← See the axis · The enigma of consciousness
ArgumentThe argument from mental efficacy
Our thoughts move our bodies; yet in the physical world only the physical produces effects: consciousness is therefore already there, in the working brain.
Supports
Kim · Physicalism, or Something Near Enough · 2005
- Every known variation in mental life tracks a variation in the brain: anaesthesia, lesion, alcohol, fatigue, a child's development. We know of no case of lived experience without a cerebral substrate, nor of any sizeable cerebral change without an echo in what is lived.
- Our mental states have physical effects: my pain makes me cry out, my decision raises my arm. To deny it is to turn mental life into an , a spectacle with no purchase whatever on our acts.
- Yet the physical world is , that is, every physical effect already has a sufficient physical cause: the cry is explained entirely by a chain of nerves and muscles, with no remainder and no gap where something else might slip in.
- If the cry already has a sufficient physical cause and my pain causes it too, only two exits remain: either it is caused twice over, by a systematic and inexplicable overdetermination, or my pain is nothing other than that cerebral state, which is what identity theory holds.
Therefore So consciousness is not one more ingredient set beside the brain: it is the brain at work. How remains to be understood, which is a difficulty of research and not a mystery of principle.
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Deepenings
What "causally closed" means
- To say the physical is closed is not to say nothing else exists, but that if one follows a chain of physical effects backwards, one finds only physical causes: every muscle contraction has its nerve impulse, every impulse its chemical cascade.
- This closure is no decision of principle: it is the outcome of two centuries of physiology, which were looking, on the contrary, for the soul's point of insertion and never found it, and of the conservation laws, which a force coming from elsewhere would break.
- It remains possible to reject it, but at a precise price: one must then grant that physics is false somewhere inside the skull, and say where.
Therefore Rejecting closure is not a harmless metaphysical position: it is an empirical prediction, so far disconfirmed.
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Water and H₂O
- Lightning and electrical discharge, heat and molecular agitation, water and H₂O: in each case two things were held distinct because they were reached by two different routes, one familiar, the other theoretical.
- Each time, the identity at first seemed inconceivable: nothing in the experience of heat resembles a motion of particles. The strangeness of the identification was never an argument against it.
- Nothing therefore forbids that sensation and cerebral process should likewise be two approaches to a single thing, which the tradition takes to be the natural outcome of the inquiry: one from within, through experience, the other from without, through measurement.
Therefore The identity of mental state and cerebral state would be a discovery like any other, not a denial of experience.
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Put to the test
Objection