There are THREE types of ghost!
Firstly, to the age old question, do ghosts exist, I'd give a resounding yes! I firmly believe that sane, honest people quite correctly report ghostly experiences. It is the nature of those experiences that is at issue.
A more surprising conclusion is that there are THREE types of ghost. These are (a) fictional ghosts, (b) 'faction' ghosts and (c) 'real' ghosts.
Fictional ghosts are the familiar staple of ghost stories and Hollywood. They have characters, motivations and can communicate with the living. They are 'spirits', in other words. We all understand these are entirely fictional (or do we?).
Faction ghosts are those documented in popular 'real life' ghost story collections (eg 'Ghosts of Sometown'). They are usually written about by authors who have not personally investigated the cases involved though they may have talked to the odd witness. There is a sub-group of 'TV ghost' of the type of show featuring 'real ghost hunters' who usually take mediums into haunted properties. These shows appear to be documentary though they are frequently researched and scripted. The characteristics of 'faction' ghosts are that they are usually identifiable and can, usually through a medium, sometimes communicate with the living. They are, however, far more elusive than the freely interacting fictional ghosts.
Real ghosts are the ones that I, and other serious researchers, have investigated. They are quite different to the previous two types. Usually an investigation is prompted by reports of odd sounds (particularly), lights, smells and object movement. Investigation usually reveals that many of these phenomena could easily have natural causes though there are exceptions. Actual apparitions are surprisingly rare.
Until the TV Ghost era, most serious researchers could find no obvious connection between apparitions and 'spirits' (fore reasons obvious from the previous paragraph). Many, however, subscribed to the 'recording' theory. This said that ghosts tended to repeat their actions again and again, ignoring witnesses and even current room plans. The idea was that ghosts were, in fact, some kind of bizarre 'recording' of a former inhabitant which had somehow been made in the space where they used to live.
It doesn't take much imagination to see that 'fictional' ghosts have influenced the 'faction' type. Many investigators prompted by TV ghost shows have taken this influence into real investigations despite previous evidence.
The recording theory, while interesting, does have flaws as I will be discussing next time. Interestingly, the 'faction' type of ghost seems to influenced 'real' ghosts to produce this idea.