What is a Ghost?
Living beings generate energy while they are alive. A ghost is a residual image left on an organic field, much like a groove in a record. Particularly intense experiences such as an emotional crisis, extreme stress or violence sometimes burn a deeper groove on the record. When someone sees a ghost they are basically seeing a recording of a living being, not a spirit that is present. The image is always there. Under the right combination of circumstances we sometimes see it.
Occasionally people report auditory ghosts encounters; footsteps, pacing, knocking, rattling. These phenomenon are generally the same type of experience in that they are sounds that were made in tandem with a high degree of energy, usually worry or stress or fear, and they impression is entangled.
Sometimes an apparition may appear to be attempting to communicate something to the observer. The most logical explanation for this is that at the time the person (now appearing as an apparition) was in fact attempting to communicate something to someone else who was present there with them. This is why when different people report the apparition and its attempts to communicate, the apparition's actions don't really vary, despite the different
reactions from living observers.
I don't personally subscribe to the belief that there are ghosts of the deceased who do not know they are dead. (There are surely people who will differ with me on this opinion.) I hold this view because so much of our experience and conscious impressions in daily life are dependent upon the physical (sensory organs, etc.). The mind/spirit of a person may continue to exist after death, but it is a known fact the body does not. So whatever means
of cognition may or may not exist, it would logically follow that it would be in a different state than as a living person. You would have to be the world's most stupid being to not notice you lost your body somewhere, you know?
When an entity DOES interact you are no longer dealing with a ghost/apparition. Again, I am not talking about perceived attempts to communicate as described above, but communication that clearly adapts to the responses of the observer. These are rarer. Ever hear of the classic tale of people who pick up a girl who is hitchhiking? She gets in the car, they drive her for a while and then somewhere on the drive turn to find she isn't in the car
anymore? Doesn't qualify. The ghost "plays" the same every time.
Interactive entities usually get bumped up to the poltergeist category and that is a whole different ballgame.