Aristotle

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Aristotle (384–322 BCE) was a Greek philosopher of the classical age, a pupil of Plato and the founder of his own school at Athens, whose surviving works became the most influential body of thought in the Western and Islamic worlds for nearly two thousand years. Born at Stagira in northern Greece, he entered Plato’s Academy as a young man of about seventeen and remained there nearly twenty years; later biography says Plato himself called him the mind of the school. When Plato died in 347 BCE Aristotle left Athens, spending three years at Assos in Asia Minor — where he also conducted the marine biological observations that would fill later treatises — and two years on the island of Lesbos, before being invited by Philip II of Macedon to serve as tutor to the young Alexander. The tutorship lasted from roughly 343 until Alexander’s accession in 336; Aristotle then returned to Athens and, in 335, established the Lyceum in a grove outside the city walls. The school’s peripatetic name derives, in one tradition, from the covered walk where he taught. When Alexander died in 323 and anti-Macedonian sentiment rose sharply in Athens, Aristotle withdrew to Chalcis on Euboea, reportedly saying he would not allow the Athenians to sin twice against philosophy — Socrates’ execution being the first. He died there in 322.

The Philosophical System

What comes down under his name is not the polished dialogues Plato wrote for the public but the working treatises of the school — terse, compressed, in places little more than lecture notes. Across them he set out to map nearly everything: the rules of valid inference, gathered as the Organon; the study of living things in biological writings drawn from direct observation; ethics as the cultivation of character toward a flourishing life; and, in the works gathered as the Metaphysics, the question of being as such.

Four Causes, Act and Potency, Hylomorphism

All explanation, for Aristotle, runs through four irreducible kinds of cause: material (that out of which something is made), formal (the structure the matter realizes), efficient (the agent that brings the thing into being), and final (the end toward which it is ordered). For natural substances formal, efficient, and final cause habitually coincide: the form of a thing is simultaneously what it is, how it comes to be, and what it is for.

Where Plato had placed the real in a realm of separate Forms, Aristotle located form within things themselves. Every composite substance is a union of matter (the substrate of potentiality) and form (the actuality that makes it what it is) — what later philosophy called hylomorphism. Bronze is potentially round; shaped, it constitutes an actual sphere. The soul, he argues in De anima, is the first actuality of a natural organic body — its form, not a prisoner inside it. Actuality precedes potentiality in definition, time, and substance: what is eternally actual cannot be otherwise. This priority of act over potency culminates in the doctrine of the unmoved mover.

The Unmoved Mover

In Metaphysics Lambda (Book XII) Aristotle argues from the eternity of motion to a first cause that is itself unmoved. A moved mover transmits a motion it has received, but such a chain cannot regress without end; there must be something that moves without being moved. Aristotle describes it as pure actuality — no admixture of potency, no matter, no change. Its activity is thought thinking itself (noēsis noēseōs): an intellect whose object is its own thinking, the highest of activities, sustained eternally without interruption. It moves the cosmos not by pushing but by drawing: “as the object of desire and as the object of thought move things: they move without being moved” (1072a21–27). The beloved does not push the lover; the lover is drawn. Every celestial sphere, and through them the whole natural order, is oriented toward this perfection as toward a goal it can approach but never reach.

This doctrine became the great theological hinge of the traditions downstream. Medieval thinkers in three religious lineages read the unmoved mover as the philosopher’s independent proof of a first principle, and each tradition spent centuries negotiating what Aristotle’s God had and had not established.

The Active Intellect

The most contested passage in the entire Aristotelian corpus is De anima III.5, twenty-four Greek lines on what later commentators called the nous poiētikos — the productive or active intellect. Aristotle distinguishes a passive intellect (which receives intelligible forms) from an active intellect that actualizes them the way light makes colors visible. The active intellect, he says, is separable, unmixed, and impassive; it is “by its essence actuality”; and — the sentence that haunted every subsequent reader — it alone is immortal and eternal.

What he meant has been argued ever since. Alexander of Aphrodisias, the second-century Peripatetic called “the Commentator,” read the active intellect as the unmoved mover itself — a divine intellect entering from outside, not part of the individual human soul. The late antique Neoplatonists identified it with a level of their hypostatic hierarchy. Arabic philosophers, working from Theophrastus and Alexander, developed it into a separate cosmic Agent Intellect from which human souls receive illumination — a doctrine central to the systems of al-Farabi and Avicenna. Averroes went further still, arguing that there is a single universal Material Intellect shared by all humanity, a reading that generated the controversy known as Latin Averroism. Thomas Aquinas, by contrast, insisted the active intellect was a faculty of each individual human soul — a creative misreading, or a philosophical correction, depending on one’s vantage. The link to nous in this encyclopedia carries the concept’s wider survey; what matters here is that III.5 became a civilizational argument precisely because Aristotle wrote it as a crux: the passage that opens onto his fullest question.

