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Dennett’s Illusionism vs Descartes’s Substance Dualism

Dennett’s Illusionism and Descartes’s Substance Dualism, compared field by field from their entries in the Atlas.

At a glance

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Materialism Dennett’s Illusionism Daniel Dennett
Dualism Descartes’s Substance Dualism René Descartes

The claim

In brief
Dennett’s IllusionismDaniel Dennett argues that qualia, conceived as intrinsic, ineffable, private, and immediately known properties of experience, do not exist; they are philosophers’ inventions. Experience is real, but it is not what it seems from the inside: the brain’s unconscious processes produce a benign ‘user illusion’, and there is nothing to consciousness beyond the functions and dispositions involved.
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.
What consciousness is
Dennett’s IllusionismConsciousness is the functional activity of the brain, which presents itself to us as a user illusion. ‘There are no qualia.’
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.

Big questions

Can AI be conscious?Differ
Dennett’s IllusionismPossibleSince consciousness is nothing beyond functions and dispositions, a machine with the right functional organization could have it; Dennett does not take this up here.
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.
Does consciousness survive death?Differ
Dennett’s IllusionismNoSince consciousness is a product of the brain’s processes, it ends when they end.
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.
Could a mind be uploaded?
Dennett’s IllusionismNo position
Descartes’s Substance DualismNoCopying the body’s mechanism would not copy the immaterial thinking substance.
Does it give life meaning?Differ
Dennett’s IllusionismHumanistic onlyDennett’s materialism, and his place among the New Atheists, leave no room for cosmic purpose.
Descartes’s Substance DualismCosmic/UltimateDescartes’s system rests on a non-deceiving God who guarantees knowledge and created even the eternal truths.

Nature of mind

Ontology
Dennett’s IllusionismPhysicalism (illusionist)
Descartes’s Substance DualismSubstance dualism (Cartesian)
Mind and body
Dennett’s IllusionismConsciousness is wholly a product of the brain’s unconscious processes. Dennett rejects any inner, non-physical domain of felt properties.
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.
Fundamental or emergent
Dennett’s IllusionismEmergent
Descartes’s Substance DualismPrimitive
Qualia
Dennett’s IllusionismThere are no qualia in the traditional sense. Dennett calls the supposed intrinsic, ineffable, private properties ‘nothing but philosophers’ inventions’.
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.

How it works

Mechanism
Dennett’s IllusionismThe user illusion. As a computer’s desktop icons stand in for complex underlying processes, the brain presents itself to us in a simplified form we mistake for an inner world of qualities.
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.
Where it is
Dennett’s IllusionismIn the brain’s unconscious processes, with no inner theater.
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.
What it does
Dennett’s IllusionismThe user illusion is benign: it lets us manage ourselves without access to the brain’s underlying complexity.
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.

Evidence and criticism

Testability
Dennett’s IllusionismConceptually testable
Descartes’s Substance DualismConceptually testable
Tests so far
Dennett’s IllusionismNot stated
Descartes’s Substance DualismNot stated
Criticisms
Dennett’s IllusionismDennett is often read as denying that experience exists, and critics reply that an illusion of experience would itself be an experience. Dennett resisted the eliminativist label, though many philosophers apply it to his rejection of qualia.
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.

Sources

Key sources
Dennett’s Illusionism
  • Consciousness Explained, Daniel Dennett
  • I've Been Thinking, Daniel Dennett (2023)
  • Dennett’s Illusionism (Landscape of Consciousness), Daniel Dennett (1992)
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)

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