In philosophy of mind, dualism is any of a narrow variety of views about the relationship between mind and matter, which claims that mind and matter are two ontologically separate categories. In particular, mind-body dualism claims that neither the mind nor matter can be reduced to each other in any way, and thus is opposed to materialism in general, and reductive materialism in particular. 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. (source: Wikipedia "Dualism")