Physical brains are subject to the laws of physics; mental states are subject to the laws of logic. Those who think mental states are entirely physical hold a logically contradictory position. In order to think rationally about their thoughts , they must have the freedom to do so, but this freedom is unavailable if the laws of physics and chemistry are controlling their thoughts.

While physical states can be publicly known, mental states are only privately known. This characteristic of the mind is not shared with the brain; the properties of the brain and the mind are not identical.