Spiritualists (people who believe in a spiritual world) believe that ghosts and poltergeists are the same thing. They don’t doubt that the living agent is supplying the energy for the ghost to manifest in the material world, but the intention to do the damage is caused by the ignorant spirit of an actual dead guy. To the spiritualist, the all-encompassing term “poltergeist” is a sort of “weasel word”, simply an excuse used by skeptics to avoid a spiritual explanation.
To the spiritualist, poltergeists are simply spirits (actual “dead guys”) which are able to produce psychokinetic effects such as the levitation of small objects and the production of loud noises. They can do this because of the energy made available to them as a result of psychic energy released from the damaged aura of one or more living agents, especially a child or adolescent. The child (or adult agent) may be the source of the energy, but, to the spiritualist, the earthbound spirit is the source of the intention to do the psychokinetic damage. From a spiritual point of view, the earthbound spirit is the actual cause of a poltergeist disturbance with an assist from the innocent agent.
Most poltergeist infestations are caused by simple human earthbound spirits who are attached to a living human agent (via their personal spiritual portal) rather than to a property. These may be malevolent, but most of the time, they are not especially violent, and they usually resolve by themselves within a few weeks. There are, however, a few “poltergeist” cases involving demons, but unlike those caused by human ghosts, these are incredibly violent and persistent. Nor do they go away by themselves. Demonic cases are the ones most likely to progress to spiritual possession of the agent.