The popular form of substance dualism was adopted after the difficulties of Cartesian dualism could not be overcome. Rene Descartes stated that the nonphysical and the physical could not interact. this became a problem in dualism since the nonphysical mind needed to interact with the physical body. These difficulties provided a motive for the move to popular substance dualism.
The first major argument for substance dualism is religion. Each of the major religions place belief in life after death; that there is an immortal soul that will survive death. This very closely resembles substance dualism. The mind can be substituted for the immortal soul. In fact the two are almost interchangeable. This argument is primarily the basis for my own belief in substance dualism. My personal experiences as a religion student give me insight into this argument.
The second major argument for substance dualism is irreducibility. This points to a variety of mental phenomena that no physical explanation could account for what is going on. An example would be the quality and meaningful content of human thoughts and beliefs. These things cannot be reduced to purely physical terms, hence irreducibility. This is also another good argument that I can understand from personal experiences.
The final argument for substance dualism is parapsychological phenomena. Mental powers such as telepathy, precognition, telekinesis, and clairvoyance are all near impossible to explain within the boundaries of physics and psychology. These phenomena reflect the nonphysical and supernatural nature that dualism gives to the mind. Because I believe in these phenomena, it seems logical to me that parapsychology is an excellent argument for substance dualism.
These arguments give a good basis for a philosopher to believe in substance dualism. However there are also serious arguments against it
The first major argument against dualism is simplicity. Materialists state that because their view is simpler (they only believe in one thing- that which is physical) it is more rational to subscribe to their view. The materialist point of view is also easier to prove because there is no doubt that physical matter exists, while nonphysical matter is currently a hypothesis. This argument seems very illogical to me. Philosophical views should be chosen because one makes more sense to you, not because one has a smaller number of ideas within it.
The second major argument against substance dualism is explanatory impotence. Materialists can explain anything physical through scientific study, whereas dualists can explain nothing because no theory has ever been formulated. Churchland says, “…dualism is less a theory of mind than it is an empty space waiting for a genuine theory of mind to be put in”. I see one flaw with the materialist theory here. The mind in the dualist theory may use a form of energy transfer not yet discovered by science. Centuries ago, undiscovered forms of science were refuted and called “magic”. In the future, The mind may become completely understood by science.
The third argument against substance dualism is neural dependence. That the mental capacities depend on the brain’s neural activities. The materialists show that the mind is altered when the brain is altered by drugs or injuries. I would explain this by saying that since the mind is a separate nonphysical entity and cannot interact with physical matter, it needs a focal point to control the body from. This focal point is the brain. The mind and the brain are so intimately intertwined any disruption of the brain will affect the mind.
The Final argument against substance dualism is evolutionary history. The materialist states that human beings have been incrementally built up from simpler physical creatures. This is evolution. Because this is a pure physical process and the simpler creatures we were constructed from had no nonphysical mind, there is no way to account for our mind. This is a difficult argument to win.
Churchland, Paul M. Matter and Consciousness. Massachusetts: The MIT Press, 1994