Physicalism

The identity theory that anchors physicalism holds that a mental state, the sensation of pain, for instance, simply is a physical state of the brain, a particular pattern of neural firing, in exactly the way that lightning simply is electrical discharge and water simply is H2O: not correlated with the physical state, not caused by it, but identical to it, two names for one thing discovered by empirical investigation rather than by definition.

J.J.C. Smart argued this in the mid-twentieth century partly on grounds of parsimony, since positing an additional non-physical fact over and above the brain state seemed to him to multiply entities without genuine explanatory payoff once a mature neuroscience could correlate every mental event with a physical one. The theory's chief technical difficulty is the so-called explanatory gap: even granting that pain and a certain neural firing pattern always occur together, nothing in the physical description of the firing pattern seems to logically entail what the pain feels like from the inside, a worry pressed hardest by thought experiments about a color scientist who knows every physical fact about color vision but has never seen red. Functionalism arose partly to sidestep the gap by defining mental states by their causal role rather than their physical composition, while remaining broadly physicalist about what, in the end, realizes that role.

Physicalism rarely appears as an explicit article of faith in any tradition this atlas covers, but it is the default working assumption of neuroscience, psychiatry, and most of the modern academy, which makes it the quiet backdrop against which every religious claim about a soul, a spirit, or a mind surviving the body has to argue. Its critics inside philosophy are not primarily religious dualists but panpsychists and property dualists, who accept the findings of physics and neuroscience wholesale but doubt that any physical description, however complete, could ever entail the qualitative feel of experience, a gap physicalists variously deny exists, expect future science to close, or accept as a genuine but non-threatening mystery.

The position's practical stakes are considerable: it is difficult to reconcile with any doctrine of personal survival after bodily death, and most traditions that affirm such survival are, whatever their other commitments, implicitly rejecting physicalism about the person. The position's defenders answer that this cost is exactly the honest price of taking neuroscience seriously, and that a soul-based account which cannot be tested against any physical evidence purchases its comfort at the expense of explanatory accountability, a tradeoff physicalists are willing to make and dualists and property dualists are not.