The explanatory gap is the difficulty that physicalist theories have in explaining how physical properties give rise to the way things feel when they are experienced. It is the claim that consciousness and human experiences such as qualia (individual instances of subjective, conscious experience) cannot be fully explained just by identifying the corresponding physical (neural) processes.
Bridging this gap is known as ‘the hard problem.’ The explanatory gap has vexed and intrigued philosophers and AI researchers alike for decades and caused considerable debate.
To take an example of a phenomenon in which there is no gap, imagine a modern computer: as marvelous as these devices are, their behavior can be fully explained by their circuitry, and vice versa. By contrast, it is thought by some that subjective conscious experience constitutes a separate effect that demands another cause, a cause that is either outside the physical world (dualism) or due to an as yet unknown physical phenomenon (e.g. quantum mind or 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.’ The nature of the explanatory gap has been the subject of some debate. For example, some consider it to simply be a limit on our current explanatory ability. They argue that future findings in neuroscience or future work from philosophers could close the gap. However, others have taken a stronger position and argued that the gap is a definite limit on our cognitive abilities as humans—no amount of further information will allow us to close it. There has also been no consensus regarding what metaphysical conclusions the existence of the gap provides.
Those wishing to use its existence to support dualism have often taken the position that an epistemic gap—particularly if it is a definite limit on our cognitive abilities—necessarily entails a metaphysical gap. ‘The explanatory gap argument doesn’t demonstrate a gap in nature, but a gap in our understanding of nature. Of course a plausible explanation for there being a gap in our understanding of nature is that there is a genuine gap in nature. But so long as we have countervailing reasons for doubting the latter, we have to look elsewhere for an explanation of the former.’
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