Introduction

Broadly speaking, a ghost is usually thought to be the soul of a deceased person which, rather than entering the spirit realm, remains bound to the material world for a number of reasons: as a punishment, because of improper burial, or to seek revenge on the living.
 
Belief in ghosts is common to most, if not all, cultures. In ancient Egypt, for example, spells were often written on the walls of houses as protection from wandering ghosts; the naturalist Pliny the Younger (c. 61 AD - 114 AD) mentions an encounter between the philosopher Athenodorus and an apparition; and many contemporary Chinese believe that the deceased may become ghosts if the rituals associated with ancestor worship are not observed in accordance with tradition.
 
Ghosts appear in a variety of forms that can be roughly divided into the following categories:

 
The question is: do ghosts exist as extant entities, or are they purely psychological in nature, arising from processes occurring within the percipient's own brain? I shall now address these questions.
 

Brains, Minds & Souls

Is there any evidence that we possess a supernatural component to our nature that can survive the death of the body, and be a source from which ghostly phenomena could arise?
 
Some people may argue that ghosts prove we are not entirely material beings, and that there is an immaterial part to our nature that survives the cessation of the body's organic processes. Proponents of this idea, however, assume as being true what in fact needs to be proved — namely, that the soul exists, and that ghosts are manifestations of this entity.

If souls exist, then how can they be defined? In Western culture, the soul is usually associated with the mind — the Greek philosopher Plato, for example, held that the intellectual, or rational soul was immortal and located in the brain, and for the purpose of this article I shall adopt this point of view: that "soul" corresponds to the totality of our mental life.
 
Unfortunately for believers, the evidence to date clearly shows that all bodily processes, including mental phenomena, are ultimately material in nature: — complex chemical reactions and neuronal interactions that depend for their existence on the organic structures from which they arise:

 
Although all aspects of the mind are not yet fully understood, there is little doubt they depend on a material brain for their existence and, that when the brain dies, all mental phenomena cease.
 
The idea that there is more to a person than just a physical body probably arose in the Palaeolithic era of Earth's history, for it is at this point in time that the archaeological record reveals humans beginning to ritually bury their dead, a good indication that our remote ancestors were beginning to develop a belief in some kind of afterlife.
 
We may never know exactly how this idea arose, however, it is possible that, as the intellectual life of early humans developed, people began to speculate on the nature of life and death and connected these phenomena with the observation that when a person dies, the breath leaves the body, and the corpse grows cold and decays. Yet, the dead can appear to the living in dreams and visions — not as corpses, but as living beings, and it is from thinking about these experiences that the idea of the soul may have arisen:
 
 
Once the idea of the soul was established, its survival was assured, for one of our greatest fears is the fear of death, and what better way to conquer this inescapable fate than to believe that, although the dissolution of the physical body is assured, so too, is the continuation of life in an immaterial form.
 

Paranormal Explanations
 
Although there is no evidence for any supernatural or paranormal component to human nature that could produce ghostlike phenomena, proponents of the paranormal will probably continue to offer all manner of pseudoscientific explanations in order to support their belief in ghosts, and thereby attempt to clothe naked superstition in the garments of respectable scientific jargon:
 
 
In my opinion this explanation clarifies nothing. Indeed, such definitions and attributes as "non-physical" and "non-material" are negations of the very qualities that define extant entities, and can really only apply to things that have no existence in any meaningful sense of the word.
 
Indeed, incorporeal entities (even if they exist) could not interact with the material world. To test this proposition, conduct the following experiment:
 
Try picking up an object with the shadow (an incorporeal entity) of your hand. You will discover that it can't be done because the shadow, being immaterial, can't impinge upon material objects, and consequently can have no effect upon them.
 
Without meaning to belabour the point, the reason why incorporeal entities can't interact with the material world is because their very attributes negate all such possibilities. Indeed, if such things exist, then we could not be aware of them for this very reason — they would not be capable of rendering impressions to our senses.
 
An additional problem is that ghosts are reputed to display patterns of behaviour, and this suggests they must possess some kind of structural organisation that is complex enough to give rise to these actions. Complexity, however, depends on matter for its existence — in nature, there is a hierarchy of intricacy from subatomic particles to atoms; from atoms to molecules; from molecules to single cell organisms; and from single cell organisms to multicellular organisms. Now, as the complexity of an entity increases, so too, does the range of behaviour that it can exhibit: the behaviour of a human being, for example, is far more complex than that of an amoeba.

Ghosts, on the other hand, are considered to be immaterial. However, can immaterial psychons interact with other immaterial psychons and, in the process, form entities with a high order of complexity? A version of the medieval scholastic question "how many angels can dance on the head of a pin," may be of assistance in deciding the issue.
 
