Abstract

The extraordinary success of 20th century physics consolidated the thesis that all that there is to be known about the world is fully determined in terms of the ontology of physical theories (physicalism) [1]. Either explicitly or implicitly, this position is endorsed by most neuroscientists. However, objections to physicalism arise precisely from our immediate intuition that brain events can result in phenomena with properties different to those of physical phenomena. Descartes postulated a fundamental divide between mental and physical substance; for instance, the latter has the property of spatial extension, while the former does not. Descartes’ proposed solution to this conundrum [2], i.e. substance dualism, is frequently derided by the current neuroscientific community [3], yet it is fair to admit that serious objections can also be raised against all modern theses on the relationship between the mental and the physical. Commitment to physicalism leads to the possibility of conscious experience representing the physical events in the brain on which those very experiences ultimately depend. In other words, the brain can contemplate itself, and in doing so achieve simultaneous access to the properties of physical and mental phenomena. Northoff et al. address a problem with pedigree: the nature of the correspondence between the phenomenological properties of consciousness and their physical counterparts. Some philosophers have attempted to cut the Gordian knot in different ways, such as denying the existence of phenomenal consciousness and qualia [4], proposing that increasingly complete neuroscientific knowledge will eradicate the problem [5], or embracing metaphysical positions alternative to physicalism [6]. Instead, Northoff et al. build upon current neuroscientific knowledge to identify a “common currency” allowing transactions between mental and neural events. The process of trading one good for another could begin by listing all their properties, finding those that are shared by both goods, and finally comparing them to decide the exchange. While this process might work for certain specific transactions (e.g. “does my car have more or less horsepower than yours?”), trading generally requires a property that is common to all goods, which is the one represented by currency (i.e. economic value). Analogously, the properties attributed to conscious experience and to underlying physical processes in the brain appear to be radically different.