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The Oxford Companion to the Mind
mind–body problem: philosophical theories. Classifications of theories are bad masters, but may be useful servants. In the following classification of the main theories of the mind–body relationship upheld by philosophers, it is to be understood that the positions sketched are ‘ideal types’ to which actually held positions may approximate in different degrees.
If we think of mind and body as two opponents in a tug-of-war, then we can distinguish among theories that try to drag body, and matter generally, over into the camp of mind; those that try to drag mind over into the camp of body; and those theories where an equal balance is maintained. This yields a division into mentalist, materialist (physicalist), and dualist theories.
It is convenient to begin by considering dualism. The major position here is Cartesian dualism, named after Descartes, the central figure in post-medieval philosophical discussion of the mind–body problem. For a Cartesian dualist the mind and body are both substances; but while the body is an extended, and so a material, substance, the mind is an unextended, or spiritual, substance, subject to completely different principles of operation from the body. It was this doctrine that Gilbert Ryle caricatured as the myth of the ghost in the machine. It is in fact a serious and important theory.
Dualist theories are also to be found in a more sceptical form, which may be called bundle dualism. The word ‘bundle’ springs from David Hume’s insistence that, when he turned his mental gaze upon his own mind, he could discern no unitary substance but simply a ‘bundle of perceptions’, a succession or stream of individual mental items or happenings. Hume thought of these items as non-physical. A bundle dualist is one who dissolves the mind in this general way, while leaving the body and other material things intact.
Besides dividing dualism into Cartesian and bundle theories, it may also be divided according to a different principle. Interactionist theories hold, what common sense asserts, that the body can act upon the mind and the mind can act upon the body. For parallelist theories, however, mind and body are incapable of acting upon each other. Their processes run parallel, like two synchronized clocks, but neither influences the other. There is an intermediate view according to which, although the body (in particular, the brain) acts upon and controls the mind, the mind is completely impotent to affect the body. This intermediate view, especially when combined with a bundle theory of mind, is the doctrine of epiphenomenalism. It allows the neurophysiologist, in particular, to recognize the independent reality of the mental, yet acknowledge the controlling role of the brain in our mental life and give a completely physicalist account of the brain and the factors which act upon it.
Mentalist theories arise naturally out of dualist theories, particularly where the dualist position is combined with Descartes’ own view that the mind is more immediately and certainly known than anything material. If this view is taken, as it was by many of the greatest philosophers who succeeded Descartes, it is natural to begin by becoming sceptical of the existence of material things. The problem that this raises was then usually solved by readmitting the material world in a dematerialized or mentalized form. Berkeley, for instance, solved the sceptical problem by reducing material things to our sensations ‘of’ them. Berkeley thus reaches a mentalism where the mind is conceived of as a spiritual substance, but bodies are reduced to sensations of these minds.
It is possible to combine Berkeley’s reduction of matter to sensations with a bundle account of the mind. In this way is reached the doctrine of neutral monism, according to which mind and matter are simply different ways of organizing and marking off overlapping bundles of the same constituents. This view is to be found in Ernst Mach and William James, and was adopted at one stage by Bertrand Russell. The ‘neutral’ constituents of mind and body are, however, only dubiously neutral, and the theory is best classified as a form of mentalism.
Just as Cartesian dualism may move towards mentalism, so it may also move towards materialism. Surprisingly, Descartes’ own particular form of the theory lends itself to this development also. Descartes was one of the pioneers in arguing for an anti-Aristotelian view of the material world generally and the body in particular. First, this involved the rejection of all teleological principles of explanation in the non-mental sphere. Second, it involved taking the then revolutionary, now scientifically orthodox, view that organic nature involves no principles of operation that are not already to be found operative in non-organic nature. Human and animal bodies are simply machines (today we might say physicochemical mechanisms) working according to physical principles.
A view of this sort naturally leads on to the suggestion that it may be possible to give an account of the mind also along the same principles. In this way, a completely materialist account of nature is reached, and so a materialist account of the mind.
The word ‘materialism’ sometimes misleads. The materialist is not committed to a Newtonian ‘billiard-ball’ account of matter. Keith Campbell has spoken of the ‘relativity of materialism’—its relativity to the physics of the day. Materialism is best interpreted as the doctrine that the fundamental laws and principles of nature are exhausted by the laws and principles of physics, however ‘unmaterialistic’ the latter laws and principles may be. Instead of speaking of ‘materialism’ some writers use the term ‘physicalism’.
Materialist accounts of the mind may be subdivided into peripheralist and centralist views. A more familiar name for the peripheralist view is behaviourism: the view that possession of a mind is constituted by nothing more than the engaging in of especially sophisticated types of overt behaviour, or being disposed to engage in such behaviour in suitable circumstances. Behaviourism as a philosophical doctrine must be distinguished from the mere methodological behaviourism of many psychologists who do not wish to base scientific findings upon introspective reports of processes that are not publicly observable.
Very much more fashionable at the present time among philosophers inclined to materialism is the centralist view, which identifies mental processes with purely physical processes in the central nervous system. This view is sometimes called central-state materialism or, even more frequently, the identity view. Unlike behaviourism, it allows the existence of ‘inner’ mental processes which interact causally with the rest of the body.
It remains to call attention to one important variety of theory intermediate between orthodox dualism and orthodox materialism. It is a ‘one-substance’ view, denying that minds are things or collections of things set over against the material substance which is the brain. But it does involve a dualism of properties, because brain processes, besides their physical properties, are conceived of as having further non-physical properties which are supposed to make the brain processes into mental processes. Such views may be called attribute or dual-attribute theories of the mind–body relationship. A theory of this sort could be said to be a variety of identity view, since it also holds that mental processes are identical with certain brain processes.
According to the doctrine of panpsychism, not simply brain processes but all physical things have a mental side, aspect, or properties, even if in a primitive and undeveloped form.
Although the dual-attribute view is important, it inherits the considerable difficulty and confusion which surrounds the philosophical theory of properties. There are many difficulties in giving a satisfactory account of what it is for a thing to have a property, and these difficulties transmit themselves to this sort of theory of the mind–body relationship.
(Published 1987)
D. M. Armstrong
Armstrong, D. M. (1968). A Materialist Theory of the Mind, ch. 1. Broad, C. D. (1925). The Mind and its Place in Nature, chs. 1–3. Campbell, K. K. (1970). Body and Mind.

D. M. Armstrong “mind–body problem: philosophical theories” The Oxford Companion to the Mind. Richard L. Gregory. Oxford University Press 1987.


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