Mind-body dualism can exist as substance dualism which claims that the mind and the body are composed of a distinct substance, and as property dualism which claims that there may not be a distinction in substance, but that mental and physical properties are still categorically distinct, and not reducible to each other. This type of dualism is sometimes referred to as "mind and body" and stands in contrast to philosophical monism, which views mind and matter as being ultimately the same kind of thing.
Monism is further defined according to three kinds:
- Idealism, phenomenalism, or mentalistic monism which holds that only mind is real.
- Neutral monism, which holds that both the mental and the physical can be reduced to some sort of third substance, or energy.
- Physicalism or materialism, which holds that only the physical is real, and that the mental can be reduced to the physical.