The forms and habits of ghosts may be incredibly varied, but their reason for returning, the basic purposes behind their presence among us, tend according to folklore to be fairly limited.

Many of the reasons for ghosts suggested by past and primitive societies can still be found in modern legend.

True cases Return for a purpose Residual hauntings Evil creatures Mental Projection Infrasound Magnetic Fields Other modern and scientific theories

True cases

1. Cases in which the apparition conveyed to the percipient accurate information that was previously unknown to him.

2. Cases in which the "ghost" seemed to be pursuing some well-defined objective. The spirit of Hamlet's father who makes Hamlet swear to seek revenge for his murder is a famous literary example of this.

3. Cases in which the phantom bears a strong resemblance to a deceased person who is unknown to the percipient at the time of the manifestation. A case of this sort, incidentally, recently made headlines in the Berkeley Gazette, as the phantom was observed in the Faculty Club of the University of California

4. Cases in which two or more people had independently seen similar apparitions: Into this category falls your typical haunting ghost or apparitions associated with a particular location. Often such phantoms are seen by individuals who are ignorant of previous sightings. These phantoms rarely seem to speak or take notice of humans, although voices and noises may be associated with them, and they are generally not seen for more than a minute before they vanish.

Mental Projection

The point of such evidence is that the human mind seems capable of generating apparitional appearances identical to those often attributed to "departed spirits ." However, in nearly all apparitions, there is no living individual attempting to create the appearance. It is unlikely that most apparitions were consciously created although they may have been unconscious human productions.

Furthermore, even if an apparition results from efforts by a once-living person, the apparition itself is not yet evidence of a fully conscious disembodied spirit. Such phenomena may well be mere images or thought-forms hanging around in the psychic space. Very rarely do they show the characteristics of a well -developed personality, even though they exhibit some independent consciousness. The apparition evidence suggests we are continually swimming in a sea of thoughts and images that exist independently of our own minds and that occasionally intrude dramatically into our conscious awareness.

Return for a purpose

• Ghosts that return to seek vengeance on their slayers, to punish the living from crimes against them or their descendants (Shakespeare’s Hamlet father)

• Ghosts that seek proper burial. Ghosts are supposed to be souls that remain when their bodies have been improperly buried, or not buried at all as with Odysseus’s friend Elpenor. Harry Price the famous ghost buster of the 30s pretended that the main ghost of Borley Rectory departed when he gave Christian burial to some old bones he found under the Rectory.

• Ghosts that come to complete some task left undone or to continue one. The ghost of an american farmer returned for the specific purpose of informing his heirs where he had hidden his will.

• Ghosts that appears to announce their own death’s or somebody else’s. (doppelgangers and crisis apparitions).  

Evil creatures

Vampires  are a special kind of revenant that return solely for evil purposes as, in many tales, do the ghosts of executed witches. Demons usually do not bother humans except if they have been formally summoned.