Most of the arguments for dualism involve showing that there is a fundamental difference in the properties of matter as opposed to those of mind. If X = Y, then anything true of X should be true of Y and vice versa. If X has properties that Y does not have, then X is not Y. For example, the mind can logically exist without matter (such as brain-in-a-vat scenarios), but matter cannot logically exist without matter.
Most famously associated with Rene Descartes, substance dualism says that the mind is a completely different kind of "stuff" than matter. You are a non-physical person just "riding" or "driving" your physical body. The biggest problem with substance dualism is explaining how a non-physical substance can get into a cause/effect relationship with matter.
There are roughly three types of substance dualism, based on how they handle this interaction problem:
- Interactive Substance Dualism (or Cartesian Dualism): Descartes' version. He didn't really have a good explanation, but thought that there was no obvious problem with interaction.
- Occasionalism: The mind and body do not interact. Rather, when you decide to do something physical (like move your arm), God causes your physical arm to move at the same time.
- Parallelism: The mind and body also do not interact. Rather, all events are synched up from the beginning of time, like two clocks synched with each other. When you lift your arm, that event was destined to happen at the same time as your willing of your arm to move.
Concedes that the arguments for a non-physical mind are successful, but maintains that the mind is still caused by the physical brain. So there is still only one type of stuff (matter), but if arranged the right way can give rise to properties that are not present in physics.
There are roughly two types of property dualism:
- Emergentism: Claims that the physical brain gives rise to the (non-physical) mind, and that the mind can affect the body (and vice versa). I.e., two way interaction.
- Epiphenomenalism : Claims that the physical brain gives rise to the (non-physical) mind, but that the mind cannot affect the body. I.e., one way