The Fifth Element

For the celestial realm Aristotle posited a fifth element beyond the terrestrial four — earth, water, air, and fire. He called it aithēr. Where the four terrestrial elements move rectilinearly toward their natural resting places (earth downward, fire upward), aether moves naturally in circles, the motion appropriate to perfection and eternity. The heavens are composed of this divine, incorruptible substance; the celestial spheres are neither hot nor cold but luminous with a different kind of being. Later Latin authors gave this fifth element its familiar name — the quintessence, quinta essentia, the fifth essence — and it passed into the vocabulary of alchemy and natural magic as the quality the alchemist sought to extract or concentrate. The connection to Aristotle’s celestial theology is direct: what the philosopher assigned to the imperishable heavens, the practitioners of later centuries tried to capture in the laboratory.

The Esoteric Career

The Word Itself

The distinction between Aristotle’s two kinds of writing is the historical seed of the modern term “esoteric.” His published works — dialogues composed for general readers — he called exōterikoi logoi, external discourses. The treatises preserved in the corpus are something different: notes composed for and within the school, sometimes called akroamatikoi (works for the ear, lecture texts) or, in the tradition Lucian of Samosata attests in the second century CE, esōterikoi — internal, school-bound. They were not secret in any mystical sense; they were dense, technical, and presupposed the school’s method. The word’s journey from this pedagogical usage to its modern sense — hidden wisdom for the few — is traced in the entry on esotericism.

The Neoplatonized Aristotle

In late antiquity the Neoplatonists did something philosophically ambitious: they absorbed Aristotle’s logic and natural philosophy into their own ascending system, reading him not as Plato’s rival but as the necessary first rung of a curriculum whose summit was Plato himself. In the curriculum shaped by Porphyry and Iamblichus, students worked through the Organon and the physical treatises before advancing to the Platonic dialogues. Proclus wrote lost commentaries on Aristotle; the surviving commentators — Simplicius, Philoponus, Ammonius — produced glosses that shaped how Aristotle was read for a thousand years.

Two texts circulating under Aristotle’s name deepened the fusion further. The Theology of Aristotle is a ninth-century Arabic paraphrase of Plotinus’s Enneads IV–VI, adapted by Ibn Na’ima al-Himsi and edited by al-Kindi; it attached the greatest name in Greek philosophy to ideas that were purely Neoplatonic in origin, so that Arabic philosophers encountered Plotinus believing they were reading Aristotle himself. The Liber de causis — the Book of Causes — was a ninth-century Arabic compilation drawn from Proclus’s Elements of Theology; Gerard of Cremona translated it into Latin between 1167 and 1187, and it entered the required curriculum at the University of Paris in 1255 under Aristotle’s name. At least seventy-four Latin commentaries on the text survive. Only after William of Moerbeke translated the Elements of Theology into Latin in 1268 did Thomas Aquinas identify the Liber’s true Proclean source — a discovery that stripped the work of its Aristotelian authority but did not diminish its philosophical influence. The false attribution had served its purpose: Proclean metaphysics had been carried into the heart of the scholastic curriculum under the most prestigious name available.

The Arabic Aristotle

The translation movement centered on Baghdad from the eighth century onward made Aristotle the engine of Islamic philosophical culture. Al-Kindi (c. 801–873), the first systematic Arabic philosopher, drew on the genuine Aristotle and the Neoplatonic apocrypha together, often without distinguishing them. Al-Farabi (c. 872–950) systematized the logic and developed a cosmic Agent Intellect doctrine from the crux in De anima III.5. Avicenna (Ibn Sina, 980–1037) built the most comprehensive Aristotelian synthesis in Arabic, transforming act-and-potency and the unmoved mover into a proof for a Necessary Existent. Averroes (Ibn Rushd, 1126–1198), “the Commentator,” argued in his De anima reading that a single universal Material Intellect is shared by all humanity — a position condemned at Paris in 1277 but never extinguished, the controversy known as Latin Averroism. The fuller story belongs to Islamic neoplatonism.

The Scholastic Absorption

The Latin West received Aristotle twice: first through Boethius’s early medieval translations of the Organon, and then comprehensively in the twelfth and thirteenth centuries, when the natural philosophy and metaphysics arrived via Arabic intermediaries, principally from Toledo. His works became the backbone of the new universities; teachers referred to him simply as “the Philosopher.” The great project of the thirteenth century was reconciling this pagan metaphysician with Christian doctrine, a task to which Thomas Aquinas devoted most of his working life: the unmoved mover became the God of creation; the active intellect became an individual human faculty; the four causes scaffolded sacramental theology. The Aristotle who emerges from the Summa Theologiae is not quite the Aristotle of the Lyceum, and the distance between the two measures one of the Middle Ages’ most ambitious intellectual achievements.

