Ghosts are a very flexible supernatural phenomenon - easy to create and write about. But don't call it a ghost when it's not! Don't confuse them, for instance with Spirits. In this respect the Christian Bible is unhelpful because it uses the terms Holy Ghost and Holy Spirit as if they were interchangeable. A ghost can, if it wishes, be visible. A spirit can't. The only visible phenomena at Pentecost were 'tongues of fire' which hardly qualify. Shakespeare does not help by putting the wrong word into the mouth of Hamlet's father, who is quite obviously a ghost. "I am thy father's spirit", it says. One big difference is that a spirit can invade a person, altering his personality and behaviour. A ghost can only do that indirectly by informing or frightening. Confusion also arises because 'spirit' has other meanings, being used to describe whiskey and brandy and rum.
The most common sort of ghost is the appearance - apparently physical - of some dead person. Amongst a sample of, say, twenty ordinary people there will be one or more who reports having seen somebody who they later discovered to have been dead This sort of thing has several 'normal' explanations, such as mistaken identity, poor eyesight and wishful thinking. If the fact of death remains unknown, the viewer may never realise that he or she has seen a ghost at all. That raises the possibility that many more people have seen a ghost than know it. A good example of such an apparition was the British admiral who was responsible for a major naval disaster in 1893 and, very properly, went down with his ship. The same evening his wife was holding a reception in London and several guests saw the admiral in full uniform and remarked on his early return. A more recent case concerns the two pilots of Flight 401 who, after the disaster of that flight, were seen several times by passengers on other flights. It seems that such ghosts are seen in places they frequented in life.
Such ghosts are 'real' in the sense that the person recently existed and romance has not yet taken a hand. The non-corporeal variety - the sort that can walk through walls - depend on literature. There probably was an original person - sufficiently noteworthy to inspire tales - but the ghost has become the property of writers. For instance, Shakespeare did the job on several people who had been murdered by Richard III and caused them to walk past Richard the night before he was killed at Bosworth. Any writer is free to create a ghost. The only essential requirements are a significant original person and a sound reason for the ghost to walk.
The most common reason is revenge. The ghosts appearing to Richard III wanted his death in revenge for their own. Hamlet's father claimed to have been murdered by his brother and wanted revenge through action by his son. The ghost of Banquo gets Macbeth so frightened that he incriminates himself in front of two witnesses (who can't themselves see the ghost) and their change of allegiance contributes to MacBeth's end.
Another good story appears in The Ingoldsby Legends. It is about a Drummer Boy who appears to his murderer on a stormy night in the middle of Salisbury plain. The killer is frightened into a confession. He later retracts, but evidence comes to light that supports the confession and he is duly hanged.
More confusing is Herne the Hunter whose legend attaches to an oak tree in Windsor Great Park. He was a keeper murdered by his colleagues for being better than they were at his job. Rendered more incompetent than ever by a curse, they returned to the scene of the crime to seek a remedy and were forced by Herne (themselves being still alive) to hunt every night through the park with horses, hounds, and all the proper hunting gear. This made such a disturbance that the King turned out one night and asked Herne to stop it. He said, "Hang all this lot, and then I'll do as you ask". The King obliged. Since then the hunt has been entirely ghostly and silent.
There are other motives, too. The ghost of Patroclos appears to Achilles during the Trojan War to say "Get my body buried quickly instead of fighting over it". The ghostly wife of Periander told him where to find a treasure. Marley's ghost in 'A Christmas Carol' seeks to save Scrooge from condemning himself to torment. An imaginative writer can give his ghost many different reasons for appearing and even different capabilities. Marley's ghost, for instance, can cause the window to open behind his retreating form. Not all ghosts talk, but Marley's ghost is quite loquacious and Hamlet's father can explain that when day breaks " I to sulphurous and tormenting flames must render up myself".
Ghosts do not always appear of their own free will. In the Bible, King Saul wants military advice and goes to a witch who can, he believes, call up the dead prophet Samuel. There must be many other 'evocation scenarios' to be exploited.
Because ghosts have a thrill-value, stories about them are repeated many times, and exaggerated. In England there are hundreds of local ghost stories that, only a century ago, caused people to avoid haunted places at night. The thrill-factor was often increased by presenting the ghost as headless, and this was extended to include headless horses and dogs. A fine example is found is Anne Boleyn, the wife that King Henry VIII executed. On the anniversary of her execution, the story goes, her father turns up at the Tower of London driving a team of headless horses to take her body back to her childhood home at Blickling Hall in Norfolk. Having delivered the corpse, he has to drive his team over a circular course - crossing twelve bridges - and get back before dawn.
Genuine ghosts of the see-through variety are not subject to physical changes that have taken place since their death. They can walk through walls. If a floor level has been raised, the ghost is visible only from the knees upwards. If a floor level has been lowered, it walks on air a foot above the new level. If Anne Boleyn's father has to ride over a bridge that has since been demolished, he rides over the old structure regardless. This restriction works both ways. They can ignore physical changes but they are compelled to stick to their original environment.
The normal exaggeration of story-telling means that a fabricated ghost is sometimes credited with a reality it does not deserve. A true ghost comes from a real-life person and his actions. So Anne Boleyn's father fails to qualify. Anne herself would make a fine ghost, but her father is not famous enough and never drove to London like that.
Careless use of the word is common in the stories of ghost ships. By strict definition, few truly exist because the original never 'died'. In most cases the ship is a real one surrounded by mystery. One 'ghost ship' in the true meaning of the word is the Lady Lovibond which was wrecked on the Goodwin Sands (thus counting as dead) and which reappears once every fifty years. Better spectator value is the paddle streamer Eliza Battle. That burned in 1858 on a river in Alabama. It appears 'fully aflame', on cold and windy winter nights.
It would be great to include the Marie Celeste, but she was totally real. Likewise The Flying Dutchman, which fails the test because the ship in the legend never existed.