Surprisingly, this question is not as foolish as it first appears, as the answer has significant implications for the nature of paranormal entities. So, how many psychons can dance on the head of a pin? If the answer is a finite number, then psychons are material — they would occupy space, touch each other and thereby limit the number that could exist in a given area. However, if the number is infinite, then psychons are immaterial — they would not occupy space, could not touch each other and, therefore, an infinite number could pervade a finite area.
 
The problem, however, is that if psychons can't touch each other, then they could not interact with each other, and therefore would not be able to form structures from which complex behaviour could emerge. In other words, their behaviour could not be more complex than that of natural subatomic particles which, needless to say, can't act like a video camera, record events in a person's life, and then project holographic images of them after their death.
 
If proponents of the paranormal argue that psychons are particulate, then these entities come within the sphere of the natural world because they would possess attributes similar to those of material objects, and therefore be capable of detection by scientific instruments. However, it is interesting to note that no physicist has ever observed psychons in a bubble chamber, a device especially designed to discover subatomic particles.
 

Natural Explanations
 
Some people may dismiss all these difficulties, and continue to maintain that apparitions are extant paranormal manifestations. However, there may be perfectly natural explanations that can account for these phenomena, and I shall now proceed to examine this possibility.

For example, there is the belief in ghosts itself — people can often see what they consciously or unconsciously expect to see, especially under conditions that are conducive to ghostly illusions and hallucinations: if a location has an eerie atmosphere or a reputation for being haunted, then a person may experience a spectral hallucination as a result of autosuggestion — a dimly seen shape, a dream or a strange noise becomes charged with supernatural qualities. Indeed, some people may be predisposed to these experiences:

 
These phenomena, although hallucinatory in nature, can appear very real to some people. For example, on one occasion I experienced an auditory hallucination of an old woman rocking in her rocking-chair in a dark corner of my room. On other occasions I have distinctly heard doors opening and closing in various rooms of my home, and on one occasion I woke to find a shadowy figure standing over me, a figure that vanished when I tried to touch it. On other occasions I have experienced tactile hallucinations of ghostly fingers tapping the back of my neck, and the sense of a unseen presence.
 
So, do I live in a haunted house? Am I in danger of being possessed by evil spirits? The answer is a definite no — these experiences are caused by a well known phenomena called "sleep paralysis" which is often accompanied by auditory and visual hallucinations of the kind I have just described. Having personally experienced these illusions I can understand how someone who is unaware of their natural origin could mistakenly believe that they were being caused by the presence of a supernatural entity.
 
Indeed, these hallucinations are the fertile soil from which ghost stories can develop — the percipient tells someone of their experience, and this person either intentionally or unintentionally asks leading questions which further shape the account; the tale grows with the telling, and eventually a fully fledged encounter with a phantom emerges from a purely natural event.

It is also important to remember that memory is not a static thing (like a photograph), but a dynamic process that can change with the passage of time. For example, on one occasion when my mother was hanging out the washing in her garden, she saw something out of the corner of her eye which vanished when she looked at it squarely. She initially described the object as a "white shape", however, as time passed the account began to evolve and developed into a vision of my grandmother: young, beautiful and dressed in a white robe.
 
This example serves as a cautionary tale: no matter how sincere a person may be, unconscious elaborations can creep into their memory, and the final result may bear little relation to what actually occurred. As well as the psychology of the percipient, the supposed paranormal activity of ghosts may also result from deliberate trickery:

 

Conclusion

1. There is no evidence that human personality can survive the death of the physical body. Indeed, personality, consciousness and all other aspects of our mental life are dependent on material structures and, when these structures decay, we cease to be.
 
2. The idea of ghosts probably emerged from the concept of the soul, which arose in prehistory, possibly as a result of speculation on the mystery of life and death, the nature of dreams, and hallucinations.
 
3. The perception of ghosts is most likely due to psychological processes occurring in the percipient’s own brain, combined in some cases with human trickery, rather than extant supernatural entities.


Bibliography

Cavendish, R. Man, Myth & Magic, Purnell, (Ed.) England (date not shown).
 
Guiley, R.E. Harper’s Encyclopedia of Mystical and Paranormal Experience, Harper-Collins Publishers, New York, 1991.
 
Kovoor, A. Gods, Demons & Spirits, Jaico Publishing House, Bombay, 1995.
 
La Bane, W. The Human Animal. University of Chicago Press, Chicago, 1968.
 
Mulholland, J. Beware Familiar Spirits, Charles Scribner’s Sons, New York, 1979.
 
Rawcliffe, D.H. Illusions and Delusions of the Supernatural and the Occult, Dover Publications Inc., New York, 1959.
 
Restak, R. Brainscapes, Hyperion, New York, 1995.
 
Sagan, C. The Demon-Haunted World, Headline Book Publishing, London, 1996.