Well, the understanding of ghosts is that they are bound to moments in time, regardless if time has changed the environment. For example, a ghost that passes through walls… how do you know that wall was always there? Houses and buildings get remodeled a lot, especially the older haunted ones. Ghost follow the paths they walked while they were still alive, which includes going through doorways or up stairs that have been moved and are no longer there.
A ghost is not a tangible being, they cannot interact with the physical world, and thus are not affected by gravity or physics.
But ghosts are memories of the living. So they remember sitting on couches, and thus continue to do so. You don’t pass through a couch, you sit on it.
But if a wall is present that was not there when they were alive, they will not recognize it as a wall at all- they still see it as an open walk-way.
You will notice that ghosts only tend to interact with antique furniture- things that would have existed/been present when the ghost was still alive. Because ghosts do not adapt, they do not change, grow, evolve, or learn. They are memories of the living. Like a photograph. A ghost girl could move the antique doll that once belonged to her, but she can’t pick up an iphone and watch tik toks.
Btw, a ghost is the lingering remains of a “soul” who has died but was unable to move-on to the “afterlife” due to regrets, unfinished business, or a traumatic death.
A spirit is a different entity- they were never living humans to begin with- they are an energy species that can interact with the physical world and remain intangible themselves. They do not share the limitations of ghosts.