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. 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.