Descartes argued that, while they interact causally, mind and body are two distinct things. The body occupies space and is divisible, while the mind does not exist in space and is fundamentally *in*divisible. From the perspective of modern neuroscience, Cartesian dualism looks crazy, and philosophers like David Armstrong and John Searle have argued that any theory of mind must be compatible with a materialist account of reality.
One approach that meets this criterion is the mind-brain identity theory, a theory which has a strong connection to the history of philosophy in Australia. In 1956, the English philosopher U.T. Place, then at the University of Adelaide, published a paper titled “Is Consciousness a Brain Process?”. His colleague J.J.C. Smart, now emeritus professor of philosophy at Monash University, followed up with “Sensations and Brain Processes”. Both argued that mental events like sensations are identical with physical events in the brain. Conscious experiences like sensations *just are* brain processes, in the same way that lightning *just is* an electrical discharge.
Another approach compatible with a materialism is functionalism. On this account, a mental state is not strictly identified with a particular physical state, but instead relies for its definition on the role, or function, it plays within the cognitive system it belongs to. Functionalists talk of mental states being *realised* by physical states. A state like pain can be multiply realised: it can be realised by different physical states in different kinds of organisms, but it always fulfils the same functional role.
Efforts to explain consciousness in strictly materialist terms have come under attack from some contemporary philosophers, among them Thomas Nagel and Colin McGinn, who argue that there are aspects of conscious experience that materialism will never be able to capture. Can all our conscious experiences be reduced to physico-chemical processes, or is there still a role for a ghost in the machine?