The Pseudo-Aristotelian Literature

Running alongside the genuine corpus through the Middle Ages was a large body of works circulating under Aristotle’s authority but composed elsewhere. The most widely read of all — by manuscript count, possibly the most-read “Aristotle” of the entire medieval period — was the Secretum Secretorum, the Secret of Secrets. Framed as a letter from Aristotle to Alexander the Great on the art of kingship, it expanded in Arabic to cover physiognomy, astrology, alchemy, medicine, and the properties of stones and talismans. It was almost certainly composed in Arabic, probably in the tenth century (modern scholarship places it after the Encyclopaedia of the Brethren of Purity and before Ibn Juljul in the late tenth century), though it claimed descent from a Greek original via Syriac. John of Seville translated a shorter version around 1120; Philip of Tripoli produced a longer version circa 1232, which survives in over 350 manuscripts. The encyclopedist Roger Bacon gave it an extensive commentary. Medieval readers who believed they were reading Aristotle’s private wisdom to a world-conqueror were in fact reading an elaborate Arabic fiction — a fiction so persuasive it carried the authority of the most trusted name in philosophy into the heart of occult learning.

Other pseudo-Aristotelian texts — lapidaries on magical stones, physiognomical manuals, talismanic treatises — contributed to this shadow corpus. Scholarship distinguishes them sharply from the genuine works; the distinction was invisible to most medieval readers, for whom “Aristotle” designated a figure of near-unlimited authority whose teaching could extend to every domain of nature.

The Renaissance Quarrel

The recovery of Plato in fifteenth-century Florence reactivated a controversy that had smoldered since late antiquity. George of Trebizond’s Comparatio philosophorum Platonis et Aristotelis (c. 1458) attacked Plato as ignorant, impious, and dangerous, elevating Aristotle as proto-Christian and philosophically superior. Cardinal Bessarion’s In calumniatorem Platonis (printed Rome, 1469) answered over ten years’ labor with a strategy of reconciliation: Plato as theologian, Aristotle as natural philosopher, their apparent differences dissolved by reading each in his proper register. Ficino and the Florentine circle around him drove the quarrel in another direction, arguing that Plato’s ascent-philosophy was the truer preparation for Christian contemplation and that Aristotle, however brilliant in natural science, missed the Forms. The renaissance neoplatonism entry carries the full story; what matters here is that Aristotle was the foil against which the revived Platonism defined itself, and that the Aristotle being attacked was as much a medieval construction as the one being defended.

Alchemy’s Aristotelian Matter-Theory

The four elements and their transmutability gave Aristotelian natural philosophy its most persistent esoteric afterlife. If qualities — hot, cold, moist, dry — are real and substances are constituted by their combinations in prime matter, then any substance can in principle be transformed into any other by rearranging its elemental ratios. The alchemical tradition invoked this reasoning directly: alchemy was, among other things, applied Aristotelian hylomorphism. That the historical Aristotle had no interest in transmuting metals is beside the point: his matter-theory supplied the theoretical license, and the pseudo-Aristotelian literature supplied the practical authority.

The Double Inheritance

Aristotle’s presence in the esoteric traditions is genuinely double-edged. What the historical philosopher taught was methodical and immanent: a metaphysics of substance grounded in observation, an ethics of measured habit, a theology that reaches its highest point in the self-contemplation of an unmoved intellect. The unmoved mover is not a creator god, the active intellect is perhaps not personal, and the Aristotelian cosmos is eternal and uncreated. These doctrines required considerable work to reconcile with the religious traditions that adopted them, and the work was done as much by those traditions’ needs as by Aristotle’s logic.

The occult Aristotle — the Aristotle of the Secretum Secretorum, of the Theology of Aristotle, of the lapidaries and physiognomies — is largely a creature of his readers, who found in a name of immense authority a fitting place to lodge what they already wished to say. Scholarship traces these attributions with precision. The question is not whether the pseudo-Aristotelian texts represent a “real” Aristotle but why the name could authorize so much that its bearer never wrote. A man who had mapped the causes of change, the structure of the soul, the motion of the heavens, and the nature of the divine in one connected set of treatises was the kind of figure to whom nothing further seemed implausible. The tradition’s credulity, measured against his actual achievement, was a form of tribute.

Scholarship

The standard modern introduction is Jonathan Barnes, Aristotle (Oxford, 1982); his two-volume Revised Oxford Translation (1984) remains the reference English edition. W. D. Ross’s Aristotle (1923, revised 1949) is the older scholarly synthesis. Richard Sorabji’s Aristotle Transformed (1990) and the companion Ancient Commentators on Aristotle series (Duckworth/Cornell, 1987 onward) are the indispensable resources for the Neoplatonic absorption. The Stanford Encyclopedia of Philosophy maintains freely accessible entries on Aristotle, his metaphysics, and his psychology.

→ In the library: Plato — The Dialogues (Jowett, 1892)

→ Related: Avicenna · Neoplatonism · Nous · Logos · Roger Bacon · Alchemy · Esotericism · Islamic Neoplatonism · Renaissance Neoplatonism · Proclus