Dualism

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Dualism is any account of reality built on two ultimate principles that cannot be reduced to one another — spirit and matter, light and darkness, good and evil, mind and body. The word itself is modern. Its Latin ancestor, dualistae, was coined by the orientalist Thomas Hyde in 1700 to name the ancient Persian religion of two principles — so the term began with the cosmic, good-against-evil sense, not the philosophy of mind. The application of “dualism” to the mind-body distinction came later, in the eighteenth century, and is usually credited to Christian Wolff, though that attribution is best held loosely. The structure the word names is far older than either dating: it recurs across religion and philosophy alike, and what unites its many forms is a refusal — the conviction that the divided world cannot be traced back to a single source without leaving something essential unexplained.

It is worth separating two kinds that the single word tends to blur. There is cosmic or ethical dualism, which sets two opposed powers at the foundation of existence and reads the world as their battlefield; and there is the dualism of philosophy of mind, which holds that thinking substance and extended matter are two distinct kinds of thing. The first is a claim about the order of the cosmos, the second a claim about the make-up of a person, and they answer different questions. The two have crossed paths often, but they are not one doctrine, and the entry keeps them apart.

The cosmic form has the longer history. Zoroastrian tradition set the wise lord Ahura Mazda — the name means “Wise Lord” — against a hostile spirit, Angra Mainyu, the “Destructive Spirit” later called Ahriman, and made the whole of time a contest between them. But the contest is not one of equals. Scholars stress that this is better described as a monotheism with strong dualistic features than as a symmetry of two coeternal gods: the battle is unequal, bounded by time, and good is assured of its triumph at the end. The omnipotence of the Wise Lord is limited only for the duration of the struggle. To read Zoroastrianism as two balanced rival deities is to flatten exactly what its theology is careful to deny.

Manichaeism pressed the cosmic form furthest toward genuine symmetry. Founded by the prophet Mani in third-century Persia — he was executed under the Sasanians sometime between about 274 and 277 — it taught two coeternal and radically opposed substances: Light and Darkness, Spirit and Matter, Good and Evil. Its signature is a scheme of three times: a past in which the two realms stood apart, a present age in which they are intermixed and the Light lies imprisoned in Matter, and a future in which the original duality is restored and the Light set free. Mani cast himself as the last of the prophets after Adam, Buddha, Zoroaster, and Jesus, and his religion traveled west into the Roman Empire and east along the Silk Road to China before persecution extinguished it. At its core it was a kind of gnosticism, offering rescue through saving knowledge — and it is the textbook case of an absolute dualism, two first principles neither of which derives from the other.

The currents later grouped as Gnostic radicalized the split between spirit and matter. They taught that the material world was the work of a lesser, ignorant maker — the demiurge, in some schools not evil so much as blind — and that a spark of the true divine lay trapped within the flesh, kept in forgetfulness by hostile powers. Reality divides between the Pleroma, the divine fullness of light, and the material prison below; what frees the spark is gnosis, the saving recognition of where it came from and where it belongs. Here matter is not merely lower than spirit but alien and hostile to it. How far these systems were genuinely dual, and how far that charge was sharpened by their opponents, remains contested: much of what was long known of the Gnostics came from heresiologists writing to refute them, and only with the modern recovery of their own writings could the question be reopened from the inside.

Strict monotheism and Platonism both resisted this turn. For thinkers in the Neoplatonic line, evil and matter are not a rival principle but a privation, a falling-away from the One that remains the single source of everything; Plotinus devoted a tractate, Against the Gnostics, to attacking them on exactly this point, holding that matter is a deficiency of being rather than a second root of it. This is the hinge between cosmic dualism and its great rival, monism — the position, revised alongside this one, that reality rests on a single principle after all. The argument between them is old and unsettled: whether the world’s evident division demands two roots, or whether one source can be reconciled with a fractured world.

The mind-body form belongs to a later debate, though it too has an ancient lineage. Plato had already, in the Phaedo, argued that the soul is distinct from the body, exists apart from it, and survives its death — the question of the soul, which has its own entry, begins here. But the sharpest statement is associated with Descartes in the seventeenth century. In the Meditations he divided reality into two kinds of substance: res cogitans, the thinking thing — unextended, indivisible, occupying no space, not subject to physics, the seat of doubt and will and perception — and res extensa, the extended thing, matter defined by its occupation of space and endlessly divisible. His chief formal argument was the Argument from Indivisibility: the body can be divided, the mind cannot, and what differs in a property cannot be one and the same thing.

This is substance dualism, the strong form, and it must be distinguished from two weaker cousins. Property dualism keeps a single kind of substance — the physical — but holds that some of its properties, consciousness above all, are not physical properties at all and cannot be reduced to them; the mind here is not a separate thing but a separate kind of feature of one thing. Weaker still is predicate dualism, which holds only that mental language is irreducible to physical language while granting that every mental event may yet be a physical event — and this, on the standard view, is not really dualism at all but a form of nonreductive materialism wearing the name.

Descartes’ clean division left a standing difficulty: if the mind has no size, shape, location, or motion, how does it move the body, and how do the body’s states reach it? Causal traffic across the immaterial-material divide seems to violate the causal closure of the physical — the principle that every physical effect already has a sufficient physical cause. Descartes’ own answer, that the two meet at the pineal gland, satisfied almost no one, and the interaction problem went on to shape the responses to it. Some denied real interaction altogether: the occasionalists held that God coordinates mind and body on each occasion, and the parallelists that the two run in pre-established harmony like two synchronized clocks. The epiphenomenalists allowed the body to act on the mind while denying that the mind acts back on the body at all, making consciousness a byproduct that changes nothing. Each is a way of keeping two kinds of thing without letting them touch.

The interaction problem drove much of the philosophy of mind that followed, and the various monisms that rose against dualism were largely attempts to escape it — the case for which belongs to that sibling entry rather than this one. Yet dualism has not simply vanished. Its most discussed modern form is property dualism, given new life by the hard problem of consciousness, named by David Chalmers in 1995: the question of why any physical process should be accompanied by experience at all, why there is something it is like to be a conscious subject, when the physical story seems complete without it. That question has its own entry; here it is enough to mark it as the engine that keeps a chastened dualism alive, no longer about two substances but about whether the felt quality of experience can ever be cashed out in physical terms.

To call a system dualist is often less a neutral description than the judgment of a rival who held the world to be one. The label tends to be applied from outside, by those for whom unity was the thing to defend — and the cosmic sense was, quite literally, named that way, by an outside observer cataloging a religion not his own.

→ In the library: Mead — Fragments of a Faith Forgotten (1900) · Plotinus — Against the Gnostics (Enneads II.9, MacKenna 1926)

→ Related: Monism · Hard Problem Of Consciousness · Metaphysics · Soul · Gnosis