Is the monist right in arguing that both mental and physical life can be explained in terms of a single, elemental substance ?

Monism is the doctrine for theories of existence that are in response to, and disagree with, dualism. For a monist, a single elemental substance is thought to explain both physical and mental life. What that elemental substance is, is still not known. Although this would tend to unite monists, there are several conflicting views as to how this elemental substance could explain phenomena such as mental states, consciousness and self. Monists may believe that the elemental substance was in the mental or physical realm, or transcend both.

At the fundamental level there may be no distinction between the mental and the physical. The difference may only be one of semantics. Liebnitz's identity thesis calls into question whether the mental and the physical are really two separate things with separate identifiable properties. The names are different but the properties are the same. The task is to identify whether there are different properties between the two.

A physicalist would explain (or leave a scientist to explain) mental states as brain-wave activity and/or solutions of various biochemicals in the brain. The elemental substance would be entirely within the physical realm and explained by physical laws found now or in the future. For a physicalist, mental life is determined by the same cause and effect as physical life.

A non-reductive monist would argue that a purely physical account cannot do justice to describing the mind. Random synaptic bursts from a neurological entity such as the brain could not explain ideas. The synaptic activity does not cause thought. Physicalism would fail to explain what mental life is like to the self-conscious first-person self. It reduces mental life to physically based laws. Physicalism does not differentiate between primary and secondary characteristics. A non-reductive monist, or token-type identity theorist does differentiate. The difference is between a primary characteristic of brain activity and a secondary characteristic such as thought.

Modern physics has a conundrum when explaining things in terms of matter. The atom, a physical substance once thought to be elemental, has various sub-atomic particles. This sub-atomic material cannot be entirely explained in terms of matter, but (sometimes) in terms of energy. In both cases the explanation is found to be partial, as Heisenberg’s uncertainty principle shows. This wave-particle duality that besets physical science has not given monists a ready elemental substance. In fact it has played into the hands of dualists. That future physical science could find an elemental substance and therefore a grand unified theory (GUT) is not certain.

Other means of explaining mental states are needed to resolve the inability of current physical science to reduce mental life to physical laws.

Mental states can be described in terms of behaviour, or dispositions to behaviour. This is very much a third-person description of mental life. The logical behaviourists believe that the thought that mental life is somehow different from physical life is a category mistake. When there is a first-person account of their mental states, and that they are somehow very different from physical life, the logical behaviourist tend to summarise the account as a misuse, or inaccurate use of language.

The problem is that the subjective, first-person account, could really be very different from a third-person, objective account. There is a question of who does the categorisation and therefore the explanation. The behaviourist is explaining external acts, but the ‘inner life’ of thought is disregarded. The explanation is reduced to appearances given to an external observer.

Another form of monism attempting to explain mental life in terms of physical reality is functionalism. This explanation is very much an analogy of the mind or brain with modern-day computing technology. It has been useful in research into artificial intelligence. As with artificial intelligence it may have reached a point of no further development. The analogy of input such as sensory experience, processing of the inputs to produce outputs is a classic description of what a computer does. Mental states are thus reduced to ‘hard-wiring’ of the brain and the functions that brain performs.

A characteristic of mental, ‘inner’ life is intentionality. Brentano and Husserl have argued that thought is founded on objects. A thought has to be about something. This ‘aboutness’ is missing from explanations from Artificial Intelligence and functionalism. An abstract, non-existent idea such as a Unicorn, has no basis in physical reality, but as an idea or use of the imagination, can have a very real basis in mental life. This inner life can lead to delusion, form a basis for other mental illnesses, but also be instrumental to creative thought.

Intentionalists still regard themselves as monists seeking to explain mental life in terms of natural, physical laws. The ‘aboutness’ does cause serious problems in uniting the mental with physical explanations of reality. That an object can exist in ‘mental space’ but not in physical space, even if only in language terms, could be construed as dualist.

The idea that an elemental substance could explain both mental and physical life depends as much upon how far you would want to reduce explanations to necessary and sufficient conditions. Mental life, if there is such a thing, has a subjective aspect that no elemental substance could explain with first-person narrative. There would be a difference in properties between mental and physical life according to the identity thesis by dint of the explanatory powers of the subjective over the objective. This is not to say that there are two elemental substances, one mental and one physical, as a Cartesian dualist would have. There is a problem of no identifiable ready causal link between two such substances. It is to say that the subjective explanatory power of mental life cannot be replaced by an objective reduction to more physical laws.

It is believed that the Mind supervenes upon the brain. The mind can only exist with its base being the brain. The one elemental substance could be entirely physical, explained by and reduced to, physical laws. However its explanatory effect for the subjective conscious self that supervenes on the material body is limited. A subject’s depression may well be explained by neurochemical disorders at one level, but would not be sufficient explanation of the subject.

There may be no other elemental substance than that to be found in the physical realm. In that sense the monist may well be right. As a way to explain both mental and physical life there is more to doubt. There could be properties of a mental life that cannot be explained in purely physical terms.

George Graham Philosophy of Mind, Second Edition, Blackwell 1998.

Roger Scruton Modern Philosophy, Arrow, 1994. Especially chapter 16, ‘The Soul’.