Let us assume, for the sake of argument, a form of epiphenomenalist dualism, in which there are two distinct kinds of things: physical processes occurring in the brain and an associated array of conscious experiences. On this view, every physical event in the brain produces a corresponding mental event, a subjective experience, but these mental events have no causal influence on the physical. Consciousness is a passive byproduct, a kind of “ride-along” to the real causal story that takes place in the material world.

Once we grant this setup, we immediately encounter the problem of psychophysical harmony. Why is it that our conscious experiences are so perfectly aligned with our physical and behavioral states? Why does seeing a red apple correspond to the experience of redness rather than the feeling of pain or a random hallucination? Within epiphenomenalism, there is no causal reason for this mapping to be so orderly. The physical world could just as easily have produced any pattern of conscious experiences, or none at all. The fact that our inner experiences match the external world so precisely seems like an extraordinary coincidence if consciousness has no causal role.

Perhaps, to rescue dualism, we might turn to interactionist dualism, the idea that mind and matter do interact. Yet this immediately raises another problem: how could such an interaction occur without violating the laws of physics as we understand them? The brain appears to be a closed physical system governed by conservation laws. To allow non-physical causes to influence it would require new physics or a revision of our current understanding of causation, and we have no evidence for either.

If every mental event must have a corresponding physical event, then mental events cannot exist independently of their physical substrate. But if they are completely determined by physical events, then positing a separate mental substance adds nothing to our explanation. The mental either influences the physical, which would violate physical closure, or it does not, which returns us to the original harmony problem.

In earlier posts I considered the possibility of top-down causation as a way to resolve this difficulty. Perhaps the mental could emerge from the physical while exerting some kind of global, system-level influence consistent with physics. However, on further reflection, this approach does not truly solve the harmony issue. It simply shifts the problem elsewhere. We still need to explain why the mapping between conscious states and physical brain states is so precise, when any arbitrary mapping would have been logically possible.

This leaves us with two unsatisfying possibilities. The first is a form of radical dualism that openly violates physics and posits a mysterious causal bridge between mind and matter. The second is monism, which holds that mind and matter are not two separate kinds of things at all, but rather that consciousness is a particular organization or pattern within the physical, not something over and above it.

Given the implausibility of perfect psychophysical harmony under dualism, monism seems the only coherent position left. Consciousness is not something added onto the physical world. It is the physical world itself, viewed from the inside.