← See the axis · The enigma of consciousness

The explanatory gap objection

That experience depends on the brain and acts through it, no one disputes; but the step from dependence to identity has not been taken.

Objects to Physicalism

Levine · "Materialism and Qualia: The Explanatory Gap" · 1983

1. The argument establishes at best that mental and cerebral states are correlated and occupy the same place in the chain of causes. Yet a correlation, however perfect, is not yet an identity: two inseparable things may still be two, and one may hold that the mental supervenes on the cerebral without concluding that they are one.
2. In science's successful identifications, identity comes with an explanation: once molecular agitation is understood, one sees why that amounts to heat, and one can no longer conceive of heat without it.
3. Nothing of the sort here: knowing everything about the circuitry of pain, the question "but why does it hurt?" stays open and perfectly intelligible. An explanatory gap remains that no other scientific identification has left behind it.
4. The causal argument cannot decide between the two possible readings of that gap, provisional or final: it treats experience as a causal link, whereas it is precisely its qualitative face, the qualia, that raises the problem.

Therefore The argument proves that experience is moored to the brain, not that it reduces to it: physicalism here remains a promise, the promise that one day the gap will close.