This essay assesses property dualism, a theory of mind. It proclaims the existence of a single, physical substance (unlike Cartesian dualism), but argues that this single substance has two potential properties: physical and mental states that are not reducible.

The idea that mental states are non-reducible properties of brain states is the central tenant of a theory of mind called property dualism. However, before we can assess the theory we must be aware that the question assumes the existence of mental states and as such we cannot answer this question from some perspectives (e.g. eliminative materialism)

Property dualism proclaims the existence of a single, physical substance (unlike Cartesian dualism), but argues that this single substance has two potential properties: physical and mental states that are not reducible. It is not just that we might talk of mental and physical states in different ways, but that the difference is in ontology as well as language. This is equivalent to historical notions that living things contained some 'vital force'. Essentially mental states are an extra property of matter in the brain.

Property dualists argue that consciousness is an emergent phenomenon of the physical processes of the brain and thus it is important to note that this leads to a belief in asymmetrical causation. Mental properties are caused by physical properties, but have no effect themselves on the physical properties, making the relationship one way.

This can be seen in the illustration below where the same object has both physical and mental properties that exist inextricably alongside each other. The object's physical properties can cause a change in its physical properties, but not the other way around:

The theory of property dualism arose as a defence of consciousness that responded to the key problems of Cartesian dualism (i.e. the problems of location and interaction) caused by the notion of two different substances. Property dualism also allows for the primacy of the physical over the mental. This is critical because it allows for matter to cause mental states, which in turn allows for the rejection of the notion of two substances.

By supporting the notion that our experience of mental states cannot be reduced or eliminated the theory is intuitively compelling. This is a benefit over materialist theories of mind that fail to capture or explain our intuitive experience of consciousness.

Fundamentally, property dualism is an advancement of substance dualism, and over this theory it has several advantages. Firstly, by invoking only a single substance it avoids to the problems of interaction and location associated with the non-spatial Cartesian mental substance. Secondly, it is not rooted in religious beliefs and is thus more scientifically based than Descartes' theory. Thirdly property dualism is compatible with Descartes' arguments that the mind has properties that are distinct from the body, thus taking the benefits whilst leaving the drawbacks. Finally, property dualism is compatible with advances in brain science in the same way that materialist theories are, thus seemingly creating a 'best of both worlds' scenario.

Another advantage of property dualism is that it allows for first-person perspective. Materialist theories do not normally allow for the same degree of privileged access to one's own internal states that Descartes proposed. However, the Cartesian model is solipsistic, whilst property dualism, being materialist, allows for scientific investigation and public third party access to the causes of mental states.

However, there are also a number of objections to property dualism. The first applies Occam's razor ("Entities should not be multiplied more than necessary"). Surely it would be simpler to suggest that we are simply talking about one thing, as in reductive or eliminative materialist accounts of mind? The notion of two properties seems overly complex.

A further point to make, which can be considered an objection by some is that the reliance by property dualism on physical causes implies determinism of mental states.

A more damaging attack is to question whether property dualism does indeed solve the problem of location associated with substance dualism. Just because mental properties supervene physical properties does not explain where they are, just how they interact with physical properties.

Furthermore if mental states are properties of physical matter in the same way that physical states are, then how is it so that we can scientifically measure physical properties, but not the mental sates that they give rise to? It seems highly problematic for property dualism to claim that there are facts that cannot be measured scientifically; and this issue also renders the theory unfalsifiable.

To continue this thread, what is different between physical properties in my brain that supposedly give rise to mental states and the physical properties in my washing machine that apparently do not? In response to this issue, complexity has been invoked as this can give rise to emergent properties. However, if complexity is used as differentiating property between systems with and without mental states, can we not point to other systems with complexity rivalling that of the human mind and ask if they experience mental states? Maybe the internet experiences mental states, or weather systems? In addition we must be entitled to ask at what point a biological system becomes sufficiently complex to experience mental states. Would this make a dog conscious, but not a bacterium? At what point in development might a human being become conscious? These problems might not form a knockdown refutation, but compromise the theory by bogging it down in questions over the minutiae of implementing it in the real world.

Another attack on the theory is from an evolutionary perspective. Ironically, property dualism allows for the evolution of mind from matter as an emergent property. However, by postulating an asymmetrical psycho-physical causal relationship whereby mental states cannot cause physical states we are surely entitled to ask, then why did mental states evolve at all? Frank Jackson responded to this objection by arguing that brain states evolved to respond to external stimuli, and that mental states were merely a by-product or emergent property, and that as such there was no evolutionary pressure for them to evolve. However, Jackson's response seems somewhat contrived and counter-intuitive; it would appear simpler and more compatible with existing knowledge to say that consciousness does have an evolutionary advantage and thus developed as a result.

Finally, we could invoke the many material monist theories as objections to property dualism. Without assessing them all we can nevertheless use a central principle invoked by materialist theories: that of reduction or elimination of mental states. This argues that talk of mental states can be reduced to talk of physical states (or that talk of mental states can be eliminated) as physical matter and explanations are all that exist. If, as property dualism suggests, mental states are properties that emerge from and are caused by physical properties then in what way can they not be reduced to physical states or eliminated? Dale Jacquette responds to this point by arguing that this objection misunderstands what is meant by emergence, emergent properties resulting from the 'complex organisation' of matter. Recognising that complexity alone cannot prevent reductive explanation by scientific investigation, he goes on to state that the mind is emergent in a non-reductive way 'such that it cannot be explained in terms of behavioural, material and functional properties'. However, we could argue that biology cannot be 'reduced' to physics and chemistry (e.g. properties such as adaptation or function), but that this does not mean that these form non-material properties; neither does this mean that there is something about psychology that is special because it cannot be reduced.

Thus, in conclusion to this assessment of the view that mental states are non-reducible properties of brain states, we can say that property dualism does manage to successfully draw together themes from materialism and Cartesian dualism. However, it is not a convincing theory of mind because it fails to explain how emergent non-reducible properties actually form consciousness, or why these properties might be facts that cannot be empirically verified. This leads to a host of practical issues regarding the evolutionary development of consciousness and which systems can be said to be conscious.

1. The stanford encyclopedia of philosophy entry for Dualism by Howard Robinson
2. www.dictionary.com
3. Dale Jacquette -(personal page)
4. Unidentified (but excellent) article on Jacquette's property dualism
5. Curtis Brown of Trinity University, Texas

Tutor: Oliver McAdoo MA

WWW www.arrod.co.uk