Epiphenomenalism

Epiphenomenalism is the view that conscious mental states are causally inert byproducts of physical brain processes — the smoke above the fire of neural activity, not the fire itself. In this picture, your experience of deciding to raise your arm plays no causal role in the arm's rising; the neural events that cause the arm to move also cause the experience of deciding, but the experience itself causes nothing.

The view is the most honest form of property dualism: it grants that consciousness exists as something beyond pure physics while admitting that it does no causal work. Its critics argue that epiphenomenalism makes the evolution of consciousness mysterious — why would natural selection preserve a feature with no causal efficacy? Its defenders reply that the correlation between brain states and conscious states is tight enough that consciousness is always 'along for the ride,' and evolution tracks the physical states it is correlated with, not the consciousness itself.

Epiphenomenalism is philosophically uncomfortable precisely because it preserves the reality of phenomenal experience while making it metaphysically weightless — a ghost in the machine that is neither the machine nor in control of it.