Cartesian dualism
Explanation
In the seventeenth century, René Descartes faced a pressing problem: the new mechanical science was describing the material world as a vast clockwork of particles in motion, with no room for subjective qualities. Where, then, did the mind fit, with its thinking, doubting and feeling? His solution, set out in the Meditations on First Philosophy (1641), was to divide reality into two completely distinct and independent substances.
On one side stands res extensa, material substance, characterised by occupying space and being divisible. It is the raw stuff of the physical universe: rocks, planets, bodies, brains. On the other side there is res cogitans, thinking substance, which has no spatial location and no parts, and whose only attribute is thinking in a broad sense (doubting, willing, feeling, perceiving). Consciousness belongs without remainder to this second category.
Descartes reaches this conclusion through his famous experiment of methodic doubt: is there anything I cannot possibly doubt? I can doubt the external world, my body, even mathematics if I imagine an evil genius deceiving me. But I cannot doubt that I am doubting, that is, thinking. Hence the cogito ergo sum: I think, therefore I am. Consciousness becomes the absolute foundation of knowledge.
The great problem was to explain how two such different substances can interact: if the mind is not physical, how does it move my arm when I decide to lift it, and how does it register pain when I prick my finger? Descartes proposed that the point of contact was the pineal gland, located at the centre of the brain. The choice proved arbitrary and unconvincing, and Princess Elisabeth of Bohemia raised this objection in her correspondence with him.
An uncomfortable consequence of the system was the treatment of animals as mere automata, biological machines without souls or genuine suffering. This clashed with everyday observation of animal behaviour, but it was consistent with his dualism: if thinking and feeling require res cogitans, and only humans possess it by divine grace, then everything else is just clockwork.
Despite its problems, Cartesian dualism founded the modern agenda of the mind-body problem, and almost every later theory positions itself, explicitly or implicitly, in relation to it. The intuition that there is a qualitative gulf between the subjective and the objective remains powerful: today we call it the hard problem of consciousness, and it is the direct heir of the Cartesian split between the extended and the thinking.
Strengths
- Captures the phenomenological intuition that the mental has its own quality (qualia) that seems to resist physical description.
- Grants human beings a special ontological dignity, connecting with the Christian theology of its time.
- Established the mind-body problem as a permanent philosophical agenda.
- The cogito introduced first-person experience as an epistemological bedrock, the precursor of all subsequent phenomenology.
Main critiques
- The interaction problem: how can two substances of opposing natures cause effects in each other? Elisabeth of Bohemia already put this to Descartes himself without receiving a satisfactory answer.
- The choice of the pineal gland is ad hoc and arbitrary; it lacks biological plausibility.
- Treating animals as automata without consciousness conflicts with behavioural and biological evidence accumulated since the nineteenth century.
- It multiplies entities without explanatory gain (criticism from the principle of parsimony).