Ghosts are apparitions of deceased people. While not proven scientific fact, the existence of ghosts is widely accepted, even by academics.
Ghosts are caused by a conscious "imprint" left by a living being at some point during his or her life. This does not have to be the moment of death, but often is. Once the soul has entered the The Afterlife, these imprints might begin to manifest themselves; after the soul has moved on to the Antelife, the ghost no longer appears. (This explains why the graveyards are not simply brimming over with ghosts.)
The ability to perceive ghosts is known as seance. It is considered one of the core senses and is present in all races, but not all individuals.
Ghosts are described as small, semi-corporeal beings similar to humans. While they are not described as transparent, they do appear to bend the air around them, and can disappear and reappear at will. People who see ghosts can suffer from headaches, nerves, or a sudden gripping fear. They will not look "quite right" and are impossible to mistake for an actual, living person.
The size of ghosts is debatable. Some report seeing ghosts of normal height, while others report seeing small, child-sized ghosts. Very few have reported seeing the ghosts of animals, but nevertheless there are records of this phenomenon. In Anhau, ghosts are seen in indistinct forms; this could be related to their practice of cremation.
Purpose and Abilities
Ghosts are not malicious, but can be hungry; a ghost longs for a warm body to enter and control. If you go near a ghost, you run the risk of being possessed by it. Once a ghost has possessed a body, it will not leave unless forced out by a strong Warding spell, which is dangerous and can take many galdori to cast.
While possessing a body, a ghost may try to live out its last recorded moments again and again. Some particularly strong aspects of the ghosts' former personality might leak through, amplified. Possession is usually quite painful for the victim, and it is not always possible to free the victim before the ghost enters the body and consumes it. In rare cases where a Warding spell was not available (for example, in human possessions), the ghost eventually learns to control the body fully, though the victim's lifespan is severely shortened. This is not the same as a Raen take over.
Research into the ghosts of Brunnhold's crypts has shown ghosts are often able to project feelings or a phantom field onto an area. It has also been noted that upon being touched, many subjects have found themselves connected to the beings in some profound way. Often a touch is precursory to possession. Some subjects, prompted to take items of sentimental value from the research tombs, have reported seeing the apparitions outside of their usual haunts, which seems to suggest a connection. (Prof. J.T. Winterbald, 2576)
The Question of Consciousness
Ghosts are not conscious or sentient in the usual way of defining these terms; as they are essentially a record of the moment of death, they carry with them only a fraction of the personality and memory of their former life. They cannot be reasoned with, as they are not fully aware of the living around them, or indeed anything; they have no idea that they are dead. A ghost only has the ability to obsess endlessly about whatever strong emotion drove them to imprint themselves upon the world in the first place.
The Ghostly State
Ghosts can become "trapped" in their state if they are, for some reason, unable to move into the antelife and find a new life form to inhabit. However, this state seems to be limited. Ghosts can not exist for longer than about a century; they seem to have a lifespan, like living things. The average "life" of a ghost is quite short, only five to ten years.