Paranormal writers explore the unexplainable. There are things that are either beyond the human ability to clearly understand through scientific examination, or entirely a product of the fertile human imagination, depending on your beliefs. This fertile ground provides endless opportunity for the writer to make up his or her own explanations, shine a light on new mysteries, or just re-invest us with the old ones. The intent might be to scare us, show us what is possible, to question our preconceptions, or just to tell a good story.
The study of the paranormal is nebulous and always changing, but as the leading edge of science advances like a wildfire, the core things that make us human do not change. We still jump at shadows, still fear death, and we still feel and experience things that we can't explain. While the methodology and terminology we use to try and share and understand it may change, the feeling of something outside of the normal stays the same. The most important core element to paranormal is the word "normal." Paranormal is grounded in our common understanding, and will always have elements that tie the story to the real world.
Classic Paranormal stories have within them: Ghosts,extrasensory perception, Psychic Abilities, reincarnation, aliens, and demons.
The lines between science fiction, horror, fantasy, and paranormal are often blurry. Paranormal almost always includes one of the other genres, and paranormal elements may be just a discardable element in a fairly traditional plot. For instance; does it matter to the story if the villain makes people's head explode with telepathy or shoots them with a gun? But the great paranormal stories make the paranormal the main element.
The classic paranormal story we all immediately can identify is A Christmas Carol by Charles Dickens. In this story, we see a normal man of his day haunted by ghosts to show him the error of his ways. This is to a certain extent, a discardableelement, as Scrooge might just as well have been educated by a living person. But adding the ghosts into the story adds a very compellingly story tool. Is Scrooge dreaming? Is he being haunted? The question is never answered, and the question itselftitillates the reader.Paranormal / Science Fiction
All paranormal is science fiction to a certain extent, but not all science fiction is paranormal. Paranormal refers to anything outside of current scientific understanding.
Frankenstein by Mary Shelley is an excellent example of early science fiction, but it also has many paranormal elements. The monster has elements of a revenant soul, a modern reinvention (for its day) of zombies or draugrs, with a scientific explanation to replace the mythological. This is a common element of the genre, and it can be seen in more recent stories, such as the Underworld movie series, where an ancient curse is replaced with a medieval virus.
This is also where stories about ESP end up, but they may be defined as fantasy as well, depending on the mechanism used. Professor X has ESP from a genetic mutation, but in the movie Constantine, ESP has a supernatural basis making it a paranormal / fantasy.
Alien Science Fiction is another area of paranormal, not often identified as such. Aliens who abduct, probe and release, are an active area of paranormal investigation. In Independence Day, this link is used without restraint.