Intelligent Haunting
This type of haunting is perhaps the most widely accepted kind of ghostly activity, although it's not as common as you might think. Here, the spirit or entity involved is an "intelligent" presence in a location. It is there because of a connection to the site or to the people in the location. This ghost is best (and most simply) described as the personality of a person who once lived and who has stayed behind in our world instead of passing over to the other side.
This sometimes happens in the case of a murder, traumatic event or unfinished business. At the time of death, the spirit refuses to pass over because of these events. The spirits often linger because of emotions that tie them to the earth, from anger to love. Or perhaps the person does not pass not because they couldn't, but because they did not want to. In other cases, there is the chance the spirit does not even realize they are dead (like Patrick Swayze in Ghost). This can occur when the death is sudden.
These spirits are made up of the energy that once made up the personality of a living person. These intelligent spirits are not evil or demonic, as some would have you believe. Spirits are simply human personalities, or souls, and if the spirit was a kind and caring person in life, the spirit will most likely be in death. On the other hand, angry and cruel people will also keep those same nasty qualities as spirits. These negative spirits can be frightening, especially to people not trained in the paranormal. In very rare cases they have been able to harm the living, but that is generally not the case. It is much more common to hear of an encounter with a benevolent spirit than with a negative one. That's a relief, isn't it?