Abstract

Inverted sensation arguments such as the inverted spectrum thought experiment are often criticized for relying on an unconstrained notion of 'qualia'. In reply to this criticism, 'qualia-free' arguments for inversion have been proposed, in which only physical changes happen: inversions in the world, such as the replacement of surface colors by their complements, and a rewiring of peripheral input cables to more central areas in the nervous system. I show why such constrained inversion arguments won't work. The first problem is that the world lacks the symmetry required to invert physical properties in the way required. The second problem concerns 'rewiring'. Empirical evidence indicates that the rewirings are either impossible, or would not result in an inversion of sensation. I propose the deeper reason for the failure of constrained inversion arguments lies in the fact that sensations are not properties of brain states, but spread into the world and the body.