The Mind-Body Problem

by Peter Saunders

Are the mind and the body separate entities, or one and the same thing? If they are separate, how do they relate? If they are one ‘substance mental or purely physical in nature? The ‘mind-body problem’, the difficulty of understanding how mind and body (or brain) relate, has fascinated philosophers for centuries and has profound implications for how we think about and treat other human beings. This File introduces some key aspects of the debate.

Stories of out of body experiences, beliefs in life after death, or diseases affecting the brain all raise questions about whether our minds and our bodies are separate entities that have the ability to exist independently.

Out of body experiences can occur under the influence of drugs, as part of religious experience, or close to death. During an out of body experience the person has the impression that their mind (or soul) is somehow leaving their physical body. Some people believe that these experiences are just ‘a trick of the mind’, but others see them as evidence that the body and mind really can exist independently.

Belief in life after death is common in many religious and cultural traditions. Some people, particularly in the Western world, believe that death is the end of existence. Others believe that we continue to live after our body has died, either as dismembered spirits, or to be ‘re-clothed’ with a new body, either reincarnated in this world or resurrected into a new world.

Schizophrenia and Alzaimer’s disease are two examples of disease affecting the mind where only the ‘shell’ of the original person appears to be left. Relatives and carers are left caring for those who appear utterly different from the people they once knew and loved. What actually happens when the mind goes?

Mind and Matter

The ‘mind-body problem’ centres in whether the mind and the body are separate things or one and the same. There are two main competing theories, dualism and monism.

The ancient Greek philosopher Plato was one of the first dualists. He believed that the soul was distinct from the body and could maintain a separate existence from it. Dualists differ on how they think the mind and body relate and interact.

Some believe in parallelism, in which the mental and physical realms do not influence each other. Most parallelists believe that God has made us that our mental and physical elements are synchronised and appear to interact. For example, placing your hand on a hot stove does not cause pain, but is rather an occasion for God to cause the mental state of pain. In this case, mind/body causal interactions become the work of God.

Most dualist, however, believe that mind and body do interact. René Descartes popularised this view, which is sometimes called Cartesian interactionist dualism. Descartes believed that mind and matter were separate substances, but that mind could cause matter to act (e.g. I can choose to make a fist), and that matter could cause mind to have sensations (e.g. I feel pain after striking my thumb with a hammer). Descartes also believed that mind and matter could exist independently. But how can mind and matter interact when they are different substances? Descartes’ view, like many parallelists, was that God was responsible for these interactions.

Some modern dualists say that the problem is with our understanding of reality. For example, in modern physics, light behaves in some circumstances like a wave of energy, and at other times like a particle. But light, in essence, is neither a wave nor a particle but something else. In the same way our understanding of matter and mind itself may be inaccurate, If we understood what mind and matter really were, they argue, we would also see how it is possible for them to interact without having to bring God into the equation.

Monism, the belief that mind and matter are essentially one substance, is often associated with Aristotle. Monists can be divided into idealist, who believe that only mind and mental processes exist, and materialist, who believe that only matter exists. George Barkeley, an idealist, postulated that the physical realm is just a collection of ideas, that exist either in our minds, or in other minds, or in the mind of God. Spinoza believed that the mental and physical were simply two modes of a more basic substance, which he called God or Nature.

Many modern philosophers and scientists are materialists, believing that everything is material or physical. They use the terms material and physical interchangeably, although strictly speaking, physicalists would say that energy exists as well as matter.

Materialism has become much more popular in recent years. Now many people in the Western world believe not only that human beings are simply very complex machines, but that all our mental processes can be explained purely in terms of physics and biochemistry. There are three main reasons for this.

First, scientific research has revealed much more of the complex biochemical changes that occur in the brain’s neural pathways when we think, act or sense what is going on in our bodies or in the world around us. Authors such as Oxford professor Susan Greenfield have popularised many of the recent exciting advances in our understanding of brain function.

Secondly, the new complex computers that mimic some of the functions of the human brain (in many cases more quickly) have led many to ask whether our brains are simply complex computers.

