Explanatory gap

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In the philosophy of mind, the explanatory gap is the difficulty that physicalist philosophies have in explaining how physical properties give rise to the way things feel subjectively when they are experienced. It is a term introduced by philosopher Joseph Levine.^[1] In the 1983 paper in which he first used the term, he used as an example the sentence, "Pain is the firing of C fibers", pointing out that while it might be valid in a physiological sense, it does not help us to understand how pain feels.

The explanatory gap has vexed and intrigued philosophers and AI researchers alike for decades and caused considerable debate. Bridging this gap (that is, finding a satisfying mechanistic explanation for experience and qualia) is known as "the hard problem".^[2] The hardness of the problem is such that mysterians believe it can never be solved by humans. Ned Block argues that there also exists a "harder problem" of consciousness, due to the possibility of different physical and functional neurological systems potentially having phenomenal overlap.^[3]

An example of a phenomenon in which there is no gap is a modern computer's behavior, which can be adequately explained by its physical components alone, such as its circuitry and software.^[4] In contrast, it is thought by many mind-body dualists (e.g. René Descartes, David Chalmers) that subjective conscious experience constitutes a separate effect that demands another cause that is either outside the physical world (dualism) or due to an as yet unknown physical phenomenon (see for instance quantum mind, indirect realism).

Proponents of dualism claim that the mind is substantially and qualitatively different from the brain and that the existence of something metaphysically extra-physical is required to "fill the gap". Similarly, some argue that there are further facts—facts that do not follow logically from the physical facts of the world—about conscious experience. For example, they argue that what it is like to experience seeing red does not follow logically from the physical facts of the world.

In addition to the qualities of subjective experiences, the existence of personal identity also poses potential problems for physicalist philosophies. The question of why an individual has their particular personal identity has been called the vertiginous question by philosopher Benj Hellie, and has been termed the "Even Harder Problem of Consciousness" by Tim S. Roberts.^[5] However, proponents of open individualism may argue that the existence of personal identity is illusory.^[6]