Some philosophers reject physicalism. Some of these philosophers call themselves naturalists and some do not. They divide neatly into two camps. We can think of each group of philosophers as denying one of the premises of the causal argument for physicalism.

The problem of consciousness: rejecting premise 2 of the causal argument

The larger of these two groups rejects premise 2. They believe that there is a special class of mental phenomena that have no impact on the physical. Consciousness, they claim, is not a physical phenomenon and has no effect on the physical. In fact, they make an even more specific claim. The qualitative aspects of consciousness, the redness of red, the way it feels to taste coffee, for example, are not physical. Philosophers have named the qualitative, what-is-it-like dimensions of conscious experience qualia. So it is to the status of qualia we turn first in our discussion of the adequacy of physicalism.

Three thought-experiments

Thomas Nagel (1974), Frank Jackson (1982) and David Chalmers (1996) have each offered a thought-experiment aimed to show that there is more to consciousness than can be captured by the physical.

Nagel asks us to imagine what it would be like to be a bat. No matter how much we know about the physics of a bat's sensory echolocation system, there will always be something missing in our description: what it feels like to find your way around the world using echolocation. The bat's qualia remain forever unknown to us.