By now you know that every season of American Horror Story is connected. Each of the six seasons share an expanded universe timeline and often feature actors reprising their previous roles. And so it's reasonable to assume that every season also operates under a shared set of rules when it comes to the limits and abilities of ghosts - a recurring feature in Ryan Murphy's twisted world.
Given that half the cast of Roanoke was just killed off and the other half is being hunted by ghosts, we figure now is as good a time as any to go over the previously established rules of ghosts in the AHS universe. Because with everything in Roanoke being so batsh-- out of control, it's nice to know there is some order to the chaos.
Ghosts are tied to the property they died on. One of the few consistencies in American Horror Story is that ghosts are restricted to haunt the place where they died. This not only includes the buildings in which they were killed, but also the properties that go with them (which is likely why the ghosts are able to roam the woods outside the Shaker mansion or appear on the lawn of Murder House). However, not every person who dies on a property necessarily returns as a ghost. In Hotel, Sally asks whether Iris has any "unfinished business" that will keep her around as a ghost, which indicates that a person needs a reason to turn into a ghost rather than go directly to the afterlife.
Ghosts can be banished. As Tate reveals in Murder House, anyone can temporarily banish a ghost by simply telling them to "go away." When discussing the lost colony of Roanoke, Billie Dean Howard also says that the Native Americans were able to get rid of the ghosts of the settlers by using the word "Croatoan." However, when Violet attempts the "Croatoan" spell it fails. Cricket and Elias were both able to use it effectively, though.
They can roam free on Halloween, Devil's Night or if they're released by magical means. In Murder House, ghosts can roam free on Halloween night, as seen when Tate takes Violet out for a date and Moira goes to see her mother. But in Hotel, this rule is never mentioned. Instead, they focus on Devil's Night, the day before Halloween, when ghosts of serial killers are able to appear at the Hotel Cortez. Coven also establishes that ghosts can be permanently freed from their location of death through magic, which is what happened with the Axeman.
Ghosts can never die. Some aspects of witchcraft, such as telekinesis, affect ghosts, and shooting them or stabbing them can cause temporary harm, but won't ever kill a ghost. Although, if ghost overcomes the issue that has kept them on earth, it is possible for them to pass on to the afterlife.
Ghosts are fated to repeat themselves. Ghosts typically appear as echoes of their human selves, stuck in an endless loop until they become self-aware, accept their ghost existence, and find their new purpose.
Ghosts choose when and how they appear. Ghosts are in complete control over how they appear to humans. They can consciously manifest themselves to reflect the way their body looked in death, or they may choose to look perfectly normal. Still, it remains unclear whether Moira appearing as both a young woman and an old woman is solely the result of her being a ghost.
The can interact with objects and humans, but aren't restricted by the laws of physics. Ghosts can move around at will, instantly changing locations without occupying the space in between. And even though they don't have corporeal forms, they can perfectly mimic them. This ability allows ghosts to interact with objects and humans in such a realistic fashion that they're undecipherable from a living person.
They can't appear physically on camera: Although never directly stated, it's heavily implied in Hotel that ghosts can't appear on camera - a rule that has seemingly been discarded in Roanoke, which has shown Edward Mott, the Jane sisters, the Roanoke colonists and Piggy Man in camera footage. It's possible that this inconsistency could be explained by their connection with the Witch of the Woods, whose role in their deaths might have created a new type of spirit. Alternatively, there's a chance that Return to Roanoke isn't the found footage it claims to be, and what we believe are ghosts are actually actors.
They can't harm humans unless there's a Blood Moon: In Roanoke, Elias explains that ghosts can't physically harm humans except during a one-week period in October known as the Blood Moon or Dying Grass Moon. This rule goes against everything we've previously seen of ghosts in AHS. In Murder House, Coven and Hotel, ghosts had the ability to harm humans whenever they pleased.
Ghosts can reproduce with humans. Murder House proved that ghost-human unions can produce a baby, but there are a few restrictions. A female ghost can't become pregnant by a human or a ghost man, but a female human can become pregnant by a ghost man. Unfortunately, based on the one child we've seen produced from a human-ghost pregnancy, it appears as though these children are inherently evil and will potentially become the Antichrist himself. Oh, and they'll also give the mother a craving for brains.
American Horror Story airs Wednesdays at 10/9c on FX.