Head to head
Descartes’s Substance Dualism vs Epiphenomenalism
Descartes’s Substance Dualism and Epiphenomenalism Theory, compared field by field from their entries in the Atlas.
At a glance
- Both belong to the Dualism family in Kuhn's Landscape of Consciousness.
- Descartes’s Substance Dualism treats consciousness as fundamental; Epiphenomenalism treats it as emergent.
- On AI consciousness, Descartes’s Substance Dualism says “No” and Epiphenomenalism says “Likely”.
- On life after death, Descartes’s Substance Dualism says “Yes” and Epiphenomenalism says “No”.
- On mind uploading, Descartes’s Substance Dualism says “No” and Epiphenomenalism says “Likely”.
- On meaning and purpose, Descartes’s Substance Dualism says “Cosmic/Ultimate” and Epiphenomenalism says “Humanistic only”.
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The claim
In brief
Descartes’s Substance DualismRené Descartes holds that consciousness, which he calls thought (cogitatio), is the essence of an immaterial thinking substance (res cogitans) wholly distinct from extended, mechanical body (res extensa). Every conscious state, from reasoning and willing to pain, color, and emotion, is a mode of the thinking thing and is immediately present to it. Sensations and passions, though, arise only in the union of mind and body, where brain processes stand in regular relations to experiences they do not resemble.
EpiphenomenalismThis theory posits that consciousness is a non-reducible product of the biological brain, but mental states have absolutely no causal power over physical reality. Our subjective awareness is real, yet our perception that our thoughts cause actions is mistaken, as consciousness is entirely inert, like foam on an ocean wave.
What consciousness is
Descartes’s Substance DualismConsciousness is thought, defined as everything that happens within us insofar as we are immediately conscious of it, and it is the principal attribute of the mind.
EpiphenomenalismConsciousness is identified as phenomenal properties that are ontologically distinct from physical properties but are causally dependent on them (Physical → Phenomenal).
Big questions
Can AI be conscious?Differ
Descartes’s Substance DualismNoSince thought belongs only to immaterial substance and matter is pure extension, a machine, however complex, would be mechanism without a mind.
EpiphenomenalismLikelyIf consciousness is merely a non-causal byproduct (foam) of physical processes in the brain , replicating those physical processes in AI should produce the same conscious states without the non-causal mental states hindering functional replication.
Descartes’s Substance DualismYesDescartes presented the real distinction of soul and body as what makes the soul’s survival intelligible, and the Meditations announce that aim in their subtitle.
EpiphenomenalismNoConsciousness is entirely physical and solely the product of biological brains. This physical dependence precludes survival beyond bodily death.
Descartes’s Substance DualismNoCopying the body’s mechanism would not copy the immaterial thinking substance.
EpiphenomenalismLikelyThe inert nature of consciousness means that uploading the physical states would necessarily duplicate the epiphenomenal mental states. The inert 'foam' should have little impact on achieving virtual immortality.
Descartes’s Substance DualismCosmic/UltimateDescartes’s system rests on a non-deceiving God who guarantees knowledge and created even the eternal truths.
EpiphenomenalismHumanistic onlyAs a philosophical materialism theory, it provides no ultimate meaning or purpose. Since consciousness is causally inert, it cannot confer cosmic teleological value.
Nature of mind
Ontology
Descartes’s Substance DualismSubstance dualism (Cartesian)
EpiphenomenalismWeak form of Dualism or Non-Reductive Physicalism. It affirms the complete causal closure of the physical.
Mind and body
Descartes’s Substance DualismMind and body are really distinct finite substances with exclusive essences, thought and extension, and could by divine power exist apart. They are joined in the human being, where bodily motions give rise to sensations and the mind moves the body, though Descartes never explained that interaction satisfactorily.
EpiphenomenalismMental states are entirely the product of biological brains. Physical states cause phenomenal states, but phenomenal states have no causal effect on the physical (one-directional causation).
Fundamental or emergent
Descartes’s Substance DualismPrimitive
EpiphenomenalismEmergent. Consciousness is solely the product of biological brains.
Qualia
Descartes’s Substance DualismSensory qualities are not properties of matter, which has only size, shape, motion, and arrangement. Experienced redness or pain is a mental mode arising in the embodied union and cannot be captured by extension.
EpiphenomenalismPhenomenal properties (qualia) are real and ontologically distinct from physical properties , but they are epiphenomena and thus causally inert.
How it works
Mechanism
Descartes’s Substance DualismMechanism on the bodily side and non-reduction on the mental side. Light mechanically affects eyes, nerves, and brain, and the mind then experiences color, distance, and shape in regular correspondence with those motions.
EpiphenomenalismThe principle of the 'causal closure of the physical' dictates that mental states, whatever their nature, must be entirely inert byproducts.
Where it is
Descartes’s Substance DualismThe mind is unextended. Sensations and passions are felt as belonging to one’s own body, and Descartes located mind-brain communication in the pineal gland.
EpiphenomenalismEntirely located in the physical, biological brain.
What it does
Descartes’s Substance DualismPassions are caused and strengthened by movements of the animal spirits and dispose the soul toward volition and action. The will can in turn move the body.
EpiphenomenalismMental states have no causal powers. The mind is entirely inert and there is no 'top-down causation'; consciousness is a non-functional byproduct.
Evidence and criticism
Testability
Descartes’s Substance DualismConceptually testable
EpiphenomenalismConceptually challenged. Its primary claim—that conscious states lack causal force—is counterintuitive and difficult to test empirically, as it involves proving a negative causal link.
Tests so far
Descartes’s Substance DualismNot stated
EpiphenomenalismNot stated
Criticisms
Descartes’s Substance DualismPrincess Elisabeth of Bohemia asked how an immaterial soul could move a material body, and the interaction problem remains unresolved. Arnauld and later critics charged circularity, since the proofs of God that guarantee clear and distinct perception themselves rely on clear and distinct perception. The standard reading denies consciousness to animals, which most now find implausible.
EpiphenomenalismThe theory is counterintuitive because it strongly seems to us that our phenomenally conscious states causally matter. It forces the acceptance that our sense of mental causation (thoughts causing things) is a 'kind of illusion or trick'.
Sources
Key sources
Descartes’s Substance Dualism
- Meditations on First Philosophy, René Descartes (trans. J. Cottingham, R. Stoothoff, and D. Murdoch) (1984)
- Principles of Philosophy, René Descartes (trans. J. Cottingham, R. Stoothoff, and D. Murdoch) (1985)
- The Passions of the Soul, René Descartes (trans. J. Cottingham, R. Stoothoff, and D. Murdoch) (1985)
Epiphenomenalism
- Consciousness (2019)
- Facing up to the Problem of Consciousness (1995)
- What Is Consciousness? (Little Debates about Big Questions), A. Kind and D. Stoljar (2023)
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