13 theories

Non-Reductive: theories of consciousness

Consciousness is wholly physical, a product of brains, yet mental properties form a distinct higher level that physical laws alone cannot fully explain. Minds emerge from matter and still do causal work of their own.

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Non-reductive physicalism tries to hold two positions at once. Everything that exists is physical, and the mind depends on the brain. Yet beliefs, desires and felt experiences cannot be rewritten as statements about neurons or molecules. The view grew out of problems with early identity theory. Hilary Putnam pointed out that the same mental state, such as pain, could be realized in very different physical systems. Donald Davidson’s anomalous monism held that mental events are physical events while denying strict laws that link mental and physical descriptions. Jerry Fodor argued that the special sciences cannot be reduced to physics.

Its main tool is emergence. At higher levels of organization, new properties appear that could not be read off, and perhaps never predicted from, the levels below. Many defenders add top-down causation, in which conscious states act back on the physical processes that give rise to them. George Ellis defends strong emergence of this kind, and Roger Sperry argued that consciousness steers brain activity from above.

The view also attracts religious thinkers. Nancey Murphy uses it to describe the human person without a separable soul, and Peter van Inwagen pairs a materialist account of persons with belief in the resurrection of the dead.

Jaegwon Kim pressed the strongest objection. If mental properties are irreducible, depend on physical ones, and also cause things, they compete with physical causes that already do the whole job. Kim concluded that the three commitments together leave the mind with no causal power. A further worry is how a property can be fully physical and still be impossible, in principle, to explain in physical terms.