Thirdly, increasing numbers of people accept an atheistic world view. They believe that everything, including the origin of life and the universe itself, can be explained in term of random chance and natural processes. Such people look to physical matter to provide all their answers. They deny the existence of anything ‘supernatural’.

Mind-Body Problem – the problem of describing the relationship between the mind and the body (or brain)
Dualism – the view that mind and body exist as separate entities, which may or may not interact
Monism – the view that all reality is of one kind, either mental or material
Materialism – the view that only material objects exist
Idealism – the view that only minds and mental events exist

Questioning Materialism

Of course these various views of how mind and body relate cannot all be equally correct. In fact, some are mutually exclusive. So which view best explains the diversity of ‘physical’ and ‘mental’ phenomena that we experience in the world about us? The answer has eluded some of the greatest minds in history, but we can start by assessing the predominant world view in Western society, before bringing a Christian perspective to bear on the issue.

Materialism has been criticised because it fails to explain everything and it has unfortunate implications for the way we treat human beings.

Explanatory Power
Materialist have difficulty explaining how their theory can account for such psychological phenomena as desires, intentions, sensory experiences, thoughts and beliefs.

Most of us believe that we have freedom to make choices, and that the ‘I’ that chooses somehow stands outside the chain of cause and effect. If not, our choices are determined as Skinner and Ryle, two influential twentieth century writers, believed. But, if we have no option when faced with a choice, surely it was never a choice in the first place?

Most of us naturally believe that there is actually an ‘I’ that feels and is conscious – an ‘I’ that knows guilt, pleasure and pain. These sensations are of course accompanied by electric signals in the brain that can be measured. and body and facial movements that can be observed. But while we can measure and observe signals and movements, we can never know another person’s private subjective experience. Even if we can deduce what they are feeling we will never experience it ourselves, in the way that they do. Similarly, although we can perceive our own bodies (see, touch and feel them) that is quite different from seeing and touching through them.

In the same way, you may be aware that others exist by reading their thoughts as they appear on paper or on a screen, but having their thoughts is something unique to them. I cannot experience your thoughts. Even if I am able with some technical device to know what you are thinking, that is quite different from actually experiencing your thoughts as you do.

We all have an intuitive sense that we are more than just bodies ruled by physical and chemical laws; more than just complex stimulus-response machines. There is something about materialism that doesn’t quite ring true with our experience.

This intuition could all be an illusion produced by brain biochemistry, but it could equally be true that there is some aspect of human existence which stands outside simple cause and effect, that human beings are in some sense ‘supernatural’.

We already know that in the natural world things exist beyond our immediate perceptions, but within the perceptions of other species. For example dogs can hear high pitch sounds that are inaudible to humans, and birds can see colours we can’t. Could it be that ‘mind’ is something that human beings will never be able to measure or fully understand?

Philosophers of mind have, for the last ten years, begun to question the possibility that science will ever be able to close the explanatory gap between the brain and our conscious experience. Chalmers1 calls this ‘the hard problem’. This gap could be so unbridgeable because mind and matter are in reality different. Some have called this position the new mysterians because they insist that mind/consciousness is fundamentally mysterious and cannot be explained by standard scientific means.2

But there is also a deeper logical problem with materialism. If we believe in a closed universe, where nothing but matter exists, then the human mind, by implication, becomes part of that closed cause and effect system. This leaves us having to believe that all our thoughts, including our belief in materialism, are simply determined by physics and biochemistry. But if we are simply determined to think that materialism is true, then how can we be sure that it really is true?

If we wish to retain any claim to objective knowledge, we must accept that the human mind has some independence from nature. But that would deny materialism!

Read more: The Mind-Body Problem (Part 2)


  1. Chalmers D. The Conscious Mind: In Search of a fundamental theory. Oxford University Press, 1996.
  2. Eliasmith C. Dualism. In Dictionary of Philosophy of Mind.

Christian Medical Fellowship (CMF) Files No. 18, 2002