Dualism is based on a belief that there are two qualitatively different entities that interact with each other. Even if a number of scientists and philosophers in the 20th century were acutely aware that the physicalist perspective is inadequate and advocated various forms of dualism, this view is now largely abandoned, mostly because it does not fit the dominant ideology. Very few are prepared to publicly support such a position and risk their academic or scientific careers, be exposed to ridicule, and diminish the chance to publish their work. So, only already well established figures (e.g. Eccles, Popper, Wigner) have dared to argue in its favour. Common sense, however, never fully abandoned this idea. Descartes was the first who tried to establish it on a rational basis in the 17th century, which became the dominant view for a few hundred years. He envisaged two entities, one consisting of the immaterial mind (with properties such as thinking, feeling, willing), and the other of the material body with physical properties (shape, size, mass). By recognising the specific quality of mental states, dualism can account for many phenomena that are an insurmountable challenge for materialists. However, it has its own problems.
- The first difficulty is the very existence of mind. Brain, as a material substance, can exist independently from brain processes (as in the case of a corpse). However, this does not seem to be the case with the mind. One subjectively experiences mental events, but not the mind independent from those events. An individual in a deep sleep, for example, is aware of nothing, rather than an ‘empty' or stagnant mind, indicating that the mind is just a term for the conglomerate of these processes. However, if this is the case, the mind cannot exist on its own and cannot interact with the brain. It can only be either a product of the brain activity or a product of an interaction between the brain and something else (this option will be considered later on).
- Descartes would not allow the possibility that animals have minds. This begs the question how and why would simple organisms (without mind) evolve into creatures that have it. And where from and why has this mind substance suddenly appeared?
- Classic dualism also fails to explain how qualitatively different entities can interact (mental causation). Descartes suggested that all mental events are part of the soul, and that the connection between soul and body is in the pineal gland (the only part of the brain that is not duplicated). However, the pineal gland is definitely a part of the body, so the question remains how its physical nature can respond to that which is not physical. Popper proposes that it is a pseudo problem: after all it is accepted that ‘non-material' gravitation affects material objects without needing further explanations. This may not be a satisfactory answer in the case of mind-body interaction, though. Gravitation is a force, or a way of describing how large bodies influence each other at a distance. Every force (or energy field), as far as we know, requires a source (in the case of gravitation, a physical object). However, from the dualist perspective matter is not a source of the mind, so in order to interact the body and the mind would require a common medium and such a medium cannot be just assumed and left unexplained.