I don't have so much to do at the moment, and it's raining outside (which sets a really gloomy atmosphere) so I'll try to tackle this topic the best I can.
I'm no expert on the field, but I recall a guy named Antoine Lavoisier set out a principle which goes more or less like this: "Nothing can be destroyed, nothing can be created, but everything can be transformed", which makes me pander about the fact human consciousness, after death, can not be eradicated. Therefore, exactly in what place does it go? Anyway, the italian version of the word "ghost" comes from ancient greek (φάντασμα), which is literally defined as an "apparition, or projection" without necessarily taking into account occultism or spiritualism. I know that because I studied both latin and greek literature. By the way, there is an interesting document of the era written by Pliny the Younger which describes an "haunted house", several centuries before this concept was popularized by other authors. If you are interested to read the document, here I tried to translate it:
" There was a house in Athens, it was big and comprised of several rooms, yet also infamous and pernicious. During the silent nights, it was possible to hear a sound of grating chains, at first far away, but then much closer. Suddenly, a ghost appeared: the features were that of an elderly man, quite sloppy, with a big beard and wiry hair. His feets were blocked by strains, while he shaked the chains with his own hands. Therefore the residents of the house, easily scared, would spend sleepless nights. Due to this excessive fear, insanity and -afterwards- death, followed. In fact, even during daytime, even though the ghost faded away, there was still his terrible silhouette etched in the eyes of the residents. Due to this series of events, the house remained deserted and forgotten, left to the vagaries of that terrible monster. Yet, it was always for sale... "