do not slide as they climb to God. Without a stable concept, he says, we would commit the fallacy of four terms in every syllogism about the divine. Aquinas disagrees. Univocity flattens the difference between creator and creature. Equivocity leaves us mute. Analogy, he claims, is the middle path: God is the cause and measure of creaturely perfections, so words like “good” and “wise” reach him by proportion and dependence. The metaphysical picture underwrites the grammar. Maimonides steps away from both. Positive predicates, he argues, risk carving God into pieces. Better to follow the via negativa: say what God is not (not finite, not ignorant), or speak in “attributes of action” (God delivers, judges, creates), which tell us about effects in the world without pretending to dissect the divine essence. Pseudo-Dionysius had already counseled the same restraint in Christian dress: affirmation, negation, and then a final silence before the superabundant. The sentence ends, and the mind keeps moving.
The Christian case adds a delicate pressure: the doctrine of the Trinity. If God is absolutely simple, how can there be three? Aquinas answers by distinguishing real relations in God (paternity, filiation, spiration) from accidental or compositional differences. The persons are not parts; they are subsistent relations, identical with the divine essence, distinguished by their relations of origin. The formula is spare and technical; it was designed to protect both simplicity and the tripersonal life confessed in liturgy. Jewish and Islamic thinkers, committed to strict unity without internal relational distinctions, often watched this Christian maneuver with suspicion. The cross-traditional conversation, on this point, mostly produced clearer definitions of what each side would not say.
One more hinge: goodness. Here the medievals follow Plato and Aristotle but walk them into monotheism. God is not a moral agent among others with a very high score. God is the good as the source of being. Degrees of goodness in creatures trace back to participation in that source. Hence the moral life, on many medieval accounts, is not only obedience but alignment: intellect and will trained to love what is, and is good, because it comes from God and returns to him. Ethics, metaphysics, and theology are not separate shelves. They sit in the same bookcase.
A word about method, because the texture matters. These doctrines did not float free as pious opinions. They were nailed to arguments, cross-checked against authorities, and tested against objections that bit. Objections were not straw. “If God is simple, how can he know many things?” “If God is immutable, how can he answer prayer?” “If God is powerful, how can evil persist?” The reply moved carefully, often by distinguishing senses in which a term is used, or by showing that an apparent incompatibility dissolves at a higher level of analysis. (Some readers grin here and complain about scholastic hairsplitting. Sometimes they are right. Often, though, the hair was the nerve.)
By the close of this second part, the outline of the medieval God stands on the page: necessary, simple, eternal, the source of being; knowing and willing without change; named by us with caution—by analogy for some, by univocal flashes for others, by negation for the boldest. The picture does not yet show how the world hangs from such a source, or how providence, causality, and freedom fit into a single frame. That is the next turn. For now, the concept is sharpened. The names are weighed. And language has learned, at least a little, to stretch without tearing.
For more insight:
- Aquinas, Thomas. Summa Theologiae. Translated by the Fathers of the English Dominican Province, Christian Classics, 1981.
- Avicenna. The Metaphysics of The Healing. Translated by Michael E. Marmura, Brigham Young University Press, 2005.
- Maimonides, Moses. The Guide of the Perplexed. Translated by Shlomo Pines, University of Chicago Press, 1963.
- Al-Ghazālī, Abū Ḥāmid. The Incoherence of the Philosophers. Translated by Michael E. Marmura, Brigham Young University Press, 2000.
- Pseudo-Dionysius. The Complete Works. Translated by Colm Luibheid, with notes by Paul Rorem, Paulist Press, 1987.
- Anselm of Canterbury. The Major Works. Edited by Brian Davies and G. R. Evans, Oxford University Press, 1998.
- Scotus, John Duns. Philosophical Writings. Translated by Allan B. Wolter, Hackett, 1987.