The thing I’ve always liked about the Ghostbusters is that they treat ghost hunting like it’s pest control. They’re New York schlubs. Regular people. They’re plumbers, only instead of fixing leaks, they’re fixing spiritual anomalies.
They’re also professionals. And, as professionals, they use a classification system to deal with and identify supernatural entities. They call it the CDI System — for Classification, Description, and Identification.
According to this system, the various spooks, spectres, or ghosts that may trouble you fall into one of seven classes, each with their own unique characteristics. While the CDI System was alluded to briefly in the 1984 film, it was fleshed out by the official Ghostbusters RPG, the IDW comics, and the 2009 video game.
Let’s take a look with some, let’s say, “real world” examples.
The most basic of paranormal entities is the Class 1. These include amorphous forms or phenomena that may not be visible to the naked eye, such as strange noises, disembodied voices, mists, vapors, and orbs. They may also be noticed by the existence of cold spots or other changes in temperature.
Class 2 entities, while in some cases similar to Class 1, are able to manipulate the physical world, and even possess inanimate objects. They may also accomplish partial visible manifestations. George the ghost might be considered a Class 2 — while he’s never appeared as anything other than a floating orb or mist (that I know of), he has been known to cause cold spots, turn on lights, and tap people on shoulders.
These entities have human or humanoid forms and personalities, though their identities are unknown. They can be corporeal, appearing just as living humans would. For example, the ghost of Mary, while a named spirit that has allegedly manifested in a fully human form, would possibly be Class 3, as her true identity is not confirmed.
Exactly as Class 3, these entities have visible human forms and personalities, but with known identities. Communication should be possible. The alleged ghost of Inez Clarke would likely fall under this classification, as she is identified, has appeared dancing in thunderstorms, and, you know, haunts her own statue.
Class 5 includes non-human, non-intelligent entities brought about by extreme psychokinetic or emotional energy. They may also manifest as the result of ritual summoning, and may contain some minor human characteristics. According to Ray Stantz after the incident at the Sedgewick Hotel, Slimer was a Class 5.
Spirits of animals, or entities that take on animalistic characteristics. Perhaps one example would be the ghost of a cat.
Class 7 is where the real fun begins — manifestations of gods and demons, otherwise known as “metaspectres.” These are the most dangerous and powerful of supernatural entities. Our best example is Gozer the Gozerian, Gozer the Destructor, Volguus Zildrohar, also known as the Traveler, who made a brief appearance at the top of 550 Central Park West back in 1984. The Gatekeeper and the Keymaster — Zuul and Vinz Clortho, respectively — would also fall under this classification.
When encountering a Class 7 entity, just remember to clear your mind, and if anyone ever asks if you’re a god, you say YES!