Dualism is the view that mental phenomena are, in some respect, nonphysical. The best-known version is due to Descartes (1641), and holds that the mind is a nonphysical substance. Descartes argued that, because minds have no spatial properties and physical reality is essentially extended in space, minds are wholly nonphysical. Every human being is accordingly a composite of two objects: a physical body, and a nonphysical object that is that human being’s mind. On a weaker version of dualism, which contemporary thinkers find more acceptable, human beings are physical substances but have mental properties, and those properties are not physical. This view is known as property dualism, or the dual-aspect theory.
Several considerations appear to support dualism. Mental phenomena are strikingly different from all others, and the idea that they are nonphysical may explain just how they are distinctive. Moreover, physical reality conforms to laws formulated in strictly mathematical terms. But, because mental phenomena such as thinking, desiring and sensing seem intractable to being described in mathematical terms, it is tempting to conclude that these phenomena are not physical. In addition, many mental states are conscious states – states that we are aware of in a way that seems to be wholly unmediated. And many would argue that, whatever the nature of mental phenomena that are not conscious, consciousness cannot be physical.
There are also, however, reasons to resist dualism. People, and other creatures with mental endowments, presumably exist wholly within the natural order, and it is generally held that all natural phenomena are built up from basic physical constituents. Dualism, however, represents the mind as uniquely standing outside this unified physical picture. There is also a difficulty about causal relations between mind and body. Mental events often cause bodily events, as when a desire causes an action, and bodily events often cause mental events, for example in perceiving. But the causal interactions into which physical events enter are governed by laws that connect physical events. So if the mental is not physical, it would be hard to understand how mental events can interact causally with bodily events. For these reasons and others, dualism is, despite various reasons advanced in its support, a theoretically uncomfortable position.
The mind-body Cartesian dualism and psychiatry
